Spaceflight Now: Breaking News

Star tracker problem keeps Deep Space 1 in safe mode
NASA/JPL STATUS REPORT
Posted: Dec. 21, 1999

  Deep Space 1
Artist's conception of ion propulsion engine firing on Deep Space 1. Photo: NASA
 
Deep Space 1, which successfully completed its primary mission of testing advanced technologies late last September, remains in a safe standby mode. The mission team conducted crucial tests on the spacecraft on Wednesday, December 14, in response to a problem with the spacecraft's star tracker that caused Deep Space 1 to enter this mode last month.

In the tests, the team successfully maneuvered the spacecraft's orientation to point its high-gain antenna toward Earth as part of a rotation movement. This capability not only begins the important process of developing the ability to point the spacecraft without the star tracker, but also opens up the possibility of uploading software that can compensate for the apparent loss of the sensor so that the spacecraft's instrumentation can return further technology validation and scientific information during its current extended mission.

The tests included a series of maneuvers, including stopping the slow rotation that is typical of Deep Space 1's safe standby mode; turning the spacecraft so that it was no longer pointing its antenna at the Sun, which is also typical of this mode; turning and stopping the spacecraft in 10-degree increments; rotating the spacecraft in a cone-like, circular movement, during which the low-gain antenna was intermittently aimed toward Earth; switching to the high-gain antenna while continuing with this rotation; stopping the rotation; returning to the low-gain antenna; rotating further; and stopping again. At the end of the tests, the team returned the spacecraft to its standby state.

These maneuvers helped the team gain experience in turning and pointing the spacecraft without the star tracker. There will be future tests as the team continues to work on the techniques necessary to operate the spacecraft independent of this sensor.

The star tracker, a new, sophisticated device that helps determine the spacecraft's orientation, is neither part of the navigation system nor one of the 12 advanced technologies whose testing was the focus of Deep Space 1's primary mission. Since shortly after launch, it has displayed many unexplained, intermittent problems in reporting its orientation properly to the spacecraft computer. In all previous cases, the device resumed normal operation within less than one hour. This time, however, it has not resumed functioning correctly, and the team has determined that it probably cannot be used for the duration of the mission.

Deep Space 1 is now more than 246 million kilometers, or 153 million miles from Earth. At this distance, radio signals, traveling at the speed of light, take more than 27 minutes to make the round trip between Earth and the spacecraft.


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