CAPE CANAVERAL, Fla. Two American astronauts performed a major test of a balky $600 million robot arm at the International Space Station Thursday, inadvertently banging the outpost with the high-tech construction crane in the process.
And while no damage apparently was done, ground engineers are no closer to pinpointing the cause of recent troubles with the arm, and thats crucial to clearing shuttle Atlantis for NASAs next station assembly mission in July.
Operating the Canadian-built arm from within the U.S. Destiny science laboratory, flight engineers Susan Helms and Jim Voss carried out a dry run of the cranes first major job: Mounting a $164 million airlock on the outpost.
The test, however, got off to a rocky start when the tip of the 57.7-foot (17.5-meter) arm suddenly sprang away from an external anchor and then rebounded, striking the 17-story outpost.
The mishap clearly troubled ground engineers, who sounded extremely dismayed during a space-to-ground radio debriefing with Helms and Voss.
"Im a little stressed out," flight controller Ian Mills told Voss from NASAs Mission Control Center in Houston, Texas, after the test wrapped up.
"Now, its not that bad, is it?" Voss asked.
"Nah. Well survive," Mills responded.
"Hey, youre not the one that banged the station with the arm today," Voss said.
"No, I just happened to be here to see it," said Mills.
The so-called "dry run" test was designed to put the arm through the same motions that will be required to install the 6.5-ton airlock, which is to be hauled up to the station aboard shuttle Atlantis during a mission now scheduled for launch July 12.
The station crane must be operating properly to carry out the installation work because the shuttles 50-foot (15-meter) robot arm is not long enough to do the job.
Recent troubles with the arms shoulder joint, however, have prompted NASA officials to consider delaying the Atlantis mission.
Over the course of several weeks in May and early June, the joint failed to work properly when back-up systems were being used to operate the crane-like device. Then the joint started to operate as advertised during tests last week.
NASA and Canadian Space Agency engineers so far have been unable to pinpoint the cause of the original problem or duplicate it.
Consequently, there still are questions about whether the problem might recur during the Atlantis mission, leaving the airlock stranded at the end of the crane while astronauts are trying to mount it to the station.
"The dilemma is do you have a perfectly healthy arm, or do you have a problem that just hasnt shown itself in a couple of weeks?" said Kyle Herring, a spokesman for NASAs Johnson Space Center in Houston. "Thats basically the gist of this right now."
In a bid to replicate the problem, back-up control systems were used to operate the arm during the dry run of the airlock installation work. But beyond the start-up glitch, the arm operated without problems during the test.
That was both good news and bad news to flight controllers, who had been hoping that the shoulder joint problem would crop up again so that engineers can devise a fix for the fleeting glitch.
"I would have liked to see the failure induced today, so that we could figure out what was causing the (problem)," NASA station flight controller John Curry told Voss and Helms.
"But it didnt present itself, so Im left with this: We think the arm is working great, but we dont know for sure."
Ground engineers, meanwhile, already think they understand the start-up glitch.
Mills told Voss that tension likely built up within the arm before computer commands were sent to release it from a pin-like grapple fixture. That force likely caused the tip of the arm to spring off its anchor, rebound and then hit the station.
Herring said no damage was done. And the problem isnt expected to factor in to an upcoming decision on whether to delay the Atlantis mission, a move that might be made to give engineers more time to sort out the situation with the station arm.
As it stands, Atlantis is scheduled to roll out to a Kennedy Space Center launch pad next Tuesday in preparation for a July 12 launch.
Mission managers, however, are expected to meet Monday and could decide to delay the airlock delivery mission until late September.
In that case, NASAs next flight to the station would be the planned Aug. 5 launch of shuttle Discovery on a mission to ferry a new crew up to the outpost and return to Earth with Voss, Helms and Yuri Usachev.
Their replacements: U.S. astronaut Frank Culbertson and two veteran Russian cosmonauts, Vladimir Dezhurov and Mikhail Turin.
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