From: Brian D Williams (talon57@well.com)
Date: Wed Nov 22 2000 - 08:39:43 MST
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Martha Heil Jet Propulsion Laboratory (818)354-0850
Bob Roseth University of Washington (206) 543-2580
FOR IMMEDIATE RELEASE November 21, 2000
STARDUST SPACECRAFT ENCOUNTERS SOLAR FLARE
Quick-thinking NASA engineers and scientists helped the
Stardust spacecraft survive a close encounter with a storm of
high-energy particles from the Sun after a recent solar flare.
Stardust, a NASA mission to return samples of a comet,
was only 1.4 AU (130 million miles) from the Sun on the
afternoon of Wed., Nov. 9. It was flying at about 20,000
kilometers per hour (over 12,000 miles per hour).
Engineers from the Stardust team were a little worried,
since they had heard that the fourth largest solar flare since
1976 was heading toward Earth. This monster cloud of
energized particles was 100,000 times more intense than usual,
and it was heading toward Stardust.
The engineers' fears came to pass in the middle of the
night, when the solar wind's stream of high-energy protons hit
the spacecraft. Its two star cameras, which it uses to control
the spacecraft's orientation, got a large dose of energy.
Protons from the solar wind electrified pixels in the star
cameras, producing dots that the camera interpreted as stars.
The 12 brightest images, the ones the spacecraft relied on to
point its way, were electrified pixels, which showed up as
false stars. Hundreds of these star-like images inundated the
star camera's field of view, which meant it could not
recognize its attitude in space.
The spacecraft did the safest thing it could it went
into standby mode, turning its solar panels toward the Sun and
waiting for communication from Earth. While it was waiting,
the spacecraft tried again to determine its attitude by using
two different sets of cameras. It repeatedly turned up
hundreds of bogus star-like images. It also switched between
electronics systems on either side of the spacecraft. So
Stardust began to slowly rotate in place, pointing its solar
panels at the Sun.
The flight team didn't hear from Stardust when they tried
to communicate with it the next morning. They deduced that the
solar flare had caused it to go into standby mode, and they
knew that meant the spacecraft would send a signal within 24
hours.
Scientists confirmed their theory when they reviewed data
from the spacecraft that verified that the problems had begun
when the solar flare occurred. The influence of the proton
stream would diminish over the next few days but still posed
some danger, so the team left the spacecraft in standby mode
until the threat passed.
On Saturday, November 11th, the flight team reset the
first star camera and turned it back on. They used another
method of orienting the spacecraft, called inertial measuring
units, while they inspected the cameras. Engineers retrieved
the last images the camera took before the spacecraft reset
itself and saw hundreds of false star images. Although the
camera normally uses a circular area in the middle to take
pictures, the proton hits were so strong they even penetrated
parts of the camera usually hidden from the light.
On Monday, the Stardust flight team commanded the
spacecraft to leave its safe mode. The star camera was back on
the job, controlling the orientation of the spacecraft
perfectly. The engineers retrieved more data from Stardust to
ensure the entire spacecraft had not been affected by the
solar flare.
An image taken days after the solar flare subsided shows
that the camera had completely recovered from the proton hits.
All the bright objects in the picture can be identified as
stars, Jupiter or Saturn.
Stardust was launched onto a perfect flight path on Feb.
7, 1999 from Cape Canaveral, Fla. The spacecraft is headed for
an encounter with Comet P/Wild 2 in 2004. Stardust's mission
is to collect samples of dust flying off the comet nucleus,
and to collect interstellar particles flowing through our
solar system. Stardust will fly back toward Earth in 2006 to
drop off the samples in a parachute-equipped return capsule.
Stardust, part of NASA's Discovery Program of low-cost, highly
focused science missions, is managed by JPL for NASA's Office
of Space Science, Washington, D.C. JPL is a division of the
California Institute of Technology. For more information on the
Stardust mission and images from the recent encounter, go to
http://stardust.jpl.nasa.gov .
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11/21/00 MJH
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