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Deep Space 1, which successfully completed its prime mission
of testing advanced technologies late last September, has added a
new accomplishment during its extended mission. On January 14,
the mission team directed the spacecraft to point its main
antenna toward Earth in a complex and innovative maneuver.

This challenging maneuver allowed the spacecraft to transmit
a large volume of important science and engineering data to the
operations team at NASA’s Jet Propulsion Laboratory. Further,
the maneuver was accomplished without the use of one of Deep
Space 1’s primary sensors, the star tracker. The star tracker,
which failed in November, was used to help determine the
spacecraft’s orientation by tracking the positions of stars. It
was a new and advanced sensor, but was not one of the 12 advanced
technologies that were the focus of Deep Space 1’s successful
primary mission.

Prior to this maneuver, Deep Space 1 was pointed toward the
Sun. Without the star tracker, the spacecraft did not know which
direction to turn to search for another target; in this case, the
Earth. Working with NASA’s Deep Space Network, the operations
team watched the radio signal grow in strength as the spacecraft
antenna pointed closer to Earth and then fade as it went past.
After two sweeps, engineers calculated what time the next one
would occur. Then, accounting for the time it takes a radio
signal sent from Earth to reach the spacecraft and for how long
it takes to tune to the correct frequency and transmit an
instruction, a code was sent to trigger commands stored in the
spacecraft’s computer that would halt the rotation. Spacecraft,
like sailboats, cannot “stop on a dime.” But engineers had taken
that into consideration and designed the commands to include an
instruction to rotate back to the desired point. The design
worked perfectly and the spacecraft was right on target.
Commands were sent to Deep Space 1 to transmit stored onboard
data at a high rate. Some of the information returned included
observations of Mars from November.

“This was an exciting and interesting problem to solve and
represents another challenge for the mission that has so
successfully accomplished so many remarkable feats. And our
success in keeping the antenna pointed toward Earth shows that we
are well on the way to developing an effective solution,” said
Dr. Marc Rayman, Deep Space 1’s chief mission engineer.

Now that the spacecraft can point its main antenna reliably
toward Earth for extended periods, the mission team will be able
to develop new computer programs to operate Deep Space 1 without
the star tracker.

Deep Space 1 is now over one and two-thirds as far from
Earth as the Sun is and over 650 times as far as the moon. At
this distance of more than 252 million kilometers (about 156
million miles), radio signals traveling at the speed of light
take almost 28 minutes to make the round trip.