Repairing Hubble: now a waiting game.
The apparent success of the $674 million Hubble mission may usher in a rosier future for manned space flight as well as buoy NASA's sagging reputation. In a call to the astronauts, President Clinton hailed their efforts as "one of the most spectacular space missions in our history"
"It's extremely difficult to keep from getting excited now," says Hubble scientist David S. Leckrone of NASA's Goddard Space Flight Center in Greenbelt, Md.
Nonetheless, the repair mission aimed at restoring Hubble's mechanical and optical health during an overhaul in the cargo bay of the space shuttle Endeavour - had its anxious moments. During the first space walk, astronauts found they couldn't completely shut two doors housing the gyroscopes they had just replaced. The gap between the doors could allow light to leak into the telescope and ruin observations. Using a strap to pull the doors closer together, the astronauts managed to shut them just minutes before the end of their walk.
Another cliff-hanger came during the third space walk, on Dec. 7. Story Musgrave and Jeffrey Hoffman had gently slid the old Wide-Field and Planetary Camera (WFPC) out of its compartment on Hubble, and Musgrave was about to remove the "lens cap" protecting a key, pristine mirror on the new camera, exposing it to the environment of space for the first time. Removing the cap, says Hubble project scientist Edward J. Weiler, "was delicate; he couldn't touch it, and we were watching it at the control room. And sure enough, just as he reached for it, we lost the [video]." But minutes later, the astronauts radioed that they had removed the cap and installed the camera.
Later that night, as the astronauts clamped new magnetometers onto the old ones at the top of the telescope, the cover of one of the old magnetic detectors came loose. Members of the shuttle crew crafted makeshift covers out of extra insulation. Then, with the blue-white marble of Earth clearly visible behind them, Hoffman and Musgrave attached the covers during the final space walk two days later.
The aftermath of the fourth space walk was like a roller-coaster ride. First, astronauts Kathryn Thornton and Tom Akers deftly installed COSTAR, a device that sharpens the blurred light bouncing off Hubble's main mirror. But after they added a coprocessor to improve the memory of Hubble's flight computer, ground controllers were dismayed to find that the computer intermittently radioed spurious signals. Engineers later that day traced the problem to faulty communications rather than a hardware flaw.
Leckrone notes that several initial tasks, such as calibrating the new gyroscopes and determining whether any of the scientific instruments were jostled out of alignment during the mission, must be completed in the next couple of weeks. Only after that can scientists determine the success of the optical repairs. Next week, ground controllers will begin a two-week process of ridding Hubble of contaminating vapor that might otherwise settle on the new WFPC's electronic detectors once they are cooled.
Engineers will then begin aligning Hubble's secondary mirror to aim light precisely into the camera. Around that time, technicians will also deploy a mechanical arm inside COSTAR that holds corrective mirrors. This should enable Hubble's Faint Object Camera to see more clearly.
After finding the optimum focus for both cameraS, scientists will perform the ultimate test some six weeks from now: They will take several images of crowded star fields and faint galaxies to find out whether the repair mission has paid off with a sharper view of the heavens.