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 .