the magellan venus explorer's guide

8/8/2019 The Magellan Venus Explorer's Guide

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The MagellanVenus Explorer's Guide


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(1>WlGINABPAGELACK AND WHlTE PHOTOGRAPH


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JPL Publication 90-24

The Magellan

Venus Explorer's GuideCarolynn Young, Editor


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The research described in this publication was carried out by the JetPropulsion Laboratory , California Institute of Technology , under a cowith the National Ae ronautics and Space A dministration.

Reference herein to any spec ific commercial product, process, or servtrade name, tradem ark, manufac turer, or otherwise, does not constitimply its endorsement by the United States Gove rnment or the Jet Psion Laboratory California Institute of Techn ology


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AbstractThi^:gublicatro^i describes the M agellan radar-mapping missio

the planet Venus. Scientific highlights include the history of U .S. Soviet missions, as well as ground-based radar observations, that h,provided the current knowledge about the surface of Venus. Descrof the major Ven usian surface features include controversial theoriabout the origin of some of the features. The organization of the M

lan science investigators into discipline-related task groups for datanalysis purposes is presented. The design of the Magellan spacecand the ability of its radar sensor to conduc t radar imaging , altimeand radiometry measurem ents are discussed


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Foreword

During the evening hours of August 9, 1990, the Magellan spac

will near the end of its 15-month journey to the planet Venus. By ttime, the superior force of Venus' gravity becomes evident as the spcraft begins a gradual, overn ight acceleration that results in a morthan-twofold increase in its velocity.

By the morning of August 10, the Jet Propulsion Lab oratory (JP

Pasadena , California, will be a hub of activity and anticipation asMagellan flies over the north pole of Venus, dives toward p eriapsis(closest approach) at 10N latitude, rapidly dece lerates from the pof l thr st of its solid rocket motor and mane ers into an elliptica


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If we have an u lterior motive in writing this Guide, it is simply tyou will be caugh t up in our excitement about the possibility of findanswers to the many questions about the surface features of Venus athe processes that have formed them.

The information provided is accurate as of mid-May 1990, when had to stop writing and begin publication. In the interim, the last ofthree trajectory-correction mane uvers will be execu ted, and we havereason to be lieve that it will be anything but successful.

When we began this Guide, a decision was made to use materialthat had already been written. Therefore, it is quite possible that soof you may recogn ize text that is your own. We ask you to consider use of your words as a compliment and to know that we thought yo


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Table of Contents

1 . NTRODUCTION ..........................................................................

2 . H E M A G E L L A N M I S S I O N . . .. . .. . .. . .. . .. . . . . .. . .. . .. . .. . . . . ..93 . H E G E O L O G Y O F V E N U S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

There are Many Unanswered Q uestions ....................................1A Few Words About the Mapping Phase ....................................1The Venus Coordinate System ....................................................1

A Tour Around Venus .................................................................14 . H E M A G E L L A N S P A C E C R A F T . .. .. . . . . . . .. . . . . .. . . . . . . .. . . .5

Overall Physical Appearance ....................................................5Spacecraft Equipment 5


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Magellan's Path to Venus...............................................................103

Back to the Drawing Board.............................................................107Cruise Activities...............................................................................107Getting to K now the In-Flight Spacecraft.......................................109Planning for O rbital Operations....................................................111Practice Makes Perfect.....................................................................112

10. IN ORBIT AT LAST!.........................................................................113Venus Orbit Insertion......................................................................113In-Orbit Checkout...........................................................................114

11. MAPPING TH E VE ILED PLANE T.....................................................119The M echanics of the Mapping Pass..............................................120

Alternate M ission Strategies...........................................................126ExtendedMission............................................................................128

12. GE TTING THE JOB DONE...............................................................129PlanningandCoordination 129


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E arth Observing System Synthetic Aperture Radar (E OS SAR ) Space Infrared T elescope Facility....................................................17Mars Exploration Initiatives...........................................................17

1998 Mars Global Network.........................................................12001 Mars Sample Return With Local Rover ...................:.....2003 M ars Site Rec onnaissance and

Communications Orbiters..................................................1

2005 ars Rover..........................................................................1Mission C oncepts...........................................................................18

SolarProbe...................................................................................1PlutoFlyby .................................................................................18Rosetta: Comet Nucleus Sample Return.....................................18

Mercury D ual Orbiter.................................................................18Global Land /Ice Altimetry M ission............................................18Submillimeter Imaging _and Line Survey...................................18Astrometric Imaging Telescope..................................................18


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T here w as the Door to w hich I found no ICey;There was the Veil through which I might not see.

Omar Khayyam

Ci1Apt@Y 1

Introduction


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fable 1-1 . V en usMissionChrono logy

Mission aunch Date Description

Mariner 2 8/27/62 E ncountered Venus from 34 ,745 kilometers (21,594 miles(U.S.A.) 12/14/62; disclosed 468-degree-centigrade (900-degree-Fa

heit) surface temperatures and absence of magnetic field.Venera 4 6/12/67 Relayed information on Venusian atmosphere for 93 minu( LT. S . S . R . ) during entry on 10/18/67.

Mariner 5 6/14/67 Flew within 4,023 kilometers (2,500 miles) of Venus on 10(U.S.A.) furnished data on surface temperatures and atmospheric

composition.Venera 5 1/5/69 Transmitted atmospheric measurements during aerodyna(U.S.S.R.) and parachute descent on 5/16 /69; confirmed high carbo

dioxide content and lack of water vapor.Venera 6 1/10/69 Similar to Venera 5; 5/17/6 9 entry date.(U.S.S.R.)Venera 7 8/17/70 First probe to soft-land on V enus; descended v ia parachut(U.S.S.R.) 12/15/70; transmitted data for 23 minutes.Venera 8 3/27/72 Radioed surface temperature and pressure readings after (U.S.S.R.) on sunlit side of Venus on 7 /22/7 2.


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abundant volcanism, impact craters, complex tectonic deformation,

well as coronae unusual, large, ovoidal features of apparen t volcantectonic origin (see F igure 1-3).

Y et, for all our accumulated knowledge about the atmosphere anthe large-scale surface features, we kno w very little about the hills anvalleys, craters, and lava flows the telling details of Venusian geo lo


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Venus' grav itational field. These measurements will provide import

clues about the nature of the p lanet's interior.Magellan's innovative method of radar mapping, called syntheti

aperture radar (SAR ), is key to fulfilling our long-awaited desire to uthe secrets of our closest and most mysterious planetary neighbor.


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It's a long road f rom the inception of a thing

to its realization.

M oliere

^h6^ptCP Z

The Magellan Mission


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reinstatement p roviso that the spacecraft be built for about h alf the

originally estimated co st, VR M u sed mission-proven techno logies anspare componen ts from other flight programs such as Voyager, Galileand Ulysses. The m ajor contractors selected for this JPL-m anagedmission were the M artin Marietta Astronautics Group in Denver, Colrado, for the spacecraft and the H ughes Aircraft Company o f E l

Segund o, California, for the radar sensor. VR M was officially renamMagellan in 1986 .

Thus, with ascaled-down experiment package and w ith othercomp romises, such as the use of an elliptical orbit compa red with VO

circular one, the Venus mission was ontrack again with a launch planned forMay 1988.

The Cha llenger disaster in 1986

Did you know .. .

T he M agellan m ission


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from a Voyager spacecraft on public display at the National Air aSpace M useum in Washington, D.C.

The loss of the Challenger and the 32-month suspension of shmissions delayed and reshuffled many planned space activities. TGalileo mission to Jupiter, for one, would hav e to launch in Octob1989, the date initially set for Magellan, or wait another two yea rthe necessary alignment of planets. The result for Magellan was aMay 1989 launch and the u se of a Type-IV trajectory. This meanthe spacecraft would spend 15 months traveling one and a half tiaround the Sun before arriving at Venus. The original May 19881date would have allowed Magellan to reach Venus in 4 months by

traveling less than 180 degrees around the Sun via aType-I trajecThus, the $551 million mission (see T able 2-1) and the spacecrthat will soon arrive at Venus are much d ifferent than NA SA hadplanned a decade earlier yet the basic scientific mapping ob jectiv


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M an m as te rs natu re no t by fo rce bu t by unde

standing. This is why science has succeeded. Jacob Bronowski

Chapter 3

The Geology of Venus


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Of course, the most interesting answers may com e from question

not even asked yet!With the addition of gravity-field measurements, Magellan scienhope to improve their understanding of the geophysics of Venus bydetermining how mass is distributed within the p lanet and by ascering the nature of the interior processes and how they affect the surf

features.

A Few Words About the Mapping Phase

Magellan will maneuver into orbit around Venus on August 10,1990. H owever, the mapp ing phase will not begin for 22 days. Durthat time, the spacecraft and the radar sensor w ill be tested and thewill be adjusted, if necessary. M agellan's orbit will be fixed inertial

space, which means the spacecraft


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arbitrary conven tion that determines the direction of increasing lontude on planetary bodies other than E arth: longitude shall be measin a direction opposite to that in which the planet rotates. BecauseVenus rotates in a clockwise direction as viewed looking down on thnorth pole, longitude on Venus increases in num erical value towardeast from the planet's prime meridian.

A Tour Around Venus

For the remainder of this chapter, we will take an imag inary jouaround Venus and discuss some of the important facts and questionabout many of the surface features. So, before reading further, wesuggest you remove the map of Venus from the inside back cov er annavigate along w ith us. If you trip over som e of the terminology, hnear at hand in Chapter 16 , Glossary of G eological Terms.


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Lakshmi and its high m ountains are surrounded by regions oftesserae terrain named Fortuna, Atropos, and Clotho Tesserae (alsshown in Figure 3-2). Tesserae terrain, which w as first detected bySoviet Venera15 and 16 spacecraft in the early1980s, is characterizedby com plex intersecting ridges and grooves. This terrain may havformed by large blocks of material sliding and collapsing down slo

pulled by the force of gravity. In the extremely high -temperature environment, rock can behave m ore like a fluid, unlike the rigid bior of rocks found on E arth.

Magellan will next image Guinevere and Sedna Planitia (seeFigure 3-1), south of Lakshmi Planum. These low-lying regions ha

abundant sma ll volcanoes and long lava flows. We hope the lava will provide new and exciting information about the electrical proof the materials that make up the surface of these plains. (Determ


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group of peaks may be similar to Imdr R egio, centered at 43S latiand 210E longitude, which will be imaged by M agellan in M arch

The first major impact crater that will be imaged is M eitner (seFigure 3-4), centered at 56 S latitude and 322E longitude. Meitnemultiringed basin abou t 85 kilometers (53 miles) across, may be sito large multiringed basins on other planetary bodies, such as Ori

Basin on the M oon. It is believed that many of these basins on othplanets have been the cause of volcanism. H as this been the case Venus? G eologists also wonder about the effect of the hot Venus enment on impact basins. It is believed that M eitner may be relativeshallow because, under the influence of this heat, the crust "flowed

away" w ith time. The plains to the east of Meitner contain complebelts of lineam ents (also shown in Figure 3-4 ). Magellan data w ill studied to determine whether these lineam ents are ridges or groove


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pools of lava, is surrounded by extensive flow features that seem tcascade dow n its flanks. Is this feature now active? If the MagellaProject is extended for additiona1243-day m apping cycles, scienticould com pare images of volcanic features, such as Sif, to detect cvolcanic activity.

Traveling again into the southern hemisphere, we come across

highland region of Alpha R egio (see Figure 3-8). Previous radar imindicate that this is a region o f tesserae. Tesserae tend to occur in polygonally shaped plateau regions, as well as in small islandlikeregions in the p lains. Do tesserae underlie all of the plains? Somegeologists believe regions of tesserae have formed as the result of c

pressional forces, while others believe they were c reated at a spreacenter and m oved laterally out into the p lains. Alpha R egio is simsize and appearance to Tellus Tessera, centered at 35N latitude an


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lost through the process of p late tectonics. On Venus, the internamay be creating many mantle plumes that form highland regions andvolcanoes. H igh-resolution gravity data, which would be obtaineduring extended mission cycles, would help scientists solve this pu

Also in mid-November 1990, Magellan will image what is prothe most actively debated region on Venus: Aphrodite Terra. Appr

mately the size of A frica, Aphrodite straddles the equator, is over kilometers (6 ,214 miles) long, and is made up of four smaller higOvda, Thetis, Atla, and Ulfrun R egiones. Some geologists believeAphrodite is a spreading center, a linear zone where new crust is and sp read ou t laterally to the north and south, similar to the m i

ridge spreading centers on E arth (see Figure 3-11). Others believeAphrodite is underlain by mantle plumes w ith little or no crustaling.

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subsurface layer? If there is evidence that wa ter existed in Venuswe can determine when the g reenhouse effect turned the planet i

place where no human can survive.H eading north again, we see to the east of Fortuna Tessera a f

mented region of tesserae called M eshkenet Tessera (see Figure 3-This terrain appears to be flooded by volcanism from the surrounplains, and thus seems to be relatively old. To the east of M eshkenseveral large circular structures called coronae. Nigh tingale Coro56 0 kilometers (348 miles) in diameter, is surrounded by a ring ofover 1.5 kilometers (0.9 mile) high. Coronae a re believed to form hot mantle plumes that rise from the interior of the p lanet. Coron

range in size from 17 0 to 1,000 kilometers (106 to 6 21 miles), wiof the features lying in clusters to the west and east of Ishtar Terr

To the south of Thetis Regio in Aphrodite lies Artemis (see Fig


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South of Vinmara, on the eastern end of Aphrodite, are two elhighlands called A tla and Ulfrun Reg iones. Atla and U lfrun cont

many high peaks thoug ht to be volcanic in origin, but which havbeen imaged at high resolution. Will they be characterized by laflows, like Sif Mons in E isila Regio, or are they long-dormant, erovolcanoes?

Back up north again, Magellan will image several large coronvolcanoes in March 1991. Bachue Coron a (see Figure 3-16 ) is locMetis Regio and is raised over 2 k ilometers (1 mile) above the suring region. Bachue may be a corona in the process of forming, sionly partially surrounded by a ring of ridges. Mokosha M ons, a l

the south of Bachue, is a 350-kilometer- (217-male-) wide volcanicstructure (see Figure 3-17 ). It has a complex central caldera surroby many lava flows. Mokosha probably formed over a long perio


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Figure 3-18. This imageof Themis Regio, a highland region rising about 2.5 kilometers (1.6 miles)above the surrounding plains, was taken atthe A recibo Radar O b s e r v a t o r y.


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Chasma (see F igure 3-19). Beta is similar in size and general morpogy to the E ast African Rift Zone on E arth, a region where the crus

the plane t is being pu lled apart. Scientists will use M agellan data determine how much extension has taken place. Some scientists abelieve that Beta is the most likely place on the planet to detec t actvolcanoes.

Over the course of one Venus rotation (243 E arth days), the M alan spacecraft will map most of the surface with detail that exceedof the best p revious radar images. The resultant maps will reveal traces (if they exist) of many fundamental planetary forces: volcanwind, water, and meteorite impacts in short, all the processes tha

determine a p lanet's history and shape its face. By giving us this ninformation, Magellan will not only tell us more about Venus, ournearest planetary neighbor, but perhaps w ill provide the insight w


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The ship, a fragment detached from the earth,

went on lonely and swift like a small planet.

Joseph Conrad

Chapter 4The Magellan Spacecraft


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Table 4-1. Equipme nt from Other Sp acecraft

Component ource

Medium -gain antenna

High- and low-gain antennas

Equipment bus

Star-scanner design

Radio-frequency traveling-wave tube assembliesAttitude-control computer

Com mand and data subsystem

Thruster rockets (small)

Electric-power distribution unit

Power control unitPyrotechnic control

Solid-rocket motor design

Mariner Mars 1 971

Voyager

Voyager

Inertial Upper Stage

UlyssesGalileo

Galileo

Voyager

Galileo

P-80 satelliteGalileo

Space-shuttle payload assistmodule (PAM)


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The altimeter antenna (ALTA) is mounted on the side of the forwaequipment module (FEM ), extending forward from beneath the HG A

dish. It is used exclusively for radar altimetry. During the m apping pof each Venus orbit, the AL TA is pointed vertically down at the planeprovide one-dimensional readings of the heights of surface features. 1.5-meter- (5-foot-) long aluminum structure has an aperture of 0.6 xmeter (2 x 1 feet) and weighs 6.8 kilograms (15 pounds).

The FEM houses the radar electronics, radio telecommunicationsequipm ent, certain attitude-co ntrol equipmen t, batteries, and the powconditioning unit (see Figure 4-2). The boxlike housing measures 1 .71.0 x 1.3 m eters (5.3 x 3.3 x 4.3 feet) and is made of aluminum pane

on a framew ork of square alum inum tubing that has been chem icallmilled for weight reduction. Two sides of the FEM have louvers forthermal conditioning. M irror-surfaced covers shield the louvers from


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3.7 meters(12 feet) -

( a )

MapperOrbiter

4.6 mete(15.4 fee

Magellan6.4 meters

(21 feet)

3.460 kilograms(7,612 pounds)

Low-G ain Antenna

High-Gain Antenna

Altimeter Antenna

Forward Equipment Module

Medium-Gain Antenna

Equipment Bus

Propulsion Module

Solid-Rocket Motor


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Telecommunications

Star Scanner

Gyroscopes

ReactionWheels(Three Places)

Radar ^

Sensor

Electronics


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The panels are hinged for stowage in the shuttle and were deployewhile M agellan was in Earth orbit. During interplanetary cruise and

orbit around Venus, they rotate to follow the Sun. Solar sensors on thpanel tips and a control package in the equipment bus maintain thepanels' sunward orientation. The honeycomb aluminum backingstructure, arms, and oversized joints are designed to enable the panelwithstand the force produced by the rocket burn that will insert Magel

lan into Venus orbit.The propulsion equipment shown in Figure 4-4 includes a 24-

thruster liquid-propulsion module and the solid-rocket motor (SRM ) ufor orbit insertion. The propulsion-module structure provides preciselyaligned attachm ent of the SRM , as well as the liquid-propellant thrusand associated plumbing, which are needed for trajectory/orbit corrections, attitude control during o rbit insertion, and other functions.

Th l i d l l id h h i f h


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i-Rocket

^r

^ ropulsion Module


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at a frequency rate almost four times greater than that of S-band,enables the HG A to transmit an even more concentrated signal to Ea

The use of X -band and a higher signal power (20 watts) enables the hdata rates used for transmitting radar data to E arth.

From Venus orbit, this system w ill send engineering data about thespacecraft's condition to Earth at 1.2 kilobits per second through theHG A via S-band and simultaneously transmit the radar data at 268.8kilobits per second via X-band. Backup data rates of 40 bits per secofor engineering telemetry and 115.2 kilobits per second for radar dataare available for certain circumstances or emergencies.

W orking with the radio transponder, modu lators, and am plifiers t

make up a com plete telecommunications subsystem are the high-,medium -, and low-gain com munication antennas.The 3.7-meter- (12-foot-) diameter HG A is critical to all aspects of


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the spacecraft to begin corrective actions, including switching to the LG Afor command reception from Earth. Thus, ground controllers wou ld be

able to augm ent the spacecraft's corrective actions, if required.

Attitude C ontrolMagellan is athree-axis-stabilized craft, but it is required to perform

frequent changes of its orientation in space as it orbits Venus. Keepingtrack of its precise orientation at all times via gyroscopes, this maneuvering is performed w ith reaction wheels controlled by one of two ATA C-16com puters located in the equipmen t bus.

During each orbit of Venus, Magellan will rotate four times: away

from the planet to aim the HG A earthward for data transmission,toward space to scan stars for precisely determining any spacecraft-orientation errors, again toward E arth to resume data transmission, an


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diameter) in the opposite direction. By New ton's Third Law , the space-craft turns in the intended direction w hile the reaction w heel spins in

opposite direction. The spacecraft turn is stopped by commanding. thmotor driving the reaction w heel to stop. Three reaction w heels, one each possible axis of rotation, are located in the FEM .

In theory, this system could w ork on its own, without thrusters,forever. But the reaction wheels must also be used to oppose outsideforces (i.e., solar pressure and Venus gravity) that cause Magellan torotate. As a result of the accum ulation of these d isturbances, the reaction w heels steadily build up speed. Even tually, the wheels w ould reatheir maximum speed, or saturate, and becom e useless in con trolling

spacecraft. Therefore, thrusters are fired briefly twice a day to allow threaction wheels to "desaturate," i.e., reduce their speed to near zero.Tacho meters on the reaction wheels determine the amo unt of thruste


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much the gyroscope drift has affected the com puter's know ledge of itsow n attitude since the last star scan. This error has typically been lessthan 0.1 deg ree per day during the cruise period. The compu ter autono-

Did you know .. .

A fter orb it ing V enus for m ore

than a dozen y ears , therew ill be sufficient onb oard

pr opel lant only to d esatur ate

the reaction w heels. T here

w ill not b e enough pr opel-

lant to pr event the orb it

mously upd ates its attitude, aswell as its own drift-compensa-tion m odel, based on the deter-mined error.

Round ing out the comple-ment of attitude-control hard-ware are sun senso rs and solar-array drive motors, which keep

the solar panels pointed towardthe Sun. The sun senso rs arelocated on the outboard tips of


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tions in Venus orbit; this includes recharging the batteries. The batteraugm ent solar-panel power during m apping, when the radar is drawi

maximum power. When Venus occults the Sun from the spacecraft, thbatteries supply the entire spacecraft pow er load.

Command and Data Handling

The command and data subsystem (CD S) decodes, stores, anddistributes commands received from Earth to control spacecraft activitThese include com mands to the attitude-control subsystem that regulthe position of Magellan and its back-and-forth changes between d atgathering and transmitting. Other commands control radar-operating

parameters and sequence other spacecraft subsystems through theiroperational states, as required._ Most com mands for controlling thespacecraft are stored for later distribution. The CDS can execu te com-


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10 -sided equipment bus is the single propellant tank that, at launch,contained 132.5 kilograms (29 3 pounds) o f monopropellant hydrazine.

A helium tank is attached to the struts of the propulsion-module struc-ture and w ill be used, if necessary, to offset a d rop in the pressure of thehydrazine system , a drop that wo uld reduce thruster output level. Thehelium pressu rant will be used if Magellan's interplanetary trajectoryrequires a major corrective firing of the thrusters, which, in turn, woulddrop the system pressure.

At each of the four outboard tips of the propulsion structure is agroup of six thrusters: two of 10 0-pound, one of 5-pound, and three of0.2-pou nd thrust. The large 10 0-pound thrusters, aimed aft, are used fo

large midflight course corrections, large orbit-trimming corrections, andcontrolling the spacecraft while the SRM burns during VO I. The 5-pound thrusters, aligned perpendicularly to M agellan's cen terline, keep

P t h i C t l


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Pyrotechnic Control

Attached to the underside of on e equipment bus com partmen t is a

box containing the control electronics that arm, disarm, and fire detotors to activate various explosive bolts, pin-pullers, and other dev ices.These enab le release of the solar panels from their stowed position aftedeploym ent from the shuttle, actuation of p ropulsion valves, ignitionthe SRM , and separation of the spent SRM after orbit insertion.

Thermal Control

Magellan w ill be sub jected to sunlight approximately twice asintense as that which reaches E arth, potentially for several years. On

the other hand, shaded exterior spacecraft tem peratures can plunge to-204 degrees centigrade (-400 _degrees Fahrenheit). Throughout the

mission, the constant m aneuvering of the craft will subject nearly eve


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1 c enrimeter(0.39 inch) ,^ Nine Layers of Aluminized Mylar

Alternated with Ten Layers ofDacron Net

Astroquartz Bonded toExterior ^^ Aluminized Kapton Film

Three Layers of CrinkledAluminized Kapton

Three Layers of Crinkled^..- Aluminized Kapton

Filter Cloth Aluminized Kapton

Interior

bl k i


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6,00 0 lines of code in the attitude-control software is new, including2,00 0 lines for fault protection. Of the 18 ,000 lines of code for the CDS

45 percent is unmodified G alileo code, 20 percent is new, and 35 percenis mod ified G alileo code. The fault-protection software resident in theCDS totals 1,500 lines.

Spacecraft operation is controlled for several days at a time bycom man ds sent from Earth and stored in the CDS . During m apping,this method requires accurate navigational data that are updated asfrequently as three times a week .

Control of the radar system is performed with data generated by theRadar Mapping Sequencing Software (RM SS) located on Earth. Almost

all significant comm and sequences are stored in a simplified form onmission-control computers at JPL. For m ost comm and sequences, engi-neers simply select from that set and add param eters. G round com put-

V t t i l t


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V en us, sw ee t m yst ica l s tarEarthlike, but hotter by far

No use to peruseUn less you can useSynthetic-aper ture radar

Anonymous

Chapter 5

The Radar System


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a m uch larger antenna (i.e., a synthetic aperture). The distance M agel-lan travels while a surface feature is w ithin the radar's field of view

determines the functional size of the synthetic aperture.The radar transmits energy in short pulses to one side of the plat-

form, as show n in Figure 5-1. The direction along the track of theplatform's motion is called azimuth; the direction across the track iscalled range. The SA R form s an image strip, with a width determined bythe range dimension of the antenna's illumination and a length deter-mined by the tim e the radar is in continuous imaging operation. The

image strip (or swath) produced byDid you know ... agellan will be about 25 kilometers

During mapping, the (16 miles) wide and about 16,000Magellan radar sensor kilometers (10 ,000 miles) long.

The SA R technique requires the


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MotionSpacecraft

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Planet Surface -^' ^^^^ î maged Swath ' '

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of Constant Range

^- rea Illuminatedby Beam (Real Aperture)

Î^ iGK i^fl^ ^lHITE PHt^TOGP^P^+


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( a )

SAR images can be formed using data gathered through clouds a


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SAR images can be formed using data gathered through clouds, anight, and from under dry, thin layers of sand. Because the brightnes

in a radar image is a func tion of surface roughness, angle of incidencand electrical properties of the surface, radar-image interpretation isvery different from that used for normal photographic images. Thetechnique of radar-image interpretation is advanc ing as we gather din a variety of ways and use ground truth (local observation) to incre

our understanding of the interaction betw een the radar wave and thesurface.

The Radar Sensor

The radar senso r, Mage llan's sole scientiffc instrum ent, will perfothree distinct functions in Venus orbit: SAR imaging (to produce imagof surface features), altimetry (to measure the height of surface featur

^^21^^NAE ^^E^Lp,^^y ,q1^^ ^VH1TE P^OTOGRRFf^


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Table 5-1. Magellan Mission Constraints


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That In t iuenced R adar Design

A single, spacecraft-fixed high-gain antenna

An elliptical orbit

Data rate and volum e limitations

Radar commanding from stored sequences only

simultaneously. To do this, the range to the surface m ust be predictewith high precision from second to second, which is not necessary forradar in a circular orbit. M agellan's 44-m inute mapp ing period startnear the north pole at an altitude of about 2;150 kilom eters (1,336

miles), continues through periapsis at a 275-kilometer (171-m ile) alti-tude, and finishes at a 2,400 -kilometer (1,491 -mile) altitude near 74Sl tit d D i g thi ti th d t t t f

h d 114 i f h 18 9 i bi d f d l


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three, and 114 m inutes of the 18 9-m inute orbit are used for data play-back. Additionally, the radar system em ploys a "burst-mode" data-

acquisition schem e (a data-reduction m ethod discussed below) andpasses the data through a d igital filter that reduces the data rate butdoes not sacrifice image quality.

Burst-Mode Data Collection

The piece deresistance of the burst-mode m ethod of data collection isits ability toquicklychange configurations to accom modate the ellipticalorbit and make efficient use of the data volume that can be sent toEarth.

The SA R, altimeter, and radiometer modes share a time slot calledthe burst period, which lasts less than one second (see Figure 5 -4). First,in SAR mode, the radar sends out a rapid burst of pulses through the

Commands


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Commands

Radar Sensor ( pacecraf t

Radar DataHigh-Gain ltimeterAntenna ntenna Commands elemetry

S A Radar ControlRadiometer ommand and

Parameters elemetrySubsystems

AltimetSelected A R ataRadar Data ata

Radar AR Data mage mage DataEngineering rocessing rocessingSubsystem ubsystem trips ubsystem

Figure S-S. Th e M agellan radar system .

Figure S-6. The

^Rl^IiVA^ ^,^^^t ^ACI( AND V1lHITE PHQTO^2RP4^

M ount St. Helens


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gevolution of imagingradar is illustrated inthese images of theMount St. Helensregion of Washington,which are simulationsderived from the radar-imaging data acquiredby the Seasat satellite.The still-active volcano

does not show at thePioneer Venusresolution. Althoughthe feature is visible atthe Venera resolution,

it is not possible to tellwhether it is a volcanoor a meteorite impactcrater. Magellan resolution

The Image Data Processing Subsystem (IDPS) takes the image stripin electronic form (on tape or discs) and mosaics these strips into large


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in electronic form (on tape or discs) and mosaics these strips into largearea-coverage maps of the planet surface. The radiometer data are

likew ise mosaicked into m aps. The altimetry data are accepted by theIDPS, and both raw-data processing and m osaicking are performed toproduce large-area-terrain height maps that will complement the imagdata mosaics from the SAR .

Engineers from the Hughes Aircraft Com pany of El Segundo, Califonia, and from JPL folded in all of these mission constraints; whatemerged was a fairly simple radar sensor, an innovative design for thesystem that operates it, and aSA R-image resolution of the Venusiansurface that is higher than any achieved to date (see Figure 5-6).


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soldiers and sailors returned hom e to Portuga l, they received little than


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soldiers and sailors returned hom e to Portuga l, they received little thanfor the numerou s victories that had broug ht enormo us wea lth and

prestige to their king and countrym en. Mag ellan's noble though low-grade birth entitled him to a beggarly allow ance, a pom pous, meaningless title, and the right to becom e a loafer at cou rt an unbearablesituation for a man of honor and ambition.

The first opportunity for renewed m ilitary service found Magellanfighting the M oors in Morocco , but that, too, ended in hardship. A lanwound permanently injured his left leg, and an unjust accusation oftrading with the enem y scarred his reputation. After King E manuel ofPortugal coo lly rejected M agellan's petition for a post w ithin the royalnavy, the soldier renounced his loyalty to Portugal and left for Spain.

It was the feverish quest for spices that inspired Em peror Charles VSpain to financially support Magellan's claim of a western route to the

one w ho had survived an exped ition that had unceasingly taxed his


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intellect and intuition, a man w hose character was so strikingly identi-

fied by caution and fo resight.Only one ship, the Victoria, and 18 of the original crew m embersreturned to Spain, thereby completing the first circumnavigation of theglobe. Though M agellan's route proved impractical for the spice trade,his voyage has been called the greatest single hum an achievem ent on

the seas. He w as never granted the dazzling fame bestowed on otherexplorers of the period, but Ferdinand Magellan's legacy changed manunderstanding of his world.

Art is I; science is We.


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Claude Bernard

Chapter 7

The Science Investigators

Table 7 -1. RADIG Memb ers


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Team Member Affiliation

Raymond E. Arvidson (PSG) Washington University

Victor R. Baker U niversity of Arizona

Joseph H. Binsack Massachusetts Institute of Technology

Joseph M. Boyce (PSG) National Aeronautics and Space Administration

Donald B. Campbell Cornell UniversityMerton E. D avies (PSG) The RAN D Corporation

Charles Elachi (PSG) Jet Propulsion Laboratory

John E. G uest U niversity of Lo ndon

James W . Head III (PSG) Brown U niversity

William M. Kaula U niversity of California, Los A ngeles

Kurt L. Lambeck Australian National University

been chosen to represent RADIG ; the PSG has met quarterly during theyears prior to launch and w ill continue to meet throughout m apping o


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years prior to launch and w ill continue to meet throughout m apping oerations.

The Data Products W orking G roup and the Mission Operations andSequence Planning Working G roup were established by the PSG to ap-prove the Project's plans for data products and spacec raft/radar opera-tions, respectively.

To accom plish its assignment, the RADIG is organized around sixgroups, each responsible for a general task (see Figure 7-1).

The Cartography and G eodesy Task G roup will develop a latitudeand longitude grid (know n as a geodetic control network) for Venus bywhich M agellan m aps of the planet may be coordinated and from whic

improved estimates of V enus' pole position and rotation rate may be derived.

The Surface Electrical Properties Task G roup will work with the rada

Radar Investigation Group

Principal Invesrigator: G. Pettengill

Scientific ission


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Scientific issionInterpretation esign

Cartography urface Electricaland Geodesy roperties

M. D avies (Chairman) . Tyler (Chairman)J. Head . CampbellF. Leberl . SchaberH. MasurskyL. Soderblom

^ eology andGeophysics

S. Solomon, (Chairman)J. Head (Vice Chairman)

Volcanic andTectonic ImpactProcesses

Erosional,Depositional

and ChemicalProcesses P r o c e s s e s

J. Head G. Schaber R. ArvidsonJ. Guest J. Boyce v. BakerH. Masursky J. Head C. ElachiS. Saunders H. Masursky J. WoodG. Schuber t

S. Solomon

System CalibrationI I I AR Dataand Test Processing

K. Raney (Chairman) L. Soderblom (Chairman)J. Binsack R. ArvidsonD. Campbell D. CampbellC. Flachi M. Davies

K. Raney

Altimeter andRadiometer

Data Processing

R. Phillips (Chairman)D. Campbell

B. ParsonsIsostatic and L. TylerConvection

P r o c e s s e s

R. PhillipsW. KaulaK. LambeckD. McKenzieB. ParsonsM. Talwani

Figure 7-1.RADIG organization.

The SAR Data Processing Task G roup is charged specifically with


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monitoring the design of the algorithms and data flow involved in thehandling of the SAR data by JPL's M ultimission SAR Processing Facilit

Finally, the Altimeter and Radiometer Data Processing Task G roupmonitors the algorithm s and data flow from the altimetry and radiomtry experiments through the various processing steps to a final produc

The Gravity Investigation Group

G ravity and altimetry data from the Pioneer Venus Orbiter (PVO)mission (1978 -1982) have provided the foundation for the present gephysical models of the interior of V enus. These data show a significanlink between the variations in the gravity field of Venus and its topogrphy; this link does no t exist on E arth, the Moon, or M ars. This suggestthat there are major differences between the processes acting w ithin

mapping cycle, the time around periapsis will be dedicated to SAR


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pp g y , p pimaging w ith the high-gain antenna pointed toward the surface of the

planet, making it impossible to obtain high-resolution gravity dataduring that phase of the m ission.

This does not mean that gravity data will not be obtained in the firmapping cycle. For approximately 2 hours of each mapping pass, highaltitude velocity data, which results in low er-resolution g ravity data, wibe acqu ired during the normal tracking activities while the spacecraft itransmitting radar da ta to Earth. These low-resolution data w ill be usein conjunction with PV O data to produce a revised m odel for the globagravity field of Venus.

Scientists from both RADIG and G RAVIG will work together todevelop m odels of the interior of Venus. These models will incorporateSAR and altimetry measurements of the surface of the planet as well as

Table 7-2. GRAVIGMembers


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Team Member Affiliation

W illiam L. Sjogren (PSGb) et Propulsion Laboratory

Mohan Ananda Jet Propulsion Laboratory

Georges Balmino (PSG) entre National d'Etudes Spatiales

Nicole Borderies Centre National d'Etudes Spatiales

Bernard Moynot Centre National d'Etudes Spatiales

Principal Investigator.b Project Science G roup.

Ta61e 7-3. Magellan Guest Investigators

N Affili ti


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Table 8-1. Categories for Naming Feat ures on Venus

Feature Definition Category


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Feature Definition Category

Chasmata Canyons Goddesses of hunt; moon

Colles Small hills, knobs Sea goddesses

Coronae Ovoid-shaped features Fertility goddesses

Craters (large) Craters Famous women(small) Craters Female first names

Dorsa Ridges Sky goddessesLineae Elongate markings G oddesses of war

Montes Mountains Goddesses, miscellaneous(also, one male radar scientist)

Paterae Irregularly shaped craters Famous women

Planitiae Low plains Mythological heroines

Planum (1 only) High plain Goddess of prosperity


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morning and evening "star." An an cient Babylonian psalm provides a


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glimpse of her:

"By causing the h eav en s to t rem ble

and the Earth to quak e,

B y the gleam wh ich l ightens the sk y,

B y the blazing fire w hich rains up on

a ho st ile land ,

I am Ishtar."

Admittedly this sounds a little more warlike than loving! Aphroditeis the Greek goddess of love (see Figure 8 -2); the name (which literallymeans "sea foam," because the goddess was born from the sea) brings tomind Bo tticelli's painting, "The Birth of Venus," which hangs in theUffizi G allery in Florence, Italy.


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named for either goddesses of the hunt or moon goddesses; in my thol-ogy these attributes are often combined in the same goddess Diana


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ogy, these attributes are often combined in the same goddess. Dianaw. as a Roman huntress; her chasma, in Aphrodite Terra, includes someof the lowest elevations of Venus.

Irregular, long regions (lineae) are named for warlike mythologicalwom en. Hippolyta Linea is an example. H ippolyta was Queen of theAm azons and wife of Theseus.

Regiones are circular areas of moderate topographic relief. Asidefrom Alpha and Beta, they are named for Titanesses; Atla, part ofAphrodite Terra, is named for the m other of Heimdall, the Norse god oflight. Circular features w ere recognized on the early radar reflectivitymaps of V enus, but their origin is still uncertain. In the late 19 70 s, thePVO radar resolution made possible an attempt to d ifferentiate between

volcanic features (paterae), discussed above, and impact craters, whiwere to be named for notable deceased w omen A few names w ere


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were to be named for notable deceased w omen. A few names w ereapplied to craters on the basis of those data: M eitner Crater honors thfamous A ustrian physicist, and Nefertiti Crater honors the beautiful wwho supported Pharaoh A khenaten's attempt to install mono theism Egypt. Since then, two additional names were added by the Soviets,based on Venera 15 and 1 6 data: Resnick Crater and M cAuliffe Crate

honor the astronaut (see Figure 8-3) and educator (see Figure 8-4),respectively, who perished in the explosion of the Space Shuttle Chal-lenger in 198 6.

The central peak of another crater, located in Alpha Regio, wasoriginally used to define zero longitude; this peak is named E ve. W h

the Soviet Venera missions were com pleted in the early 198 0s, anothe

small crater, Ariadna, superseded E ve as the definition for zero long i-d Thi h h I d f i i i lik l h hi d


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tude. This change has Ied to som e con fusion; it is likely that a third

crater nearer the equator will be nominated from the higher resolutionand m ore extensive data of the Magellan mission.

The Venera missions also produced two new feature terms: "coro-nae," for ovo id structures, and "tesserae," for mosaiclike terrain, wereadopted to describe terrain unlike any seen on o ther extraterrestrial

surfaces. An additiona1320 names were added to identify features inthese new ca tegories, and the ethnic representation was similarly en-larged: Bachue (Corona) is the fertility goddess o f the Chibcha Indians;the three G reek Fates Atropos, Clotho, and Lachesis (Tesserae)arenow honored on Venus. Other features are named using terms trans-ferred from established planetary nom enclature: two features, AkkruvaColles and Jurate Colles are nam ed for sea divinities; fault systems

W e m ust ask w here w e are and w hither w e are tending.

Abraham Lincoln


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Abraham Lincoln

Chapter 9

From Earth to Venus

Launch (5/4/89)

Interplanetary Cruise (462 days)


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p y ( y )

IVenus Orbit Insertion (8/10/90 )

In-Orbit Checkout (22 days)

(243 days) adar Mapping

0Superior ap RecoveryConjunction O (7/03/91)Gap (11/02/90)End of N ominal Mission

(4/29/91)End of Project(10/28/91)

Extended Missio n (4/29/91 to ...)

JAN U L AN U L AN U L AN1989 990 991 992

The cou ntdown resumed, starting this time at Launch -2 days, anproceeded smoothly. But M ay 4 did not dawn as a likely day for a


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launch. The sky was overcast, and strong crosswinds (greater than 12

knots) blew across the runway at the Kennedy Space C enter's emergenlanding site. No one w as surprised when a ho ld for weather was calleLaunch -5 m inutes.

Fortunately, a 64-minute launch w indow had been designed forM ay 4. After 59 an xiety-filled m inutes, the winds dissipated and theclouds parted just enough for launch at 2:46:59 p.m., eastern daylightime (see Figure 9-2), only 5 m inutes before the end of the launch winfor that day. The shuttle slowly rose out o f the billows of steam andaccelerated toward the low clouds. It went briefly ou t of sight and thereappeared for a few seconds, framed in a blue window amid the cloudIt was truly picture perfect.

The Space Shu ttle Atlantis compensated for the delay in launch by


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However, the positions of Earth and Venus during the late-April tolate May 1989 launch period required aType IV trajectory (see Figure


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late-May 1989 launch period required aType-IV trajectory (see Figure

9-5). This meant that the spacecraft would travel between 1-1/2 to 2times around the Sun (slightly m ore than 540 degrees) and that it wouarrive at Venus on A ugust 10 , 199 0. W hile it dictated a longer cruiseduration (15 m onths), the Type IV actually had the advan tages ofreductions in launch energy and Venus approach speed.

Since launch, Mage llan has traveled more than 1-1 /2 times aroundthe Sun at an average speed of 113,60 0 kilometers per hour (71,00 0miles per hour) relative to the Sun and has logged over 1.261 billionkilometers (788 million miles). Three trajectory-correction maneuvers(TCM s) have kept the spacecraft on track for the correct aim po int andarrival time at Venus. The TCM s were executed on May 21, 198 9, andon March 13 and July 25, 1990 .

Venus

Ascendingd


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Venus at Arrival ode8 / 1 0 / 9 0 e n u s a t L a u n c h

5/4/89

^^^-/^

^ arth OrbitMagellan

OrbitI/ Sun

/ \ .^ . .^VernalEquinox

\! enus Orbit-

\

Getting to Know the In-Flight Spacecraft

Th i i d h b i f l i f h f


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The cruise period has not been a time of leisure for the spacecraft

either.M agellan has traveled farther from the Sun than E arth's orbit

(149,669,00 0 kilometers or 93,00 0,00 0 m iles) and has approached towithin 104,640,00 0 kilometers (65,400 ,000 miles) of the Sun, 2,88 0,kilometers (1,80 0,000 miles) closer to the Sun than the orbit of VenusThis changing env ironmen t allowed us to characterize the thermalresponses of various parts of the spacecraft over a range of tem peratuas these parts faced toward or away from the Sun. Know ing theseresponses is referred to by spacecraft engineers as "having a m odel."

The ab ility to refine and validate the thermal m odel m eans that we wbe better able to predict the thermal response of the spacecraft once itin Venus orbit

the star scanner reference fram e. During flight, this offset can changef th t d b f l h


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from the am ount measured before launch.

Pointing of the HG A w as calibrated to assure its accuracy whileperform ing the dual functions of radar mapping and telecomm unica-tions. This activity is called an HG ACAL.

Another high-precision task w as determining the desired orbit andits timing. U seful SAR images can be obtained only if the exact rangefrom the spacecraft to the planet's surface is known throughout eachmapping pass. B ecause M agellan's orbit w ill be highly elliptical, therange to the surface will change every m oment and require frequentadjustments to the radar com mands. Accurate calculation of the neededadjustments is totally dependent on precise knowledge of the orbit.

The o rbit-determination task relies on a nav igation techn ique called"differenced D oppler " which involves measurements of the spacecraft's

In Decem ber 1.98 9, the radar electronics were turned on for the firtime since before launch. Both the radar system and the hardw are


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y

passed muster. This test paved the way for a more com plicated testperformed in May 1 99 0, when the radar and the spacecraft were putthrough their paces for more than three days. The spacecraft turnedthrough the intricate series of maneuvers it will perform orbit after oas it maps the planet. At the same time, the radar system issued its

com plex series of mapping com mand s. This period of simu lated m aping operations allowed us to verify many spacecraft and groundprocedures and m uch of the m apping software that will drive M agellonce it is in orbit around V enus.

Magellan has also performed some routine "housekeeping" activties. Star scans were performed daily to allow correction for the normdrift in spacec raft pointing, and the reaction wheels were desa turated

The results of the planning efforts for IOC and m apping are de-scribed in Chapters 10 and 11 respectively


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scribed in Chapters 10 and 11 , respectively.

Practice Makes Perfect

Placing a spacecraft into a precise orbit around a planet millions ofmiles away, checking out its equipment and subsystems to make surethey are working properly, and pronouncing the spacecraft ready for

mapping operations are responsibilities and pressures definitely a cutabove those we face on a daily basis. But the Magellan team w ill per-form this scenario throughout the VO I maneuv er and the IOC phase. Awith any well-orchestrated production, an intensive period of rehearsalhas been essential.

The eight-mem ber Mission E ngineering Team has devoted a portionof the cruise period to developing and conduc ting operational readiness

Now's the day and now's the hour.

Robert Burns


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Chapter 10

In Orbit at Last!

Incoming T rajectory


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Orbit Insertior.

Mapping O rbit Closest Approach(10N Laritude)

Figure 10-1. Magellan incoming trajectory at Venus.


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Sun f-

Figure 10-2. M agellan incoming trajectoryat V enusas view ed f rom Earth

the orbit-insertion event and a ssist them in designing the orbit-trimmaneuver (O TM ) scheduled for August 28. If, at that time, the space-


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craft is already in the targeted o rbit, the OTM will be deleted from thesequences and mapping operations will begin August 29. If the OTM isrequired, mapping operations will begin September 1.

Calibrations conducted during c ruise indicate the offset between theonboard gyroscopes and the star scanner reference frame. Any change

in offset between the HGA andDid You Know .. .

It took the shutt le 's thr ee

m ain engines and tw o SRM s,

the tw o IUS SR M s, and one

b it i t i SRM t t

the star scanner, resulting fromthe shock of the VO I burn, will bedetermined by perform ing aHG ACA L on August 19. Thiscalibration involves passing thesignal from the HG A back and

Test 3 (August 22) w ill provide the first full-length strips of da ta.This test will use the look-angle profile that will be used fo r the mappphase, as w ell as radar-control comm ands that vary c ontinuously as


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orbit altitude and look angle change through the mapping pass. Thedata from Test 3 should provide strips that can be m osaicked into thefirst large image.

W hile Test-3 data are being analyzed, Test 5 will be performedAugust 24. This test is intended to m easure the performance envelop

the SAR by testing com binations of look angle and radar-timing com-mands that should push the limits of the ground so ftware to process tdata into images. W hile this test is not expected to produce da ta for tfinal Magellan Venus map, it will provide invaluable inform ation tosupport data interpretation.

Several "Recovery Days" (August 14, 21, and 29) have been scheduled in case anom alous conditions occur. In such a situation, the pla

We shall not cease fiom exploration

And the end o f all our exploring


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Will be to arrive where we startedAnd know the place for the first time.

- . S. Eliot

Chapter 11

Mapping the Veiled Planet

utes of data transm ission. The spacecraft will then begin its way backdown to Venus, and the entire process will be repeated.

A total of 1,852 data-collection and playback passes (see Figure 11-1


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will occur during the 243-day m apping cycle.Each m apping pass will image a swath of the planet about 25 kilo-meters (16 miles) wide by about 16,000 kilometers (10,000 miles) long.Since the spacecraft's orbit rem ains essen tially fixed in inertial space, tslow rotation of Venus con tinually brings new areas into view under th

spacecraft. Swath overlap w ill vary, but averages around 5 k ilometers(3 miles). The 243-day mapping cycle will cover a fu11360 degrees ofVenus longitude. Nearly 90 percent of the surface of Venus can bemapped during the mapp ing cycle, if all goes well; the rest can bemappe d later if there is an extended m ission that provides add itionalmapping cycles.


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+I25 days

+I00 days


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+225 daysstart of +75 daysExtended '+25 daysMission

+250 days+ZOO days

-+SO dovs A ..r.., +175 days, \

/"\ 75 daysI

SuperiorConiunction

+250 days

Start of

Orbit

Superior Conjunction Gap ccultation


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rnvvv

aa

OrbitPastVO I

DayPast

VO I

240 70 300 330 0 0 0 20 150 180 210 240Longitude (deg)

Memo U date um Settling TimeD' P ^ \ Swath Idle Time onDelayed Swath


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Second Half of '^Data Playback

DSN Lockup

Apoapsis -

Star Scan /

/^otton

\rea Not Mapped

Record Data forImmediate Swath

- - Periapsis(10N Latitude)

Record Data forDelayed Swath

^ i

First Half ofData Playback um

DSNLockup

Swnth Idle Time onImmediate Swath

T able 11-1. Mapping Orbit T im e A llocations

Event Duration, minutes


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Tum to mapping 5.7Settling Ume 0.5

Record m apping 37.2

Swath idle time 7.5

Tum to play back 5.3

DSN lockup 2.5First playback 56.6

Star scan 14.0

Second playback 57.2

Mem ory update 2.0

Margin 0.5

Total 189.0

W e w ill study the quality of the telemetry throughout the con junctionperiod and w ill resume m apping as soon as it is safe to do so. If nature


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smiles on us, no more than 7 to 10 days of m apping data will be lostduring this period.

The occulted mapping phase (Decem ber 16, 1990, to January 26,1991) w ill find Venus between the spacecraft and Earth for part of theplayback portion of the orbit. D uring this phase, the record duration will

be reduced and the m apping parts of the orbit shifted to reduce theamo unt of playback time required to the precise am ount geom etricallyavailable. M agellan science investigators expressed a preference forobtaining cov erage at the southern extremeof the map ping pass duringthis phase, since this area will be "new " terrain. Therefore, the start of

Did you know .. .the 44-m inute mapping pass w ill bedelayed during this phase , with the

gency p lanning is best accom plished in cool, collected m ome nts, not ithe heat of an emergency. With that in mind, we have planned aheadfor a dozen o r so categories of problems that could change the way


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for a dozen o r so categories of problems that could change the way

ma pping data are collected from the time of the failure forward (seeTable 11-2).

Since the sp acecraft is built to be single-fault tolerant, most singlefailures allow the autom atic substitution of a backup com ponent for tfailed on e, and o perations can recover the o riginal m apping strategywith very little lost time o r data. More com plex failures, however, requpreplanning to avoid excessive lost time in replanning at the time of temergency.

Even so, there is no guarantee that-quick contingency planning w illnot be required at some point in the m issionnature often finds a wa yto break those things we are least prepared to have b roken. D evelop-men t of a number of plans ahead of time howev er has always prov en

Extended Mission

An extended m ission to recover data missed during the first 243-dayma pping phase (Cy cle 1) and to cond uct the high-resolution gravity


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ma pping phase (Cy cle 1) and to cond uct the high resolution gravityexperiment is a vital part of achieving all of the science ob jectives of theMa gellan m ission.

Preliminary preparation for the first extended m ission cyc le (Cycle 2)was conducted du ring the cruise period. The final planning for Cycle 2and the preliminary w ork for subsequent cycles w ill be addressed duringCycle 1 (prime m ission) operations.

Extended m ission science objectives were developed in collaborationwith the Mage llan science investigators. Those objectives are dividedamong several mission cycles, as follows.

Cycle 2 prim arily involves radar ma pping. Its m ain objective is tofill in all large coverage gap s left from C ycle 1. These gaps will be ofthree kinds: those that were geom etrically impo ssible to obtain during

Hear ye not the hum of mighty workings?

John Keats


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Chapter 12

Getting the job Done


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Instructing the Spacecraft

Although M agellan is a highly sophisticated robot, it depends onground pe rsonnel to tell it precisely what to do and when to do it Si


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ground pe rsonnel to tell it precisely what to do and when to do it. Siit is not p ractical to send instructions to the spacec raft every day, anbecause Magellan is equipped w ith its own internal clock, a set ofcommands covering a period of several weeks during cruise (one weeduring mapping) is sent to its computer a few days before the com m

sequence begins. Several teams within the P roject work together to bthe sequence of spacecraft and radar-instrument comm ands. Coordition and cooperation are the key elements in this process.

Creation of the Mission Plan marks the beginning of sequencedevelopm ent. The Plan and an a ssociated Mission Profile (a graphic

chart that shows the desired activities and app roxima tely when theyto occur) are developed by the Mission Planning Team, based on inp

the instructions do not violate spacecraft ope rating constraints and thatthey w ill fit into the spacecraft's com puter memory.

The 17-member Radar System Engineering Team (RSET) from the


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The 17 member Radar System Engineering Team (RSET) from theHughes Aircraft Com pany, but in residence at JPL , monitors the healthand pe rformance of the rada r sensor, develops the detailed instructionsfor its operation, and ensures that com ma nds to the sensor do notviolate spacecraft and/or sensor operating constraints.

O nce the final comm and load is built and verified and has receivedapproval by the Mission D irector, a final step by the SCT converts theload from a text file to the stream o f bits (1s and O s) that will be sent tothe spacecraft.

Throughout the building of a com ma nd load, the five-mem ber

Mission O perations and Com mand Assurance Team provides independ-ent checks of the ove rall quality of the comm anding process and sug-

such a dem and for D SN services, it 's no wonder that the schedulingprocess is indeed involved.

Representatives of the MGT, other flight projects, and the DSN reg


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larly m eet to negotiate equitable allocations of an tenna tracking supThe am ount of tracking time acquired by a project is dependent on threlative importance o f that period to its mission. For exam ple, Magewill receive simultaneous coverage from two tracking antennas durinthe critical Venus o rbit-insertion m aneuver on A ugust 10, and w ill hacontinuous tracking coverage during the 243-day ma pping phase of mission.

More About the Deep Space Network

The continuous 24-hour tracking of several spacecraft requires Eabased an tenna sites at strategic locations that com pensa te for the Ea


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from the ir original 64-meter (210-foot) diameters to increase theirsensitivity in prepara tion for the Voyager 2 spacecraft encounter withN eptune in August 1989.

The h igh data rate (265 8 kilobits per second) and the precise na


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The h igh data rate (265.8 kilobits per second) and the precise nagation requirements associated with Magellan's mapping phase w illimpose a support load on the D SN as heavy as or heavier than anyduring the past 30 years. To meet this challenge, the D SN has implemented m ajor mod ifications to its telemetry and navigation system s

Equa lly important is the operational support required during the maping phase. To acqu ire all high-rate mapping teleme try and generatthe requested navigational data during Mage llan's 8-month mappinphase, the D SN will be required to provide, on a daily basis, approximately 36 hours of antenna and antenna-related support.

During this time , the DSN will also support Galileo, Ulysses (to blaunched in October 1990) Voyagers 1 and 2 Pioneers 10 and 11 a

CommandingOn ce the sequence comm and load is ready and the comm unication

resources are scheduled, com mand operations get under way.


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The Operations Planning and Control Team (nine mem bers). mov esthe comm and file (via magnetic tape) to the Magellan C om m andSubsystem at the MC CC , where the file is formatted to GCF standards.The G CF e lectronically transmits the com mand file to the appropriateD SCC via a com bination of com munications satellites and conventionasurface and undersea circuits (see Figure 12-2). The DSN OperationsTeam at the DSC C checks the file for correct reception, removes the GC Fformatting bits, and routes the file to the_ appropriate antenna fortransm ission to the spacecraft. Traveling at the speed o f light, the first

com mand will reach the spacec raft in 14 m inutes; Mage llan's acknowl-edgm ent of receipt will require another 14 m inutes to reach ground

Receiving Data

The data received during M agellan's cruise and map ping phases of enorm ous value. The telemetry includes engineering data that


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indicate the perform ance o f the spacecraft and its subsystems. Thisinformation is identified with spacecraft time so that the state of thespacecraft at any given time can be completely reconstructed.

The navigation data collected during the cruise period indicate

whether the spacecraft is on the right course for Venus. Mapp ing-phanavigation data will provide precise know ledge about M agellan's orbwhich will be used to adjust the radar comm ands for optimal use of thradar sensor.

The radar-mapping data in the telem etry results from playback o

the tape reco rders during each orbit. These data w ill eventually beprocessed into photo products for interpretation by Magellan scientist

tape and w ill eventually be transferred to M agellan's Da ta Mana geme nand Archive Team (D MA T) for permanent retention.


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Processing the DataThe radar imaging, altimetry, and radiometry O D Rs shipped to JPL

are received by D MA T and routed to SFOC, where the raw radar data arinitially processed by the M agellan High-Rate P rocessor. The data are

time-ordered and put into an internationally recognized standardformat.

After the radar data are processed and returned to DM AT, they arein the form of an Experiment Data Record (ED R). The OD Rs are also

returned to DMAT for storage

Did you know ... n an env ironm entally con-

A sa way of demonstrating trolled v ault, to be used aga in

The image strips produced by the SD PS are also processed by the ID PSwhich m osaics them into large area maps of Venus.


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Data ProductsThe p rima ry image d ata product created from ea ch orbit 's data is

long, narrow image strip m entioned above, which represents a surfacarea about 25 kilometers (16 m iles) wide by approximately 16,000kilometers (10,000 miles) long. This strip, termed aFull-Resolution BaImage D ata Record (F-BID R), is the basis for all the image products thwill be used for study and interpretation. Som e 1,852 such image stripwill be produced during M agellan's 243-day m apping cycle.

However, the large vo lume and the unw ieldy w idth-to-length ratio

for these image strips m ake them unsuitable for general use. Thus,further processing will be done to produce mosaicked images (Mosaick

On the othe r hand , to ensure ava ilability of the full-resolution dataapproximately 15 percent of the F-BID Rs will be processed into full-resolution m osaics (F-MIDRs) for key regions on the planet's surface.


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( ) y g pTwenty major data products will be produced from the radar data fo

use by the M agellan scientists. Figure 12-3 shows the planetary coveragfor several of these produc ts.

P-MIDR -PIDR

(80 to 90I^ 20 to 25 k ilometersC3-MIDR r 12 to 16 m iles)(120 x 80) 0 75

60

'^ 5

C2-MIDR(45 x 45)

30

All Data Roads Lead to DMAT

All Magellan data products will be under the care and control of t20-member D ata Management and Archive Team.


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In support of M agellan m ission ope rations and science-analysisefforts, DMAT w ill collect, catalog, disseminate, and archive data products generated during the m ission's lifetime .

Included in the Magellan data set will be standard data produc ts

generated from the multiple-step processes described above, productsgenerated by the M agellan science investigators at their home institutions, and a co llection of m ission operations support produc ts.

All of these data p roducts will residein the DMAT area at JPL in avariety of form ats: magnetic tapes, pho tographs, negatives, optical di

maps, and hardcopy listings. TheDMA T library will have computer Did you know .. .

memories [CD -RO Ms]) will be produced and distributed to investigatorhom e institutions. Many of these products w ill also be provided toNASA's worldwide Regional Planetary Image Facilities.


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The D MA T will provide yet another dimension to the interface withthe Magellan science investigators: comparative analysis support. Thefocus of this activity is on scientists' requirements for data about theEarth and other planets for comparative analyses of Venus. Acting

primarily as an information resource, this effort involves the collection,organization, maintenance, and cataloging of photo products, publica-tions, maps, and other kinds of non-M agellan data.

Through all of these efforts, DM AT w ill assure that all of the ac-quired data w ill be ava ilable and accessible for current and future

analysis, and that it will be preserved as an historical record of theMagellan m ission.

The right people in the right jobs.

Otto von Bismarck


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Chapter 13

Project Organization

Zable 13-1. Magellan Project Organization

NASA Headquarters


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Lennard A. FiskAssociate AdministratorSpace Science and Applications

Alphonso V. DiazDeputy Administrator

Geoffrey A. BriggsDirector

Solar System Exploration D ivisionFrank A. Carr

Deputy D irector

Ann C. MerwarthMagellan Program M anager

Joseph M. Boyce

Magellan Program ScientistDavid J. Okerson

Magellan Program Engineer

Table 13-1. Continued

Finance Magellan Project OfficeDavid F. Quinn Anthony J. (Tony) Spear Project Scientist

Anne-Marie Krause Project Manager R. Stephen SaundersDiane L. Conner

Edwin J. Sherry, Technical Assistant/Administrative Manager

Procurement Antoinette M. Colasanti, Administrative SupportIrena Z. Petrac Project Secretary Philip C. AllinSharon L. Duncan

Patrick M. Thompson Erin Dabrushman, Secretary Mona A. Jasnow


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N

Hu hes Aircraft Flight Projects Supportechnical Divisions Martin Marietta Trackin and Mission O erations andAstronautics Group Company Office Data Acquisition Command AssuranceJ. Franklin McKinney, John F. McCarthy, Fred W. Miller, Allen L. Berman, Linda L. GranatManager Manager Systems Manager Manager D eputy ManagKenneth W. Ledbetter,

Deputy Tweet Cross,Vir ie L. W oods, Secreta Secretary

H. Kent Frewing (31) Michael Jacobs Marty Ferguson David Morris Mitch ScaffNathan A. Burow (33) Jackie Scherer Barbara Flaherty Larkin HamiltonJoseph L. Savino (34) Jon Schoeny Lois LaForrest Farinaz KavousirJoseph A. Plamondon (35) Sandy Mahoney Sherri PottsDonald D. Lord (36) Jean SobolikJ. Mike Stewart (37) Elaine Vandermay

Jerry Clark (38)Linda L. Granata (S2) Mission O perationsJames F. Scott, Mission Director

Douglas G. Griffith, Deputy Mission DirectorRay B. Morris, Deputy Mission Director

Kevin L. McNeill, Assistant Mission DirectorLuz R. Meza, Secretary

Operations PlanningOperations Monitor and nd Radar Officecience and Mission Ground Data SystPlanning Office Control Office Analysis Office Office

Table 13 -1. Continued

Science and Mission PlanningOffice

Thomas W. Thompson, ManagerStephen D. Wall, Deputy Manager

Carolynn Young, Public Information DirectorSandi Cihlar, Secretary

Sherry L. Love, SecretaryDenise E. Townsend, Secretary


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R. Stephen Saunders, Project Scientist

r n

Mission Engineering ission Planning ission Operations Science cience Planning andTeam eam upport Team nalysis Team

Michael K. Jones, Chief

Phil AllinLarry BryantSarah GavitDeborah KristofMichelle McCullarSteve OdiorneMichele StillmanJulie Webster

Anna M. Tavormina, Chief

Sarah GavitJoan HorvathRob LockDan LyonsSteve OdiorneMichele StillmanReid ThomasJulie Webster

Stephen D. Wall, Chief

Rick AustinKathie BeratanCraig LeffMark Rokey

Andrew D. Morrison, Chief

Science Investigators(See Chapter 7)


Operations Monitor andControl Office

J. Mike Stewart, ManagerJames R. McClure, Deputy Manager

Leslie J. Pieri, Technical Advisor


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Data Management andArchive Team

Jeff Miller, ChiefKen J. Bollinger, Deputy

Vicky Barlow Martha PinaLeo Bynum Patrick PoonJohn Donlin Pam W oncikCarolyn Hancock Monique YarbroughQuelynn Lewis Susan YewellPatrick LynnMario MorenoTina Pauro

NfPV

Mission Control Team

Bradley I. Compton, ChiefTheodore N. Tate, Deputy

Scott Anderson Dan MairGary Camp Robert PikeDave Doody Kathy RossPete Edwards Jack SawyerR ob yn Gib so n R ob er t S mit hBill Heventhal Robert SpringfieldJames Krug Cyndy WestmorelandBoyd Madsen John W irth

Mary L. Brancheau, SecretaryKathryn M artinez, Secretary

Operations Planning andControl Team

Frank J. Salamone, Chief

Charles Boreham insey RayEus Campos ohn SwiftJerry Clark lbert TaylorIsabel Esquivel ill Taylor

Team Representatives:120 Members

DSN OperationTeam

Alan B. Short, C

Barbara HowieWendell Keller


Radar Office

Raymond G . Piereson, ManagerHilda G. Thorossian, Secretary

Radar System AR DaTeQ^ cessing mage DTam

ocessingRadar Technical Staff

E i i T


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Do

Engineering Team

William T. K. Johnson, John F. McCarthy, Chief Kon S. Leung, Chief Jerry Clark, ChiefChief Engineer Patrick A. Hascall, Deputy Glenn W. Garneau, Deputy

Art Gussner Sue Barry on M erritt Ming Chen ichael Grimm Data ProcessingCraig Kernan Ivan Bottlik oward Nussbaum Frank Cheng ike Jin Doug Alexander ike McAuScott Shaffer Carlos Cuevas ike Smith Anhua Chu im Nguyen Martha Baxter lorance MoChialin Wu Paul Graf on Stuart Eugene Chu avid Swantek Teri DeGuire arc Pestan

Scott Hensley ick Venger Matthew Compton James Weirick Jason Hyon llen RunklBob Latter an Villani Stephen Cox ynthia W ong Danika Jensen ajime SanColin Lau en Wong John G ilbert Sue LaVoie arol StanleFred Linkchorst Cristina Link

Multimission PhotographicSupport Facility Photo Processing

Dave DeatsMark JilgDaniel LeeRobert Saul

Thara Tongvanit

Photo Lab Photo ProcessingBob PostSteve Benskin

Richard HasegawaRalph KaganCaroline Reed

Mission Sequence Design Team Navigation Team

Ta61e 13-1. C ont inued

Operations Planning and

Analysis OfficeRay B. Morris, Manager

David F. Woerner, Deputy ManagerJohn P. Slonski, Chief Engineer

Barbara A. Cantu, Secretary

Spacecraft Teamh db Chi f


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James S. Carter, ChiefAlbert Y. Nakata, Deputy

Yvonne Bonser arbara PaulsonMark Brewer ichele StillmanAlex Fernandez Will SunTerri Gaimari ruce TakenakaTammy Miyoshi Wendy TerminiLuis Morales aula WalkerDavid Myers

N

John B. McNamee, Chief

Gene Bollman Glenn KronschnablFrederic Bonneau Mark RyneCheick Diarra Richard StanfordDoug Engelhardt Aron WolfEric Graat Kuen WongRobert Haw

Kenneth W. Ledbetter, ChiefJames Neuman, Deputy

David Olschansky, DeputyTammy Griffin, Secretary

Bill AdamsMike BaileyDon BarnesTim BellFred BennettSharon BethancourtJack BooneWalt BrownAllen BucherJoe BuescherAnita CarpenterJim LavenderPam ChadbourneAllan CheuvrontDan CollinsonSteve CronauHenry CurtisStephen DonnellyEilene DukesGreg EsterlChuck Gay

Fred HamblenKeith HamlynPatty HardinCynthia HaynieMike JohnstonRick KasudaMitch KawasakiRobert LeonardBen LitoffBetsy MarloweKyle MartinChris MillerJohn MorgioneRobert MurdockMaxine ObleskiMike OchsSteve OdiorneMark PattersonArthur PeetDan PottruffGreg Privette

Dan RandolphKen RehmEthan RichDebra RoskieTodd RubanoLaura SakamotoSteve SandersEric SealeDonna SextonOwen ShortHarry SorensenStuart SpathGary StarksKen StarnesJim StruncJeff WeberJulae WebsterKatja WheelerStan WhiteRob W inslowWilliam Witt


Ground Data SystemOffice

Jody M. Gunn, ManagerRichard E. Halverstadt, Software System Engineer

David R. Kelly, Integration/Test EngineerHui-Yin Shaw, Software Test Support Engineer

Farinaz Kavousirad, Software Test Support EngineerDeborah Kristof, Test Support Engineer

Sherry Collins, Configuration Mgmt. TechnicianLuz R. Meza, Secretary

Monitor/Simulation

Richard M.(ackson,Subsystem Engineer

Command - DSN

Dung C. Doan,Subsystem Engineer

Tracking/VLBI

Douglas B. Engelhardt,Subsystem Engineer

SpacecraftEngineering

Allen Bucher,Subsystem Engineer

Rob Winslow


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NO

Data Managementand Archive

Jeff Miller,Subsystem Engineer

Leo BynumJohn Donlin

Mission and SequenceDesign

Robert K. Wilson,

Robert Cole avid MyersThomas Dale arbara PaulsonTerri Gaimari erietta WoodsLinda Lee

Sequence EventsGeneration

Bill Heventhal,Subsystem Engineer

Joseph HuYoung Lee

Navigation

Jahn E. Ekelund,

Subsystem EngineerJim Collier ynn StavertVictor Legerton Richard SunseriFaith McCreary Mike WangBmce PardoRichard Stanford

Telemetry

Betsy Wilson,Subsystem Engineer

the magellan venus explorer's guide

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