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.