"Having a deployed, 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.

"Up until now, we have been using the high-gain antenna in its stowed position, so periodically during the first three weeks of our mapping mission, we had to stop collecting science data and turn the entire spacecraft to transmit data to Earth," Beerer explained. "Now that the high-gain antenna is deployed and steerable, we have the ability to simultaneously study Mars and communicate with Earth."

The antenna was deployed at about midnight EST, Sunday, March 28. It had been stowed since launch in November 1996 to reduce its chances of being contaminated by exhaust 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 dish-shaped high-gain antenna, 5 feet in diameter, was deployed on a 6.6-foot-long boom and was pushed outward from the spacecraft by a powerful spring. The suspect dampening device worked as it should have, cushioning the force of the spring and limiting the speed of the deployment, similar to the 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 is recorded 24 hours a day on solid state recorders on board the spacecraft. Once a day, during a 10-hour tracking pass over a Deep Space Network antenna, the data are transmitted to Earth. 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 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.