SOHO Calls Home, Raising Hopes of Recovery

Ground controllers have reestablished full radio contact with the Solar and Heliospheric Observatory (SOHO), raising hopes of bringing the $1 billion spacecraft back to life. Many had given SOHO up for lost after a series of command errors caused it to spin out of control and fall silent early on 25 June, but the renewed dialogue, announced today by NASA and the European Space Agency (ESA), is a critical step on the long road to recovery.

SOHO had been tumbling for 6 weeks in a way that left its solar panels unable to collect sunlight and generate power. The first sign of life came on 3 August, when controllers achieved sporadic contact with the spacecraft, which indicated that the solar panels were in a position to collect some sunlight again (ScienceNOW, 7 August). The transmissions came in 10- to 15-second bursts, as SOHO's panels rotated in and out of the sunlight. So on 8 August, controllers told SOHO to use the power from its panels to charge up one of its batteries. The operation succeeded, permitting minutes-long establishment of full communication with SOHO by the following day, says Joseph Gurman, the SOHO project scientist for NASA.

The new transmissions carried readings from dozens of onboard temperature and voltage sensors. The message they conveyed is dryly summarized by Francis C. Vandenbussche, the SOHO spacecraft manager from ESA who heads the recovery team: "It's a little bit chilly." That chill suggests the satellite's fuel tanks are frozen.

Now an expert team of engineers will begin evaluating data from many kinds of sensors on SOHO and come up with a strategy to bring the spacecraft back from the brink. They will try to find a way to gradually return power to SOHO's many heaters, which normally keep the craft at around room temperature, without damaging frozen components. That effort "is still missing some pieces of the puzzle," says Vandenbussche. Over the next couple of weeks, he hopes the signals streaming from SOHO will provide those pieces.


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