12 Oct 2004
(Source: Jet Propulsion Laboratory)
PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Jim Doyle
MAGELLAN STATUS REPORT
FOR IMMEDIATE RELEASE
October 12, 1994
The successful five-and-a-half-year mission of NASA's Magellan spacecraft to map the surface and measure the gravity of Venus ended today when ground controllers lost contact with the spacecraft. Magellan is expected to burn up in the planet's upper atmosphere within two days.
The final chapter of the Magellan story was written as Earth-based tracking stations lost the spacecraft's radio signal at 10:02 Universal Time (3:02 a.m. Pacific Daylight Time). The loss of signal, which was anticipated, was due to low power on the spacecraft, exacerbated by Magellan's orientation as it performed a final experiment in the upper atmosphere of Venus.
The spacecraft's thrusters were fired in four sequences on Tuesday, Oct. 11, to lower Magellan's orbit into the thin upper atmosphere and set up the final experiment, before the spacecraft's failing power system or dynamic forces and friction from the Venusian atmosphere shut off communication.
Magellan gathered scientific data on the planet's upper atmosphere, including aerodynamic interactions with it during the spacecraft's final descent, by orienting its wing-like solar panels in opposite directions, like a windmill. The termination experiment was an extension of the windmill experiment performed in early September. It was carried out as the spacecraft was within weeks, if not days, of the end of its useful life due to expected decreases in solar power output from the thermal stress produced by more than 15,000 orbits of Venus.
Launched in May 1989, Magellan entered Venus orbit in August 1990 and gathered data for over four years. The mission exceeded all of the objectives defined for its exploration of Venus.
It used radar to map 98 percent of the planet's cloud- covered surface to an average resolution of better than 300 meters and compiled a high-resolution, comprehensive gravity field map for 95 percent of the planet. The gravity data will allow scientists to see "underneath the planet's skin" and compare that knowledge of the interior to the wealth of surface features revealed by Magellan's radar imaging, said Project Manager Doug Griffith at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif.
"The tremendous success of the Magellan program was made possible by the dedicated NASA, JPL , Martin Marietta (Denver) and Hughes Aircraft (Los Angeles) team that built the spacecraft and its radar, and operated the mission," Griffith said. "The data which streamed back from Magellan's radar images, its atmospheric studies, and its gravity data acquisition maneuvers have built a vast database of new knowledge about Venus and the formation of the solar system that will be studied by scientists for decades to come."
Magellan also performed a first-of-a-kind "aerobraking" maneuver by dipping into the atmosphere to reshape its orbit. This technique is now being used in the design of the Mars Global Surveyor mission to enable the spacecraft to enter orbit around the planet Mars in 1997 using less fuel, resulting in significant savings of weight and cost.
"The Magellan mission to Venus has been successful beyond all expectations," said JPL Director Dr. Edward C. Stone. "It not only fulfilled its science and mission objectives, it also demonstrated innovative technologies for future missions."
Magellan Status Report - October 13, 1994
Magellan Significant Events for Week Ending 10/14/94
1. Communication with the Magellan spacecraft was lost early Wednesday morning, following an aggressive series of five Orbit Trim Maneuvers (OTMs) on Tuesday, October 11, which took the orbit down into the upper atmosphere of Venus. The Termination experiment (extension of September "Windmill" experiment) design was expected to result in final loss of the spacecraft due to a negative power margin. This was not a problem since spacecraft power would have been too low to sustain operations in the next few weeks due to continuing solar cell loss.
Thus, a final controlled experiment was designed to maximize mission return. This final, low altitude was necessary to study the effects of a carbon dioxide atmosphere.
2. The final OTM took the periapsis to 139.7 km (86.6 miles) where the sensible drag on the spacecraft was very evident. The solar panel temperatures rose to 126 deg. C. and the attitude control system fired all available Y-axis thrusters to counteract the torques. However, attitude control was maintained to the end.
3. The main bus voltage dropped to 24.7 volts after five orbits, and it was predicted that attitude control would be lost if the power dropped below 24 volts. It was decided to enhance the windmill experiment by changing the panel angles for the remaining orbits. This was also a preplanned experiment option.
At this point, the spacecraft was expected to survive only two orbits.
4. Magellan continued to maintain communication for three more orbits, even though the power continued to drop below 23 volts and eventually reached 20.4 volts. At this time, one battery went off-line, and the spacecraft was defined as power starved.
5. Communication was lost at 3:02 AM PDT just as Magellan was about to enter an Earth occultation on orbit 15032. Contact was not re-established. Tracking operations were continued to 11:00 AM but no signal was seen, and none was expected. The spacecraft should land on Venus by 1:00 PM PDT Thursday, October 13, 1994.
6. The Magellan Project Office received many requests for television and radio interviews relating to the demise of the spacecraft. All requests were very positive in nature, relating to the tremendous success of the Magellan mission.
7. This is the last regular Magellan report.