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SOHO Spacecraft Located With Ground-Based Radar


Douglas Isbell 
Headquarters, Washington, DC                  July 27, 1998
(Phone:  202/358-1753)

William Steigerwald
Goddard Space Flight Center, Greenbelt, MD 
(Phone:  301/286-5017)

Franco Bonacina
European Space Agency Headquarters, Paris, France 
(Phone:  33-1-5369-7713)

RELEASE:  98-135

SOHO SPACECRAFT LOCATED WITH GROUND-BASED RADAR 

     Ground-based radio telescopes have been able to detect the 
Solar and Heliospheric Observatory (SOHO) spacecraft and have 
found it rotating slowly near its original position in space, a 
potentially important step toward possible recovery of direct 
communications with the spacecraft. 

     Radio contact with SOHO, a joint mission of the European 
Space Agency (ESA) and NASA, was interrupted on June 24, an event 
under review by a joint ESA/NASA investigation board. 

     With the encouragement of Dr. Alan Kiplinger of the National 
Oceanic and Atmospheric Administration's Space Environment Center 
in Boulder, CO, researchers at the U.S. National Astronomy and 
Ionosphere Center (NAIC) in Arecibo, Puerto Rico, used the 
facility's 305-meter (990-foot) diameter radio telescope to 
transmit a signal toward SOHO on July 23. The 70-meter dish of 
NASA's Deep Space Network in Goldstone, CA, acted as a receiver, 
locating the spacecraft's echo and tracking it using radar 
techniques for more than an hour. 

     Preliminary analysis of the radar data, which is ongoing, 
indicates that SOHO is still in its nominal halo orbit near the 
so-called "L-1" Lagrangian point in space, (a gravitationally 
stable vantage point 1.5 million kilometers ahead of the Earth) 
and is turning slowly at a rate of roughly one revolution per 
minute.  Staff members of NAIC and the Deep Space Network, in 
close cooperation with ESA and NASA, are continuing to analyze the 
radar data to extract more precise information on SOHO's location 
and motion, which in turn could help in future recovery efforts, 
as SOHO's solar panels turn toward the Sun. 

     ESA and NASA engineers also are continuing their efforts to 
re-establish radio data communication with the spacecraft, 
encouraged by the radar measurement of a slow spin rate, which 
suggests minimal structural damage has occurred. 

     The NAIC team was led by Dr. Donald Campbell.  The NAIC is 
operated by Cornell University, Ithaca, NY, under a cooperative 
agreement with the U.S. National Science Foundation, Washington, 
DC.  The Deep Space Network is managed by NASA's Jet Propulsion 
Laboratory, Pasadena, CA. 

     More information on SOHO, including mission status reports, 
is available on the Internet at the new ESA science website at:  

                    http://sci.esa.int
                           or at 
              http://sohowww.nascom.nasa.gov/ 


                           -end-


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