Douglas Isbell
Headquarters, Washington, DC           October 26, 1995
(Phone:  202/358-1753)

Franklin O'Donnell
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-5011)

RELEASE:  95-193

GALILEO ON TRACK AFTER TAPE RECORDER RECOVERY

     NASA's Galileo spacecraft is proceeding toward its
December rendezvous with Jupiter, with spacecraft engineers
greatly relieved at last weekend's test results showing
that its onboard tape recorder remains functional.

     On Tuesday, Oct. 24, a revised spacecraft command
sequence radioed to Galileo began issuing instructions
ordering the spacecraft to resume regular readouts of data
from the memories of several science instruments.  The
spacecraft also returned to normal housekeeping duties,
executing scheduled engineering operations such as flushing
of rocket thrusters.

     The new command sequence replaced the one ground
controllers stopped after the Oct. 11 tape recorder
problem, in which the data tape recorder failed to cease
rewinding after recording an image of Jupiter.

     The tape recorder had remained in a standby mode until
Friday, Oct. 20, when it was tested and proved still
operational.  Detailed study of engineering data from the
spacecraft indicates that the tape recorder can be
unreliable under some operating conditions, project
officials said.  However, the problem appears to be
manageable, and should not jeopardize return of the nearly
2,000 images of Jupiter and its moons that are to be stored
on the recorder for playback over the course of Galileo's
two-year tour in orbit around the planet.

     Tuesday's work on the spacecraft included commands for
the tape recorder to wind 25 extra times around a section
of tape possibly weakened when the recorder was stuck in
rewind mode with the tape immobilized for about 15 hours.
Due to uncertainty about its condition, spacecraft
engineers have declared that this portion near the end of
the tape reel is "off-limits" for future data recording.
The extra tape wound over it secures that area of tape,
eliminating any stresses that could tear the tape at this
potential weak spot.  Unfortunately, the approach image of
Jupiter that Galileo took Oct. 11 is stored on the portion
of tape that is now unavailable, and it will not be played back.

     With only weeks to go before Galileo's Dec. 7 arrival
at Jupiter, project engineers are busy analyzing the tape
recorder's condition to fully understand its capabilities
and weaknesses.  "We need to be sure we fully understand
the system that we have now," said Galileo Project Manager
William J. O'Neil.

     The tape recorder is a key link in techniques
developed to compensate for the loss of use of Galileo's
high-gain antenna, which is stuck in a partially open
position.  Data must now be sent at a much lower data rate
through Galileo's low-gain antenna.  The tape recorder is
to be used to store information, particularly imaging data,
until it can be compressed and edited by spacecraft
computers and radioed back to Earth.

     Since the tape recorder incident, Galileo project
officials have decided to not take pictures of Io and
Europa on the day the spacecraft arrives at Jupiter.
Instead, they will devote the tape recorder that day to
gathering data from Galileo's Jupiter atmospheric probe as
the cone-shaped probe descends into the giant planet's
swirling atmosphere over the course of its 75-minute
mission. During that time, the probe will collect the
first-ever direct measurements of the chemical makeup and
weather of the solar system's largest planet.

     "Our priorities are clear," said O'Neil.  "We have to
get all the probe data."  Other flybys of the Jovian moons,
including frequent "volcano watch" monitoring of Io, occur
throughout the mission, giving ample opportunity to collect
data on all the moons.  Late in the mission, O'Neil said, a
close flyby of Io might be made to make up for the Io flyby
data that will be sacrificed on Dec. 7.

                    -end-

NASA press releases and other information are available
automatically by sending an Internet electronic mail
message to domo@hq.nasa.gov.  In the body of the message
(not the subject line) users should type the words
"subscribe press-release" (no quotes).  The system will
reply with a confirmation via E-mail of each subscription.
A second automatic message will include additional
information on the service.  Questions should be directed
to (202) 358-4043.