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astronautix.com Magellan

Magellan
Magellan -

Credit: NASA. 15,100 bytes. 276 x 300 pixels.



Class: Planetary. Type: Venus. Nation: United States. Agency: NASA, JPL . Manufacturer: Martin Marietta.

The primary objectives of the Magellan mission were to map the surface of Venus with a synthetic aperture radar (SAR) and to determine the topographic relief of the planet. At the completion of radar mapping 98% of the surface was imaged at resolutions better than 100 m, and many areas were imaged multiple times. Additional studies included measurements of surface altitude using radar altimetry and measurements of the planet's gravitational field using precision radio tracking. The mission was divided up into "cycles", each cycle lasted 243 days (the time necessary for Venus to rotate once under the Magellan orbit - i.e. the time necessary for Magellan to "see" the entire surface once.)

A total of 4225 usable SAR imaging orbits was obtained by Magellan. Each orbit typically covered an area 20 km wide by 17,000 km long, at a resolution of 75 m/pixel. This raw SAR data was processed into image strips called full-resolution basic image data records (F-BIDRs). Adjacent F-BIDRs were then assembled into full-resolution mosaicked image data records (F-MIDRs). These images were then compressed once (by a factor of 3), twice (9), or 3 times (27), to give C1-, C2-, and C3-MIDRs.

The Magellan mission scientific objectives were to study land forms and tectonics, impact processes, erosion, deposition, chemical processes, and model the interior of Venus.

Spacecraft: 3-axis stabilised using 3 reaction wheels. A 3.7 m diameter high gain antenna was used for both telecommunications and radar. Attitude sensors include 2 cruise sun sensors, 1 star scanner, and 2 inertial reference units. Power system included a 12.5 m2 solar array (1029 W EOL) and NiCd batteries (2 x 30 AHr). Hydrazine propulsion system with 0.9N, 445 N thrusters. X-band (20 W) and S-Band (5 W) communications. Downlink rates of 268.8 or 115 kbps. Uplink rates of 31.25 and 62.5 bps. Payload: A single radar instrument operated simultaneously as a Synthetic Aperture Radar (SAR), altimeter, and radiometer. Radar frequency 2.385 GHz, with 325 W peak power and 25 km swath width (variable). Altimeter resolution 30 m. Radiometer accuracy 2 deg C. SAR resolution 150 m (range and azimuth). An X- and S- band radio subsystem precisely tracked the spacecraft's orbit to make measurements of the gravity field.
Financial/Operational:
Original name was Venus Orbiting Imaging Radar. Hughes supplied the radar mapper, and Martin the satellite.



STS-30STS-30 - STS-30 Magellan spacecraft & IUS deployment from Atlantis' payload bay (PLB)

Credit: NASA. 30,901 bytes. 433 x 454 pixels.


Specification

Design Life: 4 years . Total Length: 6.4 m. Total Mass: 3,444 kg.


Magellan Chronology


04 May 1989 Magellan Launch Site: Cape Canaveral . Launch Vehicle: Shuttle. Mass: 3,444 kg.

SAR radar imaging of the Venusian surface, gravitational field mapping. The Magellan spacecraft was deployed from shuttle STS-30 on May 5, 1989, arrived at Venus on August 10, 1990 and was inserted into a near-polar elliptical orbit with a periapsis altitude of 294 km at 9.5 deg. N. The primary objectives of the Magellan mission were to map the surface of Venus with a synthetic aperture radar (SAR) and to determine the topographic relief of the planet. At the completion of radar mapping 98% of the surface was imaged at resolutions better than 100 m, and many areas were imaged multiple times. The mission was divided up into 'cycles', each cycle lasted 243 days (the time necessary for Venus to rotate once under the Magellan orbit - i.e. the time necessary for Magellan to 'see' the entire surface once.) The mission proceeded as follows: 10 Aug 1990 - Venus orbit insertion and spacecraft checkout;15 Sep 1990 - Cycle 1: Radar mapping (left-looking); 15 May 1991 - Cycle 2: Radar mapping (right-looking); 15 Jan 1992 - Cycle 3: Radar mapping (left-looking); 14 Sep 1992 - Cycle 4: Gravity data acquisition; 24 May 1993 - Aerobraking to circular orbit; 3 Aug 1993 - Cycle 5: Gravity data acquisition; 30 Aug 1994 - Windmill experiment; 12 Oct 1994 - Loss of radio signal; 13 Oct 1994 - Loss of spacecraft. A total of 4225 usable SAR imaging orbits was obtained by Magellan. Magellan showed an Earth-sized planet with no evidence of Earth-like plate tectonics. At least 85% of the surface is covered with volcanic flows, the remainder by highly deformed mountain belts. Even with the high surface temperature (475 C) and high atmospheric pressure (92 bars), the complete lack of water makes erosion a negligibly slow process, and surface features can persist for hundreds of millions of years. Some surface modification in the form of wind streaks was observed. Over 80% of Venus lies within 1 km of the mean radius of 6051.84 km. The mean surface age is estimated to be about 500 million years. A major unanswered question concerns whether the entire surface was covered in a series of large events 500 million years ago, or if it has been covered slowly over time. The gravity field of Venus is highly correlated with the surface topography, which indicates the mechanism of topographic support is unlike the Earth, and may be controlled by processes deep in the interior. Details of the global tectonics on Venus were still unresolved.



STS-30STS-30 - STS-30 Magellan spacecraft & IUS deployment from Atlantis' payload bay (PLB)

Credit: NASA. 29,675 bytes. 431 x 450 pixels.



Bibliography:



STS-30STS-30 - IUS with Magellan spacecraft drifts into space after STS-30 deployment

Credit: NASA. 2,507 bytes. 194 x 202 pixels.



STS-30STS-30 - Magellan radar image compared to high resolution Earth-based image of Venus

Credit: NASA. 46,192 bytes. 381 x 470 pixels.



STS-30STS-30 - Global view of Venus from Magellan, Pioneer, and Venera data

Credit: NASA. 43,148 bytes. 463 x 445 pixels.



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Last update 12 March 2001.
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