NASA's Terra satellite during pre-launch processing at Vandenberg Air Force Base, Calif. Photo: NASA

Activation of the Terra spacecraft, which was launched on Saturday, December 18, is continuing, with the mission going extremely well. A number of spacecraft components have been powered-on over the past two days, and the performance has been nominal.

The high gain antenna, which communicates with the Tracking and Data Relay Satellite (TDRS) system, has been placed back in the normal program track mode. In this mode, the antenna tracks one of four of the on-orbit TDRS spacecraft which are used by Terra. Stored commands from the spacecraft's flight computer direct the high gain antenna to point to the proper TDRS satellite. The anomaly which occurred on Sunday evening, where the high gain antenna program track mode stopped, is now believed to have been a transient event. The motion of the antenna today eliminated the potential for any mechanical interference type issue.

During the period in which high gain antenna pointing was not occurring, the flight operations team took the opportunity to flow 16 kbps data from the spacecraft's omni to the TDRS system. This mode, which was not an operational requirement, will be a significant asset for the flight operations team during future non-nominal Terra operations.

Initial instrument activation activities also are proceeding. The MISR instrument will be powered-up shortly to unlatch 3 launch latches contained in the instrument. Immediately after that, both of the CERES instruments will be powered-up and placed in a standby mode while outgassing continues. "The spacecraft has been operating quite well," said Kevin Grady, Terra project manager at NASA's Goddard Space Flight Center, Greenbelt, Md. "All data indicate we have a very healthy spacecraft."

The Lockheed Martin Atlas 2AS soars toward space with Terra from Vandenberg Air Force Base, Calif. Photo: U.S. Air Force

Terra began a new generation of Earth science - one that studies the Earth's land, oceans, air, ice and life as a total global system, when it launched from Vandenberg Air Force Base, Calif., on Dec. 18, 1999, at 1:57 p.m. EST. The Terra mission is the "flagship" to the Earth Observing System series of satellites, part of a precedent setting program designed to provide daily information on the health of the Planet.

The Terra satellite was built by Lockheed Martin assembled and tested the Terra spacecraft at its production facility in Valley Forge, Pa., under management from NASA's Goddard Space Flight Center, Greenbelt, Md. The primary objective of the Terra Mission is to simultaneously will study clouds, water vapor, small particles in the atmosphere (called "aerosol" particles), trace gases, land surface and oceanic properties, as well as the interaction between them and their effect on the Earthıs energy budget and climate.

Terra is managed by NASAıs Goddard Space Flight Center, Greenbelt, Md., for NASA's Office of Earth Science, Washington, DC. A goal of the Earth Science Enterprise is to expand knowledge of the Earth System, from the unique vantage point of space. Earth Science Enterprise data, which will be distributed to researchers worldwide at the cost of reproduction, is essential to people making informed decisions about their environment.