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Science & Exploration

N° 29–1998: SOHO maintains contact with ground control

6 August 1998

Having succeeded in receiving a response from the SOHO spacecraft late on Monday night (3 August 1998), controllers at NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, USA have continued to coax information from the spacecraft concerning its on-board status.

The spacecraft has responded so far to the attempts to activate the on-board telemetry data system only by sending a simple carrier signal with bursts of 10 second duration. This signal has been tracked consistently since the satellite was contacted on Monday night and has been received at ESA ground stations in Perth, Australia and Redu, Belgium, as well as by NASA Deep Space Network stations worldwide.

For the time being, the bursts of carrier signal are too short to allow the sensitive ground station receivers to 'lock-on' to the signal and ESA engineers are currently assessing the steps necessary to obtain a more continuous signal from the spacecraft. The intermittent nature of the signal is caused by the cyclic variation of the on-board power supply as the solar arrays are shadowed due to the spacecraft's unintentional spin motion. Attempts will be made to charge the on-board batteries sufficiently to ensure that more continuous power availability to the spacecraft transmitter system.

"Recovery will be a slow and careful operation" said ESA's Head of Science Projects, John Credland, "The main thing is that the spacecraft is now responding to us and we will take one step at a time to bring the spacecraft into a more favourable attitude before assessing any damage which may have been caused by its six-week unforeseen hibernation".

Radio contact with SOHO, a joint mission of the European Space Agency and NASA, was interrupted on 25 June 1998. The delicate recovery activities are being directed by the ESA SOHO project team from the NASA Operations Centre at GSFC.

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

For further information, please contact:
Franco Bonacina European Space Agency, Headquarters, Paris,
France Tel:+33.(0)1.5369.7713

Don Savage NASA Headquarters, Washington D.C.

Bill Steigerwald NASA Goddard Spaceflight Center, Greenbelt, MD