PR 30-1998: SOHO: on the road to recovery
11 August 1998Six days after receiving the first signal from the dormant SOHO Spacecraft, several blocks of telemetry data giving the spacecraft's on-board status were acquired late Saturday night, 8 August, at 23:15 hrs GMT. Further data acquisitions took place on Sunday 9 August and will continue in the following days."This is the best news I've heard since we lost contact with SOHO on 25 June" said Roger Bonnet, ESA's Director of Science. "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 on-board conditions by engineers from the European Space Agency and Matra Marconi Space (builders of the SOHO spacecraft) a series of command sequences was up-linked through the NASA Deep Space Network (DSN) station at Goldstone,CA. These sequences were designed to divert the available solar array power into a partial charging of one of the on-board batteries.
After 10 hours of battery charging, the telemetry was commanded on and seven full sets of data of the on-board status were received. After one minute telemetry was switched off from ground controllers in order to preserve on-board resources. Further details on the on-board conditions were obtained the following day (Sunday 9 August) in two subsequent telemetry acquisitions lasting four and five minutes respectively. Data gathered included information on temperature and voltages for payload instruments, which are currently being analysed.
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 NASA DSN has accepted this request as a "Spacecraft Emergency" giving it priority over other DSN scheduled activities. The procedure is currently on-going.
ESA's Francis Vanderbussche, in charge of the SOHO Recovery Team at GSFC, said "I am truly satisfied with the information the data we acquired gives us. Conditions on-board are as good as we expected them to be". At the moment the team is working on the next series of procedures which will be aimed at thawing the on-board hydrazine fuel, currently at 0°C, to enable attitude control of the spacecraft to be re-established. This will be attempted once full charge can be established in both on-board batteries later this week.
Radio contact with SOHO, a joint mission of ESA and NASA, was interrupted on 25 June 1998. The delicate recovery activities are being directed by the ESA SOHO project team from the NASA Operation Centre at GFSC.
SOHO had 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.