Magellan

Launch data: Designation  19969 / 89033B Launch date  04 May 1989 - 18:47 UT Deployed from Shuttle on 05 May 1989 Launch site  KSC, LC-39B Launch vehicle  Shuttle STS-30 Mission  Venus Orbiter Operator   Venus orbit Perihelion / Aphelion   Incl. to ecliptic   ° Period   min

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

A diagram of the Magellan spacecraft.

Description:

Mission details:

• 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;
  • 03 Aug 1993 - Cycle 5: Gravity data acquisition;
• Magellan lowered its orbit around Venus with orbit trim maneuvers on Mar 10, 1994 to lower periapsis, resulting in a 184 x 530 km orbit. More burns were made on Apr 4 and Apr 5, and further trims are due Apr 11 and Apr 12. The target orbit is 220 x 390 km.
• The Magellan Venus probe lowered its periapsis to 182 km on Aug 25, 1994 in preparation for the Windmill experiment to study the amount of torque produced by the Venusian upper atmosphere.
• Magellan carried out the Termination Experiment on Oct 11, 1994 firing its thrusters at 1321 to descend into the atmosphere of Venus.
  • 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. 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.
• 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.