Dwayne C. Brown
Headquarters, Washington, D.C.                                                 
March 14, 1994
(Phone:  202/358-0547)

Michael Finneran    
Goddard Space Flight Center, Greenbelt, Md. 
(Phone:  301/286-5565)


RELEASE:  94-42

NASA OPENS GROUND STATION FOR COMPTON GAMMA-RAY OBSERVATORY

   NASA has opened a new, remote ground station in Tidbinbilla, 
Australia, called the GRO Remote Terminal System, to receive 
scientific data from the Compton Gamma-Ray Observatory (GRO) via a 
Tracking and Data Relay Satellite (TDRS) that was moved into 
position over the Indian Ocean.

   The decision to build the ground station and devote a TDRS to 
the Compton GRO came after the observatory's tape recorders 
failed, restricting transmission of scientific data to real time 
only.  Since Compton was compatible with TDRS, this ground station 
option was feasible.  An on-orbit repair of Compton GRO was an 
alternative, but would have been much more costly. 

   "While the new ground station is devoted to Compton at this 
time, it has the potential for use by other Earth-orbital 
spacecraft.  The TDRS system was designed to operate with all the 
TDRS spacecraft in view of a single ground station.  As a result, 
coverage could not be provided in a small region on Earth -- the 
so-called Zone of Exclusion over the Indian Ocean.  

   "With activation of this ground facility, the TDRS system can, 
for the first time, provide global coverage," said Charles Force, 
Associate Administrator, Office of Space Communications, NASA 
Headquarters, Washington, D.C.

   Work on the station was completed in a relatively short time 
and within its $12 million budget.  Work began in September 1992 
to implement a remotely controlled terminal at an existing NASA 
site and was a cooperative effort between the Australian Space 
Office and NASA


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   "We're very pleased that this project came in on budget and on 
time and that we are able to collect additional significant data 
from Compton in a cost-effective manner," said Frank Stocklin, 
Head, Radio and Frequency Interface and Mission Analysis Section, 
Goddard Space Flight Center (GSFC), Greenbelt, Md. 

   With GRO tape recorders not working, the observatory had been 
able to relay only slightly more than half of the science data it 
collected, because it could not point at a TDRS at all times.  
While coverage had been about 65 percent of each orbit, scientists 
could not collect that percentage of data because Compton's 
instruments had to be turned off during the part of the orbit when 
the spacecraft passed through the background radiation caused by 
the South Atlantic Anomaly.

   "That had represented a significant obstacle to the scientific 
teams, even though we have been able to collect more science than 
expected," said Goddard's Dr. Neil Gehrels, Compton Project 
Scientist.  "Now with the ground station and the TDRS, we're back 
where we want to be."

   With a TDRS devoted to Compton, scientists will be able to 
collect about 30 percent more science.  In addition, engineers 
will be able to keep better tabs on the health of the $500-million 
observatory, launched from the Space Shuttle Atlantis (STS-37) on 
April 5, 1991.

   "It's difficult to place a dollar value on the additional 
science data obtained in this effort," Stocklin said, "but the 
restoration of data recovery capability is similar to that done 
for the Hubble Space Telescope and marks the second successful 
recovery of a major NASA observatory."

   TDRSs receive data from Earth-orbiting satellites and 
re-transmits the data to a ground terminal in White Sands, N.M.  
Data from the Compton will be relayed from TDRS-1 to Tidbinbilla 
to an Intelsat satellite to a West Coast location and then routed 
to White Sands.  Data then will be distributed to scientists 
around the world.  Control of TDRS-1 and this highly automated 
ground terminal remains at White Sands, N.M., marking the first 
time NASA is controlling an out-of-view TDRS from that location.

   Launched in 1983, TDRS-1 was the first satellite in the TDRS 
system and was operating beyond the end of its design life of 8 
years when it was moved over the Indian Ocean.  TDRS-1 had been 
located at 171 degrees west longitude over the Pacific.  It is now 
at 85 degrees east longitude, in view of the Tidbinbilla ground 
station. 

   "In its current use, TDRS-1's useful life may be extended to 
the end of the decade and perhaps beyond," Stocklin said.
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