NASA Space Science News
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
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.
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| 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. |
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. It repeatedly turned up hundreds of bogus star-like
images. It also switched between electronics systems on either
side of the spacecraft.
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.
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.
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 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.
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