Stardust Prepares to Pick Up Speed from Earth’s Gravity Assist

As it completes the first of three laps of about a
billion miles each around the heart of the solar system,
NASA’s Stardust spacecraft is getting ready for a pit stop of
sorts, flying by Earth in mid-January for a gravitational
speed boost. The added energy will put Stardust on course to
meet Comet Wild 2 (pronounced “vilt-2”) in January 2004.

“It’s a big event in the sense that it’s a mission
milestone,” said Dr. Donald Brownlee, a University of
Washington astronomy professor and the mission’s principal
investigator. “We don’t have to do anything during the flyby.
It’s all celestial mechanics.”

The Earth-gravity-assist phase of the mission actually
began on Nov. 14, as the desk-sized craft cruised toward Earth
after traveling beyond the orbit of Mars. Engineers at NASA’s
Jet Propulsion Laboratory in Pasadena, Calif., have made
course changes and other adjustments to ensure that Stardust
gains the proper amount of energy from Earth’s gravity.

The gravity boost will lengthen the spacecraft’s orbit,
setting up its rendezvous with Wild 2 in early 2004. Stardust
will capture particles being boiled off the comet’s surface by
solar heating. During the gravity-assist phase, the closest
Earth approach will be at 3:20 a.m. PST on Jan. 15, as the
spacecraft flies just southeast of the southern tip of Africa.
It will be traveling about 5,950 kilometers (3,700 miles) from
the Earth’s surface and moving at about 36,050 kilometers per
hour (22,400 miles per hour).

“The science of the mission is basically ahead of us,”
Brownlee said. “We’ve dealt with a number of problems, but
they have been fewer than most spacecraft experience.”

Perhaps the most heart-stopping problem came last Nov. 9-
10, when Stardust was bombarded by photons from a solar flare
some 100,000 times larger than normal. The energy overwhelmed
the navigation camera, which is used to help pilot Stardust by
focusing on stars and planets and then comparing that image
with a star map in its memory. Normally the camera sees only a
few stars at a time, but in this case its electronic imaging
chip interpreted the solar flare’s photon flashes as thousands
of stars. The spacecraft went into safe mode, with its solar
panels pointed toward the sun. Eventually the photon flashes
faded and ground controllers were able to reset the star
camera.

There also has been some intriguing science. The Cometary
and Interstellar Dust Analyzer, operated by Germany’s Max-
Planck-Institut f¸r Extraterrestrische Physik, came up with an
unexpected analysis of interstellar particles the spacecraft
encountered.

“The surprise is that they were high-molecular-weight
materials, probably large organic molecules,” Brownlee said.
“It would be something analogous to tar or coal.”

Stardust was launched from Cape Canaveral, Fla., on Feb.
7, 1999, and this is its first return to its home planet. The
next encounter with Earth comes in January 2006, when the
return capsule will separate from the spacecraft and parachute
into the Utah desert. The capsule will carry comet material
and interstellar dust particles, captured in a wispy material
called aerogel. The particles will be sent to laboratories
around the world for analysis. It is expected the samples will
yield clues to the origins of the solar system and possibly
life itself.

The spacecraft’s encounter with the comet will occur just
outside the orbit of Mars, 242 million miles from Earth. There
is a possibility that Stardust may be visible from the west
coast of the United States and the Pacific Ocean just after
the flyby, for observers using sophisticated telescopes with
CCD detectors.

Mission collaborators are the NASA, JPL, the University
of Washington, and Lockheed Martin Astronautics in Denver.
Other key team members include The Boeing Co., The Max-Planck-
Institut, NASA Ames Research Center and the University of
Chicago. The Stardust mission is managed by JPL for NASA’s
Office of Space Science. JPL is a division of the California
Institute of Technology in Pasadena.

For more information on the mission, see
http://stardust.jpl.nasa.gov