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Deep Space 1 Mission Status

November 17, 1999

Deep Space 1, which successfully completed its primary mission of testing advanced
technologies late last September and is now on an extended mission, placed itself in a
safe standby mode late last week in response to a problem with the spacecraft’s star

This sensor, a new, sophisticated 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

A second instrument that received special attention 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 is now more than 630 times as far from Earth as the moon is. At this
distance of 241 million kilometers, or 150 million miles, radio signals, traveling at
the speed of light, take nearly 27 minutes to make the round trip.