Magellan: Mission Plan


Magellan orbited Venus from north to south at periapsis, so "left-looking" radar was pointing east, and "right-looking" radar was pointing west. The initial orbital period was 3 hours, 15 minutes, and the (elliptic) orbit ranged from 294 km above the surface at periapsis to 8,540 km at apoapsis.

Cycle 1

Radar mapping (left-looking)

15 Sep 1990 - 14 May 1991
Cycle 1 covered about 83.7% of the surface with left-looking radar. The spacecraft altitude varied from about 2000 km near the north pole, to 290 km at 9.5 degrees N latitude. Imaging was performed from the north pole to about 75 degrees south latitude. At the north pole, the cross-track resolution was 250 m and the along-track resolution was 110 m, and at 9.5 degrees N the cross-track resolution was 101 m and the along-track resolution was 110 m. The incidence angle ranged from 16.5 degrees at the north pole to 45.7 degrees at periapsis.

Cycle 2

Radar mapping (right-looking)

15 May 1991 - 14 Jan 1992
Cycle 2 was performed in a right-looking mode, with the purpose of filling in the gaps from Cycle 1 and covering the south polar region. Cycle 2 covered 54.5% of the surface, but combined with Cycle 1 data accounted for 96% coverage. Imaging was done from about 75 N to the south pole. The incidence angle was about 25 degrees from 75 N to 55 S latitude, and then decreased to 12.7 degrees at the south pole.

Cycle 3

Radar mapping (left-looking)

15 Jan 1992 - 13 Sep 1992
Cycle 3 was devoted mainly to acquiring images that could be combined with images from cycle 1 to form stereo pairs. A slightly different left-looking profile from that of Cycle 1 was used. This cycle covered from 75 N, at an incidence angle of 13.4 degrees, to 45 S, incidence angle 14.3 degrees. The incidence angle reached a maximum of 25.6 degrees at 15 N. Part of the cycle was geared towards coverage of Maxwell Montes, from 75 N to 20 N at incidence angles from 27 to 36 degrees. About 21.3 % of the surface was covered, bringing the cumulative coverage to 98%

Cycle 4

Gravity data acquisition

14 Sep 1992 - 23 May 1993
Gravity data were obtained by pointing the Magellan antenna towards Earth and measuring the Doppler shift in the radio transmissions. These measurements can be converted into spacecraft accelerations along the line-of-sight (LOS), which can be used to estimate variations in the gravitational field of Venus. (With the antenna pointed away from Venus, radar imaging could not be done, so gravity measurements required their own cycle.) Spacecraft LOS velocity was measuered to an accuracy of 0.1 mm/sec.

Aerobraking

Circularization of orbit

24 May 1993 - 02 Aug 1993
The resolution of gravity estimates degrades rapidly with increasing spacecraft altitude. Since Magellan was in an elliptical orbit, the resolution of the gravity data was much higher near the equator than at the poles. The aerobraking maneuver was used to circularize the orbit to allow uniform high-resolution global gravity coverage. Magellan was dipped into the Venus atmosphere, causing a loss of orbital energy and bringing the spacecraft into a lower, more circular orbit. The final orbit had a periapsis of 180 Km from the surface, an apoapsis of 540 Km, and a period of 94 minutes.

Cycle 5

Gravity data acquisition

03 Aug 1993 - 29 Aug 1994
Gravity data was acquired from the newly circularized orbit in much the same way as it was in Cycle 4. High-resolution gravity has been measured in this way for about 95% of the planet.

Cycle 6

Windmill experiment

September 1994
The windmill experiment requires Magellan to be dipped into the Venus atmosphere. The solar panels are tilted at an angle so that atmospheric drag will put a torque on the craft, and measurements of the corrections required to offset this torque give information on the upper atmosphere. A press release describing the experiment is available.

End of mission

Atmospheric entry

11 Oct 1994 - 14 Oct 1994
On October 11, Magellan began its descent into the Venus atmosphere. On October 12 at 10:02 UT the radio signal was lost. The final orbit should occur on October 14, when the craft is expected to burn up on entry. Some parts of the craft may survive to impact the surface.
Author/Curator:
Dr. David R. Williams, dave.williams@nasa.gov
NSSDCA, Mail Code 690.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771
+1-301-286-1258

NASA Official: Ed Grayzeck, edwin.j.grayzeck@nasa.gov
Last Updated: 08 January 1997, DRW