Paula Cleggett-Haleim
Headquarters, Washington, D.C.                                                        
July 31, 1992
(Phone:  202/358-1547)

Jim Elliott
Goddard Space Flight Center
(Phone:  301/286-6256)


RELEASE:  92-127

HST TO RESUME NORMAL OPERATION AFTER BRIEF DELAY


     While recovering from a benign standby condition, which began 
late Wednesday night, NASA's Hubble Space Telescope (HST) entered 
a deeper safe condition on Thursday night.  A plan for resuming 
normal operations will be developed over the next several days.

     Currently, the cause of both conditions, or safe modes, are 
understood and can be fixed promptly.  Spacecraft managers, 
however, are now analyzing all related data before sending HST new 
computer commands that would resume science data collection.  

     The project director, Joe Rothenberg, said, "The system 
operated exactly as designed."

     Safe modes are a capability built into all NASA spacecraft.  
They are invaluable "safety nets" to protect against spacecraft 
anomalies caused by on-orbit hardware problems or erroneous 
commands sent from the ground.

     On Wednesday at 11:49 p.m., EDT, HST went into a standby 
condition, called an "inertial hold mode."  This condition was 
caused by some erroneous data contained in a standard ephemeris 
uplink.  The ephemeris tells where the spacecraft will be at 
certain time.  Such uplinks occur routinely to update stored data 
contained in the HST flight computer.

     Hubble's safety checking system detected the error and 
entered this hold condition until spacecraft controllers could fix 
the problem.  The recovery process from this type of hold should 
take about 36 hours.  

                          - more -- 2 -

     While recovering from that inertial hold, another problem 
occurred that caused HST to enter a deeper, "hardware safe mode."  
Revised software loaded on board Hubble's flight computer in May 
1992 contained an error, which caused it to enter this type of 
safe mode.

     Currently, spacecraft controllers are further analyzing and 
testing spacecraft data to develop an appropriate recovery plan.

                             - end -