Brute force Hubble fix saves the day--again
Astronaut Mike Massimino, confounded by a stripped screw, deliberately tears away a handrail inside the Hubble Space Telescope to clear the way for a successful instrument repair.
Held up by a stripped screw, spacewalker Michael Massimino applied brute force to an otherwise delicate operation Sunday, breaking off an offending handrail inside the Hubble Space Telescope and then carefully unscrewing more than 100 small fasteners to get inside a dead science instrument.
After pulling out a blown power supply circuit board, Massimino and crewmate Michael "Bueno" Good carefully installed a replacement card, closed the instrument up and began collecting tools and equipment while engineers at the Goddard Space Flight Center sent commands to verify electrical connectivity in a quick-look "aliveness" test.
Somewhere along the way, Massimino developed a rip in his left spacesuit glove, but officials said he was never in any danger.
"Atlantis, Houston, with a bit of news from the STOCC (Space Telescope Operations Control Center) if you're ready," astronaut Dan Burbank radioed around 5 p.m.
"We are definitely ready," astronomer-astronaut John Grunsfeld replied from Atlantis.
"We're all happy to report that STIS (Space Telescope Imaging Spectrograph) has come back with a good aliveness test."
Amid cheers from space, Massimino laughed and said, "that sounds great. Thanks so much, Dan."
With the apparently successful repair of the imaging spectrograph, Hubble scientists expect to have access to five operational instruments for the first time in the telescope's 19-year history.
"This was an astounding victory day for science," said Jennifer Wiseman, chief of exoplanet research and stellar astrophysics at Goddard. "We are thrilled. When the STIS instrument failed back in 2004...the disappointment around the scientific community was like a terrible cloud. There were so many good scientific programs yet in the works that we had planned to do...Today is like a dream come true for the science community."
During the first of the Atlantis astronauts' five planned spacewalks, the powerful new Wide Field Camera 3 was installed, along with a replacement science data computer. On Friday, six new stabilizing gyroscopes and three fresh nickel-hydrogen batteries were bolted in place. On Saturday, the new Cosmic Origins Spectrograph was installed and astronauts John Grunsfeld and Andrew Feustel successfully repaired the wide-field channel of the Advanced Camera for Surveys.
The ACS and the Space Telescope Imaging Spectrograph were not designed to be repaired in orbit and as such, they represented the greatest technical challenges for the crew. Going into the mission, engineers said they had more confidence in the maturity of the STIS repair plan and warned reporters that the ACS work was much more uncertain.
As it turned out, they were partly wrong and partly right. The ACS repair went much more smoothly than anyone expected and the astronauts successfully revived the heavily used wide-field channel. But they were unable to restore the camera's high-resolution channel to operation.
During Sunday's spacewalk, Massimino and Good had to replace a blown power supply inside the Space Telescope Imaging Spectrograph. To reach the circuit board in question, the astronauts had to remove a cover plate held on by 111 small screws.
To get the cover plate off, they first had to remove a handrail preventing the attachment of an ingenious "fastener capture plate" designed to trap the small screws and washers as they were released. The handrail was held in place by four screws. Three came out with no problem, but the head of the fourth, in the bottom right position, was stripped by Massimino's power driver.
Despite multiple attempts and a different tool bit, the screw refused to budge. Flight controllers briefly considered attempting to remove smaller screws holding the base of the handrail in place, but they ultimately hit upon the brute force solution. With the top of the handrail free, controllers suggested Massimino simply pull it away until the lower screw snapped off.
"Yeah, and Drew, before we get into it, just wanted to give you a little bit more information," Burbank called from mission control. "This was just done, just now, at Goddard on a flight equipment unit and it took 60 pounds linear (force) at the top of the handhold to fail the single bolt in the lower right position at the bottom."
"OK. Mass, you copy that?" Feustel asked. "Sixty pounds linear at the top of the handrail to pop off that bottom bolt. I think you've got that in you."
"I can try," Massimino agreed. "So what do we do? Just give us the steps."
With flight controllers laughing in the background at Massimino's eagerness, Burbank told the astronauts to stand by while engineers reviewed the plan and the techniques needed to capture any released debris. It was decided to use Kapton tape over the ends of the handrail to help trap any loose washers or debris.
"Just tell me what your hand placement plan is and what you think about managing the sharp edges after it breaks, if you want to try and rock it to fatigue it or just a straight pull?" shuttle commander Scott Altman radioed from the flight deck.
"I don't know. I think maybe rocking it a little bit and then pulling it off, you know, I can feel it now, starting to come away. I'm not going to have a big death grip on it, but do what I can to pull it off. Mike, you handy with the disposal bag? If we're lucky enough to break this thing?"
He then got a grip and prepared to pull the handrail away.
"Easy, easy, Mike, just real easy, OK?" Feustel said.
"Here we go," Massimino said, pulling the top of the handrail away. There was no television coverage at the time, but he apparently had no problems.
"Mass, I didn't get a good look at it, but it looked like it all stayed intact with the tape."
"Yeah, it did, I don't think we scattered any debris," Massimino said.
Even though the sheared screw was sticking up a bit from the surface of the instrument, flight controllers and the astronauts decided it was not a sharp-edge threat and that they could press ahead with the repair.
"Awesome job," Burbank said. "We agree, we're back in with the regularly scheduled programming."
Running nearly two hours behind schedule by that point, the battery in Massimino's power tool suddenly died, prompting an "oh, for Pete's sake!" from the frustrated spacewalker.
After retrieving a fresh battery and topping of his suit's oxygen supply, he returned to Hubble and the spacewalkers got back to work.
The astronauts installed the fastener-capture plate and unscrewed 111 small screws, trapping the Torx- and allen-head fasteners and washers between the electronics box cover and capture plates. The cover-capture plate combination then was pulled away, exposing the blown power supply card to view.
Using a custom tool to avoid handling the fragile boards, Massimino and Good promptly swapped them out. The electronics box was sealed with a different cover plate, one requiring just two locking pins.
It was the second time in the shuttle Atlantis' ongoing Hubble servicing mission that astronaut muscle power was called on to save the day. During the crew's first spacewalk Thursday, Feustel had to force a stuck bolt out with a socket wrench to release an old camera, making way for installation of the new Wide Field Camera 3.
While Sunday's repair work apparently was successful, the time lost on the handrail and the dead battery left too little time to accomplish the final planned task of the day: installation of an insulation blanket.
Flight planners told the crew they could attempt two such panels during a final spacewalk Monday if time is available. But the primary goals of the final excursion are installation of three more batteries and a refurbished fine guidance sensor.