This week marked the transition from the inner-cruise to the outer- cruise phase of the mission. One of the first transition tasks occurred early Monday morning when the flight team sent a set of commands to change Surveyor's pointing orientation. The commands turned the spacecraft from its previous orientation of +X axis pointed 60 degrees away from the Sun to a position where the +X axis is pointed directly at the Earth.
One of the benefits of this new pointing orientation is that Surveyor can now use its high-gain antenna to communicate with the Earth. This antenna is mounted on the spacecraft's +X axis and its narrow-beam signal requires that the spacecraft point directly at Earth. Until now, Surveyor was utilizing its wide-beam, low-gain antenna for communications. The high-gain antenna broadcasts with greater power and will allow the spacecraft to transmit data at higher data rates.
Before January, it was impossible to use the high-gain antenna because an Earth-pointed orientation would have placed Surveyor at an unfavorable angle with respect to the Sun. The switch from the low-gain to the high-gain antenna occurred early Thursday morning. The flight team is continuing to diagnose the position discrepancy in Surveyor's -Y solar panel which is deployed, but 20.5 degrees from its proper position. Engineering data transmitted to Earth during the five solar array "wiggle tests" conducted in December supports the current model regarding the nature of the obstruction keeping the array out of position.
The model suggests that a damper shaft in the solar array's deployment mechanism broke shortly after launch, approximately 43 seconds after the start of the array's deployment. This damper is a device that was installed to minimize the mechanical shock of deployment by slowing the motion of the array during deployment. The flight team theorizes that the broken shaft caused the damper arm to wedge into the hinge joint connecting the solar panel to the spacecraft. Attitude-control telemetry recorded by the spacecraft during solar array deployment corroborates this theory.
Plans are currently being developed for three more solar array "wiggle tests" during the week of January 20th. Data from these upcoming tests and the five previous tests in December will assist the flight team in determining the best method to attempt to free the damper arm from the hinge joint.
Today, the flight team transmitted the C4 sequence to Surveyor. C4 contains commands that will control Surveyor for the next five weeks. The first activities in C4 will start on January 13th and will involve using the Mars Orbiter Camera to image stars over four consecutive days. These star images will allow the camera team to refine the camera's focusing capability.
After a mission elapsed time of 64 days from launch, Surveyor is 14.79 million kilometers from the Earth and is moving in an orbit around the Sun with a velocity of 31.32 kilometers per second. This orbit will intercept Mars on September 12th, 1997. All systems on the spacecraft continue to be in excellent condition.
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