Investigation Information |
|
IDENTIFIER | urn:nasa:pds:context:investigation:mission.magellan::1.0 |
NAME |
MAGELLAN |
TYPE |
Mission |
DESCRIPTION |
Mission Overview ================ The Magellan spacecraft was launched from the Kennedy Space Center on 4 May 1989. The spacecraft was deployed from the Shuttle cargo bay after the Shuttle achieved parking orbit. Magellan, using an inertial upper stage rocket, was then placed into a Type IV transfer orbit to Venus where it carried out radar mapping and gravity studies starting in August 1990. The Mission has been described in many papers including two special issues of the Journal of Geophysical Research [VRMPP1983; SAUNDERSETAL1990; JGRMGN1992]. The radar system is also described in [JOHNSON1990]. Magellan was powered by single degree of freedom, sun-tracking, solar panels. The spacecraft was 3-axis stabilized by reaction wheels using gyros and a star sensor for attitude reference. The spacecraft carried a solid rocket motor for Venus orbit insertion. A small hydrazine system was used for trajectory corrections and certain attitude control functions. Earth communication with the Deep Space Network (DSN) was by means of S- and X-band channels. The high-gain antenna also functioned as the SAR mapping antenna during orbital operations. The interplanetary cruise phase lasted until 10 August 1990. During the cruise phase there were small trajectory correction maneuvers to ensure proper approach geometry. Using the solid rocket motor, the spacecraft was placed into an elliptical orbit around the planet, with a periapsis latitude of approximately 10 degrees north, a periapsis altitude of 295 km, a period of 3.263 hours, and an apoapsis altitude of approximately 7762 km. After orbit insertion, the radar system acquired test data. Then, unexpectedly, the signal from the spacecraft was lost twice. Following an intense recovery process, commands were sent to avoid further communication interruptions, and the spacecraft resumed mapping operations on 15 September 1990. Each mapping cycle lasted 243 days, which was the time required for Venus to make one rotation under the spacecraft orbit. The first mapping cycle ended on 15 May 1991. Typical activities during a single mapping pass on Cycle 1 were as follows. As the spacecraft neared periapsis, it was oriented so the high-gain antenna pointed slightly to the side of the ground track. At a true anomaly of -59 degrees, the radar was commanded on. The radar continued to take data to a true anomaly of 80 degrees and then the radar was commanded off. On the next pass the swath started at -80 degrees and went to 59 degrees. Alternating north and south swaths were repeated throughout Cycle 1. The range of latitudes covered by the synthetic aperture radar (SAR) during Cycle 1 was 67 degrees S to 90 degrees N. The range of SAR incidence angles was from just under 20 to just over 40 degrees. The SAR data were taken at a data rate of 750 kilobits/second and were stored in the spacecraft tape recorder. Altimeter and radiometer data were also taken when SAR data were acquired. The altimeter data were taken using a small fan beam antenna at a data rate of 30 kb/s. As the spacecraft moved away from the planet toward apoapsis, the spacecraft reoriented the high-gain antenna towards Earth and the stored radar data were transmitted to DSN stations. This data taking- and transmitting-cycle was repeated for every orbit. By 15 May 1991, the planet had been completely mapped except for the area near the South Pole and a few regions which had been missed because of temporary equipment failures. Cycle 2 observations focused on filling the gaps in Cycle 1 coverage (including the south pole area), acquiring SAR data at a constant incidence angle (25 degrees), and conducting a suite of ad hoc experiments, including high resolution imaging and radar stereo. To observe the south pole the spacecraft was rotated 180 degrees about its nadir-pointing axis so as to conduct right-looking SAR observations. Gaps in the Cycle 1 coverage were filled by rotating the spacecraft back to its initial left-looking direction. The orbit plane was adjusted slightly at the beginning of Cycle 2 so that altimetry tracks would be offset by about 10 km at the equator, bisecting the orbit-to-orbit offset of altimetry tracks in Cycle 1. The spacecraft was rotated 90 deg about the HGA boresight on orbits 3716-3719 to obtain SAR and radiometry data with VV polarization. Radio occultation measurements were made on orbits 3212-3214. The principal objective of Cycle 3 was to perform radar stereo mapping of the Venusian surface. About 30 percent of the Cycle 1 coverage was remapped in this cycle with a different, left-looking incidence angle on the surface. Gravity data were collected over Artemis Chasma. In addition, high resolution altimetry data were collected by pointing the high gain antenna straight down during orbits 4919 to 4921. Transmission of acquired radar data to Earth became nearly impossible after spacecraft equipment failures late in Cycle 3, and the radar was not used for science purposes after that. Cycle 4 was used for full (360 degree) longitudinal collection of gravity data because of favorable planetary and spacecraft geometry. The cycle was extended by about ten days to compensate for passage of the radio ray through the Venus atmosphere during the first ten days. To improve sensitivity to gravity features, orbit periapsis was lowered on orbit 5752. Radio occultation measurements were made on orbits 6369, 6370, 6471, and 6472. The aerobraking phase of the mission was designed to change the Magellan orbit from eccentric to nearly circular. This was accomplished by dropping periapsis to less than 150 km above the surface and using atmospheric drag to reduce the energy in the orbit. Aerobraking ended on 3 August 1993, and periapsis was boosted above the atmosphere leaving the spacecraft in an orbit that was 540 km above the surface at apoapsis and 197 km above the surface at periapsis. The orbit period was 94 minutes. The spacecraft remained on its medium-gain antenna in this orbit until Cycle 5 began officially on 16 August 1993. During Cycles 5 and 6 the orbit was low and approximately circular. The emphasis was on collecting high-resolution gravity data. Two bistatic surface scattering experiments were conducted, one on 6 October 1993 (orbits 9331, 9335, and 9336) and the second on 9 November 1993 (orbits 9846-9848). Mission Phases ============== Mission phases were defined for significant spacecraft activity periods. During orbital operations a 'cycle' was approximately the time required for Venus to rotate once under the spacecraft (about 243 days). But there were orbit adjustments and other activities that made some mapping cycles not strictly contiguous and slightly longer or shorter than the rotation period. PRELAUNCH --------- The prelaunch phase extended from delivery of the spacecraft to Kennedy Space Center until the start of the launch countdown. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1988-09-01 Mission Phase Stop Time : 1989-05-04 Spacecraft Operations Type : ORBITER LAUNCH ------ The launch phase extended from the start of launch countdown until completion of the injection into the Earth-Venus trajectory. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1989-05-04 Mission Phase Stop Time : 1989-05-04 Spacecraft Operations Type : ORBITER CRUISE ------ The cruise phase extended from injection into the Earth-Venus trajectory until 10 days before Venus orbit insertion. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1989-05-04 Mission Phase Stop Time : 1990-08-01 Spacecraft Operations Type : ORBITER ORBIT INSERTION --------------- The Venus orbit insertion phase extended from 10 days before Venus orbit insertion until burnout of the solid rocket injection motor. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1990-08-01 Mission Phase Stop Time : 1990-08-10 Spacecraft Operations Type : ORBITER ORBIT CHECKOUT -------------- The orbit trim and checkout phase extended from burnout of the solid rocket injection motor until the beginning of radar mapping. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1990-08-10 Mission Phase Stop Time : 1990-09-15 Spacecraft Operations Type : ORBITER MAPPING CYCLE 1 --------------- The first mapping cycle extended from completion of the orbit trim and checkout phase until completion of one cycle of radar mapping (approximately 243 days). Mapping orbits included in the first cycle were 373 through 2165. Orbits 2159-2171 were used for an interferometry test, and orbits 2172-2175 were used to conduct an orbit trim maneuver (OTM). Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1990-09-15 Mission Phase Stop Time : 1991-05-15 Spacecraft Operations Type : ORBITER MAPPING CYCLE 2 --------------- The second mapping cycle extended from completion of the first mapping cycle through an additional cycle of mapping. Acquisition of 'right-looking' SAR data was emphasized. Orbits included in the second cycle were 2176 through 3976. Radio occultation measurements were first carried out on orbits 3212-3214. A period of battery reconditioning followed completion of Cycle 2. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1991-05-16 Mission Phase Stop Time : 1992-01-17 Spacecraft Operations Type : ORBITER MAPPING CYCLE 3 --------------- The third mapping cycle extended from completion of battery reconditioning through an additional cycle of mapping (approximately 243 days). Acquisition of 'stereo' SAR data was emphasized. Orbits included in the third cycle were 4031 through 5747. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1992-01-24 Mission Phase Stop Time : 1992-09-14 Spacecraft Operations Type : ORBITER MAPPING CYCLE 4 --------------- The fourth mapping cycle extended from completion of the third mapping cycle through an additional cycle of mapping. Acquisition of radio tracking data for gravity studies was emphasized. Radio occultation measurements were carried out on orbits 6369, 6370, 6471, and 6472. Because of poor observing geometry for gravity data collection at the beginning of the cycle, this cycle was extended 10 days beyond the nominal 243 days. Orbits included within the fourth cycle were 5748 through 7626. Periapsis was lowered on orbit 5752 to improve sensitivity to gravity features in Cycle 4. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1992-09-14 Mission Phase Stop Time : 1993-05-25 Spacecraft Operations Type : ORBITER AEROBRAKING ----------- The aerobraking phase extended from completion of the fourth mapping cycle through achievement of a near-circular orbit. Circularization was achieved more quickly than expected; the first gravity data collection in the circular orbit was not scheduled until 11 days later. Orbits included within the aerobraking phase were 7627 through 8392. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1993-05-26 Mission Phase Stop Time : 1993-08-05 Spacecraft Operations Type : ORBITER MAPPING CYCLE 5 --------------- The fifth mapping cycle extended from completion of the aerobraking phase through an additional cycle of mapping (approximately 243 days). Acquisition of radio tracking data for gravity studies was emphasized. The first orbit in the fifth cycle was orbit 8393, and the last was orbit 12248. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1993-08-16 Mission Phase Stop Time : 1994-04-15 Spacecraft Operations Type : ORBITER MAPPING CYCLE 6 --------------- The sixth mapping cycle extended from completion of the fifth mapping cycle through an additional cycle of mapping (approximately 180 days). Acquisition of radio tracking data for gravity studies was emphasized. The first orbit in the sixth cycle was orbit 12249, and the last was orbit 15032. The sixth cycle ended when radio contact was lost as the spacecraft entered the atmosphere and was destroyed in a 'terminal windmill' experiment. Spacecraft Id : MGN Target Name : VENUS Mission Phase Start Time : 1994-04-16 Mission Phase Stop Time : 1994-10-12 Spacecraft Operations Type : ORBITER |
START DATE |
1989-05-04T12:00:00.000Z |
STOP DATE |
1994-10-12T12:00:00.000Z |
REFERENCES |
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