MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Jane Platt (818) 354-0880
FOR IMMEDIATE RELEASE
May 5, 1999
GALILEO PROVES OLD SPACECRAFT CAN LEARN NEW TRICKS
NASA's Galileo spacecraft team members are all smiles after
Galileo proved to be a star pupil by successfully demonstrating
specially designed, newly installed software and saving this
morning's flyby of Jupiter's pockmarked moon Callisto.
During previous flybys of Jupiter's moons, a recurring
electrical glitch caused the spacecraft computer to reset and
enter "safing" mode, shutting down all non-essential functions
until ground controllers could restore normal operations.
The Galileo team pooled engineering and problem-solving
talents to develop special software, known as a "bus reset
patch." The name refers to Galileo's "data bus," which transfers
information to various parts of the spacecraft. The software was
designed to boost Galileo's I.Q. by teaching it to recognize
symptoms of the glitch and correct the problem itself, without
entering safing mode.
The spacecraft was put to the test twice on Monday, May 3,
when the glitch popped up as Galileo was approaching Callisto.
Galileo quickly diagnosed the problem, determined there was no
threat to spacecraft health, and decided for itself not to enter
safing mode. This allowed all spacecraft and scientific
functions to continue uninterrupted, with Galileo snapping
pictures and gathering observations from an altitude as close as
1,322 kilometers (821 miles) above Callisto.
"Galileo proved it's an 'A' student," said Project Manager
Jim Erickson. "This is an example of our efforts at JPL to make
the spacecraft more independent and better able to evaluate and
deal with problems without intervention from ground controllers."
"We're so thrilled that our efforts paid off and Galileo
performed as we had hoped," said Nagin Cox, who helps oversee the
team of current and former Galileo personnel that developed the
new software patch.
In an unrelated occurrence during this morning's Callisto
flyby, the pointing control for the scan platform, which aims
Galileo toward observation targets, switched on its own from a
very accurate gyro-controlled system to a less accurate backup
mode that uses the star scanner without gyros.
Nonetheless, the spacecraft continued to record its
observations, but observations taken by an instrument called the
near infrared mapping spectrometer may be less sharp than
planned. Preliminary analysis shows this anomaly occurred just
after Galileo's closest approach to Callisto, or 7:56 a.m.
Pacific Daylight Time, the time the signal was received on Earth.
The Galileo team is investigating this anomaly, and preliminary
analysis shows it may be related to previous gyro anomalies.
Galileo has been orbiting Jupiter and its moons since
December 1995. Its original, two-year mission ended in December
1997, and the spacecraft is currently more than halfway through a
two-year extended tour, called Galileo Europa Mission.
JPL manages the Galileo mission for NASA's Office of Space
Science, Washington, DC. JPL is a division of the California
Institute of Technology, Pasadena, CA.