A steady stream of new data from Mars, including high- resolution images, will begin arriving next week at Earth receiving stations following last night's deployment of the Mars Global Surveyor's high-power communications antenna.
"Having a deployed, or steerable, high-gain antenna is like switching from a garden hose to a fire hose in terms of data return from the spacecraft," said Joseph Beerer, flight operations manager for Mars Global Surveyor at NASA's Jet Propulsion Laboratory. "We now have a steady stream of data."
"Up until now, we have been using the high-gain antenna in its stowed position, so during the first three weeks of our mapping mission, we had to stop collecting science data and turn the entire spacecraft periodically to transmit data to Earth," Beerer explained. "Now that the high-gain antenna is deployed and steerable, we have the ability to simultaneously make measurements of Mars and communicate with Earth without turning the spacecraft."
The antenna was deployed about 9:30 p.m. Pacific time Sunday, March 28. It had been stowed since launch in November 1996 to reduce the chances of it being contaminated by the exhaust plume from the spacecraft's main engine, which was fired periodically throughout the mission. The spacecraft entered orbit around Mars in September 1997 and used a technique called aerobraking to gradually lower the spacecraft's altitude to the desired orbit for mapping. The mapping mission began March 9; full-scale mapping begins April 4.
Because engineers were uncertain that a device intended to dampen the force of the deployment would work correctly, engineers used the antenna in its stowed configuration for the first three weeks of mapping. This allowed the team to meet the mission's minimum science objectives before risking the antenna deployment.
Last night, the 1.5-meter-diameter (4.9-foot) dish-shaped high-gain antenna was deployed on a 2-meter-long (6.6-foot) boom and was pushed outward from the spacecraft by a powerful spring. A damper mechanism cushioned the force of the spring and limited the speed of the deployment, somewhat similar to the piston-like automatic closer on a screen door. With the antenna successfully deployed, Mars Global Surveyor will return a nearly constant stream of observations of Mars for the next two years.
Information from the science instruments are recorded 24 hours per day on solid-state recorders onboard the spacecraft. Then the data are transmitted to Earth once a day, during a 10- hour tracking pass over a Deep Space Network antenna. In addition, every third day a second tracking pass is used to transmit data "live" at a very high rate directly to Earth without being put on the spacecraft's onboard recorder. These data, which will contain high-resolution images of Mars, will be transmitted at rates between 40,000 and 80,000 bits per second.
Mars Global Surveyor is managed by JPL for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology.
Further information about the mission is available on the Internet at:
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