MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CA 91109 TELEPHONE (818) 354-5011
Contact: Martha Heil (818) 354-0850July 27, 2000
SPACE RESCUE MAKES CLOSE ENCOUNTER POSSIBLE
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
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
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.