Deep Space 1 loads up for trek to comet

NASA’s Deep Space 1 spacecraft, sailing through the solar
system today, has taken delivery of a new cargo: the latest
software for its ambitious encounter with Comet Borrelly this
September.

After successfully finishing its primary mission in 1999
as a testing ground for important new technologies, NASA
approved a risky bonus mission to Comet Borrelly for Deep
Space 1. There the spacecraft will take black-and-white
pictures, use infrared pictures to find out the nature of the
comet’s surface, measure and identify the gases coming from
the comet, and measure the interaction of solar wind with the
comet. To take pictures of the comet, Deep Space 1 must
upgrade its software’s pointing system to turn the spacecraft
from a testbed for advanced technologies to a chronicler of
Comet Borrelly.

“Deep Space 1’s previous version of software, which was
transmitted to the spacecraft eight months ago, has proven
itself during the surprisingly successful flight through the
solar system since then, but now we’re giving the probe a new
assignment,” said Dr. Marc Rayman, the project manager. “And
in order to prepare for this exciting and daring comet
encounter, the software needs to be upgraded.”

The spacecraft team will be checking the software,
radioed to Deep Space 1 throughout the week of March 5. The
first check came when the team actually received a signal from
the spacecraft after it shut the main computer off and
restarted it. Since the software sent by the team works well,
the spacecraft sent a signal indicating it is healthy. Now
engineers are giving the spacecraft’s new software a thorough
physical checkup.

“The process of transmitting the new software to the
spacecraft, rebooting the on-board computer to begin running
it, verifying that the spacecraft is working properly with the
new software and restoring the craft to its cruise
configuration, all when the spacecraft is 318 million
kilometers (197 million miles) away, is a complex and tricky
operation, ” said Daniel Eldred, the Deep Space 1 mission
manager.

The new software contains capabilities that will be
needed when the spacecraft gets to Borrelly. The new commands
will include lessons that Deep Space 1 learned in its 1999
encounter with asteroid Braille about the behavior of the
spacecraft when it gets close to a solar system object.

The spacecraft carries a device, part of the successful
new technology system, which holds two cameras. One uses a
conventional charge-coupled device detector, the other a new
technology detector. The test camera, though performing its
initial tests successfully, wasn’t equipped to deal with the
very dark object that Braille turned out to be. Small bodies
like asteroids and comets are still a mystery. Since they’re
so small and distant, their exact size and shape can’t usually
be determined from Earth. Deep Space 1 plans to use its tried-
and-true CCD camera to try to snap photos of Borrelly. The
team will send commands to the new software to stop using the
test camera and start using the CCD camera, which will take a
larger picture with more light.

In late 1999, after the successful end of its primary
mission, Deep Space 1 lost its star tracker, and the
spacecraft had to be reconfigured to use the photographic
camera to orient itself by the stars around it. In order to
take pictures of Borrelly, the camera can’t align the
spacecraft and snap photos of the comet at the same time.
Instead, the spacecraft will have to rely on its fiber-optic
gyroscopes to help maintain its orientation. But the gyros are
not accurate enough by themselves, so the new software will
try to correct for those inaccuracies. The new software is
designed to help the camera stay pointed at the comet’s
nucleus during the 15 minutes that the camera will attempt to
observe the comet.

Deep Space 1 was launched in October 1998 as part of
NASA’s New Millennium Program, which is managed by JPL for
NASA’s Office of Space Science, Washington, D.C. The
California Institute of Technology in Pasadena manages JPL for
NASA.

Deep Space 1 completed its primary mission testing ion
propulsion and 11 other advanced technologies in September
1999. NASA extended the mission, taking advantage of the ion
propulsion and other systems to target a chancy but exciting
encounter with the comet in September 2001. More information
can be found on the Deep Space 1 Home Page at
http://nmp.jpl.nasa.gov/ds1/ .