Download - STAR Light PDR – 3 October 2001
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.1
STARLightSTARLightSTAR Light PDR – 3 October 2001
SYSTEM REQUIREMENTS
Roger De Roo
734-647-8779, [email protected]
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.2
STARLightSTARLight
Outline:•Science requirements & instrument concept
•STAR and DSDR technologies, instrument configuration
•Platform requirements (power/weight/balance)
•Flowdown requirements
•Noise Budget, sampling, interference rejection
•Calibration
Outline
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STARLightSTARLightScience Requirements
Soil Moisture Monitoring (L-band radiometer w/ 4K accuracy)
Land Surface Process Model Development (long term operation, plot scale )
Polar Operations (airborne access only)
STAR-Light Design GoalsMeasurement Objectives
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STARLightSTARLightPlatform Requirements
STAR-Light Design GoalsAircraft Sensor Concept
For weight stability, plane must be a tail-dragger rather than equipt with tricycle gear
STAR-Light Sensor Module
STAR-Light Control Module
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STARLightSTARLightScience Requirements
Soil Moisture Monitoring:Radio astronomy band: 1400 – 1427 MHzNoise Equivalent Brightness Uncertainty (NET) < 0.5 K
Land Surface Process Model Development in Polar Regions:Swath out to +/- 35 deg from sensor normalDaily operations for 3 hours near dawnSynthetic beamwidth from 15 deg to 22 degAmbient thermal environment –30C to +40C (243 K to 313 K)
STAR-Light Design GoalsDerivative Measurement Objectives
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STARLightSTARLightPlatform Requirements
STAR-Light Design GoalsAerial Environment
Max altitude: about 3000m (higher requires oxygen)Min altitude: about 300m (lower sacrifices safety)Surface to altitude temperature difference: -30C typicalSurface to altitude pressure change: 1000mb to 700mb typical
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STARLightSTARLightSensor Concept: Configuration
Mechanical arrangement on aircraft belly
Cross section
Cold Plate
Antenna
DigitalAnalog
Radome
Cold Plate
Receiver
Receiver assembly is a field-replaceable unit
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STARLightSTARLightSensor Concept
STAR-Light Aircraft Sensor Concept
Use Synthetic Thinned Array Radiometry to-provide imaging capability-achieve multiple angle of incidence electronically-keep the sensor robust to partial failures
Use Direct Sampling Digital Radiometry to-move complexity of STAR from analog to digital domain-keep the sensor head compact-reduce component count requiring thermal control
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STARLightSTARLightSensor Concept: STAR
STAR-Light Concept: STAR Technology
Vi
90o
Vq
Different antenna baselines sample different spatial Fourier components of the scene
Baseline d
Vi + j Vq = Tb() F1() F2() exp(j 2 sin d / ) d*
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STARLightSTARLightSensor Concept: DSDR
Direct Sampling Digital Receiver Technology
A/D DSP
A/D
Vi
Vq
Transfer • Noise bandwidth definition• I/Q detection (Hilbert transform)• Complex correlation from analog to digital domain
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STARLightSTARLightSensor Concept
STAR concept
Use a standard antenna array with missing elements:
To simulate an array of larger dimensions, by using eachElement in turn as the phase center of the array:
+
=
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STARLightSTARLightSensor Concept
STAR-Light Antenna Configuration:1-D vs 2-D STAR
1-D: requires long antenna elements to achieve narrow beam-single angle of incidence (pushbroom operation)-alias free spacing is 0.500 -demonstrated (ESTAR)
2-D: requires electrically small antenna elements -multiple angles of incidence (snapshot imaging)-many configurations; 3-arm appears optimal-alias free spacing is 0.577 -proposed (SMOS), but not yet demonstrated
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STARLightSTARLightSensor Concept
STAR IssuesHuge sidelobes: STAR requires an aperture taper which increases synthesized beamwidth by a factor of 2 (canceling the aperture doubling)………but the advantages of thinning remainOptimal taper is Blackmann [Camps etal ’98]
Increased noise: Noise in STAR image = Real Aperture Area . Noise in real aperture pixel Actual Aperture in STAR
………but longer dwell time for STAR to reduce noise equals time required to scan the real array or real aperture [LeVine ’90, Ruf ’88]
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STARLightSTARLightFlowdown Rqmt: Antenna Spacing
STAR-Light Antenna Design: Inter-element spacing
Brightness Scene
d=0.800
d=0.577
A trade-off between
*reduction of field of view due to aliasing (ie. Grating lobes)
against
*loss of beam sharpness due to reduced array size
Ideal spacing is about d=0.75 to achieve 35deg FOV
STAR image
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STARLightSTARLightSensor Concept
STAR Image Generation: Gain Correction
{V(GT)}=F(GT) T=F-1(V(GT))/G T=F-1(V(GT))/F-1(V(G))
FOV=35o
G is gain pattern of commercial patch antenna;Correction is not as pronounced for G=cosn
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STARLightSTARLightFlowdown Rqmt: Antenna Elements
Pattern knowledge requirement
Errors induced by imperfect knowledge of antenna gain patterns:
Image DC offset = +30mK/K/deg2 + 12mK/K/%2
Image rms error = +/- 0.4 mK/K/deg +/- 0.35 mK/K/%
Constant brightness temperature scene inverted by system with gain pattern uncertainty of 1dB and 10o
Goal is 0.5dB and 5o
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STARLightSTARLightSensor Concept
STAR Image Generation:Impulse Response
cos2
patch antenna
0o 30o 60o 89o
Array spacing driven by horizon alias generation d=0.68 = 14.4 cm
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STARLightSTARLightSensor Concept: Thermal
A/D DSP
High AccuracyMonitoring: 0.1C;Moderate Control
High Precision and Control:0.011C
Low Precision and Control:2.0C
keep in operating range
Heat Dissipation and Thermal Control
27 W steady54 W typical;70 W maximum
150 mW steady;2.9 W intermittent
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STARLightSTARLightSensor Concept: Geometry
Mechanical arrangement
Problem: orientation of cold plate to antenna
Preferred Orientation for Cold Plate: easy side access for cooling fluid conduits
Required Orientation for Linear Pol Antennas:Parallel or anti-parallel
A D
A D
Analog side needs high precision control, moderate heat removal
Digital side needs low precision control, large heat removal
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STARLightSTARLightSensor Concept: Receiver Module
Solutions to Cold Plate / Antenna Orientation Conflict
Cold Plate
Antenna
DA
Solution 0: disconnect Antenna from Receiver to allow Receiver orientation to Cold Plate
Very difficult field cal
Cold Plate
Antenna
DA
Solution 1: flexible connection between Antenna & Receiver to allow Receiver orientation to Cold Plate
Questionable quality
Solution 2: multiple fixed Antenna & Receiver modules
Expensive
A D
Solution 3: Circular Polarized Antennas
Tricky
A D
A D
A D
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.21
STARLightSTARLightFlowdown Rqmt: Antenna Elements
Single Feed Circular Polarization Patch
Notches create two modes w/ different resonances
Proper feed allows these two modes to be fed w/ equal amplitude and 90o phase
1.4% circular polarization bandwidth at AR=1dB while 11% VSWR bandwidth (VSWR=2)
Q=8.6; Eff=90%
Cupped design to reduce mutual coupling
Parameters shown from design paper; must be modeled w/ EM analysis SW
14cm
7.75cm
=2.2, t=4.6mm
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STARLightSTARLightPlatform Capabilities
STAR-Light Design GoalsAircraft Capabilities
Parameter Aviat Husky A-1B Piper Super Cub PA-18 150
Power available 420 W ?
Carrying capacity
(pilot + instrument)
810 lbs 767 lbs
Min Safe Speed
(Stall Speed X2)
110 mph = 50 m/s 74 kts = 38 m/s
(40 deg flaps)
Availability New or used Used only
Aircraft acquisition costs and aircraft integration are not part of STAR-Light project
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STARLightSTARLightPlatform Requirements: Weight
Aviat Husky Weight Limitations
Max. Gross Weight: 2000 lbs (normal category)
Design Empty Weight 1190 lbs
Equipment Changes 80 lbs
Std Zero Fuel Empty Weight
1270 lbs
Oil and Unusable Fuel 27 lbs
Equipped Weight Empty 1297 lbs
Fuel (50 Gal max) 300 lbs
Useful Load (excl. Fuel) 397 lbs
Gross Loaded Weight 1994 lbs
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STARLightSTARLightPlatform Requirements: Weight
Useful Load Weight Breakdown
* Present estimate + 10 lbsWeight Margin: 4 lbs (from previous viewgraph)
Pilot* 200 lbs
Survival Package 20 lbs
Sensor Module* 83 lbs
Control Module* 70 lbs
Cabling 20 lbs
Pilot Interface 4 lbs
Useful Load (excl. Fuel) 397 lbs
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STARLightSTARLightPlatform Requirements: Balance
Weight and Balance
CG Envelope
13001400150016001700180019002000
71 72 73 74 75 76 77 78 79 80
Inches Aft of Datum
Tak
e-o
ff G
ross
W
eig
ht
(lb
s) w/ full fuel tanks
w/ empty fuel tanks
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STARLightSTARLightPlatform Requirements: Power
Constant Power RequirementsAvailable Power (70 A @ 12 V) 840 W
Essential Flight Loads (33.1A) 400 W
Power Available for STAR-Light 440 W
S-L Sensor Module (RF Amps) 27 W
S-L Sensor Module (Digital) 76 W
STAR-Light Control Module 15 W
STAR-Light Thermal Control 85 W
STAR-Light Direct Power Rqmt 203 W
STAR-Light Power Supply Losses 31 W
STAR-Light Total 232 W
Power Margin 208 W
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STARLightSTARLightPlatform Requirements
Intermittent Power Requirements
Aircraft systemsTaxi/Landing Lights (14.2A @ 12V) = 170.4 WRadio Transmissions (6A @ 12 V) = 72 W
STAR-Light Components:RF switches: 2.9W at 0.3% duty cycle = 10mWCooling System on climb to altitude
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STARLightSTARLightSensor Concept: Thermal
-30-20-10
0102030
5040
GroundAmbient
CoolingControlSetpoints
-30-20-10
0102030
5040
AirborneAmbient
Increase in altitude to 3000 m
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STARLightSTARLightFlowdown Requirements
Integration Time for STAR-Light:2x Husky no-flap stall speed
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STARLightSTARLightFlowdown Requirements
Integration Time for STAR-Light:Slower speed
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STARLightSTARLightFlowdown Rqmt: Noise Figure
For any taper [Camps, ’98]: T d=constantNET(uniform) = d(Blackman)/d(uniform) * NET(Blackman) = (15deg)^2 / (10deg)^2 * 0.5 K = 1.12K
For uniform taper [LeVine, ’90],NET = Tsys Asyn = Trec + 300K 73 sqrt( B ) n Ael sqrt( 20e6 . 1.5 ) 10
For NET < 1 K, Tsys< 750 K or Trec<450 K (NF < 4.1 dB)
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STARLightSTARLightFlowdown Rqmt: Noise Figure
Antenna
Cal injectionTeledyne switch
Interference Reject FilterIMC
Low Noise AmpMiteq
IL=0.45dB
IL=0.25dB
IL=0.60dB NF=0.80dB
Interconnect losses < 0.5dB
Downstream components: add 0.1dB
System Noise Figure = 2.7 dB (Trec=250K)
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STARLightSTARLightFlowdown Rqmt: Gain
Signal amplitude at ADC must be > 4 levels (2 bits) for bias levels to not matter [Fischman, ’01]
At Tsys=250K, k Tsys B = -101.6 dBm;
LSB=15.63mV for typical ADC (SPT7610) => Padc=-26.6 dBm
Overall gain must be > 75 dB
For amplifier w/ G=26dB, 3 amplification stages minimum(to allow for losses in receiver, use 4 stages)
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STARLightSTARLightFlowdown Rqmt: Gain Fluctuations
Temperature fluctuations => Gain fluctuations => system noise
dG/dT = -0.02 dB/K per gain stage
dG/dT = -0.08 dB/K for system: requires 2mK rms to keep gain fluctuation component < fundamental NET
Thermopad: temperature compensating attenuator
Thermopads come in loss coefficient increments of 0.01 dB/K Goal: Use Thermopads to get system to +/- 0.015 dB/K; thermal control to 11mK rms
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STARLightSTARLightFlowdown Rqmt: ADC levels
Need a minimum of 4 levels for darkest target [Fischman ’01]
Is a 3-bit Analog to Digital Converter (ADC) enough?
Tsys(max) / Tsys(min) < (8 levels)^2 / (4 levels)^2 = 4
where Tsys=Tb+Trec
If we wish to look at the sky, Tb(min)=~0K; On Earth, Tb(max)=~300K
Then, Trec>100K or we need more bits
Therefore, 3 bit ADC is enough
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STARLightSTARLightFlowdown Rqmt: Pre-Sampling Filter
IMC Ceramic Filter
A pre-sampling filter is used to define sampled bandwidth:• interference rejection• out-of-band noise rejection
The Fringe Wash Function measures the differences between bandpass filters, and reduction in measurable visibility due to receiver differences
FWF=0.996
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STARLightSTARLightFlowdown Rqmt: Pre-Sampling Filter
The half-bit level for a 3-bit ADC is –24dB
Variations over temperature define the bandwidth extent for sampling
IMC Ceramic Filter
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STARLightSTARLightFlowdown Rqmt: ADC sampling
Sampling Rate considerations [Feixure etal ’98]
For a noise bandwidth (approx -3dB BW) of 1403 – 1423 MHz, the sampled bandwidth (approx –24dB BW) is 1390 – 1435 MHz
For I/Q demodulation, 2fH/m < fs < 2fL/(m-1), where m=1,2,…mmax and mmax=floor[fH/(fH-fL)]
92.58 MHz < fs < 92.66 MHz or95.67 MHz < fs < 95.86 MHz or98.97 MHz < fs < 99.29 MHz or102.5 MHz < fs < 102.96 MHz… fs=102.8 MHz
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STARLightSTARLightFlowdown Rqmt: ADC sampling
Sampling skew:If |tskew| < 6.7 ns, reduction in visibility envelope is less than 3%
ENV=sinc(Btskew)Vi=ENV*cos(2f0tskew)Vq=ENV*sin(2f0tskew)
Fischman was unable to verify this form for the envelope
Verification is a primary objective of the two channel system
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STARLightSTARLightFlowdown Rqmt: ADC sampling
Sampling jitter produces a Coherence Loss (CL) in a visibility value [Fischman ’01]:
CL = 10 log( 1 + ( 2 f0 )^2 )
for = 20 ps, CL = 0.14 dB, or, in other words, 20 ps jitter reduces a visibility value by 3% over a zero jitter visibility
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.41
STARLightSTARLightFlowdown Rqmt: Noise Budget
Noise source Noise (K rms)
RCVR+Antenna
Noise (K rms)
Image (Blackman)
conditions
Fundamental .101 .326 Tsys=600 K
B=20MHz; =1.5s
Gain Fluctuations .080 .260 dG/dT = -0.015 dB/C
To = 11 mC rms
Passive Parts .004 .013 IL = 1.75 dB
To = 11 mC rms
Antenna .022 .072 Efficiency = 90% (IL=0.45dB)
To = 200 mC rms
Radome .022 .072 Efficiency = 95% (IL=0.22dB)
To = 400 mC rms
ADC .048 .156 dSpan/dT = 50 ppm/C
To = 200 mC rms
Total (RSS) .141 .460
x (73/10)x(0.45)= x 3.25
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STARLightSTARLightFlowdown Rqmt: Interference
Keep cultural sources of RFI out of receiver chain to the extent that• Amplifiers do not saturate• Intermodulation products do not get generated in Radio Astronomy band• RFI does not alias into ADC sampling window
Some worst-case sources of interference:
1. Air Traffic Control Radar Beacon System (ATCRBS) Transponder*Responds to 1030 MHz radar pings, reporting aircraft altitude to ATC*Transmits from the STAR-Light aircraft at 1090 MHz w/ peak power
between 70 and 500 W (+48 dBm to +57 dBm)
2. Air Route Surveillance Radar (ARSR)* Transmits from the ground from 1250 to 1350 MHz w/ peak power up
to 5 MW (+97 dBm)* Some similar military systems have high resolution modes which use
up to 1375 MHz, 1380 MHz, or 1400 MHz
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.43
STARLightSTARLightFlowdown Rqmt: Interference
Keeping the ATCRBS Transponder from saturating STAR-Light amplifiers
4 m
Moving the transponder antenna to the top of the tail gives a distance of 4 m to STAR-Light
Coupling < –42 dB at 4 m
Typical model (Garmin GTX 320A) transmits 200W (+53dBm) at 1090 MHz
+53 dBm
Cumulative Rejection Needed:
31 dB 51 dB 76 dB 101dB140 dB-156 dB
P1dB=+8dBm P1dB=+14dBm
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STARLightSTARLightFlowdown Rqmt: Interference
Keeping the ARSR 1250 - 1350 MHz intermodulation products out of the 1400 – 1427 MHz Radio Astronomy band
f (MHz)
1345+/-5f2
1277+/-5f1
1413+/-102f2-f1
P2=Pr-F
PIM=2P2+P1-2IIP3
Rqmt: Keep PIM < -140dBm
At 50 km, ARSR-3 power at antenna terminals is Pr =–5dBm (assuming gain is down by 8dB, and polarization match = 50%)
Miteq IIP3 = -9dBm
Requires filtering of F= 37dB at 1350 MHz
We will get hit w/ intermodulation interference from ARSRs. ARSRs sweep at 5 rpm, and our recovery time is on the order of microseconds.(Subsequent stages also need protection from amplified f1 and f2; M/A Com amp has IIP3=-2dBm)
P1=Pr-2F
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STARLightSTARLightFlowdown Rqmt: Interference
Quadrant Engineering, Inc. ExperienceScanning Low Frequency Microwave Radiometer (SLFMR) [Goodberlet ’00]
SLFMR system:
• f = 1413 MHz; B = 100 MHz
•Phased Array antenna, not STAR
•Designed NET=0.3K; verified in lab
•Observed NET=5K over water (Tb=100K) in field tests 20 miles from interference source(Norfolk, VA)
STAR-Light Implication: With just 15dB of Interference Rejection Filtering, we can drive that interference NET down to 0.15K
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.46
STARLightSTARLightCalibration: Hardware List
STAR-Light Calibration Design:Pre-flight / In-flight Calibration
To calibrate each antenna-receiver channel, we need* a hot load* a cold load
to estimate the receiver temperature and overall receiver gain
To calibrate each pair of channels, we need* correlated noise* uncorrelated noise
to estimate the receiver correlation in magnitude and phase
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.47
STARLightSTARLightCalibration: Warm + Cold
To calibrate each antenna-receiver channel, we need* a warm load* a cold load
to estimate the receiver temperature and overall receiver gain
Tb=300K Tb= 77K
Tb
-Trec 0K 77K 300K
Slope Gain
x2
V(d=0)
V(d=0)
STARLight PDR 3 Oct ‘01 R De Roo System - Page D.48
STARLightSTARLightCalibration: Warm + Hot
To calibrate each pair of channels, we need* correlated noise* uncorrelated noise (to determine Vi, Vq offsets)
to estimate the receiver correlation in magnitude and phase
Tb=300K DSP
Delay = t
Delay = t + t
ViVq
t
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STARLightSTARLightCalibration: Receiver Two-Point Cal
STAR-Light Calibration Design:Two-Point Calibration of a single channel
Trec=300K
B=20MHz =1.5 s
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STARLightSTARLightCalibration: Cold Noise Source
STAR-Light Calibration Design:Quality of Cold Load
50 at 77KVSWR=1.05
L=0.3 dBVSWR=1.1
RCVR
L=0.4dBVSWR=1.1
VSWR=1.1
Phase Uncertainties:Reflection +/- 6 degTransmission +/- 12 deg
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STARLightSTARLightCalibration: Correlated Noise Source
STAR-Light Calibration Design:Correlated Noise Distribution Network
3-diode design allows any one diode failure while maintaining calibration
=0.743
=0.754
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STARLightSTARLightTwo Channel Prototype
Two Channel prototype tests:
•NEDT verification (Dec ’01)
•End-to-end fringe wash function measurement (Jan ’02)
•Receiver calibration validation (Feb ’02)
•Antenna radiation efficiency measurement (Spring ’02)
Tasks to be done prior to CDR:
•Antenna specification and design (Oct ’01)
•Antenna manufacture and integration (Nov ’01– Mar ’02)
•STAR model evolution (continuous)
•Cold load final design (Oct-Dec ’01)
Post CDR:
•Antenna characterization
•System validation