Updated on
Summary
A pair of spacewalking astronauts finished installing a fresh storage tank outside the International Space Station on Tuesday, but a stuck valve was threatening to jeopardize half of the cooling system.No sooner had Rick Mastracchio hooked up the fluid valves for the new ammonia tank on the third and final spacewalk of shuttle Discovery's flight, then flight controllers encountered the valve trouble in a separate pressurizing unit.Flight director Ron Spencer said the problem needs to be resolved as soon as possible and that spacewalking repairs may be needed sometime after Discovery leaves this weekend. The problem is exasperated by the fact that a period of intense sunlight on the space station is fast approaching, and the ammonia will be expanding more than usual with the added heat.The stuck valve is in a nitrogen tank assembly on the right side of the space station. Nitrogen is used to pressurize the ammonia, which circulates through large radiators. Without that capability, half of the station's electronics eventually might have to be turned off. The cooling system on the left side left alone on this flight is operating just fine. For now, so is the one on the right side.We do have a couple tricks up our sleeves to remotely free the valve, Spencer told reporters. He said a spacewalk would be a last resort and that it was too soon to know when a decision might need to be made.The seldom-used valve cannot be replaced alone. The entire nitrogen assembly would have to be swapped out. Fortunately, two spares already are at the space station.As engineers struggled with the nitrogen valve, Mastracchio and Clayton Anderson were dealing with a stubborn bolt on the old ammonia tank, which had been removed on the previous spacewalk.In what almost seems to be a common occurrence on this flight, one of the four bolts on the tank would not engage. Mastracchio and Anderson were trying to secure the boxy, 1,300-pound tank in Discovery's cargo bay when the problem cropped up. It appeared to be a misalignment, and they pulled out a pry bar to try to fix it. The pry bar wasn't needed, but a torque-increasing device was.
