During the hectic coming-and-going of visiting space crews aboard the International Space Station in September, the startling bulletin about a fire in its all-important oxygen-generating system was quickly denied and just as quickly overtaken by events. But the emergency—which, it turns out, was not a fire—has profound implications for the space station’s immediate performance and long-term survival.

On 26 October, the Russian robot space freighter Progress safely arrived at the station carrying supplies and some very special spare parts. Normally, there is tension and suspense during such dynamic space operations, but this time the tension only gets higher after the docking. The question is: Will the spare parts, added after the earlier oxygen system incident, fix the problem and allow the recently resumed orbital assembly to continue as planned?

The team aboard the station is now finishing the first of six planned months in orbit. Michael Lopez-Alegria and Mikhail Tyurin have inherited three assets: a powerful orbiting infrastructure, a renewed space construction site, and Thomas Reiter, of the European Space Agency, who stayed over from the previous crew.

However, they also inherited some headaches, chief among them generating enough oxygen to breathe. Their Russian-built system, called the Elektron, uses electrolysis to split surplus water into oxygen; it then dumps the useless hydrogen into space. Although the system is cranky and hypersensitive, it is simple enough for crews to repair, adjust and replace. The current unit, however, has malfunctioned, and the crew has not yet been able to get it working again.

They have enough backup oxygen—in tanks and in solid-fuel generators, or candles—to support the three-man crew until they are resupplied. However, they do not have enough to cover an additional seven people for at least two months, as the “safe haven” rule requires. That rule was adopted to give shuttle crews who discover damage to their heat shields the option of taking refuge aboard the station until a rescue shuttle can be launched. No such option was available to the doomed Columbia crew in 2003. They re-entered the atmosphere, the heat shield failed, the craft burned up, and all the crew members died.

If the space station’s crew cannot get the Elektron up and running, then the resumption of shuttle flights will either have to be postponed from its scheduled start in December—costing the program immeasurably—or the safe-haven rule will have to be modified—something today’s much more safety-conscious NASA would be very reluctant to do.

Latest Troubles Begin

The latest round of oxygen woes came on 18 September, shortly after the space shuttle Atlantis had departed from the station. U.S. crewman Jeff Williams reported a bad smell, as if from a fire, and he and Russian shipmate Pavel Vinogradov described what looked like light smoke around their Elektron oxygen generator.

Mission Control in Houston declared a Spacecraft Emergency, the first in the space station’s eight-year history, and controllers directed the crew to shut down the Elektron, turn on air purifiers and put on goggles, gloves and breathing masks. At first the odor was attributed to a fire, and then officials attributed it to a chemical leak, but when detectors on the station later could find no residue, specialists in Moscow’s Mission Control Center came to a different conclusion.

The electrolysis begins as it does in high-school experiments here on earth. The water is rendered conductive by adding a conductor, then a current is sent through, causing oxygen to bubble out at an electrode. That is when the difference comes, for in the weightlessness of space, the bubbles have no tendency to rise. It takes considerable work to separate them from the water. At the same time, a residue tends to precipitate out at the edge of bubbles, creating a crust.

Together, these processes can create jams in the fluid flow—that is one reason why the device wears out. The jams and crusting also affect the current, concentrating it in “hot spots.” Scientists at the Russian space agency believe one such hot spot melted a seal, creating the odor the crew originally smelled. It may also have damaged sensors and small valve solenoids. All these things may explain why the Elektron unit would not start again after it was given the chance to cool down.

The resupply ship brought new sensors and a new valve – the old one is believed to have a burned-out solenoid, probably as a result of the overheating — and on Monday the crew members put them in, but to no avail. Tyurin told Moscow Mission Control that the unit appeared jammed with free-floating air bubbles much larger than desired, a problem encountered often in the past. He will spend the rest of the week trying to remedy it, and then he will activate the unit, coaxing it along as gently as possible. Success will be achieved not when the unit starts up, but when it continues to run for more than a few hours before its control system shuts it down.