Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!trident.arc.nasa.gov!yee From: yee@trident.arc.nasa.gov (Peter E. Yee) Newsgroups: sci.space.shuttle Subject: STS-30 Press Release pack (Part 1) (Forwarded) Message-ID: <23863@ames.arc.nasa.gov> Date: 12 Apr 89 20:46:50 GMT Sender: usenet@ames.arc.nasa.gov Reply-To: yee@trident.arc.nasa.gov (Peter E. Yee) Organization: NASA Ames Research Center, Moffett Field, CA Lines: 937 [This came to me with lousy formatting. I've tried to fix it, but in so doing, the page numbers will no longer be correct. -PEY] SPACE SHUTTLE MISSION STS-30 PRESS KIT APRIL 1989 PUBLIC AFFAIRS CONTACTS Sarah Keegan/Barbara Selby Office of Space Flight NASA Headquarters, Washington, D.C. Charles Redmond/Paula Cleggett-Haleim Office of Space Science and Applications NASA Headquarters, Washington, D.C. Jim Ball Office of Commercial Programs NASA Headquarters, Washington, D.C. Lisa Malone Kennedy Space Center, Fla. Kyle Herring Johnson Space Center, Houston, Texas Jerry Berg Marshall Space Flight Center, Huntsville, Ala. Mack Herring Stennis Space Center, Bay St. Louis, Miss. Nancy Lovato Ames-Dryden Flight Research Facility, Edwards, Calif. Robert J. MacMillin Jet Propulsion Laboratory, Pasadena, Calif. Jim Elliott Goddard Space Flight Center, Greenbelt, Md. CONTENTS GENERAL RELEASE 1 GENERAL INFORMATION 2 STS-30 QUICK-LOOK FACTS 2 LAUNCH PREPARATION, COUNTDOWN AND LIFTOFF 3 IUS/MAGELLAN PRELAUNCH PAYLOAD PREPARATION AT KSC 4 STS-30 MISSION OBJECTIVES 4 MAJOR COUNTDOWN MILESTONES 5 SPACE SHUTTLE ABORT MODES 6 SUMMARY OF MAJOR FLIGHT ACTIVITIES 7 TRAJECTORY SEQUENCE OF EVENTS 8 LANDING AND POST-LANDING OPERATIONS 9 MAGELLAN 10 Mission Description 10 Magellan Spacecraft 11 Radar System 13 Command and Data Systems 15 Gravity Experiment 15 MAGELLAN SCIENCE TEAM 16 VENUS FACTS 16 MAGELLAN MISSION HIGHLIGHTS 16 RADAR INVESTIGATION GROUP 17 GRAVITY INVESTIGATION GROUP 17 INERTIAL UPPER STAGE 17 MESOSCALE LIGHTNING EXPERIMENT 20 MICROGRAVITY RESEARCH WITH THE FLUIDS 20 EXPERIMENT APPARATUS 21 Floating Zone Crystal Growth and Purification 21 Fluids Experiment Apparatus 22 AIR FORCE MAUI OPTICAL SITE TESTS 23 PAYLOAD AND VEHICLE WEIGHTS SUMMARY 23 STS-30 CARGO CONFIGURATION 24 SPACEFLIGHT TRACKING AND DATA NETWORK 25 CREW BIOGRAPHIES 26 NASA PROGRAM MANAGEMENT 29 --------------------------------------------------------------------------- RELEASE: 89-46 SPACE SHUTTLE TO DEPLOY MAGELLAN PLANETARY SCIENCE MISSION Space Shuttle mission STS-30 will deploy the Magellan Venus-exploration spacecraft into low-Earth orbit, the first U.S. planetary science mission launched since 1978 and the first planetary probe to be deployed from the Shuttle. Following deployment, Magellan will be propelled from Earth orbit in to its Venus trajectory by an Air Force-developed, Inertial Upper Stage (IUS) booster. The spacecraft will cruise through space for some 15 months, including flying around the Sun, before reaching its Venus destination in August 1990. Magellan's orbit insertion rockets will be fired to slow the explorer into a highly elipical orbit around planet Venus. Magellan will complete 1 orbit of Venus every 189 minutes. During its 243-day orbital mission, the spacecraft will acquire surface imaging, radiometry, altimetry and gravitational data. Magellan will map up to 90 percent of the surface of planet Venus for the first time using a synthetic aperture radar instrument to gather high resolution, mapping data. Commander of the 29th Space Shuttle mission is David M. Walker, captain, USN. Ronald J. Grabe, colonel, USAF, is pilot. Walker flew as the pilot aboard Discovery on mission STS-51A in November 1984, and Grabe was pilot of Atlantis on mission STS-51J in October 1985. Mission specialists are Norman E. Thagard, M.D.; Mary L. Cleave, Ph.D.; and Mark C. Lee, major, USAF. Thagard previously flew as a mission specialist on STS-7 in June 1983 and STS-51B in April 1985. Cleave previously flew on STS-61B in November 1985. Lee is making his first Space Shuttle flight. Liftoff of the fourth flight of orbiter Atlantis is scheduled for 2:24 p.m. EDT, April 28, from Kennedy Space Center, Fla., launch complex 39-B, into a 160-nautical-mile, 28.85-degree orbit. Nominal mission duration is 4 days, 56 minutes. Deorbit is planned on orbit 64, with landing scheduled for 3:20 p.m. EDT on May 2 at Edwards Air Force Base, Calif. Liftoff on April 28 could occur during an 18-minute period beginning at 2:24 p.m. EDT. The launch window will grow each day by 6 to 8 minutes, reaching a maximum of 121 minutes on May 13. From May 13 until the close of the window on May 28, the launch window each day would remain at 121 minutes to protect a Transatlantic Abort Landing (TAL) abort capability. The launch window increase is dictated by the need for a daylight landing opportunity at the TAL sites. Atlantis also will carry secondary payloads involving fluid research in general liquid chemistry and electrical storm studies. After landing, Atlantis will be towed to the NASA Ames-Dryden Flight Research Facility, Edwards, Calif., hoisted atop the Shuttle Carrier Aircraft and ferried back to the Kennedy Space Center to begin processing for its next flight. GENERAL INFORMATION NASA Select Television Transmission The schedule for television transmissions from the orbiter and for the change-of-shift briefings from Johnson Space Center, Houston, will be available during the mission at Kennedy Space Center, Fla.; Marshall Space Flight Center, Huntsville, Ala.; Johnson Space Center, Houston; and NASA Headquarters, Washington, D.C. The television schedule will be updated daily to reflect changes dictated by mission operations. NASA Select television is available on Satcom F-2R, Transponder 13, located at 72 degrees west longitude. Special Note to Broadcasters For approximately 5 days before launch, audio interview material with the STS-30 crew will be available to broadcasters by calling 202/755-1788 between 8 a.m. to noon EDT, Monday through Friday. The material will include short sound bites, with introduction, for a total of 2 minutes. Tapes will be changed daily. Status Reports Status reports on the countdown, flight mission activities and landing operations will be produced by the appropriate NASA news center. Briefings An STS-30 mission press briefing schedule will be issued prior to launch. During the mission, flight control personnel work 8-hour shifts. Change-of-shift briefings by the off-going flight director will occur at approximately 8-hour intervals. STS-30 QUICK LOOK Launch Date: April 28, 1989 Launch Window: 2:24 p.m. - 2:42 p.m. EDT Launch Site: Kennedy Space Center, Fla., Pad 39B Orbiter: Atlantis (OV-104) Altitude: 160 nautical miles Inclination: 28.85 degrees Duration: 4 days, 56 minutes Landing Date/Time: May 2, 1989, 3:20 p.m. EDT Primary Landing Site: Edwards Air Force Base, Calif. Alternate Landing Sites: Return to Launch Site - Kennedy Space Center Transatlantic Abort Landing - Ben Guerir, Morocco Abort Once Around - Edwards AFB Crew: David M. Walker, commander Ronald J. Grabe, pilot Norman E. Thagard, mission specialist-1 Mary L. Cleave, mission specialist-2 Mark C. Lee, mission specialist-3 Primary Payload: Magellan Secondary Payloads: Fluids Experiment Apparatus (FEA) Mesoscale Lightning Experiment (MLR) SPACE SHUTTLE LAUNCH PREPARATIONS, COUNTDOWN AND LIFTOFF Processing activities began on Atlantis for the STS-30 mission on Dec. 14, 1988, when it was towed to Orbiter Processing Facility (OPF) bay 2 after arrival from the Ames- Dryden Flight Research Facility. Atlantis' most recent mission, STS-27, was completed with a Dec. 6, 1988, landing at Edwards Air Force Base. Post-flight deconfiguration and inspections were conducted in the processing hangar. As planned, the three main engines were removed and taken to the main engine shop in the Vehicle Assembly Building (VAB) or the replacement of several components. During post-flight inspections, technicians discovered cracks in one of the high- pressure oxidizer turbopump bearing races on the number 3 main engine. That pump was removed and sent to Rocketdyne for analysis. It was determined that the most likely cause for the cracks was the presence of moisture inside the pump which leads to stress corrosion. The buildup process of oxidizer pumps was modified to eliminate the presence of moisture. While in the VAB, main engine technicians replaced the turbopump that had been sent to Rocketdyne for testing. The other two pumps were replaced following rollout to the pad, where testing of all three new pumps was conducted. Atlantis' three main engines were installed while the vehicle was in the OPF. Engine 2027 is installed in the number one position, engine 2030 is in the number two position and engine 2029 is in the number three position. The right-hand orbital maneuvering system pod was removed in early January and transferred to the Hypergolic Maintenance Facility for repairs of a helium regulator that failed in flight. The regulator was reinstalled on Feb. 9, 1989. Stacking of solid rocket motor (SRM) segments for flight began with the left aft booster on Mobile Launcher 1 in the Vehicle Assembly Building on Jan. 2, 1989. Booster stacking operations were completed by Feb. 19 and the external tank was mated to the two boosters on March 2. Flight crew members were at KSC on Feb. 4 for the crew equipment interface test to become familiar with Atlantis' crew compartment and equipment associated with the mission. The assembled Space Shuttle vehicle was rolled out of the VAB aboard its mobile launcher platform for the 4.2 mile-trip to Launch Pad 39B on March 22. The terminal countdown demonstration test -- a dress rehearsal for STS-30 launch countdown, the flight crew and the KSC launch team -- was conducted April 6-7. Preparations scheduled the last 2 weeks prior to launch countdown included final vehicle ordnance activities, such as power-on stray-voltage checks and resistance checks of firing circuits; loading the fuel cell storage tanks; pressurizing the hypergolic propellant tanks aboard the vehicle; final payload closeouts; and a final functional check of the range safety and SRB ignition, safe and arm devices. The launch countdown is scheduled to pick up at the T-minus- 43-hour mark, leading up to the STS-30 launch. Atlantis' fourth launch will be conducted by a joint NASA/industry team from Firing Room 1 in the Launch Control Center at Complex 39. IUS/MAGELLAN PRELAUNCH PAYLOAD PREPARATION AT KSC The Magellan spacecraft arrived at KSC from Denver, Colo., on Oct. 8, 1988. It made the trip aboard a specially cushioned, instrumented and environmentally controlled truck-trailer supplied by KSC. It was taken to the Spacecraft Assembly and Encapsulation Facility-2 (SAEF-2) planetary spacecraft check- out facility for integration. The high-gain antenna was installed on Dec. 4, but removed later to facilitate other payload element integration. The forward equipment module and spacecraft upper body were mated with the liquid propulsion module on Dec. 21. Magellan's radar module was installed on Jan. 6, 1989. The storable propellants used for mid-course corrections and spacecraft control at Venus were loaded aboard on Jan. 18. The spacecraft was then mated with the Star 48 solid propellant orbit insertion motor on Feb. 3. The two solar panels were attached and tested on Feb. 5. Together with the Deep Space Network, testing was performed to demonstrate the ability of the worldwide tracking network to communicate with Magellan and to simulate Magellan's functions at Venus. These tests also highlighted the unique characteristics that will aid flight controllers in understanding idiosyncrasies in the spacecraft's performance enroute to Venus and while in orbit around the planet. On Feb. 15, the spacecraft was relocated from SAEF-2 to the Vertical Processing Facility for mating with its Inertial Upper Stage booster 2 days later. On Feb. 18, a week of integrated testing began. The electrical connections between the IUS and Magellan were verified, and a test was run to affirm the ability of all the principal ground control facilities and the Deep Space Network to communicate with the payload. The high-gain antenna was reintegrated with the spacecraft on Feb. 26 and tested for flight. A test also was run to simulate the payload's deployment from Atlantis. STS-30 astronauts Mark Lee and Mary Cleave participated in the deployment exercise. Riding in the payload canister atop the associated transporter, the IUS/Magellan payload was transported to the launch pad on March 17. The payload was installed in the payload bay of Atlantis on March 25. An integrated electrical test with the orbiter was performed. This was followed by testing to verify that the principal ground stations could communicate with IUS/Magellan via the communications systems of the Space Shuttle. STS-30 MISSION OBJECTIVES The primary objective of this Space Shuttle mission is to successfully deploy the Magellan spacecraft on its way to Venus. Deployment will occur on orbit 5, 6 hours, 18 minutes into the mission. Alternate deployment opportunities are available on orbits 6 and 7, with additional backup deployment opportunities available throughout flight day 2. Additionally, the Fluids Experiment Apparatus (FEA) and Mesoscale Lightning Experiment (MLE) middeck experiments and Air Force Maui Optical Site (AMOS), along with Detailed Test Objectives (DTO) and Detailed Secondary Objectives (DSO) will be performed during the flight. The objectives of the Magellan mission are to obtain radar images of more than 70 percent of Venus' surface, a near-global topographic map and near-global gravity field data. The mission should help develop an understanding of the planet's geological evolution, particularly its density distribution and dynamics. MAJOR COUNTDOWN MILESTONES Countdown Event T-43 Hours Power up the Space Shuttle vehicle. T-30 Hours Activate orbiter's navigation aids. T-27 Hours (holding) Enter the first built-in hold for 8 hours. T-27 Hours (counting) Begin preparations for loading fuel cell storage tanks with liquid oxygen and liquid hydrogen reactants. T-25 Hours Load the orbiter's fuel cell tanks with liquid oxygen. T-22 Hours, 30 minutes Load the orbiter's fuel cell tanks with liquid hydrogen. T-22 Hours Perform interface check between Houston Mission Control and the Merritt Island Launch Area (MILA) tracking station. T-20 Hours Activate and warm up inertial measurement units (IMUs). T-19 Hours (holding) Enter 8-hour built-in hold. T-19 Hours (counting) Resume countdown. T-18 Hours Activate orbiter communications system. T-11 Hours (holding) Start 15 hour, 4-minute built-in hold. Perform orbiter ascent switch list in the orbiter flight and mid-decks. T-11 Hours (counting) Retract Rotating Service Structure from vehicle to launch position. T-9 Hours Activate orbiter's fuel cells. T-8 Hours Configure Mission Control communications for launch. Start clearing blast danger area. T-6 Hours, 30 minutes Perform Eastern Test Range open loop command test. T-6 Hours (holding) Enter 1-hour built-in hold. T-6 Hours (counting) Start external tank chilldown and propellant loading. T-5 Hours Start IMU pre-flight calibration. T-4 Hours Perform MILA antenna alignment. T-3 Hours (holding) 2-hour built-in hold begins. Loading the external tank is complete and is in a stable replenish mode. Ice team goes to pad for inspections. Closeout crew goes to white room to begin preparing orbiter's cabin for the flight crew's entry. Wake flight crew (launch minus 4 hours, 55 minutes). T-3 Hours (counting) Resume countdown. T-2 Hours, 55 minutes Flight crew departs O&C Building for Launch Pad 39-B (Launch minus 3 hours, 15 minutes). T-2 Hours, 30 minutes Crew enters orbiter vehicle (Launch minus 2 Hours, 50 minutes). T-60 minutes Start pre-flight alignment of IMUs. T-20 minutes (holding) 10-minute built-in hold begins. T-20 minutes (counting) Configure orbiter computers for launch. T-10 minutes White room closeout crew cleared through the launch danger area roadblocks. T-9 minutes (holding) Enter 1 hour, 10-minute built-in hold. Perform status check and receive Launch Director and Mission Management Team "go." T-9 minutes (counting) Start ground launch sequencer. T-7 minutes, 30 sec. Retract orbiter access arm. T-5 minutes Pilot starts auxiliary power units. Arm range safety, SRB ignition systems. T-4 minutes, 55 sec. Start liquid oxygen drainback. T-3 minutes, 30 sec. Orbiter goes on internal power. T-2 minutes, 55 sec. Pressurize liquid oxygen tank for flight and retract gaseous oxygen vent hood. T-1 minute, 57 sec. Pressurize liquid hydrogen tank. T-31 seconds "Go" from ground computer for orbiter computers to start the automatic launch sequence. T-28 seconds Start solid rocket booster hydraulic power units. T-21 seconds Start SRB gimbal profile test. T-6.6 seconds Main engine start. T-3 seconds Main engines at 90 percent thrust. T-0 SRB ignition, holddown-post release and liftoff. T+7 seconds Shuttle clears launch tower and control switches to Houston. SPACE SHUTTLE ABORT MODES Space Shuttle launch abort philosophy aims toward safe and intact recovery of the flight crew, orbiter and its payload. Abort modes include: * Abort-To-Orbit (ATO) -- Partial loss of main engine thrust late enough to permit reaching a minimal 105-nautical mile orbit with orbital maneuvering system engines. * Abort-Once-Around (AOA) -- Earlier main engine shutdown with the capability to allow one orbit around before landing at Edwards Air Force Base, Calif.; White Sands Space Harbor (Northrup Strip), N.M.; or the Shuttle Landing Facility (SLF) at Kennedy Space Center, Fla. * Transatlantic Abort Landing (TAL) -- Loss of two main engines midway through powered flight would force a landing at Ben Guerir, Morocco; Moron, Spain; or Banjul, The Gambia. * Return-To-Launch-Site (RTLS) -- Early shutdown of one or more engines and without enough energy to reach Ben Guerir, would result in a pitch around and thrust back toward KSC until within gliding distance of the Shuttle Landing Facility (SLF). STS-30 contingency landing sites are Edwards AFB, White Sands, Kennedy Space Center, Ben Guerir, Moron and Banjul. SUMMARY OF MAJOR FLIGHT ACTIVITIES Day One Ascent Post-insertion checkout Pre-deploy checkout Magellan/Inertial Upper Stage deploy Day Two Magellan/IUS backup deploy opportunity Air Force Maui Optical Site (AMOS) tests Detailed Test Objective (DTO)/Detailed Secondary Objective (DSO) Fluids Experiment Apparatus (FEA) Mesoscale Lightning Experiment (MLE) Day Three AMOS DTO/DSO FEA MLE Day Four AMOS DTO/DSO MLE Flight control systems checkout Cabin stowage Landing preparations Day Five Deorbit preparation Deorbit burn Landing at Edwards Air Force Base, Calif. STS-30 TRAJECTORY SEQUENCE OF EVENTS [This section is too confusing for me to reformat. Any volunteers? -PEY] ________________________________________________________ __________ RELATIVE EVENT MET VELOCITY MACH ALTITUDE (d/h:m:s) (fps) (ft) ________________________________________________________ __________ Launch 00/00:00:00 Begin Roll Maneuver 0/00:00:09 183.16774 End Roll Maneuver 00/00:00:17 365.322,825 SSME Throttle Down to 65% 00/00:00:30 711.649,043 Max. Dyn. Pressure (Max Q)00/00:00:59 1,368 1.3535,133 SSME Throttle Up to 104% 00/00:01:02 1,428 1.4337,284 SRB Staging 00/00:02:05 4,2123.93 153,405 Negative Return 00/00:03:58 6,9157.39 319,008 Main Engine Cutoff (MECO) 00/00:08:31 24,286 22.70362,243 Zero Thrust 00/00:08:38 ET Separation 00/00:08:45 OMS 1 Burn 00/00:10:31 OMS 2 Burn 00/00:44:27 Magellan/IUS Deploy (orbit 5) 00/06:18:00 Deorbit Burn (orbit 64) 03/23:53:00 Landing (orbit 65) 04/00:53:00 Apogee, Perigee at MECO:85 x 3 nm Apogee, Perigee post-OMS 1:160 x 51 nm Apogee, Perigee post-OMS 2:160 x 160 nm Apogee, Perigee post-deploy:176 x 161 nm LANDING AND POST-LANDING OPERATIONS The Kennedy Space Center is responsible for ground operations of the orbiter once it has rolled to a stop on the runway at Edwards Air Force Base. Those operations include preparing the Shuttle for the return trip to Kennedy. After landing, the flight crew aboard Atlantis begins "safing" vehicle systems. Immediately after wheelstop, specially garbed technicians will first determine that any residual hazardous vapors are below significant levels in order for other safing operations to proceed. A mobile white room is moved into place around the crew hatch once it is verified that there are no concentrations of toxic gases around the forward part of the vehicle. The crew is expected to leave Atlantis about 45 to 50 minutes after landing. As the crew exits, technicians enter the orbiter to complete the vehicle safing activity. Once the initial aft safety assessment is made, access vehicles are positioned around the rear of the orbiter so that lines from the ground purge and cooling vehicles can be connected to the umbilical panels on the aft end of Atlantis. Freon line connections are completed and coolant begins circulating through the umbilicals to aid in heat rejection and protect the orbiter's electronic equipment. Other lines provide cooled, humidified air to the payload bay and other cavities to remove any residual fumes and provide a safe environment inside Atlantis. A tow tractor will be connected to Atlantis and the vehicle will be pulled off the runway at Edwards and positioned inside the Mate/Demate Device at the nearby Ames-Dryden Flight Research Facility. After the Shuttle has been jacked and leveled, residual fuel cell cryogenics are drained and unused pyrotechnic devices are disconnected prior to returning the orbiter to Kennedy. The aerodynamic tail cone is installed over the three main engines, and the orbiter is bolted on top of the 747 Shuttle Carrier Aircraft for the ferry flight back to Florida. Pending completion of planned work and favorable weather conditions, the 747 would depart California about 6 days after landing for the cross-country ferry flight back to Florida. A refueling stop is necessary to complete the journey. Once back at Kennedy, Atlantis will be towed inside the hangar-like Orbiter Processing Facility for post-flight inspections and in-flight anomaly troubleshooting. These operations are conducted in parallel with the start of routine systems reverification to prepare Atlantis for its next mission. MAGELLAN Mission Description The Magellan mission will map up to 90 percent of the surface of Venus to a high degree of resolution. The spacecraft's primary science instrument is an imaging radar, called a Synthetic Aperture Radar (SAR). In addition to mapping, precise tracking of Magellan radio signals will improve our knowledge of the Venusian gravity field. Magellan is the first planetary probe to be launched from a Space Shuttle and the first planetary spacecraft to be launched in nearly 11 years. The imaging radar is capable of performing both surface imaging and altitude measurements. It is able to resolve surface features measuring from about 120 meters near the equator to about 300 meters near the north pole through the thick clouds that perpetually shroud the planet. The altimeter will measure elevations accurate to about 30 meters. Following insertion into Venus orbit in August 1990, approximately 18 days will be spent checking out the spacecraft and its imaging radar. The prime mapping mission then will begin, lasting 243 Earth days or 1 Venus day. A proposed extended mission would be used to map those areas missed when the Sun is between Venus and Earth and when Venus is between the spacecraft and Earth. It also would be used to determine irregularities in the planet's interior by measuring gravity. Magellan's trajectory to Venus is called a Type IV transfer. It requires the spacecraft to go one and one-half times around the Sun before it goes into orbit around Venus. Although the Type IV transfer has advantages of lower launch energy and lower Venus approach speed, the main reason for using this trajectory is that it allows the Galileo mission to be launched by the Shuttle in October 1989, the launch time required by Magellan for the shorter and faster trajectory to Venus. In the mapping orbit, the spacecraft will approach the planet as close as 155 miles. That is called periapsis. At its furthest point in its elliptical orbit, the spacecraft will be 4,977 miles from the planet's surface. That is apoapsis. Magellan will make one orbit every 3 hours, 9 minutes. The approach to Venus is over the northern hemisphere with a mapping swath that goes from north to south. The radar mapping is done for a 37-minute period each orbit when the spacecraft is close to the planet, and when it is at apoapsis, it transmits the data back to Earth. The mapping profile of Magellan includes two swaths of coverage done alternately, one beginning further north than the next. As the spacecraft approaches the planet, it will begin mapping the north swath at 90 degrees north latitude and continue to 54 degrees south latitude. On the next orbit, it will begin 4.7 minutes later for the south swath and begin mapping at 76 degrees north latitude and continue to 68 degrees south. Magellan will make 1,852 mapping swaths around the planet during the primary mission. Mapping data are transmitted back to Earth at 268.8 kilobits per second. The data are received by the 70-meter tracking station network, that is, the largest radio telescopes of the Deep Space Network locations at Goldstone, Calif.; near Madrid, Spain; and at Canberra, Australia. As each orbit continues toward apoapsis, the spacecraft plays back the data to Earth. During this time, it interrupts its playback to make star calibrations to confirm its attitude data base. Magellan looks at the positions of two stars in the sky and compares them with a star map in its computer. This fixes its attitude in relation to the planet. Then it resumes its data playback. When the second playback is completed the antenna is rotated back toward the planet for the next mapping sequence. Magellan Spacecraft The Magellan spacecraft was designed and constructed by Martin Marietta Astronautics Group, Denver, Colo. The height of the spacecraft is 21 feet. It is 15 ft. in diameter and weighs 7,604 pounds. Several subsystems make up the spacecraft system. They include the structure, thermal control, power, attitude control, propulsion, command data and data storage, and tele- communications. The structure is composed of four major sections: the high- gain antenna, forward equipment module, spacecraft bus including solar array and orbit-insertion stage. The high-gain antenna is used as the antenna for the synthetic aperture radar as well as the primary antenna for the telecommunications system to send data back to Earth. The 11.8-ft. diameter parabolic dish is made of strong, lightweight graphite epoxy sheets mounted on an aluminum honeycomb for rigidity. It is a spare from the Voyager project. There also is a cone-shaped medium-gain antenna used for receiving commands by and sending engineering data from Magellan during the 15-month cruise from Earth. A low-gain antenna provides the ground team with an alternative means of commanding the spacecraft in case of an emergency that prevents use of normal data rates. The altimeter antenna is mounted to one side of the high- gain antenna and is pointed vertically down at the surface of the planet during the radar data acquisitions. The forward equipment module contains the radar electronics, the reaction wheels which control the spacecraft's attitude in space and other subsystem components. The bus is a 10-sided structure consisting of the remainder of the subsystem components, including the solar panel array, star scanner, medium-gain antenna, rocket engine modules, command data and data storage subsystem, monopropellant tank and a nitrogen tank for propellant pressurization. The orbit insertion stage contains a Star 48 solid rocket motor to place the spacecraft into orbit around Venus. Once in orbit, the motor casing is jettisoned. A combination of louvers, thermal blankets, passive coatings and heat-dissipating elements are used to control the spacecraft's temperature. The normal operating temperature range for the spacecraft components is between 25 to 104 degrees Fahrenheit. Power for the spacecraft and the experiments is provided by two solar panels with a total area of 12.6 square meters. The array is capable of producing 1,200 watts. Both direct (dc) and alternating current (ac) are provided with dc power at 28 to 35 volts and ac power at 2.4 kilohertz. Two 30-amp hour, 26-cell nickel cadmium batteries provide power when the spacecraft is in the shadow of the planet and allow normal spacecraft operations independent of solar illumination. The batteries remain charged by using power provided by the solar arrays. The three reaction wheels, which control the spacecraft's attitude in relation to the planet, are driven by electric motors and store momentum while they are spinning. At a point in each orbit near apoapsis, the monopropellant rocket motors are used to counteract the torque on the spacecraft as the reaction wheels are despun to eliminate the excess momentum. There is one reaction wheel for each of the spacecraft's three axes -- yaw, pitch and roll. The Star 48 rocket used to put the spacecraft into orbit around Venus weighs 4,721 lbs., of which 4,430 lbs. are fuel. It has a thrust of 15,232 lbs. The spacecraft also has 24 thrusters used for trajectory correction and attitude control. Eight of the thrusters have 100 lbs. of thrust each. Four have 5 lbs. of thrust and 12 have 0.2 lb. of thrust. The smallest thrusters are used for attitude control and momentum unloading of the spacecraft at apoapsis. Radar System The radar system was built by the Hughes Aircraft Company, Space and Communications Group. The radar is used for Venus mapping because it can penetrate the thick clouds covering the planet. Optical photography cannot penetrate the clouds. Real aperture radars can be used to make images, but the resolution is poor. Magellan's synthetic aperture radar (SAR) will create high-resolution images by using computer processing on Earth to simulate a large antenna on the spacecraft. The onboard radar system will operate as though it has a huge antenna, hundreds of meters long. The antenna is actually 12 ft. in diameter. The radar system will measure the strength of the received signals (brightness), how long each signal took to make the round-trip to the target point and back (range) and changes in the signal frequency (pitch) resulting from the spacecraft's motion. That information will allow computers on Earth to develop high-resolution pictures from the data. The SAR is sometimes called a side-looking radar because it looks at its target at an angle to the side of the flight path, while the altimetry radar looks straight down. A digital computer on Earth forms elements of the image by taking into account the time delay, the phase (or frequency) of the radar wave and the magnitude of the radar return echo as the spacecraft moves along its path. While the primary function of the SAR is imaging, it also performs altimetry and radiometry. In the imaging mode, the radar views Venus with the large mapping antenna. The length of the synthetic aperture varies with the altitude and speed of Magellan as it flies by. At its closest point to the planet, the resolution will be about 120 meters. In the altimetry mode, it uses a separate antenna to look at the planet directly beneath the spacecraft and determines vertical features to a resolution of about 30 meters. When the radar system is operated in the passive mode it operates as a radiometer and measures natural thermal emissions from the surface. That will help scientists determine the composition of surface materials. Command and Data System (CDDS) The brain of the spacecraft is its command and data system. It receives commands transmitted from Earth and controls the spacecraft in response to those commands. The system also controls the acquisition and storage on tape recorders of scientific data and sends that information back to Earth through the radio frequency subsystem. The core of the system consists of computers in redundant pairs. All are fully reprogrammable and all are modified Galileo equipment. The system, called the CDDS, stores commands for up to 3 days of radar operation during the orbit phase. There also is a provision for receiving and executing separate commands transmitted from the ground. Engineering data normally will be transmitted to Earth in real time. When a real-time link is not possible, the data will be tape recorded and played back on a high-rate link. The imaging radar data will be stored on two multitrack digital tape recorders for later playback over the high-rate band. There is no provision for real-time transmission of the SAR data because the large antenna must be pointed at Venus during mapping. The data storage capacity of the two digital tape recorders is about 1.8 billion bits. The recorders will be used primarily for the recording of SAR data, but low-rate engineering data can be stored during mapping or other periods when engineering data cannot be transmitted back to Earth in real time. Gravity Experiment An experiment to measure Venus' density at different locations will use the radio subsystem. The gravity measurements will be taken when the high-gain antenna is pointed toward Earth, instead of the surface of Venus, and is in a radio transmission mode. When a spacecraft is close to a massive body such as Venus, it experiences changes in acceleration due to irregularities in the density of the planet. Those speed variations can be determined by measuring the speed of the spacecraft every few seconds with an Earth-based radio tracking system. The changes in speed are gravity measurements. The differences in speed will be very small, but even a small speed-up would be apparent by measuring the doppler shift of the radio wave. It would indicate a planet area of greater density. If the spacecraft showed a small deceleration, it would indicate an area of lesser density. These readings would give scientists a better understanding of the planet's interior. Since Venus rotates very slowly beneath the orbiting spacecraft, one orbit profile will be very similar to the one preceding it. If many sequential orbits are obtained, their gravity profiles can be added to the topographic map. With the present mission geometry, high-resolution gravity data will not be obtained until well into the extended mission. Then the gravity data will be acquired for only 160 more days because the Sun will come between the spacecraft and Earth for a period of time. This factor limits the global gravity coverage to 66 percent. However, there is a subsequent period of 265 days during which complete high-resolution global coverage can be obtained without interference caused by planetary positions.