pointing-and-tracking mmmmmmmmmmmmmm … · 2014. 9. 26. · technical document 1287 june 1988...
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NAVAL OCiAN SYSTEMS CENTER, SAN DIEGO, CA ILOW-COST POINTING-AND-TRACKING SYSTEM FOR OPTICAL NOSC TD 1287"
COMMUNICATIONS (PATSOC) BY: KH JOYCiF UNCLASSIFIE• ! JUN 1988
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Technical Document 1287June 1988
Low-CostPointing-and-TrackingSystem for OpticalCommunications(PATSOC)
K. H. Joyce
Applied Technology Associates, Inc.
Approved for public release. distributicr is unlimited
The views and conclusions contained in this report are thoseof the authors and should not be interpreted as representing
'4a : rC
NAVAL OCEAN SYSTEMS CENTERSan Diego, California 92152-5000
E G. SCHWEIZER, CAPT., USN R. NI. HILLIERCommander Technical Director
ADMINISTRATIVE INFORMATION
This report was prepared by Applied Technology Associates, Inc. under contract
N6f300I-88-C-0004 for the Naval Ocean Systems Center.
Released by Under authorltv of'
R. November, Head J. Silva, Head
Industry R&D Programs Program Director for
Office Technologv
jIj
LNCLASSIFIED
REPORT DOCUMENTATION PAGEa -IE-0:'- SE>-z -I -A3S'F CA' Y.f ES-R C''E MA~" -GS
L- sCLASS I FlE D L___________________________
A Ppr. d for PUhhIC eC~l(~ : t~'u
TA NMem, tP.!R-' 2 \O~sc "D lz Fa '~ME9~ PEZAM CC~A'a 4 IKAMS O NACKTORIP.G C, 9 A'.A 7'
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-. A'~ 3 -- s -- -------.--"lie-
xeu~>I
Final Ma 1") pointing0
tracking
Th- crhe ',hcdc~lopicntof low\-cost. ship-to-ship optical comnmunications s~sienr(C undarT a six mion'.'Bh, !'oa-.snn~hv eeac (BR contracti
La'er ccmnicaiion slctm, ha'.e been dcvc-iopcd lor u'c: at fixed ground stahions, aircraft, and s~'la'~thase n,' rcc-i qucce f~fll used in hip-to-ship applicahionu Thu: difficulis is that ships have large. random :nua inkt angtiii ina bier. n -crcrc ;-n~sding a narroa-hearn lasecr -" an optical ruCccir Thi' stud\ prepared it concepltiat dc....r ~ ' j . 0
ran owpoac' rn-to-ship sNsIei that would operale Under severe ca conditions The erinphasi' of the c A- 'ituu'-cA-c- g!mna: se and it, associaited trac kng'msp
$ O'SAJ C'. A ,A: ABS I ' O A- 2AOjc'"-- ,F-jW -. A"'-,A
SJNC-ASSF:IE7 J'JLINAED W7 CAMC A5
I7 cas iCLASlf If 1
LJD FORM 1474. 84 JAN > ''~ t~- .
UNCLASSIFIED
SECJRITy 3ASSIFZCATION OF '-11S PAGE (W D Em'm
DO FORM 1473. 84 JAN __ _"__ _ _ "
' EX FC UT: :F W~A PY AND C N : LU: S.
S- ~s t em a 41a ion .
-. Benefits........ .. .........................
I. fConclus~ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
VINTRODUCTI,'N .
Advantages . 2-1 .........
Technoogy, Revie-w . .2- ........
2.DESIGN APPROACH ......................... .. .. ...
I- perational Scenarios ......................... 3-1
1Target Acquisition........................3-2
..2Initial Inputs to rrarsmi,-,ng System . ............. -
7-23 Target Search . . ........................
.. ~ Tait ,?t Detection . . . . . . . . . . . . . . . . . . . . . . .
TraivJ ig..
: .i :en ti f i ca ior, of Low~er Le.'e -Cons tra in ts..... .. .. .. .. .
.2 P ~ne r/ T ra fer A zi nmu t IE Ie,.-a o n C o vePra g-...........
Conceptujal Design. ......................... -
D- iZn: (in~ Requ i .9men,..a . *'.. .. .. .. .. .. .
86F SaB 1 -82
T~eIi..a ri~ 0 ont K e,. 5. 's Eme c-n_
Nested oprical loops .'.2
Dig--al 'ontroilers . .~ -26 . . . . .
Girrbal.............. .. . . .. . .
Development of Evaluation ',odels ......... 4-51
-.!Performance Models . . . .. .. .. .. .. ... I. .. . . .. 4-51
IEvaluation of '-he System....... ....................
-. Servo Modei'Pertormance Esttmation.................. 4-~64
OICAL SYSTEM .............................. 5-1
Laser and Optical Detector.......................5-1
3..1 Laser Safety
7 xed and Steered Optical Zlemrent........ ... . .. .. .. ......-
Primary/Secondary Mirror M'ssemblv .. ...............- 4
3.2- Shared Aperture. ........................ -
.3Tracking Electronics . . . .. .. .. .. .. ..... 9
- . Ma: imum Search/Acquisition Tm.................51
.3DATA SYSTEM .. ............................
6. lype/Quantity of Information to oe Transferred............6-
.2 Maximum Transfer Timc ......................... 6-
E.23 Minimadm information IKapacity of the System........ ...... 6-
. Maximum Error Rate of the S-v--en....................-2
<I Naval Ta r !ica] Iaa~~ec(TS Data Trano-fei
,-,7T ELEMEN;T' . . . . . . .. . . . . . .
3BLLIOGP.APHYf . . . . ... . . . . . . .. .. ....-
FAFPLIED EH:kI; AS'-CAE k5='Fnl ro
.1 Recent Related ' Ior- b.- ATA Staft Merrbers . 8-1
o. Recent Related 'Jork from DTT- LIIE-T-RE'-PACH .. 8-2
S.3 Recent Related W'ork at SPIE Conierene-... ..... .............. 8-2
5. Other Recent Peiated 'Work . . . . . . . . . . . . . . . . . . . . .
APFLD TECHN-L-, ASS" <IF. l:NC. A7A. "'70 SEIR - 2E3R,',t Y-p 7a, : a:'; Report
Fi :e "-1. Scnematic of an Optical communicatior Setem .- 3
Figure !-Z. Schematic of an Optical Communication Ssterm ....... 1-4
Figure 2-l. Spiral Scan .. . . . . . . . . . . . . . -
Figure 3-2. Rastei Scan .................... 3-4
Figure 3-2. Schematic of an Optical Communication System ...... 3-8
Figure 3--. Schematic of a Two Optical Fath and a shared apertureSystem (Showing Transmitted Beam Path). .... 3-10
Figure 1-1. lave Motion PSD 110/,3)=10.8. T2.7.93 . ..
Ftgre --2. Wave Motion PSD 11(1/;)53.1 T2=14.5 .... ........... 4-6
Figure -3. Response of the Vehicle in Pitch versus Ratio of ShipLength to Wave Length. ...... ................... 4-8
Figure . Amplitude Response Normalized Pitch. .................. -
Figure -- I. Pitch Response A00 ft. Ship, fi.] ft. Wa-es . . . . . . . . 0-11
Fi re ,-6. Pitch Disturbance Spectrum due to Wave Motion. .... .. 4-12
Figure --7. Roll Response 400 x 35 ft. Ship, 53.1 ft. Waves ...... 4-13
Figure "-8, Poil Disturbance Spectrum due to Wave Motion ..... . 4-14
Figure !-9. LOS Spectrum for 400 ft. Ship. 53.1 ft. Waves .. ....... .4-16
Figure -!,P. LOS Calculation ........ ..................... 4-18
Figur -- i!. Atmospheric Conditions . . ................ -18
Figur -12. Atmospheric Transmission ....... ..................
Figure -13 LOS Angular Spectr-m Lon; Frequency; Plus High Frequen:Envelope ............. .......................... -25
0ure -14 . General Scanning, inn.. Fact Steering Mirto:. . ...... 4--2
Fizure a-:i. n'rol: Moduilar Flow . ._............
::e -6. VP,E 5w'tem Under Development: CONCA., ................
AP---FD TECHNI Lu" k SS( " ... T E . .TA M.emo SBIR-('2SSSR;I6, rp Parson Final Report
May 1Q88
Figure 4-iL .'YE SYstem Under De;elopment: SSP ............
Fizure -18. Possible Configuratior . . -
' ure 4-19. Digital Control Electronics ............... 4-33
Figure 4-20. Digital Computer Controller ...... ............... .. 4-36
Figure '-21. ROTO-LOK Rotary Drive Concept ..... .............. .. 4-38
Figure 4-22. Drive Related Friction Losses less than 1 .. ........ .4-39
Figure 4-23 Blacklash Comparisons ....... .................. .. 4-"0
Figure .-2-. Demonstration Tracker ....... .................... 4-42
Figure 4-2-5. Optical System for Tracking Demonstration ........ Z-"3
Figure 4-26. Signal Flow for Tracking Demonstration .... .......... -44
.igure --27. Candidate Configuration of Ship-to-Ship Communicator . 4-45
Figure 4-28. Ship v Acquires Ship x .......................... 4-46
Figure S-I Laser ODtions ....... .. ...................... 5-rm
ig-gure 7-2. Possible Laser Design ............ . . . ..
Figure 7-3. Ball Telescope/Sensor Assembly .................... .5-5
Figure 5-4. Ball Sensor Printed Wiring Assembly .... ............. .5-7
Figure 5-5. Telescope Design ......... ..................... .. 5-8
Figure 5-6. Quad-Cell Photodetector ....... .................. .5-10
Figure 5-7. Bit Error Probability for ASY Communications .. ....... .5-12
Figure S-8. Bit Error For a Given SNP ....... ................. .. 5-13
F9igure -. Receiver Input SNP: Tatm= 10', Pointing Error =1-rad 5-1
Figure 5-10. Optical Impact .......... ...................... .. 5-15
A? LE TEH. -A ASCIT 'z-, - -~ 'P'T? - y
TA RLE S
Tab -. Adariages of an upti cal C~ommunica, ion Sy.ster. 'o. hp-sni nD Use .. . . . . . . . . . . . . . . . . . . . . . . . . .-
Tac-e P rev._ous ';ork in Optical Po.,nting and Tracking .~ . 2 -2
.a--:Tles-ope Speccficarions.....................................
Ta - -I.'a%,e Characteristics .....
Ta'~Pelarivc Displacement Induiced Ang'e . . .. .. .. 4-3
Table .-. P:tch C:harac-eristics
Table P-- Residual RMS Motion wi.th Error Rejection Band-w~dthr.... . ...
Table -- Component Tweights, Volumes, and Costs........ .. . 7-i
Tabe -2 Approximate Costs for Phiase !I . . .. .. .. .. .. . .. 7-
s a I repor des-:rro es tre "P,. Pnpe'. 0 t a i v--s snap- s
a i~a err Rx' ee s e a-o r1B ,r~ Rr Bsns
SVS: a ~r sytems ri - E- fl F F-erl 1 a- d - I go un-a' crs on a .t::-af' . and on -a-e : te' Ho v e F r t) p ha venot been
S e Ef lyu- .' :zed, in shr p-- -,'p appo , at ions n- d u t: iI vJs rha*sr.P -a-.e large, random, linear an - angui a mc<:on. h in'etleies i,ho1 nairov.-beam laser oni ani opt cal -rcei %er Th sud, p-cpared ansesria. design of a -elati.'eIy nor ranwe. lo.-power snp-to.sh~p 7stett58.' -ioui..l operate under s:eesea ontor. The emphasis of the Stud';
rMs th e design of a 1ov-cost g-mbai set and i ts associatec rack ig
.ereqr iremner r f ocr a ship-to inp ('ClI are rot , vell-defined and the.e 7 _:re-ernrx s-e-ed as Dart of tri uidy a re -;i eed asf goa ls . T he t r1eeg a- 7mat infuenced ire ecivnsgxxan.;ae
T ommun .ria t ove r a d:fstance o f 11_ kt u n c- favorableamospnerir conorcin!, e transmission gzreater than 30' .
7, tr-ansmi t PC' h it pe - secnd wi th an error ra-e less than
I this -vAl i iandle tv o real-time video signals.
To 1 cotimunicatE conrinuouj':v inder a condition of -ev.e r e ship
motion. ".e., that correspond to sea state 8.
*Th-r ar- mar"; other character'-t ics o: an ()(S having to, do nit operationarc( -a:nwenance that ma v e a n 0(2 a cer a hie a dd it iorn ',r, a n oe raP n av al. r-.7i _ation szvc-m. The general 'naracter~stics7 art cescriberi n thiS
7; 1-a uns.iier, 5P-r inn- r~ontair, mre: dera is.
Tne mES _g n -;an s onsidered, in e r ms of thrI ie e s ub sx'se m! z g-ba Is. beampntn.and controls. 2) optics . las:er, and d-eecor. ann 3 data
.ranm~sson sstes. .~ :ea',es drtalied desig7n -,a- eeoe fo- theXnjbeam pointing. a n i a F 0r ter cnntrols. The- or'x cn n da ta
Ir c o-iee 7r -sVt PI I f f -11 deti F n Tia An 's and;. -nre"..-TI* 7 t Ia
as t r nter' ma nut *' mus n :c ond
-, C-a a'' 'Ct fe _a:e' ar- Ei <.E >-a -' a P nc
meC-7 :"a" ia- ''~ca' r-o nw c ige0 s n on's c: a 'oa rraz'"' t: ':es a catj e .;:u~ nu~r ao in I' Ia1 a
'ie eu ocS e ta e",a -' 1 .0 1.-.1 separare cuompu- e no') -fnown n
rn~e'nar a c I on ' r's aa ase f';7 Q~ gbas n7.e "or
7 " a -are 1i r ~ e U "I e e :r r' 71otors through a unique but inexpens .'ecac Di al: --a b e s V s t ern. The f ine Doi n ting o f t ne laser L eam i s
a 7P - fa q 7 eer nF r rr. The hitato how - zeparaieaz 7,;. a-. e Pea or', as t -eeti n- rro r s; n e ve r a s In g 1e 2ax -isT mirr7or
::~::.rie. - i o scerr Can c r E -o :om Dtr- ~y ommu n ic a t on:r- cc)- ruc~q-,o-, c mo, r stri ps c- rt a fz'ne need for too sv7c-ms
.e r Ca c fe a'u r e of, I evgr is'ne us- of nesead :ontrol loop- o-hi-h-az-'m'ri~ an,' a-l(a a,,ri c' o' na.- trom a quiar --ell. Th(cse -ontrolr e e ct noth the large-amp. t rj,:, , 1 freqiren-y angular mot ion ot the
o i c)Sea stat an the nh-f: e qu en r v; stal 1 amp'itude vibrat ions- -~ ie !7n~p upon -hthe PO'e'm one
a ( xm pI Pe~: r ' "< aA, dode lTa se:r. ser.ecinc, on oral t ion ar ra 'a tran r.S io n . The beam bjl e
r:~ ~ * et EE DSpeedc up me ear(d, arid 'a.re' actruisit ion process.
'pa- Ire of th vC'e (-c - a er-retlertor inside the ex~talg-ented hv ret>',_ r, Iap o. 07 n'e outer u rf a c to establish
ora- e toeen pa i r Ct 0 f v't ems 'ner components no' shoo.n ;n theSa on are 7ne posi t r.n encoder- or; e coa re gIm bal1s, a ho(ir iz on
SenF'' or a gyro, Phe - a r rer -e sor - are- needed r o prov ide an I ner-'ia 11,;a ea r -h patr n . i.mmrary: off the imrnortan( cnaracterisincs of the
conep' .a.. design are:
-'--, o-regardi azrruth
Coars-e zi~nbal ban('.d idh 15 HCoarse~:-uairF-'r-'ior a, d
-a-- ~-rig Mirror , ejer' ; d' ft zi lnnr [)I! I er., rms 5~sicua~beamn ji -'r mm':1Io-ic" r)eamr vir for Cnmmnr'~0~
P-:'e nean' wa: ni fr arr i i r7r
Palns~ In' Mal orc ua eaan ns h n~ I* rl~ q i de
A??L-ED TECHNOLOGY ASSOQ(MATE?-'. I"'. SB R-rnoF Ai 7- FaI R ecr~
Ma1988
S ApproximateDimension
9 in. Ret~r. "efiectcrs
'.5" El evation Pointing____________:!at with PositionAEncoder and Motor Window
Optical Path,
-::80 0 oto-loc _ _ _ _ _ __ _ _ _ _
Azimth DiveFocus Drive
Motor. Ball Bearing Sucoor:Moorand Position Encocer
Secondary Mirror
2-axisPrimary Mirror
< Fast Steering
Beam Spiltter
Tracking Sensor
Power and Signal Cable
Figure :-I Schemna- of ari )mt ic 1 >jmmut rn
APLE--D :ECHNOTOlCY' ASSoCIATES, NC. emo ERQ2PATSC 7inal Repor-
l)88
.-guire 1-2. Schemna". an 1)[), a. ''rmin ,-,i
Ren
'.e '-'I c omputer o conitact zirhe )ec'~f ~C S An approximate ~torie specifted cjCS v ill shor-tern te accursition time . If the uncerta Jty
,7' ~ire- tr. is greater mnan riezree. hre r ranamm eri oeL~ o m and a fr(ara w be s ,arite d -iea. te aox i~mae
o o o te o t her 1) :S . Tuje zear-cnv the defocusea beam v i IIscann o or" at -an:an per coc-nrI-.;-.n internal ver-tica' 41'ection sensor
te 'nete Oitc-tt2)f t 'te horizcn. ne a LE-turi- abov,,e a prese-ttroc s rece, -.en. - s~ ~u e , rto be :octne , e tsceec Tor or- t ne
7ni- -Ea-a *I I rescan r h- d ir - tor, of toe return. if : a persistenttie beam biI e refocuseoi to 3jY or and a 3(it. HL spiral scan will be
_' aCur t -aget . The Ttrget 1.1 then be ma n tain-d in t rackS2, e-r'r sgnalF produced bythe quad cell.
-neC se-conc (X'S '.ill identify itself oy either modulating the retro signal orcv rroagating ,,ts own beamr to- toe irst s vst-em. At t h ,s point tw.o-'wa%
'c''-'orcat.on is estaor-sned and' toe ,.*stems ar-e ready to Transmit data.
2 )o- -seerng con-rlttons iac:- rra-ksatter "r scattered cunlignt f romr* amosnee m,' nhbrt ac'ui:ron of t Petero-.eflector at lo:ng
ta. z ro S :nthic case a Pulse mnode can ho used to gare ouIt scatter energyb o eam Pa'n. Tnih morac eqJ cur es an approx,.ma ,e knovledge of the
to, ne t arget. ccn pori,- seeing mnoj uses a search beam modulatedctI HZc. T :i rice the targ et return is- also modilated at the same
Wre: vereas atmos-Poeri. hac?'s atter is relat iel: con!tant. Thee tor)r tnese oerseigCodes must be reduc,_ed: therefore, a -,6(,
' a~e longer tanthe 6 se-conds required b', a normal search.
emr '.' a ov m n E- etrefe c o rmmand -and -contrrol of defense and,a a. operations anti, vi 1 p r vide lo'w-cos*. Ship-tc snip. optical
tion.
*n'O acr ae 3dpe n. aPP Ii c a ion _nocng optical-----a i on o,'er a s hort 7-a nge he t v,,een moving -.eh i iIe!s. oemmercial
a P -n! o od n( lIude airport anti harbor oper atons. emct, ite T'sarl'a_ n7. anti comman,- and -or r 0 r me d icral. sl 'I-. n r fire
'-acs . able 1 cnvs nar-anrages -' f n t<r a -- i: orshin-to-;ship i
AP L ED TECHL, .. ,'IATE!.M , M-3B R-P:-P7C£ Final Repot7
TaAe 4 . Adva.a -e- , a-f an Op',.d mt . S5or ' m for 7 -'-r>-ship Ui t
Hign Data Rate
- Small Transmitter and Receiver
- Secure Communications
Low Transmitter Power
- Rapidly Developing Laser Technology
- Similarity ro Ship-to-Air and Snip-to-Sateilite Communication
1.5 Conclusions
ATA's conclusions can be summarized foliows:
1) Nested control loops will lead to an inexpensive optical systemfor ship-to-ship communication.
2) The concept can be demonstrated in the laboratory using mostlyoff-the-shelf components.
: The concept in low-risk and based on current technology.
A phased program will demonstrate the tracking. acquisition, andcommunication functions.
2.1 lvanages
Qri.7d communication link's have several advantages for ship-1-5hipaprliarions over current operational sy;stems at radio frequencies. Key'
thaft Tave A Waei ba-PH , p, - nmuinlrat ion atr rAc r ivp in, liOp!
High c ata bandvidthi;Porentialiv small tranFmi'ter and rereivet hardva:
) Ease A !o,,umnIrnlIt~epi:L=y tan-mi~er pover requirements:
1) Promising technology advances to impiemen Qptical signalgeneration, muitiplexing, detection, and demu1!iplex~ing;
v-; Potential simliarity withi surface-to-satellite and surface-to-aircraf7 communication s';stems.
The advantages at optical communication, however, are linked explicitly. toreliable. maintenaiice-free. low-cost pointing and tracking systems to linkre nransmitter and receiver in tlie presence of large amplitude ship motion...r-ese systems are required so that a small optical beam from the transmitteraA ne placed onto the receiver and neld there to fac.ilitate loy -error datarYa:::er over the beam. A lo.-iost shiip-to-ship optical communication
77 o"Quld prov'ide a very attractiv short range alternative to radio and- .1!n-ave systems.
.:.ecnniogy' Review,
Dyesign.. fabrication. assembly, alignment, and performance verification of.ne outical and mechanical subsystems historically have been responsible forsignificant fractions of the budgets of experimental projects involvingprecision laser pointing-and-tracking. in the late 196W's and early 1Q70'sthe Air Force, the Navy, and the Army; each began R&D programs to exploit.rivn-energy lasers in weapons applications. The pointing-and-trackingrevirements of these programs are similar in technical difti culty to theposting and tracking problem of ship-to--chip optical communication. Bothsl:.aiions involve gimballed telescopes carried on a host vehicle w.hich isunaerzcing intentional t rajec tory changes and unintentional vibrations. Thepropagation path through which the optical communication (laser) beam must~:averse is affected by atmospheric phenomena (natural. meteroiogocal. and
man-~aae ) and bw ooundai'; layers surrounding the host v.ehicles.
The lessons learned from previous program- cndrm toe need for -ormi"'.rovements in technniogy for precision pointing and tracking systems.(Reference 1: L. Sher, Editor. "Lessons Learned from the Airborne Laserl~aboratoryf," AF'WL- 7p-83-S, June 1983. (Confidential).) Thile disturbances.size and other requirements may differ between w,,eaponsz and communications
777IMS.many. of the rwhninal challenge: in aieas: or :ost and pe-rformance.7mlar and nave been recognized an 7i;gnifican* research neelio.
2/.-ly go:m:'-ant arnr~nty of incearcln rpouires ar- being cxpended in'M areas of sensnr' . notirr, aod acvos ia rei mv' r ural c:vP,7 for
APPLIED TECHNOLOGY ASSOCIATES, IC. AT.-. Memo SBIR-,_,5?.ATS* C 7inal Report
M ay 1 ?88
acquisit'ion. tracking, and point:ng. (Reference 2: M4 Katvmor.. "LaserSatellite Communications.) Hoveve-, tne emphasis is on very Iaige space-basea and ground-based systems suitable for strategic defense roles.Optical communication involving intersateilite laser links is also receivinga great deal of attention. (Reference 3: R.D. Nelson, T.E. Ebben, P.G.Marshale k. "Experimental Verification of the Pointing Error Distribution ofan Optical intersatellite Link," SPIE Proceedings, 1987). Unfortunetely,little emphasis and few research resources are currently being devoted toidentification of low cost pointing-and-tracking technology that will beapplicable for optical communication applications involving short ranges,high vibration. and moving host vehicles sucn as ship-to-ship communicationlinks.
The performance requirements for point:ing-and-tracking systems for opticalcommunication links are demanding when either the transmitter or receiver ison a moving vehicle. Consequently, such systems have in the past beencostly to design and manufacture. This research program seeks cost-effective technology and conceptual designs for the pointing-and-trackingsystem. Phase I provides a design of a low-cost pointing-and-trackingsystem which is free of undesired complications and cost impacts on theoverall communication system.
Table 2-1. Previous Work in Optical Pointing and Tracking
Name Manufacturer Application Range ; Beam Data(km) (pm) Width Rate
(4r) (Mb/s)
APT Hughes Weapon 5 10.6 10 CW
AFTS Mc9)D Air-ground 100 0.53 100 1 Gbis
ISL Ball Satellite 42,000 0.8 10 360 Mbs
Comm. System/Ootronics Ground 0.6 0.8 800 70 Mbs
89 .... ._n !.'TSM' F:nal Report
... --' A- __AC
DESIGTN Aprrm~
The design of a ship-to-ship optical communication sysem involves manyscientif:c and engineering discip.ines. it requires a Knoledge of manyaspec:s of the sncipsea envi-onment and the design must consider the needsanc oeraiona: constraints on naval ships. The optimim design, where cost
ir a -alor concern, requires a large number of trade-offs, many of which are
bevonc the scope of this paper. The empnasis in this paper i- on the designnf !he gimbal nontrol svstem. This section presents tne approach, the
reQc:rements and some alternate conceptual designs. Subsequent sectionspresent derailed analyses of the control, the optical, and the data
subsvs-ems.
1 tu Emphasis
Previous R&D efforts have demonstrated the ability to perform accuratepointing and tracking in bcnign environments such as ground bascd or
airoraft-based systems. The pointing jitter measured uring thesedernavions has been in the tens of microradians range which is adequate
for optical communication. There has been no demonstration of this accuracy
it" In& shipboard. high-ampictude vibratin environment. The same R&Deff~c's have demontrated high transfer rates over laser links at ranges of
-crecs of kllometerF. The data rates and ranges na':e oeen adequate forone snip-to-ship system. Vith the excepvion of short-range, ground-based
laser communication systems. the cost of these previous R&D efforts has beenin tco tens to hundreds of millions of dollars. "'hat has not been
demonstrated is the trnnnoingy to transmit in the high linear and angular
v;crat:on environment of an ocean-going ship. Therefore, the emphasis inthis study is to develop, in a preliminary design sense, the gimbals.
controls, and stabilization systems needed for a low-cost pointing and
;racking system.
k nonceptual design of the entire oti-al communication system ihcluding the
lase: and the data transmission subs stem will be developed because the size
and weight of these subsystems impact tne control subsystem.
For ezample. the current technologv of small, light-eighht. easily modulated
dirne lasers can be used to reduce the weight on gimbals without the'o 'lex beam transfer optics for an off-gimbal laser: however, it places
-eranr constraints on the bedM width and the allowable "itter esulting
fr-,- n tracving system.
-perationa. Scenarios
"arv nf the reouirements and 'ocrstraiNrn placed on an optical si.-to-ship
7-te- ~r~come evident by cl~ring the tprp that mo, be performed toe- a isr communtnation. 7,; the oilo'in; .renaio the hip initiating
_'--"niation i ,efered 'n a h- ran mit-in n;p '.'s e'- . The sh:p94:7Zru , c ntactel ortainc the laiZnr '"-t, , iv: 'no, ane:atnine of Wh :--eivin;7,
Vi 11 M I I FI;1h 1 hP i h
Yav 1988
c': *" moon¢ *b';.-~vm , ,qml m'r- , p , e ' b i~he' , ho}: ,, :t pm v*ii]
LdLaST. a d L e: e.
a arget Acquisition
Before tracking o f t he receiving system and two- way communication vi th itca. be established, several steps must be executed which are defined here astz:ge, acquisition. These steps are:
The person or computer responsible for iniriating communication'iil identify the ship to be addressed and its approximatedirection;
" The communication system ,,ll perform a search for the target;2) Detect the target;
Establish closed loop tracking of the target; andz) Receive an answer back from the target system to confirm two-way
communication.
The 7ast step is not required in cases where the receiver has no transmitteror does not care to go on the air. Both systems in the communicating pairare identical and each must perform target acquisition. The time required
- ompietu acquisition is an important parameter and .:ill depend upon whatis .no'n about the target location. Possible situations are:
.Aporoximate location ot the receiving ship is known through visualol. radar sightings:
Several ships need to be contacted and their locations are unknown:however, the order in which they are contacted is not important;
;mne ship of several in the area Js to be sontacted and its location
is unknown.
The communication system processor will have several acquisition algorithmsto n oose from, based on the input information accompanying the request toinitiate a communication link and on the motion of the transmitting ship.The following paragraphs describe the steps listed above.
Initial Inputs to Transmitting System
The -dentification code of the chip to he addressed i a .eqiired :iput. .dpsired input is the direction to the 7hip. This intormation till redurethe search time. Without initial pointing data, the search may tar e timeson the order of ir seconds which is acceptable in riost situations. An issueis how. initial pointing information might be obtained, in what -oordinates"ould it be measured, and h ow wouH V he provided to the optical
o)Tmun i cat on s s tem.
,.o anguldr cooroinate s's tem can hE ,7 : hzmm: h anc E" eva I Ionia','e to, the ship and V an ier':al c.'tec. Te e!a<* as mathh arid
e e':un~f 'e a~e v 1 a ~ a ap:'1 dur ng min e u'.'e r -
wea ne r herezcu"e. if ship-baseci ,oct-dinates are used. t le -rt o rat Io omu s!)e ,_-ao-sferred e':ra~DAIv. .i aLrc: w>:amate shiD-based azimuth and tne :ac.t
a. - e target 1 I e n ear necoron can be uiSed tr redu ce th-Ie -earco
n, inoora te an i ne ra i anglIe sys t em. This' is required: (1) -omc~r a::a systemat 1( sea,, ch Pat tern -. IIlcilehe ship is rolling.,2 to know
r ~'e sne ho;rizoni i s. and pern aps (_') to provide inputs to the trackIngexcess:"e bearr riccer JS enrcounterenl. The types of censors w.h ich
~e- 'onls ide Led -.ere gyros, magnet ic compass, artificial horizons ow, turniand.) an, cnlcators of the ty;pe us ed n iignt aircraft. and an inexpensiveanil -a r ale sensor developed 0'; A l. ncorporating some combination ofsensfor Of this type ir the OCS -will per-rit the system to slew,. to a givena zi-Lnancl elevation measured in an inertial c-oordinate system.
n hould be designed to accept an initial pointing direction in either-n,.) c:inertial oordinates and, depending on thle accuracy of the
o a on.begin a lirrited 7earch or go directly to closed loop tracking.
7,,eC ay lie laetca rmote ranual ac quisition device through azimuthan,: e_--?'ationai position sensors . iie manual acquis7ition de.-"ice may be
-a, a telescope, or a s 7,j~ in sight. y;hen The operator has the-.ze entered in the w"pr :ai ve a 61 trn pressed tran!sferring
to the )CS. I f t h WS mcatn t e ni easy reach of theDelc e I teesco C ) '. it"er, o!n to; of toie case, iov stick control on the
g 7m'-' . and a button to t ur'n controj 'e to toie tracking system prov'ide a_oacquisition mlans inner gon oewn conditions.
.2:Target Search
The sytmcompu ter -will contain one or mnore search patterns which 'Will send*he appropriate commands to the fast steering mirror and gimbals. Thepattern could he a spiral Twhich begins at toe estimated target positions andov *1e s ouLItward . The maximum spiral frequency will be limited !by the fast
- teering mirrors to approximately'3( Hz. The radial advance per cy;cle isaDproXimatel,; one beam w.idth. The transmitter has a defocurs capability;
niere~ore. the radial advance could range from 30 ur using the narrowestnar to 1 7r., wh ich has !-u f f i en t beam energy H(enzi ry t hat can nict ec t the
le-~ reicoi linear search aionv the horizon would reduce thea sI S- io n t'e . under come ci.-xumstances. FPigutl -I and f iure -
*~'-t e e~rca 1 earrm PAt trns.
APLLIED TECHNOLOGY ASSOCIATES, INC. -.TA Memo SBIR-,92588RO006i rp PATSOC Final Report
May 1988
WideFOV
________ ____ ____ _ __ ____ ___Narrow
SpiralS FOV Scan
,_ _Horizon
Figure 3-1 Spiral Scan
Raster
Wide M Narrow ScanFOV FOV
Horizon
Figure 3-2 Raster Scan
P.-. Ta-g o DePe -io
re-urn above a given thresnoid ,:21 be tnterpreted b, toe sy ,tem :a the
'a:ge. The target of i it r t r s toe tetro-reflector on 'he receiving
ss e7. The system will occastonally receive false alarms from other parts of
toe receiving ship's structure and possibly from the sea su-face. The ratio
o the signal from the retro-reflector to the detector noise is high enough
teat toe probability of false alarms resuitng from detector noise .s very
small. The probabilitv of false alarms trom other sources will beir:','er gated during Phase I!. Beause eaon re'urn abn-e a thre-hoid "-viM2 be
considre'd automarcalLv by the system for tI-acking. te nuMser of talse
a'arms must be kept very low so a- not to over,'-nelm the system. This system,
as ir ost detection systems. viii nave a thresho'd ad 3ustment wha-n can ne
cnangec o the operator.
. Tracking
Eacn time a return is detected, the system vill go into a tracking mode and
analyze he position of that return and establish that it is a persistent
return. The return from a retro-reflecror could be modulated by the receiving
nrc " ind icate ato iD, there: confirming acquisition of the desired
recerver.
_ ear'h pattern for ise when track ac momentarily broken would be available:
nts case. the system would immediately go to a spiral scan in which the
beam is spiraled above the position of last contact with the receiving system.
n aternative approach is that the receiving ship could come on the air and
ident'fy itself with its laset . Each system would have a repertoire of search
patterns and the amount of beam defocus available to the operator. By
experience, the operator would select the appropriate pattern for the
situation at hand. The parameters the operator would use to select search
patterns are: 1) the uncertainty of tne position of the receiving system to
be contacted: 2) the motion of the ships: 3) a threshold which would be set
1epeitcing on the number of false returns expected.
The construction of the system could be a shared aperture system as described
.n toe summary of a two-aperture system in which the transmitting aperture and
rece:ving aperture are on the same gimbal but are separate.
A.cquisitlon mode is completed when more than one return above tnreshold is
rece:ve at a particular location or if the unique ID of the receiving system
'- he-ted. The system then transfers to the track mode. The method of
,losing the track loop depends on the type of vstem invorved. vwo choices
are possible: I) a singular frequency system in which both the to
commun:caring syz tems are on the same wavelength: a protoc-oi would be
established to interweave the transmitting and receiving functions while
maintaining track. 2) Using two frequencies, one for each communicating
ster. the s.,stems couid transmit simultaneous>: and ( se the tncominz signal
7om the opposite svstem an th- trarking cigna".
C - - -1A* .hE -. , - t
rate tor data trarsfer .:ould e uc , 1<. e megahertz range. .iie track, In gC)o Pcc d be te k ilounie i t z fdi.z e t i e f o r the dat a ,- s sieimposed on.teSiZna- voc e InVISIble to -le tatig cr c 11 -r.
R e a - R ee u ir e f ome n tio cesu j .
Requirements- f--ie ocpuis em 6esigned in this pap* er- reflect the goalID te oiogiam. vdhicr is that a ow-cost system be developed vh-ich can trackwni;e su!nected to tne large amplitude motion of snips. The field-of-regardof "he s.stern -will be 36(-" in azimuth and 450 in elevation. The laser must bean off-e-shelf. inexpensi-ve device that will handle up to 199) megabits persecond. The maximum range that can be expected of such a system is about 15kllomre~ers which is li.mited by the curvature of the earth. The system .,ili bedesigned to communicate under atmostpheric -ondi.tions up to 15 kilometers.
3.3.1 Iduentification of Lowet Level C onstraints
i e rved the follov ing list 1-loer-level suhsystem requ:rements and
Pointer/tracker azimurh/elev-at(on coverage;~aximum gimbal sde, rate:',ax, mum searcn'acquisrtl on *, -Vn imum i nfo rma Crin c apac it r:. t h e sy st em:,
- ,1ax~rsum error rate of t Iie sy st em:Bandv idth of disturbance reiection loops;.:aximum aperture size,
EBudgets for volumes. weights, Dover.
These -cwer-level subs,,,-t em requi remen ts and constraints -ere essentialingres-Iiuts in the process of selecting the evaluation criteria to identifythe opt~jmurn overall communiciation system.
Pointer/Tracker Azimuth/Elevation Coverage
Based" on calculations of maximum sea conditions, a gimbal coverage of
4os degrees snould be suffic-ient.
The- need to achieve maximum range. maximum protection from sea .,ater, and 3600f el ;.regard 7suggestS an installation as high abo-.e the v a t er line aspossi.O-e. The desire for minimum linear and angular motion, reotuires aninStala-ion on a rigid structure. The desliabiii tv of shor t-ommrunicationpathc for high data rate 3izna - suggests a location near the communicationienter. This latter- location iF probabl,. a reasonable trade-oft hetveen the:omrpet:nz requirements. The need for 3 6 0c f ield-of comMunicationr~ vould tend
o r ac the unit qr top of thp bridge,, forn! e xa mpl1e. Tvo- -75" m ay h er eq ec on a snip to gilve a- firl I>l fi-i o-ic The nee-, lo mairlalrl
nsI jr- oul alsrc Dsace it trn. a reai~vaenhelocation. :rise andve..znt eh an ma n ac n-, v a i n gie prsor and 1h oIl t 'nrelrgh a
.. W.a i a > e ~ 1 1o'cw E-~i '-" Ia yec_
-- ncep _.a C sgi
Vn eor 5e: bed lie Ie 'Ad c, F tecue-e de ai~ A candidate design --as estac s te c s: C-!.: ae I 'at
-!"e :onroi sy s 7em and gimbas- 1) r: des -ine and te performancees<:7maed. Alterna'ive designs :or) %'arcu o ) lncvserr, are 'Jgge s: ec ateve.,al po in t S. :ii order to LJ'i-a~e ma.'.rew 'n)o:oes alloy,ar~at:onc-whi-h "Tigmt be InIeed e c o -!E rro e ertan f ff U' lt: Thissec on i scusses the candidate design r'.and thriera ic~ a~e!na t 1vesare Suiggested. The candidate Ia.esign is a single shared-aperture xsem Theopt--a: sy sterr.s, the opti-a. component and kmen, )f t e el e,'on i -s ar e'-ornairned ir a s'.ngle. air- rght. rv.'indr i-al c7: ir 'onje. T-h- (P.I v optic al
o T p o nern exposec, to the elerren-n~ the ex,.t ri,''. The poinig -ontrolso.1S 0 i coarse azimutn drncie -riat rnta-ec he scaled 1; rr an,1 a conar ser
e ~at.-In T I I-or %,h ic h i : n , i o Fe ( i n te s ea e d un it The finje t ra c-king iSa-ccm.:sred by a tyc-;-axi!c m - rro
7a0 aor e 1esent,-s nK I rie in nI ng and tracv~n r. subsyst er f or .h i o,m:crnents, materia'ls, and t enne_ .oz e -.ee Pri.entifei arie:
imbal't dn c'acn- Fied and steered op!irai e'ns
T.- a ce ing e 1e_ t r run-. Di tai -onr. e'e o
A tracp ig 'r~no or: iccn op' ional
PTA andveloped the f el Ivi ng def ign a - be ing rthe Tr.nos Practical f or thFtlc sip-to-sh. ip optical comrmun:_at~on system (see Figure 3-3).
Tine 'nof the system rotates, -Thile !ne bottonm part is attached to the baseSisoiation built into itto orevent transmission of -vibrations of low-
f recenc'; motion caused by the .:aves and ship. A15-centimeter telescope isci. The snared aperture is also rime shared. The whol azimruth housing
* :rr7S and is driven by a motor. The not tirr part is fixed and does not need to'un. h;s deig alouesa nrcl ndow. It is possinni- 'o spoil the
ea7 r:.uring acquisition and then to narr.ov. it, during tracking. The glass hasa seconoary glued to t
- nuiatet. the -worst.: o I woud e or minus 4- deg-eP-. 'na p) Ihor Tnlii 11, dere-s. Thei -.,c- w used rpju- or -rlnu, degi ees i n
Z leIgn.
A. be ieves that the shared aper turm. "terr in t his les izn . whn eimina Te!7,le~ -eundancies, volume. p~gf a n -. er p e naltires of a senara'e a r)e itu-re
1Z~ "15O 1.: another v P v ei mnt in a-hieving a -os' feci: ship-to-shnr
a 'a sles and on'iP A f iI , ar, come ot 'he- pen a re- a 7o1 a e;a nhared aner -,re tip,"t e a'a M" Cth man '-ffce n-s ie rPdui r r-~'--~'if 'he 'a~ a~'r ''- r1~(dir sa ;'~ ia
a1- "r- e g imha~ cc ;r e tan in a te- io,! ra: : - ,a ii a:.....av:e tl(
-APLLIED TECHNOLO3G" ASSOCIATES, Nc ATA Memo SBIR-021:87Q6 p PATSOC Final Repor:
MaY 1988
ApproximateDimension
9 in. Retro Reflectors
- 50 Elevation Pointing ___________
~at with PositionEncoder and Mc~toi i o
Optical Pattn
=18C" Roto-loc*
'v-_. Ball Bearing SuooortMotor adPsto noe
Secondary Mirror
2 Primary Mirror
Fast Steering
Beam Sriitter
Tracking Seisor
Power and Signal Cable
Figure 3-3 Schematic of an opti.cal Conunicatzor. Systerr,
LFD T"PCHN(-hL-.9GY A.SSi)CIAT-E!S 1',C. >MmoSI-2
ma.'; )88
i'-" 'H i ra st~lii v n'~e T~~a 1- lad. cze cf I izer 19 t
f tnr:e gimbals. such as composites anc plasticsQ. results :n ic'wer cost.
.ie -4Sho-wS a Schema t ic of a t'WO-orti alI path s,,'st--r..
HPL:D TECHNeLY,'Y ASSOCIATES. -INC. .. A emo SBIR-O."33R~O5 :c ATSOC 7P4nal Reoorr
May 19,88
TOP VIEW
E e vati onPointing no
DriveTransmitted
Approximate Dimensioni Beam
Lenses
P:ast, SteeringMirrors
TraC~ir Sersc-,
'gule -'-4 Srhema~ioc of a T'r!, (plilca' TParh -irim -hcired lper'r ?.-e'(Sho,.-ng Traismw-et Beam Pa'ti.
-. 75NTROL SYSTEMS
a.! Definition of Requirements and Constraints
The definition of requirements and constraints is the most critical elementin the identification of the optimum system for low-cost ship-to-shipoptical communication. ATA has identified these constraints in a two-levelprocess that starts with top-level requirements and then derives lower-levelsubsystem constraints.
4.... identification of Top-Level Requirements and Constraints
ATA started by identifying the following top-level requirements andconstraints:
1) Maximum/minimum distance between ships;2) Maximum relative motion between ships, worst-case sea state;3) Worst-case pitch/roll;4) Worst-case base disturbance spectra;5) Worst-case propagation medium characteristics;6) Type/quantity of information to be transferred:7) Maximum transfer time;8) Maximum volumes, weights, power.
The above constraints were then quantified with figures and ranges, and aredescrised in the following subparagrapns.
L.I.1.1 Maximum/Minimum Distance Between Ships
ATA is designing its system for a maximum range of 15 kilometers and aminimum range of 0.3 kilometers. Major considerations include mpintainingline-of-sight between the two ships while accounting for the earth's:urvature and degraded optical path. Considerations at short range includeadequate slew rate and gimbal angle coverage in worst case sea state.
4.1.:.2 Maximum Relative Motion Between Ships. Worst Case Sea State
One can place an upper bound on relative motion between ships by estimatingeach ship's maximum heave and pitch response to heaw,' seas. Dynamics ofMarine Vehicles. by Rameswar Bhattacharvyp presents the perrnent Hata as afunction of sea state and Beaufort wind force. Table 4-I presents typicalvalues.
The ship's response to waves sets the low frequency inpurL and bounds. Toestimae the relative motion nt ships in these sea-. the ship's heave.pitch. and roll response W t-ese ampli tuden must a- he knowr.
APP IE -rECH"L ASS(J( ." S , -:' . :.T. ?'e"o SBiP-
S SR!), , .nii ?T?:C FTAL PEP)HFT
Ma;, ] 2S
Tabea' IeSaraers
Sea ind Vind Significant Average ageState -rce "el I-'," (kt ) "a:e Heignt Kf} Period (se. , aveietg.h ( f t
S 3 8: i>32 1K . 8 17'
7, -7
-. ~~4 'F / 7 4~
S6.6 QQ5 - -,' 71 5 ,1
6 24 1, 6, b'5 666 26 12.3 7.0 188
* 8 14.3 7.52118.6 8.6 285
3 40 29.1 !0. - ""Z8 9 44 3S.2 1.8 534
o 54 44. 815), -' ... . . 4 7C0
0, 17' 32.51 14.5 810
"'-S. Relative Motions and Related Phenomena" by M.F. Van Shijis presentsresults of experiments of the heave and pitch response of a ship and showeda st-ong dependency on Froude number (F = V igi) and the ratio of shipn
,engthc Io wavelength. The orst case response presented -was at a Froudenumber of ..5 and a sh:p length that "-as half tnr wavelength. As shorn inTable --. in high seas the wavelengths can be very long (400 tu 800 feet).Some "cestroyers, frigates, and submarines aie around 400 feet long, but-;ouid nave to be making 3f) knots to achieve this Froude number. Since thisis uniokely in such high seas, a more realistic estimate would be that rt.e-eiative ship heave would be enual to three-quarters of the wave height;nicn. corresponds to a Froude inumber of 0.3 and a length-to-wavolength ratioo0 : -.
Using -his factor, the worst case painting-and-tracking requirements occur2n-1S,4en -ne ships are 2 waves apart. For most ships, n must be greater than
one o:nce ship separatiot. vill likely be at least tvo ship lengths.Dar*-:-.Lariv in rough seas. Accordingly. for this calcuiation minimumcepa:-" .on of 1000 feet (0.30. kin) is assumed required. Tabe ,-2 presentsne - 'ation anzle covera we ror the t',vo .-'orse rough Q.a condin r.
APPLIED TCHNUOGY ASSOCIATES, IMC. A> emo SBIR-032880R006,"rh PATSOC Final Reprt
May 10F8
Table Y-2. Reiative D.spia'ement Induced Angle
SignificantTave Height ;ft) Wavelength (ft) Heave (ft) Separation (ft) Anglef
53.1 810 40 1215 1.9045.5 700 34 1050 1.9035.2 534 26 1335 1.1029.1 444 22 1110 1.1023.6 363 18 127 0.8018.6 285 14 1000 0.80
For an angular pointing system, the pitch and roll of the ships must also beconsidered since these can be significantly larger than the relativedisplacement. From the Van 5hijis' book. we see a maximum pitch response ofe = 1.25(360)/X, at L/AX - u.65 at a Froude number of 0.5. In Table 4-3, forthe sea states previously analyzed, we find the following pitch response fora 00-foot ship dt a Froude number of 0.3 (17 kt):
Table 4-3. Pitch Characteristics
Significant Wavelength (X) Pitch';a',e Height (ft) (ft) 9/Kia = 1 Pitch (Degrees)
53.1 810 11.8 13.345.5 700 11.7 13.233.2 534 11.9 11.329.1 444 11.8 6.523.6 363 11.7 5.318.6 285 11.7 1.2
Since the maximum pitch would occur in a different part of the wave thanmaximum relative displacement, the two effects cannot be added. The maximumcombined effect would be where one ship is pitched down and the other is at
4n 3the top of a wave. This would occur when the ship was 4 wavelengths
apart. The worst case for the 53-foot waves would result in a 14.4 degreelook angle. To estimate roll motion a typical roll response to a wave wassimulated (see Section 4.1.1.4) and the response to the 53-foot wave wascalculated. This resulted in an estimated RMS roll motion of 8.7' If weassume a Gaussian distribution, one can say that 90% of the time the rollwould be less than 26' (3). If one wanted to include 99% of theoccurrances, the limit would be +43'. Based on these calculations, plusinput from operational Navy personnel. the gimbal limits for the pointingsystem will be _45', driven primarily by roll.
.i.1.3. Worst-Case Pitch/Roll, Worst-Case Sea State
A7A in using values whicn allow up to plus or minus &> degree7 nf pitch androll. Yaw motion is minimal and azimuth requirementc drive thc cutergimbai. Wavp periods of up to 10-15 geconds ap fa!iv .vpical.
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-02588RO006/mh PATSOC Final Report
May 1988
a.!.l.4. Worst-Case Base Disturbance SpectLa
Perhaps the most widely accepted spectra of wave motion is the Pierson-Moskowitz spectrum from D. Hoffman's paper "Analysis of Measured andCalculated Spectra", of the form:
,. .4 -5(2,\4 -4
S(w) = n1/3 ( -) exp [2 2
where: H1/3 is the significant wave height in feet
T, is the average apparent period in seconds
L2
S(w) is the wave energy spectrum in ft 2/(rad/sec)
W is the frequency in radians/second.
The Hoffman paper compares this analytic form with many measured spectra andshows general agreement. Figure 4-1 shows this spectra, plottedlogrithmically, using the same values of H1/3 and T 2 as were used in the
Hoffman paper. Figure 4-2 presents the wave spectra for the worst casew'ave we have previously considered with H1/3 = 53.1 feet and T 2 = 14.5
seconds.
The Bhattacharvya book presents analytical methods for constructing theresulting pitch and roll motion from wave amplitude spectra. There are twoeffects: (1) the natural freqjency response of the ship and (2) theexciting moment for the ship, which is a function of the ship design and thewavelength-to-ship length or wavelength-to-ship width ratio.
The angular frequency response of a ship to an applied moment is anunderdamped second-order response. Table 4.9 in the Bhattacharvya bookgives typical values of the pitching time constants. These range from 4.4seconds for a 500-foot destroyer to 9.0 seconds for a 1,040 foot aircraftcarrier. This would correspond to a natural pitching frequency of between0.7 and 1.3 radians/second with the higher frequency corresponding to thesmaller vessel. For roll, Bhattacharvya states that roll periods aretypically twice as large as pitch and gives typical values ranging from 9seconds for a destroyer to 17 seconds for a battleship. Furthermore.Bhattacharvya states that the roll damping coefficient is very small and"the magnification factor may reach a value between 5 and 10."
ApLID EC1NLOY SSOC>-TES, INC. ,TA Memo S7B1R-025
SSRQO6'mnPATSOC Final Reportmay !Q88
20-
71 A
-0
-120
I- 1_A I I I I I t I I l-L'rr~Qy9Ic' I-4
F ~ure4-~. ave Mot ion PSD 11K r. =9
.PPL:7D TECH9NCOLuOGY ASSCOC.IEE. TIIC. rATA Memro SBIR-025m3 O n ?ATS(C: FiLnal Report
May 1988
Q1 I TJT1 T1FTFFFI rFT - rT fl-t--r-T-r-1 T
20-
N"N,
2 0K_10N
-2 -2 -'
ILI
_120
_IILJA I ILJKF r- ,EII
Figre 2. avpMoton SD -=-1 T=1
(Sp ctal ha ac er f 7--X r, - Ca c
APPLIED TECHNOLOGY ASSOCIATES, PNC. ATA Memo SBIR-02588R0006, mh PATSOC Final Report
May 1988
The other factor is how the pitching moment is related to the waves. TileBhattacharvya book shows that this pitching moment can be calculated by:
L/2Me = Pg f 2y(x)E(x)dx
-L/2
where: p = density of waterg = gravitational accelerationy(x) = location of the ship's hull in the vertical direction(x) = wave amplitude as a function of horizontal ship station.
The Bhattacharvya book plots this as a function of the ratio of thewavelength to the length of the ship. As shown in this reference, thisfunction falls off very rapidly where the wavelength is shorter than theship's length. The Van Shijis' paper depicts the measured combined effectsof both of these phenomenon for a scaled ship. This ship had a naturalpitch period of 0.783 seconds which corresponds to a natural frequency of 8rad/sec. However, the experiment was scaled so that this correspondedcorrectly to the dynamic response of a large vessel. Figure 4-3 shows theresponse of the vehicle in pitch versus the ratio of the ship length to the-wavelength. Notice the sharp dropoff at L/X = 1.0. By fitting a straight
1; 6iine to the data, this falloff goes like (L/X) -
. Since the circularfrequency. w, is related to the wavelength by w =V/X = 2n where V is the
T-
velocity of the wave in the iwater, we can scale this b using theapproximate wave velocity at a given sea condition. For the 53.1 foot wavecondition, this velocity is approximately 350 feet/second. The ratioplotted in Figure 4-3 is Ea/ka. If we model the high frequency behavior of
-6this ratio as a failing off by (L/X) , beginning at (L/X) = 1, one can showthat:
Oa 2n 5a = L
6
By relating this to the circular frequency. w, using the wave velocity
relationship above, one finds that:
ea (2rV5) I rad
fa L6 5 ft
Using values from above, one has a high frequency behavior of:
Ea _8 mr in the region where L > X.E~a ~ 7 ft
9a 2rt 2T mradBelow that region - W-- = 18 -E V ft
APLID EHNLOY SOCIATES, INC. ATA Memo SBIR-025
8BROO6imhmay 1988
88P0UT4, PATSOC FAjinas epr
5.-, -' -' ,0, -S 2irc 2
1
Figure '.-3. Response of the Vehicle inl Pitch versus Ratio of Ship Length to
Wave Length.
WAN TECHNIDGY AS..CATES. !NC. ATA Memo SBTR-Q.2188RH006 Q PATOC Final Retvm,
May P88
Using these two !eiationslips. one can snow tnat L A = corresponds to =7.90 rad sec for our YU(.-foot snip. To construct a frequency domain rodelof this iesponse, it is assumed tnat the denominator can be approximated bytnree second-order systems with natural trequencies w,. w, w,, and dampingratios ' , and 3" Onp of the natural frequencies, w,. -will correspond
to the natural pitching motion of a small ship. such as a destroyer. Forthis case wI " 1.3 rad/sec and we assume a damping ratio of II = 0.5. For a
Froude number of 0.3. there is a peak of about 14% at L.X = (1.5. This wouldcorrespond to a damping ratio of =0.5 and a natural frequency of w,
Q,, rad/sec. The third natural frequency, w, is set to that corresponding
to L. = I which is 3 0.90 rad/sec. The damping ratio was selected so
that the normalized pitch response would have a unity gain at thisfrequency. This results in T3 = 0.60. The resulting analytic frequency
response is shown in Figure 4-4, which appears very similar to Figure 4-3.
The analytic expression for this function is:
<a2 22
($22iW1S+w, ) (-2 ,wS-w,_ )(S 2 W )S- )
70o7. 3n /= (K 211 x on the right side of the equation. one has:
6 ().Ul8)( wl °2 w3 )S rad" '9 " 2. ft
This last response function is calculated and plotted in Figure 4-5. Whenthis response is subjected to the wave spectra shown in Figure --2. theresulting base motion spectrum is as shown in Figure A-6.
A similar process was followed to estimate the roll spectrum. :n this case.the natural rolling motion of frequency was adjusted to be half that forpivch (W 1 = 0.65 rad/sec) and the damping ratio (c,) was adjusted to be
:.jl. which corresponds to an amplification factor of 1'. The other twofrequencies were adjusted for the difference between the rolling momentcoefficient and the pitching moment coefficient. There was no data given inthe Van Shijis' paper. therefore we assumed we could s"bstiute the width ofThe ship (assumed to be 55 feet) for the previously assumed "00-foot length.This resulted in shifting w, and w to 4.65 and 6.11 rad,sec respectively.
Figure 4-7 shows 'he roll response due to wave amnl:'ude and Figure -- 8ieplcts the resulting rol spectrum on 'he dArP of A -ffoo w:d -hip.
APPLIED TECHNOLOGY ASSOC.:A:'ES. m,C kTA Memo SBIR-i2-"38R000'th PTSQC Final Repor*
may 1988
1~ P LE
-igure 4~.Amp11i'ude Re!sponse 'lri-al ,ezP ~n
APPILIED TECHNOLOGY ASSOCIATES, !NC- LATA Memc SBIR- -
88RO00b. nrn .A:SOC Final FePortMay !1988
r i -~ T~iTtT ------ 7 7 T vr T--- TT T
rr)
I-.-
F r- 0I rjc-Y
FiurJ'np
..PPLIED T7ECHNOLO)G' ASSOCIATES, .,NC. I- %A Memo SBIR-02-138RQU~ rnh ATSuC Final Repout
Mayi 1988
Ir; L~-1 T t- ~ i t-I I I i i -j I- L7T t -1 - 1
F-: 1
/g r Pi - i7 ran c )e
A.PPLIED TECHNOLOGY ASSOCILTES, TI;C. A 7 MAemo SSBIR-Cil88ROC06 mn PA. TSOC Final Rcpcr:
RLL ES=:ONSt -&',Xn5 F- SHiP. n:3., r7vA. E
0ECK A(DTCON
- j
Fiur ~-.Roli1 Resp~onse I *~
A ?PLIED TECHNOL,)GY ASSOCIA-TES. ,INC. AAmemo SBTR-'
ESROOO 'nn ?TSC EnaI Repo"tM ay lose
VITZH- CIS7IJP~dkNCE 53"=MIM CU .'.EI. iC-
DECK Mr)TICN~iO::CC:O~OC~ONP7S:
77
z-
Figure 4-;. Roi' Dis-turbance Sp,-' rn 1c ' ave MIo~or
:-,F=_'_1 TECHNOLJGY1 ASSOCIATES- 7INC. ,.;~ Memo SBIP-;>l-8~O'6mn PATSOC Final Report
May 1' 88
1..5 C alIcul1aio n of SLO S ura nc e
...e system must also remove the relative motion of the two snips due to::ei idiiua havngmtionls. The angle between the two can be
ca.lcul.ated approximrately as:
eLOS Ri
wnere Z,., Z, . are the vertical displacements of two ships and P is rhe
separation disrance. If the motions were unco.-related. on~e could calculate:ne ?SD of the angular motion by adding the two displacement spectra and
-nen dividing by R'. However, in this case the moticn is correlated atsnort distances, therefore we can bound the problem by calculating the anglesPecrum as:
t LOS (Wi) - Z
.gain, we must compute the effective frequency response of the ship related-o tne circular frequency, w. For a Froude number of 0.3, the normalizedm ave response is 0.-7 at L/X Accordingly, for the heave response, we
assign w, = (n 75)((O.9() a -. 68 P 'sec and E .I . ;e .:ill maintain
1 .2 Risec with ~ .. To achieve a response of '.57 at w,=0.,
requi res 2= 0.5. Therefore, the neave response has the following
:recuency responses:
E a 2 -
(S W S-w'bS R2,sec - (S -0.7
0 ,. =. .
kApl-lng this transfer funct-ion to the wave spectrumr mrownT in 7FivUr- 4-2results in a ship displacement spectlum. Assuming a mjinimum- sepatation of1,.'01, feet, mne resulti.ng line-of-sign, spectrum i!7 m'own in Figure -.~9These spectra can no-w be used to design 'tip poitino anoi !od.:nssem.
iPPLE!-D TECHL&G SSU TS C Memo SBIR-02fmr'. PTS('C nai Report,
May 1988
SA: LI :'iFz*&~ME 'JC:~O~':CO~OC~ZC 4~ PS
-1~~~~~~~ a. -r.T)- .'~5 2
z N
'( a : o
*P' " r~qrLI]YS.?2CI.' : -.,a- ' T..... .:u. ATA ' ero SBIR-%i
,?AT'F -nal ReP Cr
c .o s-Casp ?rpagatron ie, :U Chara lei-sticE
;'hen optical communications occurs over a direct line-of-sight path, as is
tne case here, the propagation analysis is concerned -with radiant flux on a
receiver apert'Lz. Her --'c ccnsi!er trc losses due to the atmosphere.
Atmospheric absorptionscattering at optical frpquencies limirs the
separation Detween ships. This is Jue primarily to the high absorption and
scattering coefficients of sea water. Beam clearance above the sea surface
Is or paramount importance for two major reasons: 1) in reducing the
Probability of waves breaKing the !cne-ot-sight and 2) in reducing the
amount of sea mist and spray over the path to a minimum. Using simple
geometry "ith two ships placed on the surface of the sea, .e approximate the
_.ne-of-sight separation between the ships by
R : , . h h c REp E
w-here:
F_ = Radius of the earth Pxl". m)
= height above the sea le.el of the platform carrying the
.ransm i ter-re-eivpr
2 = height above the sea 'e.'el of the line-of-sight,. i.e.. the line-
of-sight clea.r nce ar)ove sea level
P= line-of-s:gh- range be' ',wn The communicating chips See Fig.1O).
APPLIED TECHNOLOGY ASSOCIATES, 1Nc. ATA Memo SBIR-0288R06/mrh PATSOC Final Report
May 1988
MC Sea Level
Figure 4-10. LOS Calculation
rlain/Mist/Haze
60%1 Km Saturated Air Humidity
j3Km~ 4 Km i 3Km
Transmitter Receiver
Portion of Path Nearestto the Ocean
Figure 4-11. Atmospheric Conditions
4-18
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-02588R0O06imh PATSOC Final Report
May 1988
For a clearance of 10 meters (h = 10) and package height of 15 meters (h =c p
15) the maximum ship separation is approximately 15.5 kilometers.
This derivation is shown below:
h = height of pole or mast carrying XTR/RCVR above sea levelP
h = beam clearance height above sea levelc
A= h - hp c
R- = Radius of earth = 6x106 m
RE .h 1 2E SecO + -9= 1
R E h - cose -2 25 C i e -
I' E + hc) + 6 2 2L _ 2 LRE+ h 1+ E+ hc) ore hE+ (RE+ hC)
(Range =R):
R RZ (RE + h) 9 126 (RE ( = - hc ) E = 2=~R ' hC) e = 2R h
R 2 /Z depends on A only (approximately) whereas h is determinedE p
by h_.
Example: For h = 15m; h = IOm; A = 5m; R = 22 10 3 m = 15.49 km.p c
4.1.1.7 Atmospheric Transmission Calculations
The path that the beam travels from one ship to the other passes closest tothe water surface at the midpoint between ships, so let us break the path upinto the following atmospheric conditions for calculation of one waytransmittance for 15.49 km (approximately 16.0 km) range. See Figure 4-11.
First 3 km: 60% saturated air at 23'CNext 4 km: saturated air at 23'CNext 2 km: haze and mist
Next 4 km: saturated air at 23'CLast 3 km: 60% saturated air at 23*C
/-iQ
-PPLIED TECHNOLOGY ASSOCIATES, INC ATA Memo SBIR-02588ROPOO,,mh PATSOC Final Report
May 1088
Tli, pnirion nf 'he path nearest to the ocear. surface (approximateiy 2 kin) ismodeled separately as a region of rain,,mist/haze.
The path attenuation due to this atmospheric segment is calculated for
several wavelengths as follows:
( X = 0.5urn) = 0.5
(A 0.BWM) = 0.697 (X l.Tum) = 0.77
(Reference: Hudson's "Infrared System Engineering, Table 4-13; pg. 164).
An intermediate segment of 4 km is modeled as 100% saturated air and watervanIr mixture. The outer segments are modeled as 60% saturated air andwater vapor mixture. The amount of precipitable water in these segments
2 (4 x 20 l 3 x 12) = 232 mm of H20.
We will approximate it as 250 mm of H20.
Path attenuation at a given waveleng' for this amount of precipitable water
is obtained from standard references (Rand Report, pp. 898, July 1956).
Total one way transmittance for the assumed range model is
for X = 0.5um, r = 0.351125 x 0.5 : 0.1756for X = 0.8um, r = 0.4618 x 0.69 = 0.3186for X = 1.71im, r = 0.89 x 0.77 = 0.685
The table values for absorption and scattering vary with wavelength byorders of magnitude. A window for absorption and scattering resides in therange from a wavelength of 400 to 600 nanometers (nm). There are severalchoices of available lasers in this region. The EXIMER laser wavelength at451 nanometers is an excellent choice but is expensive and bulky. The
compact, inexpensive GaAs laser diodes present a poor choice withwavelengths from 750 nanometers to 880 nanometers. A good compromise,
however, is the laser diode pumped doubled Nd:YAG laser. This gives awavelength of 530 nanometers with good propagation characteristics through
water saturated air and rain. This device is small and rugged, and with the
pumping being performed with GaAs laser diodes, the lifetime is in the tensof thousands of hours.
For each of the beam pathway sections we use 500 nanometers, slightly lowerthan the 530 nanometers doubled Nd:YAG only because studies using a 500nanometer wavelength are readily available in atmospheric tables. For thepath sections, we find that the major contributor to losses is inscattering. We therefore ignore absorption losses and consider on!-"scattering (reference Deirmendjian, 1964). For a rough order of magnitudeof the transmission through the 16 km path. we have at 500 nm the sum of
p e- P I ta b Ie r-. 50 mm vtrc a --a ns ar!-~c ir r>~~ (T 1 c-? 7
a c ite .3. Hud son) F,)i th11e 2km of. c a, ~ eh'e ansmi tanc,,e ofa ccut 1 <5 , the to.tal transm Itt rnc E th
T 20(l 67) (1.5) - R '.15 (Ta blIe 4.13, Hudson)
fr tine entire 16 km path which is very close to the T(A=<..Sun) obtainedfrom- the Rand report above. For a more precise analysis of the propagation
.-ansmttance and boundL,'-laver effects the LU() TRAN simulation package canD e_ r-i r.. For the next phase, an in-depth analysis wilbe rut, -whicn shouldnlex 7narrow1. down the appropriate -:aveleng~h of operation.
ioz we have pr-sented only a rough order-of-magnitude analy'sis, we havehonOtat we have atmospheric losses that ate reasonable for incorporating
into toe design of the ship-to-shiP line-cf-sight link. -he kE- point intois anal',sis is that an appropriate choice of the propagation wavelengthra7 result in acceptable losses, -hat the douhled Nd:YAG or a GaAIAS laserdiode may be a good choice.
7cg!_re 4-12 shows atmospheric transmission results for mostly clear withnaze conditions.
-re study also considered the condition of fog mixed with light rain and astorm. Both these conditions dramatically reduced transmission. The
re_:' obtained by ATA agree with tne resuits obtained, b,. A.. Goroch.and C. Trust'; in their art ice., "The Near-Ship and Arrhient Marine
_:-nent" in JDP. (recfive-d c.>.a8)
Tn >Drj'sion, ATA's studv showed that the best a-.ailable? derivied laserZ)Um e o (yer all meteoro,'ogical conditions were the GaAlAs and Nd:*IAG whichoperate -with approximate -wavelengths of 0-1.80 urn and 0.53 irn, respectively.
-or- communication purposes. iaser output must be modulated. The diode lasermay: .e directly modulated by changing the input current. The Nd:YAG laserm7a. -e modulated via Q s-witching or cavity dumping.
..115Bandwidth of DisturbancE_ Rejectaon Loops
tr~n 'e spectra presented in Figures 46 4-8 and 4-q. one can determine
.... m7inimum error rejection bandwi6 h to achieve cerra~n levels of residual--, i ter on target. To provide a quc nls 'e assumed a Ty.pe 'I
~oo ti to 5 7 and 10 Hr- Error rejection band-widths. Table -be~ow..te residual jitter on the other recei,.,er *or this handwi-.dtn.
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-025
88ROO06/mh PATSOC Final ReportMay 1988
* Naval Research Laboratory Conducted Study of Infrared RadiationTransmission over Chesapeake Bay under a Wide Range of Atmospheric andMeteorological Conditions
* Results of Study are:;=100-
60 -
€ 40 - t-
Talo & ats 95-5
06 70 09 10 111 12 L3 14 15 16 1.7 ISWAVELENGTH tMICRONS)
032 1 06
CURVE PATH. TIME TEMP ARK PRECIP TA LELENGr, *AYERS Ital
A 0000' 3PM 311F I 1M#A 22144
a 14 Mj I3PM 34 51F 4m~ (3?P4 IGMIC 101ML 2ZAM 4WOf 46% SZOMM 24k&
Taylor & Yates 1955-56For Mostly Clear with Light Haze Conditions
Figure 4-12. Atmospheric Transmission
'4- -.-
APPLIED TECHNOLOGY ASSOCIATES. INC. ATA Memo SBIR-1'2588R0006.'mh PATSOC Final Report
May 1988
Table 4-4. Residual RMS Motion With Error Rejection Bandwidths
RMS MOTION ERROR REJECTION BANDWIDTH
DISTURBANCE NO CORRECTION 5 Hz 7 Hz 10 Hz
Roll Motion 151.2 Mrad 50.8urad 25.urad 12.5uradPitch Motion 59.4 Mrad 27.2wrad 13.9urad 6.8wradLOS Motion 51.8 Mrad 9.2urad 4.7wrad 2.2prad
For a 1-meter beam at 15 km, a jitter less than 32 wrads would besufficient. It is clear from Table 4-3 that the error rejection bandwidthneeds to be between 5 - 10 Hz. For a 5 Hz loop, the roll motion is toosevere while the LOS is adequately rejected. At a 10 Hz rejectionbandwidth, even the worst case residual is adequate. The 10 lz bandwidth isadequate for coarse gimbals. Actual loop implementations must be consideredto pick the bandwidths more carefully. Also, when details of the noiseintroduced by the gimbal torquer and other high-frequency vibrations areconsidered, these bandwidths may need to be adjusted.
To make an attempt at doing this, a simulated spectrum was generated to addsome high frequency vibration. These levels were chosen to provide, with ahigh-bandwidth loop, equal residual RMS noise in the high-frequency bands.Figure 4-13 givep a combined LOS angular spectrum low 'requency plus thisadded high-frequency vibration.
4.1.1.9 Maximum Aperture Size
ATA plans a maximum aperture size of 25 centimeters.
4.2 Identification of Key System Elements
ATA identified the following components as being key to an optimal system:
1) Nested optical loops;'2) Digital controllers;
3) Gimbals.
The search for a ship-to-ship optical communication system that is optimalin cost and performance was therefore constrained to shared aperture systemsemploying digital controllers to position gimbals and steering elements inmultiple, nested control loops. Such a configuration provides a systemwhich is optimum in a global sense. These components are described in moredetail in the following subparagraphs.
4.2.1 Nested optical loops
The use of nested optical loops is key to achieving a low-cost pointing-and-tracking system for the ship-to-ship communication. With nested loops, the
n r .. Fr:-May :'..
....... -e -',i~ " a . ..e '' rig oprt i:e !-r eme:lte, ; I n 7u "- i
qe':c[! e aopica elements as topse: a s ")le large f " G IImirrr or telesccce. Single loop systems Jsua-. v nave resu ted :i: in.Dan'i:th pointi:.g-arid-tracking surs'stems because of the large iner'asinvcl.ed and finite actuator powers available. Further. tne.,' providerta no reecton of high-frequencv base motions and c:sturbances 'un
are inevitably coupled to the pointer tracker line-of-sight to becomeopticai communication beam jitter. This beam Jitter becomes increas:nglymortan."t as the size of the receiving aperture decreases in relation to the
;idn~ of the optical beam as will be the case for a low-cost system.
ih nested loops, the tracking error controls small, lo w-inertia. high-banwi:dth steering elements, such as General Scanning Inc.'s Fast SteeringM:rror (FSM) (shown in Figure 4-14). These steering elements can becontr.led directly or indirectly, as described by Held and Barry of theHughes Aircraft Company n "Precision Optical Pointing and Tracking fromSpacecraft with Vibrational Noise". SPIE Vol. 616, pp. 160-166, OpticalTechnologies for Communication Satellite Applications, 1986. Such a mirror
:currently be-ig used in our conical scanning laboratory experiment.
Wnen controlled indirectly, the steering elements follow a -tabilized massr-ncc is pointed along the desired LOS by the tracker. The steering
elements follow the mass via high-bandwidth slave loops. In either case.the zceering elements move the optical beam at high rates, decoupling itfrom -he higher frequency base motions and disturbances.
.he c. inrer tracker gimbal set which houses these steering elements followsthem or the stabilized mass to which the steering elements are alignedthrougn 'ow--bandwidth slave loops. The gimbals with their larger inertiasonly nave to follow the faster beam-steering elements or stabilized mass~wi tneir smaller inertias in an average sense, just as single-loop low-bandwidth pointeritracker systems follow their targets in an average sense.in either case, the gimbals move the optical beam at low rates. decouplingit from the lower-frequency base motions and disturbances without requiringprec:sion pointing of th? gimbals, as is the case in single-loop systems.
APF -IKD 7CHNALiG'i ASS%, IA rES , .
T eoSRt PATSOC Final REt)(-'
~ay
O48MIIWadl I0 10 Hz
6-S lcr-ordj 1,- 100 I
6 Micmoad 10 1000G Hz-
Figure 4-13. LOS Angular Spectrum Low Frequency Plus High FreauencyEnvelope.
APPLIED TECH; LYI '":ATE . M. AKm. _emr - L
! .n','e '}/ '} q rc 1a" n:ia- ' e p i,, l ed '.itt g:eat P:Pcl2 1 o"r f- 'v;
ela'i ',s'- to nave high pre:i-ion, *hey can be mantufac,:ed tocrosiderablv less rigid specit:natfons than gimbals for singie-lonp -yr' T"- eftec, tne requirements for precision hae been dist::butec betweengimbals and sreeri~g elements, thUs relieving the gimbals of the hurcen 41prec-sion pointing. By so distributing the precision requirement ., !'eg:mbals can he manufactured very inexpensively, using lighter, less rigidmaterials such as composites or plastics. The small steering elements arethemselves inexpensive and so the mechanical elements of the resultingnested :ontroi-loop system are considerably less expensive to manufacturethan those for the single-loop system. Note that low-cost has not beenachieved at the expense of performance; in fact, the performance of thenested multiple-loop system far exceeds that of the single-loop system,hcn'further st:engthens ATA's cost and performance rationale for using
nested multiple-control loops.
-.2.2 Digital Controllers
A7A Delieves that digital controllers, as opposed to analog controllers, asa means to tie the multiple, nested control loops of the system together,:erresent another important area for cost reduction. Because of the rapidadvances in semiconductor technology and manufacturing techniques, digitalcontroi hardware is both plentiful and inexpensive. Because this hardwarei7 ar off-the-shelf item. only the control laws and the software algorithms:trn mplement the laws requife development.
ntelmigent decisions and algorithms can be implemented easily on digitalcomputer control systems. Several models comprise a complete description ofine-"1gital controller of the tracker and communications system package.First, remote and local command of the package is simplified through anintelligent user interface such as a terminal connection and/or as'atusicommand control panel. This facilitates quick communication linkstatup, z:quisition of other ship commands, and communications systemstatus. Aside from the intelligent front end, the digital controller mustperform a systematic search or scan for a designated receiver. Conical,raster scanning, or other s~anning techniques can be exercised by thecontroller. Large and narrow field-of-view (FOV) for coarse and finetracking/scanning are decisions that the controller employs. To reacquire alo-t or faint beacon, predictive algorithms can be used to minnmize down andretransmission times. A low bandwidth controller for the pitch, yaw. androil of the ship is inexpensive off-the-shelf hardware.
The digital controller for the high-frequency control will depend directlyupon the base motion disturbance rejection necessary. Here. parallelprocessing can oe incorporated if necessary.
-PP!ED TECHiNOLJG-. ASSOCIATES, INC. ATA 'Ae7cj SBIP-0_88PfR'116 .h ?ATS,5C- 7Pnal Repor,
May, IQ88
FPigu'e 4--14. CGeneral Scanning, T.,Fast S~eering Mirror.
PL.: D TPCH 'L~Y ASSm .o SBI-- p ... :> r~na- F~po
J I og- s'e5 O a.e :t _ ''.e ' 2e. " .- , p1 e7 . i',w ...e". Pccing the compute r and , 'j .. needed in -igrai p: nce s fngappl:cations. The DSPs are appicai e in tris control prorIem fr 'ohe igghtreouency'v contr c loop. Here, :n place of ganging multple conventiona-:pe processor modules together tc implement a parallel processing approach,
one DSP coupled -i th one conventional processor may indeed provide the,ecessarv computational requirements.
. g:ita. controller can handle the scan-acquire-track logic and handoffopera'ions. It can also be asked to control tne lew-frequency track loopano te high-frequency track loop, which is dependent upon t, st motion PSD.
S'J00-25,000 digital controller can handle a 1 KHz closed loopbar,dvii:h. Figure 4-15 shows control modular flow. Figures 4-16 and 4-17sho'. two VME. systems that ATA has under development, CONSCAN and SSP.Fiire -,-18 shows a possible VME bus configuration for this project.
Digital Control Electronics
7r tne digital control electronics, MC68C20-based boards, both with ano•toout parallel processing capabilities were considered. However, due to'ne rapid involvement of digital semiconductor technology, a complete04glta. controller specification at tnis point may be rendered obsolete atI;ie a,ia! time of the prototype design effort. At this time, ATA has
- a single degree-of--freedom ultra-precision controller us:ng a"ME 'e: .... architecture. This controler utilizes multiple CPU boards toePC Parallel processing, and is currently being developed into a 6, - -freedom controller.
A -ital control system offers more flexible and adaptive means ofcor 'iing a gimballed type transmitter,-receiver flat and associatedcomponents. The functional modules comprising the digital controller are:
initialization:NTDS Command front end;
> Safety operation;) Cross-link receiver acquisitior,;> Receiver tracking;6j Reacquisition
F-,,..e "'-19 is a photograph of a set '.f typical digital control electronicsn' ' t '
Apr :E D TUA-uL, F F'mrSEI-
3SRCD~ mn -ASoC Final Rerpo!,mn May
________ IDP d
-j _j - -,e i ive.
", Y,
-711
iIL EI C VIIE C01IPUTEi-1.
7C,,
Figure 4 16. VME I v t e nd rD ve2pm ntSy '
AP TTED-CHNOLOUY' A 1d~ATES. ;!.AlA Memoc SBIP- -8 RUC mh
F'TSC inal Repor,Mav IQR
68881' FF Kdr..-F
25 M~cz D,..rdnre
Figure 4-1". VME SystmUdrDv lpe : S
APPLIED EHtiG 3'ATS 2 v
8RW'mh F>Anal Reiro:'
ii
DIA S~4MIi.~
VMAE [3,s
E6030 CPU IL~ 1n~~rC~tL~
Communications Supcivso( C68 riu PQ$ilI'll ElIfIIIJIU( GluLa4
Low EPand~xJtl CunitoI Mmof
LO Gala Acqu~fi--toc
VSD Bus
Figure 4-18. Possible Configuration
FP TEECHNOiLOG ASSOCI TES. INc.mh
PATSOC Final Re orr-Ma;' 1988
Figure 4-10. Digital Control Electronics
* P,' 'n F T7 , - 'nal Repnr'*M a I T
-.-.[.. fnllt I ailcat ton
nte .nitia lzation mode, tiie contLoilei goes through a vstem status andnea tn check and then identifies a vertical frame of reference via a one-ayts %el tial gyro, horizon sensor, oz the Naval Tactical Dara Systems(NTDS) computer .. The system status and health check provide a self check todetermine the working condition of tne laser subsystem system, thecommUnication subsystem, and the Fast Steeing Mirror (FSM) and gimbaltunctionality. It then reports status to NTDS when queried. Afterassessing the functionality of the various subsystems, the vertical frame-o:--eference sensor is monitored as toe gimbals are commanded to a levelposition- . The vertical frame-of-reference is needed to reduce the searchvolume in acquiring a receiver on a second ship as discussed earlier.
-... 2.3 Naval Tactical Data System Command Front End
T- facilitate operations training, all commands, status, and data are routedtrougn a NTDS interface. The digital controller can therefore be treatedas an intelligent peripheral or as a NTDS computer. Commands sent to thedigital controller control which snip to scan and lock-on to, and controlthe dataflow to and from the communications subsystem.
... 4~. Digi*ai Tracking Controller
.esred digttal control loops consist of one high-frequency loop closeda uo.-frequenrv loop. The iol,-frequency loop controls the gimballed
po:nt:ng fiat and should maintain a Pointing accuracy to within the field ofvie'." -f the high-frequency beam steering mirror. In the process of locking-in on the target, the low-frequency -ontrol loop, using a wide field-of-
tries to minimize the error on the quad-cell or avalanche photodiodea-ra'. Only one digital processor is needed to control the FOV and senda rr correction angles to the gimballed flat since this is a relativelysilo- control loop. Stepper motors can be used to achieve the desiredacc iacy and when the error angle i- within the fast steering mirrors field-f-.ev. the second high-frequency loop kicks-in and tracks to the accuracy
neede.. Bandwidth requirements are still uncertain until actual platform.-easurements can be made. However, if bandwidth requirements are less thanr-ilonertz, a digital implementation is feasible with current off-the-shelf
p:-. v. Here, if necessary. parallel processing may be needed to achieve,;ie necessary calculations and control input/output ignals. The parallel
proce,-tcing aspect is currently being implemented in a seismically stableolatform controller at ATA (Figure .- 2h).
a.K.?. Track Reacquisition
".ring -he tracking control, the digital controllcr record- thc pla'formd n-rbances arid trajectory of the target. This cnformainn is ,ed to,i c an est imator of the target in the e..en of a irv' trask rndi' ion.
7is will allow the tracker to predict hhre he target "'ill bhe I the next-lise-ond, second, or minute. TIiis- pi i r
*<tLf for hivih sea-state sonci, itinr : n b ;h n ti ,-' , f -n( ict r;' t hips
PPLIED TECHNOLOGY ASSOCIATES. INC. ATA Memo SBIR-o25
88RK)OO/ mh PATSOC Final RepoLtMay 1988
P , "l v ] irge waves. 1ipre. fast reacquisition is reaizer4 and riuvntime is minimized. The additional computation necessary to performpredictive tracking is of little consequence to the control bandwidth, sinceseveral processors may divide up the computation.
4.2.3 imbal
Structural grade plastics, composites, and traditional metals wereconsidered for the gimbal structure. Geared and ungeared DC and AC motorswere considered for gimbal actuation and unswitched and switched poweramplifiers for the gimbal motors.
ATA determined that the gimbal sets supplied by TPAX would be the mostappropriate. These gimbal sets utilize a unique Roto-Lok Rotary Drive thatincorporates a patented friction-drive technology which smoothly couples adrive to a load using standard flexible cables in a figure-eightconfiguration. Multiple cables configured in this way increase torsionalstiffness and improve smoothness through load sharing. The performancecharacteristics include:
1) No backlash;2) Extreme stiffness;3) Elimination of slippage;
4) Efficiencies of over 99%;) Environmental stability;
6) Reliability and long life.
Figure 4-21 shows the Roto-Lok Rotary Drive system; Figure 4-22 showstypical friction losses for different drive types; and Figure 4-23 showsbacklash comparisons.
APPLIED TECHNOLOGY ASSOCIATES. INC. ATA Memo SBIR-0l2588RO0006' mh PATSOC Final Report
May 1988
S ~tTPPER MOTORLG
MFOTOR
E :R T iC A C O N T O L LE R - -
S~AL MUTIPLER
FigureTA 4- 0 Digital Com ut r on ro le
PPVLED TECHNjL)GY ASSOcATES. INC. ATA 'eme SBR - XnSP' ~'( n PA S C Final Repot-
" 1 v:-.,irr :inmbal Sle%' Pate
The largest angular excursions occur at the longest wave amolitudes due totheir long wavelength and amplitude. However, due to the low frequency ofthese waves, the required line-of-sight rates are not maximum here. Again,the snorter the ship, the greater the bandwidth requirements. Based on our.nO-foot ship, we calculate the maximum rate to be 7.3 degrees/second whichoccurs with a significant wave height of 29.1 feet. Therefore, an angularrate requirement of 7.5 degrees per second should be sufficient. ATA does
deg radiannot expect accelerations of more than 50 or 8on large
sec secgimoals. etc. ;e expect higher acceleration rates on smaller optics, i.e.
radssec
,APPLIED TECHNOLOGCY ASSOCI.ATES, INC. ATA 4emo SBTP-02588OOob. mh PATSOC Final Report
May; 1988
Figure 4~-21. ROTO-LOK Rotari Drive Concept
APPLIED TECHN()LOGY ASSOC:IATES, INC. ATA Memo SBTR-2I8R OO6; h PATSOC Final Repojt
DRIVE TYPE
Rotc-Lo,
Drive 1/21/
St r a ig r-CSour Gear 2%-4,o
Ee~t 50/80,!
Worm Gear 10%-50%o/o
I II I II I I I I -0 5 10 50
% FRICTION LOSS
Figure 4-22. Drive Related Friction Losses less than i
APPLIED TECHNOLhOGY ASSOCIATES. INC. ATA Memo SBTR-G'2-"
88ROOO6/ mh PATSOC Final Repor!May 1Q88
BACKLASHNS7RUMPU EN T
BAASK*LASH LMOTIONA-)0
RCT.LKI DIV
-BACKLA I W - .L&
Figure 4-23. Blacklash Compar,.sons
APP E TECHNOLIGY ASSnCIATES. NC. .. TA emo SBIR- 7MR" M"n PAT 97 Finra1 Repri*
Ma. 10
Onen a targe; is detected. the system oil! go immediatei, !o tracking mone.This must be accomplished in less than a millisecond so that *ne ship'smcton will not ;ause the target direction to change more than a beam w~dti.The target will be maintained in track by rotating the beam abot the targetposition.
Figure 4-24 shows a sFhematic of a demonstration tracker. Figure -21 g2:'esthe optlcal system schematic for a tracking demonstration, and Figure 4-2fg-,es the signal flow diagram for a tracking demonstration. Figure -17shows a candidate configuration for ship-to-ship communication, andFigure 4-28 shows ship acquisition. Based on these configurations, vnefollowing calculations predict the tracker performance.
.PPLIRD TFCHN()L" ASSflCIATES IN~c -T 4 Pemo S BI 17 2:
ERQO16! rnn Fina I Per(
X e - at 'Arror
Bearing so - Beam PaL'
M Aror GimtalCoarseSuoporl
/A/ Coarse
Az; mu t
Actuatr Past Steefing
Aneatr Mirrors
-iue~ -2,4. Demns':at~ofl Trac~er
-PLE ECHNO LOGY ASOITS.IC TA Iemo SBI-:-zD-_ATSQC Final Repoi-
Attenuator
C o ars eEievation -Fou LensMirror IF Beam7and! Drive pitr
_______________________Laser
BeamEJ:evation and PathsAzimuth-:ast Steering -
MirrorsIQuadCefl Detector Beam Jitter and Power
DetectorQuadAzimuthDrive
Control DataProcssorAcquisitionProcssorSystem
-~-Actuators forBase MotionSimulation
Figuire Opr:-cal S,'rerp, t,-r Traci'n7 Dernon-rat nr,
.PP:) TL) TECHN')L'.Y ASSOCIATES, INC. AT.A Memo SBIR-i25~3~~6-TnPATSOC Final Report
Ma, 1988
3carse- evatiornrve
-:ast Steenng Position Signal
CellBeam .imer and
Power Detector
Base Verticaj Reference Sensors Data4 Acquiston
System~ Base Motion
Actuators
Figure 4-26. Signal Fla-.; for Tracking Demons~ration
APPLTED ECH nO,,.D- ASSOCIATES.N.. .A T emo SBIR-l2N-S 8R C B Th 6 m n
- 4 n al R e p - .- l
AImopnellf. Pfopogbi-b Elheclb on Sons-i
absoI uilnik EJb Hotto S pple H*o.-
Link aitk on Hocica. r 5-.n OoII$1-k
-} ,' i' I and $to Haota Sample Hoiiai Llk Not..,,__ ACL.
....... rn - '
4.,-- *." .)I
& OOF 2 UUP
. \-- -- ---- --
F ~ ~ Sid .
,I . ' I ,
Figure 4-?7. Candidate Configuration of Ship-to-Ship Communicdt
~SS~CATS.iN. TAMemo SI-Z
ASSBCI TE -J Pi C Final Repo lt
Transmitter/Receiver
Relros
YReceive r/Transmitter
Shp/
SShip x
Figure 4-28- Ship yAcquires Ship
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBP-U-.i
88R0016 mh PATSOC Final RepeL,May Y8'
j = diameter of the transmitting aperture (m)
d = diameter of the receiving aperture (m)
d c diameter of the retro-reflectorcorner cube (m)cc
T = attenuation for one-way propagation
P = rated output power of the transmitter (w)
xtr
R = transmitter to receive range (m)
A = spectral wavelength of the transmitter (m)
power received by the aperture of the receiving station while the
transmitter is on a different ship (as during communication of data)(w)
P = power received by the aperture of the receiver while the transmitter
is on the same ship (as during the acquisition and tracking of afriendly ship) (w)
We assume that the transmitter beam overfills the receiver aperture of the
second ship during communication. and during tracking, the retro-reflectedbeam of the tracked ship overfills the receiver aperture of the tzacker.
Then
2
Prcvr = Pxtr dxtr d;c, (w),
4R2 (1.22X)
2
and
P d2 d2 d4
Prcvt = xtr xtr rcv cc. (w),
4n (1.22A)4 R4
Let >' 0.8 x 10- m,
and focal length of the receivers = 2cm
The spot* size of the receiver aperture in the deerti plane (image plane)
APPF TED TFECHNOLOGY ASSOCIATES, INC. ATA Memn SBIR-_..88P0K)Th mh PATSC)C Final Pepor
a' 1 988
= 2. :*- x , - m
which is < 10- .. the order of linear dimension of a detector.
Let the detector area be, Ad = 10- 6 m
The D of an off-the-shelf Silican Avalanche-Photo detector (at 300'k) is.
* 10D 3 x10 m 1Hz,
w
and the transmission of the receiver optics T = 0.9.o
We can then calculate the minimum Prcvr and Prcvt required for SNR = 100 for
the communication and the acquisition/tracking modes, respectively.
I) Assuming SNR = 100, and the bandwidth of communication to be 64MHz,tnen minimum required power rcceived by the receiver aperture for SNR = 100is:
P =2.963 x 10-8 wrcvr
with detector noise being 2.963 x 10- 1 0 w, in the communication mode.
2) Similarly, for SNR =100, and the bandwidth required for tracking to be
on the order of 400 Hz, the minimum required received power in the receiveraperture is:
P = 7.4 x 10- I1 wrcvt
with detector noise being = 7.4 x 10- 1 3 w.
Finally, with Prcvr and Prcvt shown above and the optical path transmittance
T calculated earlier, we can estimate the required minimum transmitterPpower for SNR = 100 in the tracking and communication modes.
If one decidos to use the same source as the transmitter in the above modes,it becomes obvious from above that the power requirement during thecommunication is more demanding than during tracking.
It can be seen that P and P are the detector white noise floor duercvr rcvt
to the signal bandwidth in the two modes, scaled up by the required SNR.
any pulse code modulation, we must also remember the pulse height lossdue to the finite bandwidth of the detector and the pre-amplifier. Thus,
4-aR
0~n 1 Pe Ppo
7* -;7V~ "C 1~o 1 e ' C) '&e' e er,5~~'~('~V
ia) psc a! e P again -c a(ccwlmooat- 'O P C eei loss doir it
T -s i illust!rated in the folllo.ing teaz ibllt -ud' e:,ample:
P '. power laser diodes are eas'; to mod Iare. for digital signal7 -11r 'ation over ontical 1-inilks. tne-, are ne logical choice.
*e -. ,z choo)se a f-,, tI -Ac d iode aser.- 4od r- PP I 5()m '5 manuif a, t (Ired byrv-Ee~rnisCompany. Pertinent data supplied by -he manuflacturer are:
Peak pulse power. P, i 2(- x. 1(9-,
Pulse rise time - wnePulse length, T - n s ens7
Pulse repetition rate =5i0MHz
(Thus, Pulse period. T I -)iS e'7
..- ~ assume true operat ingav.eg
e ~ceierdetector. let us 'cpcan &:~i'ePhoto) diode.,je1 -' t C3;Q92.T made b6'- RCA Elec'<""'_ c Peti co~et data supplied by
'ne 7aniutacturer are:
Peak re.sponise -4a'eiengti . W .9rn'Responsivity, P (Amp/v.attQuantum ef'iiciency.; q CI 0.35
Detec tor integrto tie'.nsec
E'1-assume a combined detector-ore-am'olifier integration 1"e- 'c',
>ij Dise period of the signal Tr 2cntze and is larger than T nte pulse
ccl- os,7 factor due to integration -i-mE of the dete-tor-pte-ao.pifier 0t.
or
d prx1
,-,c crc~a rca--.rarc V. ' 'n?- d
APFPLIED TEHL,,L.Y, ASSUOCIATVES, -__ .i. Zem SP,2SR &;"' rhAT I-l(' Filial e ,
Max 1J88
as <o:n earlier
and opt:-s transmittance,
S = .9.0
The Ioss factor for this geometry, or the range pattern attenuation from the
:al,smitteL to ,he detector input, 6. is
6 = 3.0 x 10 -.
The peak power output of the detector pre-amplifier P is (from the abovedp
data'
PpP x 1 x P 3.6 x I0 (- 'att > 10 times Pxtrp dprcv r.
The pre-amplifier pulse peak output during transmitter 'on' time is
approx:'mately a thousand times the amplifier noise floor, implying an
effec't':e signal-to-noise ratio (SNR. of 1000 for this configuration usingtne off-hle-shelf components listea above.
APPLIED TECHNOLIOGY ASSOCIATES, INC. ATA Memo SBIR-Q288R006'mh PATSOC Final Repo,
May l
)e, i'pment of 'aluatior Modeis
Two types of evaluation criteria were selected by ATA:
.) Measures of system performance;2) Measures of system cost.
4.,.1 Performance Models
Two types of performance models were used:
1) Frequency domain simulation models;2) Analytical predictions using equations.
4.4.1.! Frequency Domain Simulation Models
ATA decided upon a beam-jitter-on-target measure of system performance.
ATA used frequency domain simulations to determine various performancefactors (e.g., contributions to LOS jitter) of candidate control systemconfigurations. The frequency domain models used a control-systemperformance-evaluation code, FRQRSP, for Frequency Response Simulation.This tool was used extensively for beam control system performanceprediction during the Airborne Laser Laboratory (ALL) program and serves asthe basis for several SDI beam control investigations.
The second type of performance models are equations. These equations relatecandidate control system performance factors along with othercharacteristics of the systems to top-level performance factors which can beused directly to quantify the previously selected evaluation criteria; as,for example:
1) Aperture sizes;2) Distance between the transmitter and receiver;3) Laser power;4) Optical efficiency of the transmitter and receiver elements;5) Transmission of the atmosphere at the laser frequency;6) Residual jitter of the LOS (i.e., beam jitter as predicted by the
FRORSP code)7) Type of detection system used by the receiver;8) Received signal-to-noise ratio (SNR).
The Bit Error Rate (BER) interrelates the most significant optical systemparameters. A natural consequence in developing a BER equation is the
Sireceiver input signal-to-noise ratio (-). Here we use these equations to
parametrically change several of the critical component values to narrow thelesign for the optical system. Referring to Figure 4-29. the received poweron the detector (P cV) is proportional to the ratio of the receiver
A-PPLIED TECHNOLOGY ASSOCIATES, 1NC. A.TA Memo SBIR-KC'-
BBP006: mnPATSOC Final ReporMay. 1968
Figure 4~- 29. Single Path Communication Parameter identificaton
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-O288R0006.mh PATSOC Final Report
May 1988
effective area to the transmitter far field radiation pattern. The otherfactors influencing received power are transmitted power, transmittermodulation efficiency, optical and atmospheric losses and pointing angleoffset and jitter. In equation form, the energy per pulse (bit) on thedetector from the transmitter is:
LRCV ~RV~T T T' T [W]RCV 'RCV *XTR "TXTR TRCV ATM
he re:R Energy Received per Bit [JJ-RCV
TT M = Atmosphere TransmissionT M
R = Receiver Optical rransmission-RCV
XTR = Transmitter Optical Transmission
= Pulse Width [S]
= Transmitter Peak Power [W]
= Fractional Energy Incident upon Receiver.
Here tne far field pattern is assumed to be a two-dimensional Gaussiandistribution about some off-axis pointing error angle 9, at range R,transmission aperture diameter dxt r and effective beam width defined by ax
and cr;. For the far field pattern of the form:
2 2(x-X) {(YjY
1 -1/2 a2 -1/2a2Se x e y dd
xy
We have 86/ of the energy contained in 2a and 2a, and assuming 5xxaya
diffraction limited optics:
1 22R 2a 2ad XTR xa ya
where:
P Range between Transmitter and Receiver mi]
= Wave length ct Transmitter in]
-+" rf' ve Air'" rls: null at Cece]''r v t, cc :<axi 7 uttr cIxa
' a Effective Ait' disc nul in v-direcrion of Receiver ,itn n.
axis JIitter ir]
For an effective transmitter pointing error angle of e, the cenler of thefar field pattern ,iii be R - t meters from the receiver center boresite.
Because of the x and v symmetry,. the direction off-axis is 4rrelevant and
for computational simplicity we assume off-axis only from the v-axis (y=()).Refer to Figure 4-30 for the x-v axis coordinate system. Introducing x and
axs efective line-of-sight jitter. due to the platform base motion,
atmospneric disturoances, etc.,
.e na've a far field pattern of:
. -1 /2 -12
XR -XTR T\
R (1.22
; 2 d T ;j i t
OR pointing error offsec
7 ".-axis LOS jter
; -a:'iz LOS j ',e
APPLIED TECT ?l OGY ASSOCIATES, T'NC . _T jeoSI-2
P, C), 06 'mh P~-.TOC F.'nal Repcr,
2
2
Rec eiye rAperture
centerec at Origin
r gure 4~-1O Rerei.'er x-. orneSver
APP _ IFD ~ HZYASSO)C!ATFS. 1Y, Fr,~PR
a eoe v e r a e ac a s qa e S mq) te a rI~m::. -~h a rece-ve, diameter o CR .,E tiave toeriecevrc~et
3 d
R CV PC V
j FF e, ayi (7 R, d A) dd (eaua t ionr).
Toarie at a bit error probab-Kv ~ene oo~ ate tnp noise powerspectrum -, the receiver output. Using Peebles Bit E:or Probabilitv
o5--o2i-fl for Amplitude Shitt Keying (ASK) modulation ;' e nave:
P. erc c, f or ASK
- --- ~X '~rrc'herent ASK
where:
is the energYprbtdWddb wc the inplut no; se spectralno density
P B o0 TI
(Peer ei Eage 2 is Gauss an ,h i te nol!7r in put 1, th powe r H e ns~: i.
Here 5 o tue around scatering Power due to wnoo ,-pnerlc (condiin n
7-car ".IY. Wh is the channel bandwidth of the cornmun;-atio; system., and
'm e detector otitpu noi-Se.
Cor) , ) ngr ;eMS, We :avr:
A PPLIED TECHNOLOGY ASSOCIATES. INC. ATA Memo SBIR-C2S
88R066; Mh PATSOC Final Report
May 1988
'DET ,RCV c(PB F
where:
2rDET(Ge)2(P sPB)BRLF
"ON h- 4kB Pdrk
(from page 124 of Laser Satellite Communication)
where:G = Avalanche Photodiode (APD) Detector Gain
E = One Electron Volt [J]
'DET = Detector Efficiency
= Background Solar Power [v]
B = Bandwidth of the System [Hzj
= Lodd Resistor johms]
= Noise Factor
n'l = Energy in one Photon, Wavelength X [J]
4kTB = Load Resistor Johnson noise [w]
P = Output Noise of Detector - Resistor Circuit [w]on
P S = Signal Power incident on Detector [w
Pdrk = Detector dark current noise power [w]
For ASK, assuming no separation between pulses and a channel bandwidth
we have the input signal-to-noise ratio to the ASK receiver demodulator as(Pecbles, page 364-371):
S i
4-5,
V. ~ n r a~ ing The apprnrae et'na U on -I tr 1' ajT a pe T 0J>r-e E elating rne optical Fystem parameTer? o the inrtu, "P. in,
exa- - 7, 7g Figure -32, ,r ran he- seen, that a' re",v~~ P nrmlI -r-s-_zes :-, signal-to-ncise rar.cDs are qui~e acceprtne in. 1Dtainirig t
tvSN' F u L thkf L MU I h- I K La oja;. K4,fk:id uef Zn e SMRP b,. less than 1 d5. The solar bIac~'gr ound of nano-.al is acaze rough ord-r of magnitune estimate ass7uming no gli~t or dlitrtcnov:s~nt~ithtre sun and re'.ei 4ei (D&11irmend7 ianl. -he :a!uecz of the
7--sem ~aaeescan be for)rnd at -fir- end )f tI.- se -t i'n.
n-shn the (ZL - to from -erfler-Ed pnovei of a rEtro-reflector
Son ?-he ,e-e4-.,niy ship ,;J h retro-reflectot cf aperture diameter-e efe~edpu. er from The ! r _ 1 di-e .o -ar toad
-a=5 t"er. bur with the r-etro's fa: fi eld Pat ern centered on the
on receiver. -e nave as:
'P P.. FFR w':- A T
R P
F F C- ,, n d V- ( ec aa on 2)JT
OF,
FF~~~~ P. nIS!7 n
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-Q?2!M8R000t~ PATSOC Final Repoi-
May 98
- -Z
7, AE~'~
Figure 4-31. Bit Error Probability for a Given SN?
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-CZ588ROO06 mh PATSOC Finai Report
May 1988
LOS Jitt10q Rad
_.3o- .U 1jRad
wta
'/'
//
1- a -t- . - ,' -
-a-, 5 )£ -, 2-- =----
Figure 4-32. One-way Transmission SNR: 10 trad Pointing Error Offset
4-60
A 'PPIE ASSOCATES NC. AT Memo SBIR-Ei288R)(06 ,mh PATSOC Final Report
May 1988
Siand "herefore. the for the reflector receiver is:
DET ERCVSi DR cnNi =P , p
'B on
Again. numerically integrating appropriate equations we can snow a graphicalrelationship between the optical system parameters and the SNPR Asexpected. as we increased the transmitter/receiver diameter, the amount ofenergy captured from the retro increases which boosts the SNR. However, byinspecting Figures 4-33 and 4-34, we see that for the large optics we mayhave a tracking problem with the low SNR values when the line-of-sight (LOS)jitter is above 30 irad.
A caveat is in store in reference to the atmospheric attenuation used.Here. the transmittance is 0.1983 over the 16 km path length, which is onlya rough order of magnitude estimation. Here. because the path length istwice the ship separation (to the retro and back) the effective atmospherictransmittance is about 4%. With different conditions orders of magnitude ofmnange in SNR can be expected.
The values used for both one-way and reflected energies use the fol].ovingconstants:
= 0.50 • 10- 6m
-9= I0 • I0 s
ATm = 0.1983
TRCV = 0.7
= 0.7XTR
R : 0.8
?XTR 0.040 W
R = 16 • 10'm
- -6S= 10-106 rad
w h= B Hz
4-61
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-025
88R0006,/mh PATSOC Final ReportMay 1988
$ ; , . L I - - .
i
10 wRad- LOS Jitter
20 wRad
,/ 30 uRad
/ 7 - 40pRad
,7, //7
r" /
z; /
= - - '. -. ,
- -, ." -
Figure3. Reflected Signal SNR: 25 cm Retro. 10 wrad Pointing Error Offset
4-62
APPLIED TECHNOLOGY ASSOCIATES. INC. ATA Memo SBIR-02588P0006, nh ?ATSOC Final Report
May 1988
- ,a L - U y -. -
LOS Jitter 1 w
20 wFad/2
/ /"- /-30 &Rad/ /
z -, " .. 40 w Rad
=- 7 / /7
//
-- ,"
/
"'-_,*7e- ."
-=- .3E . / --- ~-- ,
Figure 34. Reflected Signal SNR: 100 cm Retro, 10 wrad Pointing Error Offset
4-6 3
. . '- T
s a. ' %C
, (Detertof Nn -,t ' it
= C ' .'B
drk
.va uation of the System
..ie execution or the FRORSP mode'ls provided the data needed to rank thetv ern.
F1g 3e -35 shows the Single Axis Model of Pinting. Tracking System.
.2> ,sed this model developed for Ball pointing and tracking experiment andbase motion and LOS disturbares ano ran the model to achieve a residual
- ra:-_ error of 3 nanoradians rms ;'hich is more than adequate.
: hese base motion and LOS disturbdnces did not contain high freauenc',di--:rbances, the spectrum shown in Figure 4-l-as used -o pr-ovide more
e-.a : ic high frequency disturban .
-.c.-ervo Model/Performance Estimation
-model/performance predictions are sirmaiized in the foio',ing figures:
Figure 4-36 Nested Servo Block DiagramFigure '-37 Frequency Response Characteristics foi i.5 Hz ,<.ha! ServoF7igure 4-38 Frequency Response Cnaractelistic- for 351) Hz Fast Steering
Mirror ServoFigure 4-39 Frequency Response Characteristics for 15 Hz Gi1baa and 350
Hz FSMi,r- 4 1-4, Baseline ,eic-d a r - n - L S Di-t-rirhance Reiec-con
Fg'ure , Baseline Nested St" LS Input >.imlati'e PMS',lire 4--.? Baseline Nested Se vr,- Residual LOS :tter Cumuiati;e pRMS
Figure 4-4) Baseline Nested Se' .os LC(S Input Disturbance anvd ResidualJitter
.-- ure 4-44 Nested Servo Pert(rm.ance Summa '.' - 5Hz timba Ser..,H': H.FSM Ser-,o
IT. as a result of irs anavses. tonl o udc-d ria:
APPLIED TECHNoLOGY ASSOCIATES, INC. ATA Memo SBIR-0288RO006mh PATSOC Final Report
May 1988
1) Nested servo with typical banovidths provides 1I0 microrad LOSstability:
2) Loy-frequency induced motions are handled easily:2) When a high-frequency disturbance envelope is selected, nested servos
handle the envelope to 10 microrads with equal frequency power inerror:
4) There is a choice of various implementation options.
4-65
A PPIED TECHNOLOGY ASSOCIATES. INC. ATA Memo SBIR-OZ138ROOl6, nh PATSOC Final Report
May 1988
K,.Shw
- ___ r ,... , _____.4*-o':4-
"--------- ---
g I sOI~__ _ _ _s ~ A
Figure 4-35. Single Axis Model of Pointing/Tracking System
4-66
.PLE ECHNOLOGY ASSOC:ATES, INC. AT.-. Memo BZ88RDO006,7 rn. ATS!JC Final Repor-
vESH
- F~ I ________________
as Bas b.. OIO
KO
4-67
A PVPLIED TEC~hNr-L )Y ASSOCI ATES, INC. AAMm B-28RC6i m C ina I R en oL
Max'98
-~ Open LocQ
- ---
CloseC L.oop
- Ernur Rejection
Figue 437.Frequency Response Characteristilcs for 15 Hz Gilmbal Ser-o
4-6t8
7~~~~M. C N Gi SSI
Orer -~ooc ,
A -- -------------
- - C~-osed loo
- - - --Error Reiecion
Figure 4-38. Frequency Response T7haracteris~l-z for .5( z Fas- -'eerinKgMirror Se~vrJ
NAVAL OCEANSYSTEMSCENTER, SAN DIEGO, CA 2-OF XLOW COST PONT NG-AND-TRACKING SYSTEM FOR OPTICAL NOSC TD 1287
COMMUNICATIONS (PATSOC) BY: KH JOYCE UNCLASSIFIEU
JUN 1988
ENEMhh.Eh!hE, uDIuuuuuIIIIuu///Iffl.
- -in.. - - - - - - --- -- - - -
~Op:en _ooc
A --
Closec Loo, -
--- - Error Retecmion
Figure 4-39. Frequency Response Character'stics tor 15 Hz qImtal and 32.I HzFSH
.,FFLIED TECHNOLOGY ASSOCIATES, INC. A-7A Memo SBIP-QC38P,900, rnh PATSDC Final Repor
ay. 1 F&
Figure --0 -
Figure 4-,,0. Baseline Nested Servos - LOS
APPL7ED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-025SR!JU)b06,jm PATSOC Final Report
May 1988
o' : -
Fiue44.BslieNse evs- O nu U M
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memno SBIR-O2'88R0006/mh PATSOC Fi.nal Report
May 1988
cr
C)
Figure 4-42. Baseline Nested Servos Residual LOS Jitter Cumulative RMS
APPLIED TECHNOLOGY ASSOCIATES, INC. ATA Memo SBIR-O288ROOO6,h ~PATSOC Final Report
May 1988
Input Disturbance Spectrum
_ - -- .- .
C - - - ...
--
- - ResiduaI Jitter Spectrum
. . . . , - . I -.
Figure 4-43. Baseline Nested Servos LOS Input Disturbance and Residual Jitter
• m • • m 7..
A??L:ED E-"NOLOGY ASSC-'.:ATv.S. :NC. -JA Memo SB-RtTn ?AT 0C -ina. .epor
NESTED SERVO PERFORMANCE SUMMARY
MATA J. V15 HZ GIMBAL SERVO/350 HZ FSM SERVO
BANDWIDTH (Hz)
00 1 11 1 100-:0.0 Total f0.02-1000)
LOS Input 53 mrad 0.48 mrad 66"urad 6 praa 53.1 mrad
LOS Res.dua 0 44 prad 8.2 4rad 2.4 prad 9.6 irad
FSM Angle 0.11 mrad 6.3 mrad 6.4 mrad 0.2 mrad 9.0 mrad
Figure 4-44. Nested Ser'o Performance Summary 15 Hz Gimnbal Servo/35D Hz FSMSer-o
APPLIED TOHLOGY ASSOC:ATE.7 .NC. ATA Memo SBIR-,)2SSRJD06 ' P ATUoC 7i:ial Report
May 1Q88
OPTICAL SYSTEM
5.: Laser and Optical Detectors
ATA is currently considering two types of lasers to be used as a beacon (seeFigure 5-1). Specifically, they are GaAs type semiconductor laser diodesand a solid state Nd:YAG. Because of the proposed shared aperture system,we must also base the decision as ro which laser to use on the su.tabih't'v-of the beacon laser to also be the transmitter laser.
* Semicondu-tor Diode Laser - GaAs Type. C'/Pulse Mode Operation
- Small- Fairly Efficient- Potential for Long Lifetime- Inexpensive- Can be Directly Modulated by Varying Input Current
* Solid State ND:YAG Laser. CW/Pulse Mode Operation
- Offers Higher CW Pcwer Than Diode Laser, but Larger Than Diode Laserin Size
- Can be Pumped by Diode Laser- Modulated via 0 Switching or Cavity Dumping
Figure 5-1. Laser Options
GaAs lasers operate around 0.8 micrometer. They are small, fairly efficientand nave demonstrated the potential for long lifetimes in accelerated labtests. An advantage of the GaAs laser is that it can be directly modulatedoy varying the input current to the diode. Thus, it can be pulsed fastenough to achieve the required data rates.
Nn:YAG lasers operate around 1.06 micrometers. Although somewhat largerthan diode lasers, Nd:YAG offer more power and a more collimated beam whichmeans more power in the far-field at the antenna. The Nd:YAG is modulatedvia "0" switching and/or cavity dumping. It is capable of high dar rates(200 Mbits/sec). The Nd:YAG laser may be either flashed or diode pumped. Adiode pumped Nd:YAG would make the most sense here in terms of size andlongevity.
Attenuation of the beam power by absorption in the sea mist iusr beconsidered. The optimal wavelength for minimum attenuation resides around0.45 micrometer. By frequency doubling either the diode or Nd:YAr laser, wecan reduce the absorption by nearly two orders of magnitude from theirnatural values.
APPLIED TECHNOLOGY ASSOCIATES. INC. ATA Memo SBIR-02f
38Rcu}6,p PATSOC Final ReportMay 1988
ATA recommends the use of the diode laser because of ils simpliciry ofouization and small size.
ATA has investigated a diode-laser-pumpea monolithic Nd:YAG crystal,presently being developed and used by Stanford University. for use as tneMaster Oscillator. This new laser has three advantages:
!) Extremely compact;
2) Stable frequency during operation;3) Possible to finely tune the output frequency of the laser via
controlling the temperature of the crystal. iAe ttornabilityof the laser would allow easy multipleying of thecommunication by allowing receiving, transmitting, andtracking to be done at unique wavelengths.
Figure 5-2 shows this design. This configuration may offer an attractivealternative in the future.
A number of vend(rs were contacted for information on optical detectors andlaser sources for this project. ATA recommends the use of a siliconavalanche photodiode (APD) as the optimum derect~r because of its highresponsitivity at the proposed laser wavelength. Specifically, this is thesilicon APD model C30927 made by RCA Electroptics which is suitable over awavelength band of 0.4-1.1 microns. The specifications for model C30927 areas follows:
Diameter 1.5mmPeak Response 0.9 micronsResponsitivity 60 Amps/WattQuantum Efficiency 85ZDetector Integration Time 3.0 nanoseconds
Quantity Approximate Cost1-24 $1100
25-99 $1020
Additionally, a search was made for a GaAs-type laser source. A number ofdiode lasers made by Opto Electronics will satisfy the power and repetitionrate requirements. They are all pulsed GaAlAs multimode diode lasers. Themodel numbers are PPL5OM850, PP150M785, and PPL50M820, which operate atwavelengths of 0.85, 0.785, and .82 microns respectively.
All the models have the following specifications:
Linewidth .5 nmPeak Power >20mWPulse Length 0.06 nmRise Time 0.04 nsecRepetition Rate 50 MHz
Operating Temperatures 15-30 degrees C
APPED ECH~LuY ASCIATE. IC.ATA Memo SBIR,-L.'z:9 R C' t)cc ? 'ATSuC Final Repcrt
May I88
ap 3prY:,:ia-- ots e ari laser
YAG z"EC
I AMPLIFIERSIGNAL
Figitre 5-2. Possible Laser Design
.7 aser Safety
7hroughout operation, rne digital controller maintains less than the maximum::fe,-. limits for laser power operation. The controller governs the laserpeaK power using ranged direction Information from an NTDS computer andootl-cal time-domain reflectometry (nDTR) from the laser backscatter.Reflections from another ship or object can be used for ranging and,therefore, maintain safe laser operation.
7ixed and Steered Optical Elements
-or the fixed optical elements ATA has considered the following. Materialselection will be made on the basis of cost, durability, and stability. Formiurrors, aluminum, pyrex, and Zerodur have been investigated. Metals areat-racti-te for being lightweight and having low cost. Pyrex offers a higheroptical quality at a -ost that is still inexpensive. Zerodur offers highduiraoilit; and stability since its coefficient of thermal expansion is-tec"4-iely zero, but ir has a high price. Selection of lens materials
range .between a(-r'lic plasic and crown glass along with possible anti-reflection coatings.
For the steered optical elements, traditional. non-roact~onless 7alvos andhigh-bandwidth. reacrioniess. electromagnetically-actuated beam-steeringmirrors were considered. Steered optical components have been :nvestigated,vnlcn incorporame a reaction mass for reactionless operation. The mass and-tie mirror are made of beryillium ro provide a high stiffness to mass ratio
...... Nn iY oS,(C>J... :NATA Memo SBIR-,h)2Sd P..... Final Report
May i-88
ia:,. -g t1 4:gt eamwidtn oDerator. (grearer tnan Hz possible.2:fferentia_ inoeoance Transducers 1DITS) vEil be incorporatej to sense
SI posi ion iiside rile assemlnoiv.
.n'esrigated a Maksurov Cassegrain "elescope design for -he system.h esign ises t'.o sphe:ica! mirrors v'ith a meniscus corrector lens placed
.n tne entering Deam to correct . r spnerical aberration. Spnerical mirrorsgone:alv'! cost less than the aspheiic mirrors used in a classical Cassegrainsysten. Optical design of the telescope will be based on a 15 cm clearaoer"Jre ';i~ a 1.c degree field-of-view. This design vould provide asimzier, cheaper cption than the Ball RME telescope described in the nextsect on,
.. Primar Secondary Mirr r Assembly
The relay mirror experiment (RME) being conducted by Ball AerospaceCorporation An A r-tlizes a telescope assembly for collecting radiationf-)m a satellite source (Figure s-U)
The design meets the reluirements of 'he Optical Communication System (OCS)and a copy of tnis telescope nay be incorporated directly in the OCS system.The specifications of this telescope are given in Table 5-i.
-he fitrcr, sensor and printed c:rcuit are designed for infrared operationan,: would be replaced for the present application (Figure 5-.).
' -c sho's ATA's telescope des:gn for this project.
,h -' !T '
A-?P'L.rD 7ElCH'NOLkJ)G", AS~Ci-. TES. sC. -r A S~n aSIp-
38R~p ~ cd a PT3AJ Fnal P~rM av
~-assermbled !ength 9.81 in
Figure Ball Te.iescope /Sensor .-. msrbl
APPLIED TEC-1NuILOGY AS .E ;C. .ATA !Xemo 5BR--'38Rfj0O6cdo PATS(.W F,'ral Re:)r
Table ~l eecp c~iau
zpecificat-.on erit
~'-eight Total I7e lpscopeSensor AssembIV lb
Telescope AssenD.' Carad-oplrr 4 Mirg:rn -mrr'-rTFocal length~ 2 n'!ear apertxlre 1-4 min.ransmission efficiency > .
Plid size at image plane 11m
Dptical tilter High efficiency; narrow' oanapassMul~ilayer m'lt~cavity desigr Bahr AssociatesTransmission etticierlc' >5 percent3and pass .
Blocking-
?r~nted 'Wiring Board Doubie-Esdei 6.5 in. dia.
Detector'Preamp Design Previous design exper .en(7e
:R e- anced siliron de~ecror rOf-e-heif par,ThIotovoltaic modeJra Low' Noise Transimpedance A:pitier
Ana-log-ro-Digirai Conversion Covered in electronics section (61t)I1 tS
Connec tors DataPowier
SENSOR PRINTED WIRING ASSEMIBLV
FtJNCflOlAL BLOCK DIAGRAM
2.252,00 -
.225
?0' ED -EHNO!~ >
e Maksutov Cassegrain System Design
Two Spherical Mirrors with Corrector Lens to Minimize SphericalAberrations
Inexpensive Design
Clear Aperture: 15 cmField of View: 1.5 degMagnification: 5x
APL:ED TECF{'Z,);Y;' __,(]T2. -;T o ABIR- 2 -
r8L,27 . ' "- .'".. .::a ?e? r
.?. - harec A:erture
-he sLared aperture design uses an isolateu moun,. t" as an -z~m in -o r veof plus or minus iSO deg.-ecs, a t.o -axis fast-steer'ng mirror, anr,
incorporates a signal generation processing module. The pointing fla a anturn plus or minus 45 degrees anC features an intelligent retro. There is a
focus drive and a secondary spider.
2 agitai signal processor- (D)Ps) are relatively nev types of processors useofor enhancing ,ne computational speeds orten needed .n signal processing
appications. The DSPs are applicabLe in nis control problem tor he iign-fequency control loop. Here, in place of Zdngcng multlple, ,onventiona,-type processor nodules together to implement a parallel procesting approach.
one DSP coup-ed "'-ith one convpntionai processnr may indeed provide thenecessary computational requirements.
Tracking Electronics
Fcr the tracking electronics, quadrant cell detectors "with both analog and
aig.tal signal processing vere considered. Focal plane arrays with digitalprocessing were also considered. Figure 5-6 shows a quad cell photo-oetector.
A parametriz study vas performed -o characterize optical system sensor_iTimations vith the foliowing sys-ev , design parameters:
2,.ame rr .-
Re'eieri~c" :s ITransmitter
Retro-rerLector
cource KaAIAs Diode Laser. 820f n,. Pear Poere- 20
:etector Silicon Avalanche Photo Diooe. D* - zmHz
-ootm Detector -ith 16 Hz Band-',idtn Detercr for Noise 10) J
-im Detector ";ith 30 Hz Bandwidrh De'e' -or for Noise - w
Al1 ComDonents are off-the-sheif.
Background pover a, re-elvor '.,as es-ima-d us:
Sky illumination - 1 22
Beam backscatrer ('.um particle size)
Solar bac!-scarter from fog - !.
Direct suniignr in field of 'ie- in Qensnr "and'idtc r omne'eiv )anke-ctne signal -60 m'm.zNR - li'f' in absenre of dirorr sonLi '.
C --
APPLrED TECHNOLOGY ASSOCIATES, TNC. AAMm BR0a8ROO~cdoPATSOC Final Repor:
May 7,88
Figure 5-6. Quad-Cell Photodetector
S1'
F rLD .NL 0 - C E. A. ATA Memn BR-2 ii; FnaI Rec L
T concZJeon :
1. Backgrouna nower addi'ons rave negiig, ble etter's th a 2 Inmbazidwidtn filter centere. on 'he source -avelengtn.
Transmitter modulation may be used to reject direct solar input.:)therwise, tle systeYit is detector noise limited and not backgrouiidlimi te d.
.-TA id a tracker sensor analisis for acquisition and t'ne trackingI,' ,zing a quad --ell and a conical scan.
()uaa '_e . :
:deal control loop (no jitter) SNR - 100
Tracker Error - 0.03 urad
Jith 10 wrad control loop residual error (= integrated uncorrectederror) tracker error bound - 0.05 urad: this is 0.08 cm in target planeat 15 km.
Conical Scan for Acquisition:
Beam °*aist optimized for minimum acquisition time = 0.01 sec anduncertainty in search area Is im X 18m. SNR 2
AC power return at re-eiver: PAC 1.52 X 10 - ' at 300 Hz
1l1..DC power return at receiver: p X 10-
Detector Noise for At = 300 Hz: P_= 6.4 X i0 -
or P 3.6Q X 10- 1
H{z Hz
Using a 2 Hz bandwidth filter --enter at 300 Hz. SNR -
Beam waisr. optimized for reacquisirion time = )'.12 sec and sameincertainty area, SNP= IAOO.
Fine TLacking
The SNR -was inversey proportional to the size of 'he search area.
Under the ideal control loop, the SNR is very large.
1ith910 urad ,-onrrol lqoOD rpsid,|al error Sa.-ah. orea incerainr,-- 4.5 cm -n the rarge plane iplving that 'he S',%P i -'" erv good.
APPLIED TECHNOLOGY ASSOCrATES. INC. ATA Memo SBRP,-,l':
88ROO@ 6cdo PATSOC Final Report4av i)88
Fgure 5-- gives the bic er or probabil i fo A9K communications.Fgure 5-8 gires thi hit eurir tor a given SNR. Figire 5-9 snows rnereceiver input SNR arid Figure f-', descri.bes the optical impact.
PE = e r fc"NR Coherent ASK
4 P :1/2 1SNR)* /2 ( 1 )ex Non-Coherent ASK
* SNR S Energy Per BitRMS Noise Po'er Density
* No Burst Error Analysis Addressed
- Digital Retransmission Relaxes Burst Error Problem
Figure 5-7. Bit Error Probability for ASK Communications
i: -
APPLIED TECHNOLOGY A'SSOCIATES, :NjC. ATA 4k-mo SBiR-1)"88R006 c~o?ATSOC Zinai Reoor'.
May i'188
NON-CHERET AS
COHERENTEN ASK
S a.*,
Figue '58. it ErorFor SN
APPLIED TECHNOLOGY' ASSOC.ATIES, I'47. ATA Memo SBIR-iO'-88R00 c Oo PATSOC F'nal Rep~r,
May '988
a'OuA =ODi
/ 7J7
,a -3OuRADxy Y
a=O.RD LOS jitter
Figure 5-9. Receiver Input SNR: Tatm 10%. Pointing Error =1-wuad
5-14
APPLIED TECHNOLOGY ASSOCI.TES. :xC. .TS emo 3BIR-f2f38RGC06cto ?AJSyC Final Repot
May )88
Operational Conditions:
10 cm Transmi-er'Recei'er10% Atmospheric Transmission35 mV Pulse Laser10 urad Pointing Error10 urad RMS x and y LOS Jitter
implies:
* SNR > 1000 (30 dB)
* Pe < 10-10
* Small, Light-Veignt Optics
Figure 5-10. Optical impact
5-15
6R0 '16cr c 2 .T3C Finai Pepo
. ax m m Searcn A':u .ion -i
the base 7i(- ac, u 4s. r rion sv,, e T . : jsec a P q uen I s. e.< a i i <.
a zu 'h 'ho., -on udirec on to lo ' ed Lv, a s earc,, in h e e iev a ; n d zE i ll
A Trad o, 3 arad laser beam -.'ill perform a uniform azimurh scan at Hz
:)er 26C , ev iton.} ni t r e s ip s ' r e cei -;e rs -.- iI b E f 1 te d n'~ aT- b7, P- t 1 re reflector a r rte --enter of their- receiv-,ng aperture.
Relcto : ,o rho rfetra iecne fterreevnqprue; o -m rh' n C t as a fripndly beacon for
ac:quisition and tracking. The beam -width of the recto-reflef:tor iz: bu ()
raO. -he acquisition sensors electronic bandwidth is assumed to be 3Uu Hz.>i,<. from the instant the search beam encounters the retro, a detectablesigna. ahove the noise levzel -.ill reach -'s peak in approximately I msec.
Not:ng the time instant of the return pulse peak, and the location of seari
beam axis in the search time period, one could identify an area 0.3 mrad (inaz'mu~n) by -1 -rad (in elev.ation) in the Target spa,'e containing the target
rel!o. 7f the azimuth search is limited to 130' of the horizon, the random
acquisition time to acquire the retro-reflector is approximately 2.0secondsz. Next, the search beam 'W41! be focused down to 0).3 n, rad by 0.3 mrad
area and an elevation scan will be initiated, again at the i Hz rate (0.9
iac sec.) Thus, the elevation scan will be over in 5 msec or less, and the6to .'] e contained in a ". na yf. id nd mo nd rc in.. .o:.heonindna ..3 -nrad by 0.3 ri:d d,.o in d Nnown direction.
Hign-bandwidth fine tracking in that direction will be initiated
:-mediatelv. The total acquisition and track initiation time is estimatedce aoout 2.j seto-nds or -ss. Assunting a 30 m riacker laser, a 15 km
-ange. a round-trip path tran:: tance of 1I0) and a silicon avalanchet'd "ode of 1. -rm diameter a- t , r.3 me ne sensor, the -Jzna -to-noise ratio a,
ne detector output is esti:iiated -, be lii.
' ystem is beinz e.gned to nave 3 maximum search acquisition time of
one second, assuming a coarse ". 45 degrees azimuth. 22.5 elevation)
ino7iaton of the receiver is available -o the transmirter. Fhe coarseindication can come from the radar or the last position of good
communication.
5-16
6. DATA SYT7T0
'i.en a type )7 .,mmtn..i "n Z ' eM. -he sinal noisp na,:n Q )determines -ne lit er:or impl , rommon v avaiiahp ,ig: a1
systems yeq:4re 'ne same "aX-Dark" SOX for PE-IN" D! M r.m 1recu rements a:e 1 - iB.
6.: Tpe,'Quan!:iv of infirma~iun to be Transferred
A.'.s design prov des ansfer of real-time video-ype information. 0n anideal si-uation. up to 5"u megau;ts, second of information will be able ro betransferred. However, there is a cost-versus-bandvudth tradeoff to beconsidere! it baseland video signals are to Le ransterted o;er a serialcommunication link. because data rates of several hundred megabits persecono can be expeceq:
A 4.1 megahertz baseband iideo rate v. samples'cycle x 8 bits/sample x 2cnannes = 288 megabits/second. if encryption. overhead and retransmissioneffects are included, 288 megabits x 30% encryption overhead x 10% protocoloverhead x 2?% transmission = 0.5151 gigabits per second.
For these data rates, the cost of implementing the communication system can
oe significant. Components such as laser diodes jump in price from the 20megabits per second system to the 5Q2 megabits per second system by a factor0! aoour lu.
An atractive alternate is the use of a dot matrix laser printer/FAXmacn:ne. Yhile these tend to operate at He:Ne frequencies of 630 nm and not5,> nm with information rates of 100 megahertz, with minor modificationsthey 7ay provide the base for a relatively inexpensive demonstration of anoptical communication system transmitter.
Here, existing off-the-shelf fiber optic communication transmitter-receiverpairs can be adapted for a line-of-sight link. Costs vary with bit rate andpower requirements. At the low end, a 10 to 20 Mbps off-the-shelf systemsells for approximately S6K to S8K, while a 500 to 1000 Mbpstransmitter/receiver pair ranges in price from SI/K to S2OK. Obviously.this tradeoff is a factor the Navy will want to consider in deciding on theactual Phase iT prototype. High power sources for commercial systemsinlize 20-30 mw. Fiber optic systems are easily incorporated into Navalapplications. See Table 6-1 on the off-the-shelf optical communicationsystems.
6.2 Maximum Transfer Time
ATA's initial system will be designed for the real-time case discussedearlier, i.e., 0.5 megabit/second. It will not be designed for burst orpacket communications implying higher bandwidths, i.e., transfer time willnot be considered accounted for in the retransmission factor discussedearlier.
b-i
-- ; -..5.hr;n ,, -- ; - :., ; .,' .. i R '4e c - .-
2DO" ca .- _s e'se,-es; 5)L, " S. The "equtliyer. - b *'-: ,m .-
P:7i D t 1rrm3 aeza' rC nr~s.92)~
The sgna. ir:tcrma-on nando :'.. ne 2,--- megane, r. A fc , ". . array. -w:i xe.s " Imes pe se"ond Dro:ces a 2. 7egai:* se,ind r3te.
.- '- o-.nir ?,mun cat:)n - 5atte - i.e sIla -aeon a r- a 1eq e CesuLeinform:aton excnange amonk a [e or sn ps virh "-'e or no delav.
n .rmation such as rada, images. bart le 'lan jpdate 'warts, dire,ives andoca. communica*;on. and ship omnurer ne-.orking gi'es rise to a nigh data
rate optical i ne-ot- -ignt tansmi rer-receiver. For rea.-time transmiss:onof tns t.pe or inormarton, data .ares ierived from t e fcosg kin ondda'a transmission sItuarions , an he expeed:
megabit s per second for ') radar i.agessec x 256 56 pixels x 3bits' pixel
2 megabits per second IOr i chat- image ,se x 512 . 5 2 pi:.eis 8'i ts' /ixel
- megabi *7 per -erond t a ".Ia ann S ) , x
! 'sample
m egabit:- on, I r .. k hand mD!i er sonne: ions a,
').2 bound: i7 tor encrr' pson pl prorooi overnead.
-. )a', 20 megab ts per s pcond is a reasonable bit ra e o 'wansmit thisCrn 1 .v of information, using a 2 cate o etransmissIon cue to an.
S- transmissions.
5.- Maximum Error Rate ot the Szsorm
.andard communication practices require that the maximum err-sr rare will be-6
one in a million oL 10 This rate ;'as derived from the equat:ons given in
section 2.4 1.2.
6.5 Naval Tdctical Data Systems ('ITDS) Data Transfer
The 4rai i controller v-ii handle starring and qropping data f 1o acrossthe channel and wi1 request a retransmission a necessary as vell asretransmit requested data. ATA will "dork with the customer to Provide theprotocol and encryption technology. NTDS computer -ro-sompiirer -onnections
can be accomplished wjith a very high band-width transfer'communication linkestablished for implementing a fleet command post in a single -hip commandrnom. Multiple links coild be e!tablished for networking each ship to The
control command center.
6-2.
S~- JDeL t he di g a I Kn i L i n o ,,Ie r -, )IC and deWA Oea : 0
.ayi 3 :e trnrn:e arc rece 1ver. Te3siarneaii ''-iat cn na nne i s a I -o oijpE r 1 ed b", he d igi a Is o em
6-13
'-'-. .7'~
err
_ 'nr "an eaF
* Fa-. -,r
- n-- a :. .. ; nh c
Do. Iu c
C' 71 C., -7L 1 )r DP
P)
SP.rE........ . ... .so: . ATA Memo SB1P-15O-F d" .ATSOC Ftrad Report
Ma'.' 1 8
.:Bargc .5 pro~otx'pe
B.aros 2 l"x12"x1'2" '
'>.e Suppl. Ctnnect .ota
Stemoe: Motor Controller 0.5 2OOr,
-7- u)e supplied
..e tierma_ contro. s-anner, w'hcr is a driver for the fast-steering mirror,awa:lare 'or $o25 _ for mooe G32."5DT. The G300 series of fast-steering
..... ., _-, , ,- and 3-mnillimete: size, range in price from S350.00 toBoth .he scanner and tne fast-steering mirrors are available from
genera~ Sc ariung ri,
Ranavtng by cost alone at thns point in the effort provides a reasonableap.7!oach. Most of tne var:ation in pointing-and-tracking subsystem:er '-mance is due to overall configuration of the subsystem, not specificI-:.e-entation. The implementa:o. having the lowest cost was designated as
S ow-cost poining-and-trar~ng s ubsystem. it is the design of this-. ,ser whicr is the principal result of this effort. 1t is this design*. * l be developed and implemented :n Phase I: of the effort. Table
Z: e some of The approximate 'oct o7 the Piease Ii etfort.
Table ( APFPMATE CTS FOP PHASE :
TASK LABOR (SV, HARDE (SK)
Computer Models 3('2. Atmospheric Issues 30 0
Ship Motion 20 5- Tracking Demonstration 100 5- Glint Returns 30 0t Acquisition Demonstration 50
Communication Demonstraton 100
TOTAL S360K S13
Th _ e ma'es will be defined in greater deta;i in our Phase 1" proposal.
7-2
.eapoi .....
-3~cE .Eap .nu L i ~
a --
m .~ .--. ,' ,1
At ec.mndlcr
an F Bl. Ac'wn .e I~,:a -> c v a v-P
4S: ' a 'ar -7a j;'-~ ~ F '.C n4pn a~'.H t K m :, '
APFLiED TECHNnLoGY ASSO(C1A0ES, !NC. ATA Memo SBIR-IC88ROO6DL FATSOC Final Report
May 1988
Short, 1.0. anc S:hneeberger, .J., Pt aI. "Statisica! na4- is of Beam
Control S'ste: Petromance," 01L-11-80-155, Finai Report, mctober 198,(SECRET).
8.2 Recent Related Work from DTIC LITERATURE SEARCH
Furham, R.S., "Intersatellite Link Design Issues," Report AFITCI/NP, 86-
w3T, Air Force Institute o Techitriogy, WPAFB, Ohio, 1985 (AD A166-761)
Halley, P. (Editor), "Special Topics in Optical Propagation. AG/.RD-CP-300,
Advisory Group for Aerospace Research and Deveiopmer<t." North Atlantic
Treaty Organization, 28th Meeting of the ElectromagnetiL Wave Propagation
Panel. Monterey, CA, April, 1981.
Hanson. D.W., "Reduction of Anisoplanatic Errors," RADC-TR-81-122, Rome Air
Development Center. Griffiss Air Force Base, New York, August, 1981 (AD-
AI06-689).
r:Ksunov, L.Z., "Laser-Based Information Systems," FTD-TD(RS)T-0563-85,
Foreign Technology Division. AFSCMD, WPAFB, Ohio, May, 1986. Translation
from Sistemy Informatsiis optichoskimi Kvantovymi Generatoriami, Kiev, USSR,19>.- (AD-A168-418).
Leslie. D.H. et.al.. "Technical Analysis of a Proposed Ship-to-Ship Chemical
Laser Transmission Experiment." NRL Memorandum Report 4745, Naval Research
Lanoratory. Washington. Dr. February. 1982 (AD-Ai12-804).
Maynard, J.A. et.al., "Airborne Flight Test System (AFTS)," Final Technical
Report. McDonnell Douglas Aircraft Company, Contract F33615,76.C-1002, with
HO Air Force Space Division, Deputy for Space Communications Systems,
Woridvay Postal Ctr, Los Angles, CA, October, 1981 (AD-AlIS-lO0).
8.3 Recent Related Work at SPIE Conferences
Barry. J.D. and G.S. Mecherie, "Beam Pointing Error as a Significant Design
Parameter for Satellite-Borne, Free-Space Optical Communications Systems."
Optical Engineering, Vol. 24, No. 6, pp. 1049-1054, November/December. 1985.
Barry, J.D. and G.S. Mecherle, "Communication Channel Burst Errors Inducedbv Gaussian Distributed Mispointing." SPIE, Vol. 616, 1086.
ClarKe. E.S. and H.D. Brixey, "Acquisition and Trarking System for A Ground-Based Laser Communications Receiver Terminal," SPIF Vol. 215. pp. 162-169.Control and Communications Technology in Laser Systems, l981.
Coffelt. Everett L. & Ebben, Thomas. H., "Optical Transceiver Platform forlaser Communication Experiments." SPIE, Vol. 61k. optical Technologies forCommunication Satellite (1986), pgs. 22-28.
8-2
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Approved for public release: distribution is unlimited.
The views and conclusions contained In this report are thoseof the authors and should not be interpreted as representingthe official policies, either expressed or implied, of the NavalOcean Systems Center or the U.S. Government.
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