Space Station Will Need Shuttle Water
Feb 9, 2009
By Frank Morring, Jr.
Continuing problems with the environmental control and life support system (ECLSS) on the International Space Station (ISS) mean the orbiting facility must rely on water from visiting space shuttles to support the planned crew of six arriving in May.
The next mission to the station has been delayed at least a week, from Feb. 12 to Feb. 19, for additional safety analysis in a main engine hydrogen valve. But Mike Suffredini, NASA's ISS program manager, said Feb. 3 that the station can handle six crew members as long as shuttles keep arriving within a month or two of the current schedule, regardless of the ECLSS status.
As the orbiting facility nears completion, engineers also are calculating the long-term effects of a software error that sent out-of-spec vibrations through the floating structure during a reboost last month. Suffredini said the anomaly does not appear to have eaten into the 15-year ISS design life. But it remains to be seen how much the anticipated service life beyond that was limited by structural fatigue that resulted from the shaking, which Expedition 18 commander Mike Fincke said exceeded anything he had experienced in his two tours on the station.
While the long-term effects of the reboost anomaly - which resulted when the wrong parameters were uploaded prior to a two-minute burn of the station's Russian main engines Jan. 14 - are not yet understood, continuing issues with the urine distiller in the new U.S. water recycling system are more pressing. Until now the orbiters' fuel cells have been the prime source of water for the ISS and its three crew members. But the shuttle is retiring as early as the end of next year, and the larger station crew will need to recycle urine, wash water and atmospheric moisture once the shuttle "well" dries up.
The Urine Processor Distillation Assembly has had problems since it was installed last year, and will be replaced when the shuttle Discovery arrives on the upcoming STS-119 mission. The balky distiller has slowed the sampling-and-testing process required before station crew members can begin using potable water from the system, and as a result it won't be ready in May when the crew size doubles.
A bacteria count in the system's potable water dispenser also is slightly higher than acceptable, which may require a system flush with an anti-bacterial solution to fix. Suffredini said that problem is "within our experience base."
"We'll have to get more water from the shuttle than we would normally require, but that's not an issue," he said. "We need a little time to sort through the anomalies. We'd like to get the distillation system working and processing all the water we can to save upmass."
The STS-119 mission will slip at least a week to give NASA engineers at Stennis Space Center, Glenn Research Center and White Sands, N.M., more time to run tests to see what would happen if one of the suspect engine valves were to break in a way that allows a fragment to rupture one of the gaseous hydrogen lines that pressurize the main hydrogen tank in the shuttle stack.
A drop in pressure below 32 psi could hamper engine performance during ascent, so the space shuttle program wants to be sure it understands the problem before launching Discovery.
"We don't expect a problem, but we don't have proof," Shuttle Program Manager John Shannon said. "We want proof."
International Space Station photo: NASA
