The sensor is a sophisticated new device that helps determine the spacecraft's orientation, is not one of the 12 advanced technologies whose testing was the focus of Deep Space 1's primary mission.

After several unsuccessful attempts to fix the star tracker, protective software onboard the spacecraft placed Deep Space 1 in one of its predefined safe standby configurations.

In this state, nonessential devices are turned off, the star tracker is not used, the high-gain antenna is disengaged and the spacecraft reverts to its low-gain antenna to communicate with Earth.

This event, which occurred November 11, was discovered by controllers during a scheduled communications session through the Deep Space Network on Friday, November 12, and now engineers are collecting data from the spacecraft to determine its exact condition.

Since shortly after launch, the star tracker 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 an hour, and usually in less than a minute. This time, the star tracker has not yet resumed functioning correctly.

Since its star tracker problems began more than one year ago, the Deep Space 1 team has been working with the device's manufacturer -- and with other mission teams that are planning to use the same apparatus -- to try to understand its problems.

Various laboratory experiments have been conducted with similar devices, and special data channels have been activated on Deep Space 1 to gain greater insight into the device's operation.

So far, none of these investigations has revealed the source of the problems. For now, Deep Space 1 will be left in safe standby until all the data on the spacecraft's health can be returned and analyzed.

Until November 11, Deep Space 1 spent most of the prior three weeks engaged in special activities to prepare for its encounters with comets in 2001, while continuing to coast in its orbit around the Sun, with its ion propulsion system turned off.

During this period, Deep Space 1's combination visible camera and imaging spectrometer collected a wealth of new data to aid scientists and engineers in understanding details of its abilities to take pictures and spectra under a variety of conditions.

The instrument viewed targets with well-known properties, including Mars and Jupiter, so that the instrument's electronically recorded pictures and spectra could be compared with data collected elsewhere. Analysis of the resulting data will aid in selecting exposure times and controlling the instrument's pointing for the 2001 comet encounters.

A second instrument suffering degradation during the last few weeks is the Plasma Experiment for Planetary Exploration, which measures the energy, composition and direction of movement of the constituents of plasmas (collections of charged particles, both electrons and charged atoms, or ions).

Because of some degradation of the instrument on this extended mission, it appears that it may not be able to measure the composition of some of the complex ions the comets produce.

This does not affect the measurements of electrons or of the energy and the direction of ions. The instrument's data on the solar wind -- the stream of charged particles flowing from the Sun -- will be unaffected, and it is still well suited to measure the complex structure and behavior of the expanding cloud of gas around the comet.

Deep Space 1: Rocketing to the Future

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