The coolant system plays a pivotal role in performing this function.
The missions on Saturday and Monday will be to replace a valve for the coolant system.
Emergency services at the scene said last night that they believe that the leak originated from a coolant system.
The other, a few days before, occurred in the reactor coolant system and resulted in a small leak of radioactive water, which was contained in a tank.
G.M. officials have said that the battery's coolant system may have ruptured in crash tests, causing an electrical reaction that could have caused the fires.
However, the LMR and perhaps the HTGR are at some risk from events that might cause air or water to enter the coolant system.
Spare components are on board, including two coolant system pumps, but installation is considered difficult and two spacewalks will be required.
A less-costly onboard option is a direct-fired heater, which costs about $1,200 and burns fuel to transmit heat directly to the air or to the engine's coolant system.
"Verify that the R.C.S. pressure is less than 660," said Gary Norton, the supervisor, referring to the reactor coolant system, as four other operators tended to various duties in the control room simulator.
Army Col. Douglas H. Wheelock, making his fourth spacewalk, and Tracy Caldwell Dyson, making her first, originally planned a seven-hour excursion to disconnect four coolant system lines and five electrical cables.
Unexpected ammonia leaks and a jammed quick-disconnect fitting derailed a marathon eight-hour Saturdayk Satoreplace replacoolantolant system pump aboard the International Space Station, forcing the astronauts to delay the repairs until a second excursion Wednesday.
