Managers for the international space station decided Monday to change the plan for next month's spacewalk because two of the three U.S.-made spacesuits for extravehicular activity are out of order, a NASA spokesman told MSNBC.com. The change will make a needed repair operation more difficult and will introduce some unprecedented twists in spacewalk routines.
Originally, the two crew members were to exit from the U.S.-built Quest airlock, which is close the scene of the repairs. But when the crew couldn't get the cooling systems on the U.S. suits to work over the weekend, NASA's Mission Management Team went to Plan B.
Under the new scenario, Russian commander Gennady Padalka and NASA's Mike Fincke would use Russian-made Orlan spacesuits and exit from the station's Russian Pirs docking module, about 80 feet (25 meters) from the repair site. They would then ride a Strela cargo crane to go over to the American side of the station. There, the spacewalkers would replace electrical power components for a gyroscope that failed just after they arrived in April.
Russian mission managers concurred with the decision, NASA spokesman Rob Navias said.
The revised operation, which is expected to last four and a half hours, would mark "the first time that an EVA based out of one segment would actually fulfill tasks on another segment," said Navias, speaking from the Johnson Space Center in Houston.
In the course of what Navias called "a bilateral EVA," the prime role for managing the spacewalk from the ground would switch from the Russian to the U.S. flight control team. Navias emphasized that the two sets of controllers generally look over each other's shoulders anyway, and that a provision for bilateral operations has always been included in the station's flight rules.
"It's just that we've never had to use it before," he said.
The spacewalk had originally been scheduled for June 10, but Navias said the operation has now been moved back to June 16 or later, to give more time for detailed planning.
The agenda for the spacewalk has been trimmed down to the basics.
"There would be no other tasks performed other than the remote power controller replacement work," Navias said.
The broken-down remote power controller has knocked one of the space station's three stabilizing gyroscopes out of commission -- and U.S. and Russian mission planners want to have that gyroscope fixed in advance of another spacewalk scheduled in July.
Navias explained that the later spacewalk called for work in the vicinity of the thrusters on the station's Russian-built Zvezda service module. If the station's gyroscopes were to suffer a complete failure, those thrusters would have to be used to keep the station in the proper orbital position -- a situation NASA and the Russians definitely want to avoid.
"It is in both parties' interests to get that CMG [control moment gyroscope] up and running before we approach the Russian EVA," Navias said.
Supplies due to arrive
In addition to planning for the spacewalk, the station crew's agenda includes unloading an unmanned Progress cargo craft that is due to be launched from Russia's Baikonur Cosmodrome in Kazakhstan on Tuesday, with arrival at the station scheduled Thursday.
Supplying the station has been more challenging since the Columbia tragedy of February 2003, which forced the grounding of NASA's space shuttle fleet. For more than a year, station crews have relied exclusively on the Russian-built Progress and Soyuz ships for resupply.
The best-case scenario calls for the shuttles to fly again no earlier than next March, and as a result, resupply has become an issue of greater concern.
Even basics such as water and food are being closely watched: If this week's Progress resupply flight were to fail, Padalka and Fincke would have to consider leaving the station in their Soyuz lifeboat, because their water reserves might reach unacceptable levels before another ship could be sent.
NBC News space analyst James Oberg contributed to this report.