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	Deep Space 1 in Safe Mode as Engineers Examine Instrument Glitch By Andrew Bridges Chief Pasadena Correspondent posted: 04:54 pm ET 18 November 1999

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PASADENA, Calif. - Deep Space 1 has remained in protective safe mode since November 11 in response to an unexpected problem with its star tracker, a sensor used to help determine the spacecrafts orientation.

The instrument -- which is not one of the dozen new technologies at the core of the $152-million mission -- has been plagued with many unexplained but intermittent problems in reporting the spacecrafts orientation to its onboard computer since Deep Space 1 was launched a year ago.

Previously, the star tracker has resumed working typically within an hour, and usually in less than a minute. This time, the sensor has not resumed functioning properly.

After several attempts to fix the sensor on November 11, protective software put Deep Space 1 into safe mode, where all nonessential devices are switched off (including the star tracker itself) and the high-gain antenna disengaged.

On November 12, flight controllers discovered the problem during a scheduled communications session with the spacecraft, which is now using its low-gain antennas to communicate with Earth.

Investigations into the problem have failed to uncover its source. For the time being, Deep Space 1 will be left in standby mode until more data on the spacecrafts health can be returned and analyzed.

An instrument aboard the spacecraft, the Plasma Experiment for Planetary Exploration, or PEPE, designed to measure the energy, composition and direction of movement of plasmas has also suffered a glitch. Plasmas are collections of charged particles.

According to a press release from NASAs Jet Propulsion Laboratory (JPL), the instrument may not be able to measure the composition of some of the complex ions that comets produce.

JPLs Deep Space 1 is scheduled to make two cometary flybys in 2001 as part of its extended mission. It is now 150 million miles (241 million kilometers) from Earth.