The Sciences

Here Comes the Sun: Greenbelt, We Have a Problem

The Solar and Heliospheric Observatory has been running like a well oiled machine, but it hasn't always been this way.

By Dana MackenzieApr 9, 2004 5:00 AM


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Editor’s note: This story was originally meant to accompany our May feature “Here Comes the Sun.” It appears for the first time on our Web site.

The Solar and Heliospheric Observatory, or SOHO, with an impressive retinue of 12 experiments managed by researchers from six countries, is clearly the star of the dozen or so satellites currently observing the sun or the space weather near Earth. Headquarters for the mission is the Goddard Space Flight Center in Greenbelt, Maryland. If your only concept of mission control comes from the movie Apollo 13, you’re in for a bit of a surprise here. Mission control at Greenbelt is shaped like a hub, a large meeting room surrounded by nine smaller workrooms, each devoted to a separate experiment. The faces around the table are amazingly young, hardly any of them older than 30. With the satellite running like a well-oiled machine, the principal scientists stay at home and leave their graduate students to mind the shop.

But it wasn’t always this calm. On June 24, 1998, when the satellite had been in orbit for only two years, NASA lost control of it during a routine maneuver. The main gyroscopes were left in the wrong setting, causing the spacecraft to roll. The controllers’ repeated attempts to fix the roll only made the problem worse.

“SOHO flipped over and started paddle wheeling this way, perpendicular to the sun line,” Stanford University astronomer Philip Scherrer says, taking down a model of the spacecraft and sweeping the solar panels around in a great arc like the paddles of a Mississippi River steamboat. With the solar panels facing the sun edge-on, the spacecraft had no power, and the transmitter went dead. SOHO was lost in space.

Using radio telescopes in Puerto Rico and Australia, controllers were able to get a fix on the crippled satellite, but that only showed them the magnitude of the problem. The solar panels were rotating once every 52 seconds. The good news was that the panels would be facing the sun again in three months; the bad news was that they would be pointing the right way and generating power for only 26-second bursts. Because the computer on SOHO took 18 seconds to boot up, Scherrer says, that gave controllers at most an 8-second window to send it instructions. “They gave it two commands,” he says. “Transmitter on, battery on, over and over again, and one of them finally took.”

Even after SOHO was back in contact, regaining control was a slow and arduous process. The fuel had to be thawed out, and then the fuel lines. Then the spin had to be slowed down, and finally the automatic control system had to be brought online again. It took until November to bring SOHO fully back to life—and then, in December, the last gyroscope gave out. But, having performed one miracle, the engineers weren’t about to let another piece of bad luck stop them. In a fix worthy of Star Trek, they have learned to use a different device on the spacecraft to perform the functions of the gyroscope (which was only rarely needed anyway).

On the all-time list of space rescues, says George Withbroe, who was director of NASA’s solar research program at the time, “I’d put it second to Apollo 13.” Of course, in this case there were no lives at stake. But, says Scherrer, “there’s a billion dollars up there, so you’ve got to work hard to figure out a way!”

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