The crew of the International Space Station was forced to activate back-up oxygen generating equipment on Wednesday after the ISS's main supply system broke down.Russian engineers are struggling to repair the main "Elektron" oxygen supply system, which is located in the Russian Zvezda living module. The system converts water into hydrogen and oxygen.
Both Russian and U.S. officials say the crew is in no danger. Secondary oxygen supplies should last for at least 100 days and a shuttle mission is scheduled to bring fresh supplies to the station in early June.
The back-up oxygen-generating process involves activating a chemical reaction in solid fuel canisters, known as "candles". The crew is using these to maintain proper oxygen levels within the ISS modules. "They have the candles and everything is fine," a NASA spokeswoman says. "They are working with Russian mission control to solve the trouble."
Each crew member uses one candle's worth of oxygen per day and there are enough candles to last for 50 days. Another 50 days of oxygen is located in tanks attached to the outside of the U.S. airlock. This is usually used to supply spacewalking astronauts but could be routed into the station itself.
The Russian oxygen generating system has been working intermittently in recent weeks. A NASA spokesman says a liquid pump on the Elektron unit appears to have failed. This may be due to a fault with the pump itself or with a sensor controlling it. A replacement part may have to be brought to the shuttle or new software could be uploaded to solve the sensor problem.
The current crew consists of Russian commander Yury Onufrienko and U.S. flight engineers Carl Walz and Dan Bursch. They?ve been at the ISS since December 2001 and are scheduled to depart in June.
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Flight engineer Roberto Vittori, the Italian cosmonaut who flew with space tourist Mark Shuttleworth last month, is attempting to shake the strength back into his bones using a simple vibrating plate which he stands on to exercise. Bone weakness is a big problem for anyone who spends even just a short time in orbit.
Vittori's work should help doctors find the solutions they need to better prepare long-flight space crews. The results will also help the treatment of ordinary osteoporosis here on Earth.
Even in a short 10-day trip into space, a crew's bone mass will drop by 0.3-0.6% in a kind of accelerated aging. Despite a rigorous exercise program on board the International Space Station, many space crews return to Earth with the first stages of osteoporosis. The long duration flights on Mir in the 1990s caused irreversible 20% bone loss in one cosmonaut.
Such levels of bone wasting are among the greatest problems with a human flight to Mars, says Vittori, who hopes to be on a future Mars mission. But if the vibration therapy being tested works, the conditions incurred on long-duration space flights might soon be cured.
For just a few minutes a day for two months before the flight, Roberto trained on the plates which shake his leg bones at between 20 and 55 hertz. The vibrations create a "hypergravity" environment which encourages new bone to grow. "Bones are dynamic," says Filippo Ongaro, the European Space Agency doctor leading the study. "Osteoblasts build bone and osteoclasts destroy it. This happens in perfect balance most of the time on Earth, but in space the osteoblasts stop working and bone mass decreases." Ongaro thinks that the vibrations are triggering the osteoblasts to start working overtime, replacing the bone lost in space.
Roberto's recovery will be compared with control subject Mark Shuttleworth, who flew the same mission length without the benefit of vibration therapy. If it looks like it works, one of the vibrating plates will be flown up to the ISS next year for the use of later crews.
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