The lowest point of Mars Global Surveyor's aerobraking orbit has been raised temporarily and aerobraking has been suspended while the flight team analyzes data to understand why one of the spacecraft's two solar panels, which did not fully deploy, exhibited unexpected motion during a recent dip through the upper Martian atmosphere.
Preliminary data from the panel indicates that it has moved past what would have been its fully deployed and latched position, Cunningham said. In addition, the panel has shown some movement rather than maintaining its rigid position during aerobraking. These changes occurred on October 6th, during the closest approach of the spacecraft's fifteenth orbit around Mars, when the density of the Martian atmosphere doubled unexpectedly.
During the next few weeks, the flight team will leave the spacecraft's orbit in the current, 35-hour revolution around Mars, which will not take the spacecraft through the upper atmosphere, while they analyze data and simulate conditions in the atmosphere to understand the behavior of the solar panel. This hiatus also means the spacecraft's solar panels will not be reconfigured for each close pass over Mars, but will remain in the normal cruise position.
"We can't explain yet what has happened," Cunningham said. "We saw the unlatched panel move past the latched-up position, and it remains past that point now. By raising the spacecraft's orbit above the upper atmosphere, the panel should not shift further because it will not be exposed to the aerodynamic forces of the Martian atmosphere."
Several other mapping orbits are available to Surveyor to carry out its science objectives. The flight team will explore alternatives in the next few weeks to accomplish the lowest orbit possible and possibly achieve a "Sun-synchronous" orbit that will allow the spacecraft to fly over the Martian equator at the same local solar time each orbit. These Sun-synchronous orbits are designed so that the spacecraft's instruments always see Mars at the same lighting angle on every pass over the surface.
"As we step back from aggressive aerobraking temporarily, we will have the opportunity to study the situation until we fully understand it," Cunningham said. "We will take advantage of this opportunity to return some spectacular data from the camera and laser altimeter. The thermal emission spectrometer and magnetometer also will continue to collect data while we remain in this holding pattern."
The Mars Global Surveyor atmospheric advisory group reported that the Martian atmosphere has more than doubled in thickness in the last week. The spacecraft is designed to withstand more than a 50 percent increase in atmospheric density, but began showing movement in the solar panel October 6th, at the low point and start of the 15th orbit.
After a mission elapsed time of 341 days from launch, Surveyor is 172.26 million miles (277.22 million kilometers) from the Earth and in an orbit around Mars with a period of 35.4 hours. The spacecraft is currently executing the P20 command sequence, and all systems continue to be in excellent condition.
The Surveyor flight team would like to take this opportunity to congratulate the Cassini flight team on a spectacular launch and to offer our best wishes for a successful mission.
Status report prepared by:
Office of the Flight Operations Manager
Mars Surveyor Operations Project
NASA Jet Propulsion Laboratory
California Institute of Technology
Pasadena, CA 91109
Major parts of this report prepared by:
JPL Public Information Office