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                           July 24, 1995

CRITICAL GALILEO ENGINE FIRING SCHEDULED

     NASA's Galileo spacecraft, now homing in on Jupiter, is 
scheduled to fire its main rocket engine in a critical maneuver 
early Thursday, July 27, that will put it on course for entry 
into orbit around the giant planet later this year.

     The engine firing for the so-called "orbiter deflection 
maneuver" will begin at 12:38 a.m. Pacific Daylight Time and last 
5 minutes, 6 seconds.  (This is the time when Galileo's radio 
signal reporting the event is received on Earth.  The signal 
travels at the speed of light, and one-way light time from 
Galileo to Earth will be about 38 minutes the day of the 
maneuver.)

     A press briefing originating from NASA's Jet Propulsion 
Laboratory to discuss the Galileo orbiter deflection maneuver, 
the recent release of Galileo's Jupiter atmospheric probe, and 
the major scientific goals of the mission, will be carried live 
on NASA Television at 10 a.m. PDT on July 27.
     
      A two-second firing or "wake-up burn" of the main rocket 
engine was successfully completed early this morning.  The short 
burn allowed flight controllers to check out the overall health 
of the propulsion system in preparation for the longer engine 
burn Thursday.

     The upcoming rocket firing follows the successful targeting 
and release of Galileo's Jupiter atmospheric probe earlier this 
month.  The atmospheric probe, with no propulsion or guidance 
system of its own, will continue to freefall to Jupiter and enter 
the planet's atmosphere on December 7.  

     As planned, Galileo is currently on a course that without 
further action would send the spacecraft along the same Jupiter-
impact trajectory that the atmospheric probe is flying.  This 
week's engine firing, however, will deflect the spacecraft off 
that trajectory and put it on course for its close flyby of  
Jupiter's volcanic moon Io also occurring on December 7.

     "With the completion of this maneuver, we're looking forward 
to the culmination of three weeks of intensive work in targeting 
the spacecraft for the beginning of its tour of Jupiter," said 
Galileo Project Manager William O'Neil of NASA's Jet Propulsion 
Laboratory.  "Everything is going perfectly."

     The main engine could not be tested or fired prior to 
release of the atmospheric probe because the probe was mounted in 
front of the engine nozzle. Thursday's firing also serves as a 
demonstration of engine operability for an even larger firing of 
the same engine during the December 7 maneuver that will brake 
the spacecraft and allow it to be captured into Jupiter orbit.  
That engine firing, called Jupiter orbit insertion, will be the 
largest such maneuver of Galileo mission.
  
     The orbiter deflection maneuver will provide a change in the 
spacecraft's velocity of 62.5 meters per second (about 140 miles 
per hour). By comparison, the Jupiter orbit entry maneuver will 
expend 377 kg (831 lbs) of propellant  and result in a velocity 
change of 643 meters per second (1,438 miles per hour).

     Galileo was launched in October 1989 aboard Space Shuttle 
Atlantis from NASA's Kennedy Space Center, FL.  Galileo's Jupiter 
atmospheric probe is managed by NASA's Ames Research Center, 
Mountain View, CA.  The Galileo spacecraft was built and the 
overall mission is managed by JPL.

                             #####

[NOTE TO EDITORS:  A new backgrounder, "Galileo's New 
Telecommunications Strategy," explains the software and hardware 
changes that are being implemented to allow Galileo to achieve 70 
percent of its original science objectives while using only its 
low-gain antenna.] 

7/21/95 MBM
#9555