Press Release

Space Rescue Makes Close Encounter Possible

By SpaceRef Editor
July 27, 2000
Filed under

Contact: Martha Heil (818) 354-0850

As NASA’s Deep Space 1 propels itself through the solar system about
320 million kilometers (about 200 million miles) from Earth, the tiny
spacecraft has been reenergized for a planned September 2001 encounter with
Comet Borrelly.

Deep Space 1 met or exceeded all of its primary mission objectives of
testing 12 advanced, high-risk technologies in September 1999, providing
important data for future users. However, engineers and scientists at NASA’s
Jet Propulsion Laboratory, Pasadena, CA, believed that even further
challenges could be met. NASA approved an extended mission in order to gain
more scientific knowledge of comets.

“NASA decided that it could afford to go ahead with a risky extended
mission,” said Paul Hertz, NASA Headquarters program executive for Deep
Space 1. “The talented Deep Space 1 folks at JPL are working hard to squeeze
a bonus science mission, an encounter with Comet Borrelly, out of this
already successful mission. Although there is no guarantee of success,
trying for the comet makes much more sense than just turning the spacecraft
off.”

Shortly after it began traveling to meet the comet, Deep Space 1 lost
a critical sensor — its star tracker — to determine and control its
orientation system.

“We had to rebuild a significant part of the spacecraft from hundreds
of millions of kilometers away and complete it to begin ion-powered flight
in time to keep our date with Comet Borrelly,” said Project Manager Dr. Marc
Rayman. “This was crucial, because the star tracker that had been used
previously to determine the spacecraft’s orientation in space failed in
November 1999.”

The star tracker determined orientation by tracking the positions of
stars. Without the star tracker, Deep Space 1 did not know in which
direction it was pointed. It couldn’t thrust in the direction of the comet,
since it didn’t know which way to go. Use of the newly developed camera
method allowed the spacecraft to regain full three-dimensional control.

Engineers at JPL radioed software to the spacecraft to reprogram the
camera on board to serve as a replacement for the lost star tracker. This
boost is helping Deep Space 1 go on to perform a mission that is above and
beyond the plans at launch.

“In a very short time, the spacecraft operations team developed a
very complex and innovative new system that gives Deep Space 1 a new chance
to try to reach the comet,” said Rayman. “The new system is working
beautifully. I think this is one of the most impressive in-space rescues
ever completed.”

With Deep Space 1 knowing its orientation in space, controllers
instructed the ion propulsion system to resume thrusting. Return data showed
that the system was operating successfully and the spacecraft is on its way
to Comet Borrelly.

Now that the software enables the spacecraft to point its antenna
toward Earth on its own, more software will be transmitted to the spacecraft
in February 2001.

Among the differences between the star tracker and the camera is the
amount of sky that each views. The camera sees an area only a bit larger
than the full moon as viewed from Earth, but the star tracker covers well
over 100 times as much area. Both can see stars that are fainter than the
unaided human eye can detect. The star tracker would update the spacecraft
computer four times per second, while the camera produces a computer file
containing a picture. It then takes 20 seconds to transfer the picture to
the computer for analysis. The navigation system processes the picture and
delivers the result to the attitude control system.

Scientists plan to image the comet’s nucleus and the environment
around it as well as collect infrared measurements to determine its
composition. They will also measure charged particles in the vicinity of
Borrelly, including the interaction of the comet with the solar wind.

Deep Space 1 was launched in October 1998 as part of NASA’s New
Millennium Program and served as a technology demonstrator during its prime
mission.

This program is managed by JPL for NASA’s Office of Space Science.
JPL is managed for NASA by the California Institute of Technology in
Pasadena.

SpaceRef staff editor.