PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF.  91109. TELEPHONE (818) 354-5011

Contact:  Franklin O'Donnell

FOR IMMEDIATE RELEASE                            October 20, 1995

GALILEO SPACECRAFT TAPE RECORDER TO BE TESTED

     Engineers will transmit a series of commands to NASA's 
Jupiter-bound Galileo spacecraft today in an effort to assess the 
state of its balky onboard tape recorder.

     The flight team, meanwhile, was buoyed by a preliminary 
assessment from Galileo's science team reporting that at least 
half the mission's original scientific objectives could be 
obtained in the event the tape recorder is found to be unusable.

     The tape recorder, which is mainly used for onboard storage 
of imaging and spectral data from Galileo's instruments, 
apparently malfunctioned October 11.   The problem was detected 
shortly after Galileo, due to reach Jupiter on December 7, took 
three consecutive images through different filters to produce a 
color image of Jupiter and its major moons.  The tape recorder 
failed to stop rewinding as expected after recording the imaging 
data.  Commands were sent to halt the tape recorder, which has 
since remained in a standby mode.

     "For the past week, we've looked in detail both at data from 
the spacecraft and from an identical tape recorder in the testbed 
laboratory here," said Galileo Project Manager William J. O'Neil 
at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.  "We've 
identified a number of both mechanical and electrical failures in 
the tape recorder system that could explain this problem.  Our 
efforts today and in coming days will help us determine whether 
the tape recorder can be restored to operation."

     Commands will be radioed to the spacecraft this afternoon to 
play back a small sample of data stored on the tape recorder.  
The tape-recorded data, along with engineering data reporting on 
the recorder's performance, first will be stored in memory 
located in Galileo's central data subsystem, then transmitted to 
the receiving stations of NASA's Deep Space Network this evening.  
     
     "By early next week, we will be in a position to report the 
results of our efforts to operate the tape recorder," said 
O'Neil.   "Successful commanding of the device would still mean 
additional assessment and troubleshooting."  Work concurrently 
continues on a backup plan to preserve the return of imaging and 
spectral data in the event the tape recorder cannot be used, he 
added.

     Galileo's tape recorder and the spacecraft's guidance 
control computer were called into service as data compression and 
storage links in a sophisticated alternative method devised to 
maximize data return from Jupiter after Galileo's main high-gain 
antenna failed to open properly.   Loss of the high-gain antenna 
meant that all spacecraft communications must be conducted at 
much lower data rates through a low-gain antenna.

     New techniques have been developed to edit, compress and 
encode Galileo's data, including images, in the spacecraft's 
computers, then store that data for playback to Earth.  
Additionally, new hardware and software changes at ground 
receiving stations have been installed to further increase the 
amount of data transmitted from Galileo's low-gain antenna. 

     Project Scientist Dr. Torrence Johnson of JPL reported that 
at least 50 percent of the mission's original science objectives 
could still be achieved if the tape recorder is found not to be 
working.

     "The impact of a possible loss of the tape recorder is not 
as bad as people assumed when we first heard about the problem," 
said Johnson.  "Even without the tape recorder, we have an 
exciting mission that allows us to address all our primary 
objectives.  Although the total number of pictures and spectra we 
receive would be lower than with a tape recorder, we would still 
have enough to do the job."

     According to Johnson, among the mission's three major areas 
of science investigations, it is the data return from remote 
sensing instruments such as cameras and spectrometers that would 
be impacted most by loss of the tape recorder.  Data from these 
instruments can be saved by re-routing them directly to memory 
areas in the flight computer.

     "The mission will still study all aspects of the Jovian 
system -- Jupiter's atmosphere, its moons and its magnetic 
environment -- and we plan to make a majority of the scientific 
measurements that had already been planned," said Johnson.

     One hundred percent of the atmospheric probe's science 
objectives can be achieved without the tape recorder, in addition 
to all of the Galileo orbiter's survey of the Jovian magnetic and 
charged-particle environment, Johnson said.

     "The principal loss of data, if the tape recorder is not 
usable, would be the number of images and other high-rate 
spectral data that could be returned by the spacecraft," said 
Johnson.  Galileo spacecraft and software engineers, however, are 
devising new backup methods to store imaging and spectral data in 
available memory areas within the spacecraft's central data 
processor.  

     Preliminary assessments indicate that at least 150 to 300 
high-resolution images of the Galilean moons of Jupiter and 
additional hundreds of Jupiter and Io volcanoes-monitoring images 
could be returned over the course of Galileo's two-year orbital 
tour.

     The Galileo mission consists of an orbiter spacecraft and an 
atmospheric probe, which was released from the orbiter in July.  
The probe will parachute into and directly sample Jupiter's 
atmosphere on December 7.  Its data will be radioed to the 
Galileo orbiter overhead.  Also on December 7, shortly after the 
completion of the probe's mission, the Galileo orbiter's rocket 
engine will fire to brake the spacecraft into orbit around 
Jupiter, beginning a two-year detailed study of the Jovian 
system.

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10/20/95 MBM
#9570