Astronaut Michael Massimino, floating inside the Hubble Space Telescope, and fellow spacewalker Michael "Bueno" Good, on the end of the shuttle Atlantis' robot arm, successfully installed four state-of-the-art gyroscopes Friday. But an alignment problem prevented the astronauts from installing a box containing two final gyros.
Even so, Hubble Program Manager Preston Burch said the refurbished two-gyro rate sensor unit, or RSU, that they installed instead featured two of the three improvements incorporated in newer models and that engineers are confident it will prove as reliable as its partners.
"We've run the reliability models for all the various possible permutations and combinations of RSUs that might be installed on this mission," he said. "And I would say the difference in the projected longevity of the observatory in the out years is very small.
"We don't see this is a significant detriment at all to the observatory. This was a tremendous accomplishment for us."
Time lost trying to get the balky RSU in place cost Massimino and Good nearly two hours, forcing them to extend the spacewalk to accomplish the other primary objective of the excursion: installation of three new batteries.
But that work went smoothly. The gyros and batteries passed initial "aliveness" and functional tests and the 7-hour 56-minute spacewalk, the second of five planned for Atlantis' mission, was considered a complete success.
"We are really excited that we're now two for two with our EVAs," Burch said. "We accomplished everything we set out to do today. We hit some rough spots there, and I think it's a huge testament to the perseverance and the determination of both our crew as well as our flight director that we got through and accomplished everything we set out to do. It's thrown us off a little bit in terms of our time schedule, but it looks like we can accommodate that."
Installing the new gyros was the top priority of Hubble Servicing Mission No. 4. Of the six stabilizing gyros in place when Atlantis arrived, three had failed, one that was experiencing a high run time and subtle electrical problems was offline, and the other two had issues of their own.
"Mass and Bueno, my friend (King) Leonidas has a couple of words for you guys that are appropriate right now," Atlantis commander Scott Altman said with mock seriousness. "'Remember this day, men, for it will be yours for all time.'"
The work was the equivalent to invasive surgery for Hubble.
With Massimino anchored inside the telescope, the two spacewalkers started with RSU No. 2 in the upper right corner of an equipment bay. The process required Massimino to detach two electrical cables and for Good, operating a power drill with a long socket fitting, to unscrew the bolts holding the box in place.
Good then attached the replacement RSU to an extension tool and carefully passed it into the telescope to Massimino. Once positioned properly on guide pins, Good drove home bolts to secure the new box in place.
The process worked fine for RSU 2. But when the astronauts attempted to install a new gyro pack, serial number 1007, in the RSU 3 position in the upper left corner of the equipment bay, they ran into problems. Despite repeated attempts, they were unable to get the new unit aligned on the guide pins well enough to permit the bolts to engage.
Good said it felt like the new unit was rocking slightly on its mounting plate, indicating a problem that prevented it from sitting flush and prevented the bolts from engaging. After discussing the issue with the ground, it was decided to temporarily store the 1007 RSU and to mount the box intended for the RSU 1 position.
"I'm not too confident this is going to fit anywhere," Good said at one point, referring to 1007.
But the astronauts pressed ahead and had no problems installing the RSU 1 unit in the RSU 3 slot.
"All right, Mike, let's get it," Massimino said.
Once in position, the astronauts put the RSU in position and Good drove in the bolts to secure it.
"Three (turns), four, five, I definitely got it," Good reported.
"Excellent," Massimino replied. Cheering could be heard from the shuttle's flight deck.
"You're my hero," Massimino said. "Yeah, that bolt is in. Great job, Mike."
After a second bolt was driven home, someone wryly observed: "Double-oh seven double crossed us!"
"Ah hah!" Massimino said.
The astronauts then moved to RSU position 1 and removed the old unit. But again, they were unable to get the 1007 box to fit flush on the mounting plate. Flight controllers gave Good permission to make additional attempts, but John Grunsfeld, an astronomer-astronaut making his third visit to Hubble, said he disagreed.
"It's really your guys' call, of course, but I'm a little uncomfortable with trying to make an inertial platform out of something that may not be installed flat, even if we get one of the bolts done," he said.
"John, we copy and we agree with that plan," astronaut Dan Burbank replied from Houston.
Massimino and Good then returned to an equipment carrier and retrieved a spare RSU that was carried aloft as a backup. The spare unit was removed from Hubble during a servicing flight in 1999 and then refurbished.
As it turned out, Good had additional problems getting the spare unit in place but he eventually succeeded.
"Atlantis is pleased to report RSU 1 connectors are mated," Good said.