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 Listen to this story (requires RealPlayer)
 November
22, 2000 -- Quick-thinking engineers and scientists helped
NASA's Stardust spacecraft
survive a storm of high-energy particles from the Sun after a
recent solar flare.
Stardust -- a NASA mission to return samples from comet P/Wild
2 -- was only 1.4 AU (130 million miles) from the Sun on Nov.
8th when a powerful solar flare erupted. Engineers from the Stardust
team were a little worried, since they had heard the resulting
radiation storm was the fourth largest since 1976. A cloud of
high-energy particles was heading for Earth and for Stardust.
Right: These Solar
and Heliospheric Observatory coronagraph images, captured
Nov 8-9, 2000, suddenly became cloudy when high-energy particles
from the Sun peppered the spacecraft's CCD camera following a
powerful solar flare. Star cameras on Stardust were similarly
fogged, sending that spacecraft into standby mode.
Their fears came to pass the next day when a stream of high-energy
protons hit the spacecraft. Stardust's two star cameras, which
it uses to control the spacecraft's orientation, were peppered
with radiation. Protons from the solar wind electrified pixels
in the star cameras, producing dots that the camera interpreted
as stars. The 12 brightest dots, the ones the spacecraft relied
on to point its way, were electrified pixels, which showed up
as false stars. Hundreds of these star-like specks inundated
the star camera's field of view, which meant it could not recognize
its attitude in space.
Above: (Left) A normal Stardust star camera image, captured
after the radiation storm had subsided. (Right) A "snowy"
image captured during the storm. The many speckles are caused
by high energy particles striking the spacecraft's camera elements.
[more
information]
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 using two different sets
of cameras. But the images repeatedly produced hundreds of bogus
stars.
The flight team didn't hear from Stardust when they tried
to communicate with it the morning after the solar flare. They
deduced that the flare had caused Stardust to go into standby
mode, and they knew that meant the spacecraft would send a signal
within 24 hours.
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Blast into the Past
 You
can re-live the early-November radiation storm (vicariously)
by visiting these archival pages from SpaceWeather.com:
- Nov. 9, 2000: The flux of high-energy protons near Earth soars
to ~100,000 times greater than normal following a powerful solar
flare.
- Nov. 10, 2000: A coronal mass ejection unleashed by a powerful
solar eruption on Nov. 8th hit Earth's magnetosphere today, only
31 hours after leaving the Sun. Its earlier-than-expected arrival
sparked a G3-class geomagnetic storm.
- Nov. 11, 2000: Aurora Warning: Our planet is inside a high-velocity
solar wind stream with peak speeds exceeding 800 km/s.
- Nov. 12, 2000: Radiation counts finally declined below storm
levels.
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By Saturday, November 11th, the flight team was in contact
with the spacecraft again. They reset the first star camera and
turned it back on. While they inspected the camera's stored images,
the engineers used another method of orienting the spacecraft,
called inertial measurement units. The last images the camera
took before the spacecraft reset itself were peppered with hundreds
of false stars. 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.
Finally, on Monday Nov. 13, the Stardust flight team commanded
the spacecraft to leave safe mode. The star camera started working
again, 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 radiation storm 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.
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Stardust was launched on Feb. 7, 1999 from Cape Canaveral, FL.
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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