Michael Braukus
Headquarters, Washington, D.C.                                                                     
June 14, 1991
(Phone:  202/453-1549 )

John J. Loughlin II
Goddard Space Flight Center, Greenbelt, Md.
(Phone:  301/286-5565)

RELEASE:  91-91

GRO SPACECRAFT GRABS FIRST TARGET OF OPPORTUNITY


   NASA's Gamma Ray Observatory (GRO) was maneuvered to point 
at its first scientific target of opportunity, the sun, on 
Friday, June 7, 1991, at 7:45 p.m. EDT.  The 17-ton 
observatory was repositioned by controllers at the Goddard 
Space Flight Center, Greenbelt, Md., to gather data from two 
X-class solar flares that occurred on Saturday and Monday 
nights.

   The X-class is the largest and most powerful type of solar 
flare.  Solar flares are temporary outbursts of intense solar 
radiation that have been observed blasting hot loops of gas 
more than 430,000 miles into space.  These high energy 
outbursts have been known to disrupt the Earth's magnetic 
field and cause interference with communications equipment and 
electrical power distribution systems.

   While much is known about the composition and magnitude of 
solar flares, surprisingly little is known about the 
thermonuclear processes of these dynamic solar phenomena.  The 
decision to observe the sun was made by project scientists and 
engineers about noon Friday.  The flight operations team was 
able to complete the maneuver in about nine hours.  The normal 
time for this type of maneuver is about 36 hours.  The fast 
action of the team gained 23 additional hours of observing 
time, allowing GRO to capture data on Saturday's flare which 
otherwise would have been lost, officials said.  

   All four of GRO's instrument teams report that they are 
receiving good data on the solar activity, the most sensitive 
high-energy measurements ever of the sun.  Project Scientist 
Dr. Neil Gehrels will decide this week whether to continue 
solar observations or to move on to the next scheduled target, 
Supernova 1991 T, on Thursday, June 14.

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   The repositioning of GRO demonstrates not only the 
flexibility of the spacecraft but also the efficiency of the 
planned target of opportunity program, officials explained.  
This program, they said, allows the scientific community to 
position the spacecraft toward significant celestial events 
that cannot be predicted.  In addition to solar activity, 
other examples of this type of event include supernova or 
other unplanned gamma-ray events.

   Science operations for GRO began Thursday, May 16, 1991, 
with the observatory pointed toward a pulsar in the Crab 
Nebula.  Science operation plans call for a full-sky survey 
expected to last 15 months.  GRO was launched on April 5, 
1991, aboard the Space Shuttle Atlantis and deployed on April 
7, 1991.  Its mission is to search for highly energetic gamma 
rays emitted by some of the most violent processes in the 
universe.

   GRO orbits Earth at an altitude of 287 x 280 statute miles.  
GRO is managed and operated by the Goddard Space Flight Center 
for NASA's Office of Space Science and Applications.

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