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New Information From SOHO Increases Chances For Recovery

Don Savage
Headquarters, Washington, DC                August  11, 1998
(Phone:  202/358-1727)

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:  98-149

NEW INFORMATION FROM SOHO INCREASES CHANCES FOR RECOVERY

       The dormant Solar and Heliospheric Observatory (SOHO) 
spacecraft has sent temperature and electrical data to ground 
controllers, information which could help in the satellite's 
recovery. The SOHO Recovery Team is working to recharge the 
spacecraft's batteries, which in turn will allow the team to 
assess the spacecraft's overall health and condition of the 
scientific instruments.

     The SOHO data was received Aug. 8, six days after the 
spacecraft's first signal since the end of June, at NASA's 
Goddard Space Flight Center, Greenbelt, MD.

       "This is the best news I've heard since we lost 
contact with SOHO," said Roger Bonnet, Director of Science 
for the European Space Agency (ESA), NASA's partner in the 
mission.  "I never gave up hope of some recovery of this 
fantastic mission.  We should just hope that the damage 
sustained by SOHO's enforced period of deep freeze does not 
affect the scientific payload too much."

       Following analysis of the expected onboard conditions 
by engineers from ESA and Matra Marconi Space, the 
spacecraft's builders, commands were sent through the NASA 
Deep Space Network station at Goldstone, CA.  These sequences 
were designed to divert the available solar array power into 
a partial charging of one of the onboard batteries.

       After 10 hours of charging, the telemetry was 
commanded on and seven full sets of data about the onboard 
status were received, including information on temperatures 
and voltages for payload instruments.  After one minute, 
ground controllers switched off the telemetry to preserve 
onboard resources.

     Because of the spacecraft's orientation, some 
temperatures are colder than normal, and some are hotter than 
normal, as expected. The instruments' condition will not be 
known with certainty until attempts are made to activate them 
at the end of the recovery sequence.  The hydrazine fuel is 
likely to be partially frozen.

     Data on voltages and currents in individual units 
indicated one of the two batteries on board the spacecraft is 
almost fully charged. Attempts to recharge the second battery 
are underway.

     With the battery-charging technique proven successful, 
the team has requested a full 24-hour coverage of SOHO to 
attempt a more complete charging.  The Deep Space Network has 
accepted this request on an emergency basis and will give it 
priority over other scheduled network activities.

     "I am truly satisfied with the information the data we 
acquired gives us," said ESA's Francis Vanderbussche, who is 
in charge of the SOHO Recovery Team at Goddard. "Conditions 
onboard are as good as we expected them to be."

     The team is working on the next series of procedures, 
which will try to thaw the onboard hydrazine fuel, currently 
at zero degrees Celsius. Thawing the fuel will allow 
controllers to re-establish control of the spacecraft.  The 
thawing will be attempted later this week after both 
batteries are fully charged.

      The delicate recovery activities are being directed by 
the ESA SOHO project team from the NASA Operation Center at Goddard.

       SOHO completed its nominal two year mission in April 
1998.  The spacecraft has already achieved spectacular 
results concerning the dynamics of the solar interior and has 
given a comprehensive view of the solar corona.  Its mission 
had recently been extended to 2003 to cover the upcoming 
period of maximum solar activity expected to peak in 2001.

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

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

-end-

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