CAPE CANAVERAL, Fla. (AP) - A spacewalking astronaut ran into trouble while trying to lubricate a critical joint in the power system of the International Space Station on Sunday, losing a bolt and getting a washer stuck in a crevice.
Mission Control told astronaut Mike Fincke he might have to settle for a partial lube job, rather than the complete greasing.
"Bummer," said his spacewalking partner, Andrew Feustel.
The spacewalk started out well enough, with Fincke and Feustel topping off a leaky radiator line. They successfully added ammonia to the space station's coolant system, after rerouting jumper cables and opening valves. One line leaks slightly, and the astronauts needed to recharge it.
Ammonia is extremely hazardous, and the two did their best to avoid contaminating their spacesuits while replenishing the system with about 5 pounds of the substance.
Fincke moved on preventive maintenance on the large joint that rotates the space station's solar wings on the left side. He was removing covers when a bolt got away from him. He caught it. But another bolt ended up floating away, and a washer got stuck between the cover and an attachment.
Mission Control worried the washer might get in the gear mechanisms of the joint and damage them. Fincke was advised to use "gentle backhand sweeping motions" to get the washer away from the gears, and the astronaut replied he could try to coax it out.
All this came as a surprise, and Mission Control later told the astronauts that the washers might be bent and flimsy from previous repair efforts.
"Sorry you're having such a hard time with those bolts, buddy," Feustel called out to Fincke.
"Yeah, man, I was being really careful, too," Fincke replied.
After debating how to proceed flight controllers instructed Fincke to remove only some of the covers from the joint: "We'll do the best job we can." He promised to be careful.
Another bolt popped out and almost got away, but Fincke caught it. Mission Control said, "He gets a golden glove award for another catch."
NASA wants to lubricate as much of the joint as possible to keep it functioning properly in the years ahead without any shuttle visits.
It was the second of four spacewalks planned for Endeavour's final trip to the space station.
"This is an important one for the longevity of the station, for the power and cooling, so let's get started," astronaut Gregory Chamitoff called from inside as the spacewalk got under way in the wee hours of the morning.
These are the final spacewalks to be conducted by visiting shuttle crew members; the goal is to leave the space station in the best possible condition for its next decade of operation.
As they ventured out more than 200 miles up, the two men praised one another.
"It's an honor to be walking, spacewalking with a Hubble spacewalker," Fincke told Feustel, part of the last Hubble repair team in 2009.
"It's an honor to be walking with the man with the most time in space," Feustel replied. Fincke will become the most traveled American in space by next weekend, surpassing the current record of 377 days aloft.
"Well, let's make this quality time today," Fincke said.
Feustel and Chamitoff had to cut Friday's spacewalk a little short because of a failed carbon dioxide sensor in Chamitoff's suit. That problem wasn't expected during Sunday's outing.
On Monday, three of the six space station residents will head home in their Russian Soyuz capsule after a five-month mission. In a unique photo op, the departing crew will photograph Endeavour parked at the space station.
Then on Wednesday, Feustel and Fincke will venture back out for spacewalk No. 3.
Endeavour, under the command of Mark Kelly, husband of wounded Rep. Gabrielle Giffords, will remain at the orbiting outpost for another week. Landing is scheduled for June 1.
This is NASA's next-to-last space shuttle mission. The 30-year program will end in July with the flight of Atlantis.