Breathing Easy in Space Is Never Easy

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 suffered 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.

Air Repair Cares

During the week last month when two crews were still aboard they had tried another tack. They two Russians had replaced the main electrolysis unit with an onboard spare, a job that took a full day. On 26 September, the new unit was activated, but it ran for just three hours before its primary and backup pumps shut down, apparently responding to an internal overload. The following day, Tyurin used a circuit-board tester to see if the microsensors were still connected to the computer-controlled valves that had been overheated a week earlier. A spare for that unit was also prepared for installation.

On 4 October, Tyurin performed additional circuit tests on the Elektron and confirmed suspicions that either a non-replaceable internal fuse had blown or a valve solenoid had burned out. With the device still dead and now apparently non-repairable, Tyurin replaced the percussion-based ignition system of the solid-fuel oxygen generator with an improved, electronically activated one. He test-fired one of the candles, and it worked fine. But then the Russians told the crew to hold off on using any other candles, so as to use up, instead, the last of the bottled oxygen in the Progress freighter.

The following day, the station crew began dipping into an oxygen supply that had never been tapped in the five years since it had been delivered. When the Quest airlock was attached to the station in July 2001, four pressurized tanks�two of nitrogen, two of oxygen�were also bolted into place. The 180 kg of oxygen (about 72 days worth for a crew of three) has been sitting there until needed in a contingency, which has now arisen.

The rationale for this choice was never explained, but one space program worker privately advised IEEE Spectrum Online that the solid-fuel generation option was always considered a ”last resort,” a very simple and robust system that could continue to function in an emergency when power or temperature anomalies made more complex systems unworkable. Given the choice, the very practical Russian philosophy seemed to be to use the most complicated device that was still working and save the simple systems for real emergencies.

The Quest tanks can be refilled from reserves brought up aboard shuttle missions, but this involves activating some very noisy and power-hungry air pumps inside the Quest. And this week they were directed to halt use of the Quest oxygen tanks and begin using bottled oxygen from the robot freighter that docked last week.

Orbital Catch-22

Even before Tyurin’s trouble-shooting had quashed all hope that the Elektron could be repaired, NASA officials had begun considering the impact of the loss. In a senior staff meeting on 2 October, Space Station Manager Mike Suffredini described a space picture that was far from pretty.

According to minutes of that meeting obtained by the nasaspaceflight.com Web site, Suffredini described how the reduced oxygen capabilities on board the station were a threat to the planned 7 December shuttle launch. ”The biggest challenge will be supporting [safe haven],” he stated, adding, ”the Elektron needs to be recovered.”

In the event that the spare parts about to be delivered to the station still can’t fix the Russian unit, Suffredini added that the U.S. Oxygen Generation System (OGS) delivered on a shuttle flight last summer might be brought on line sooner than originally planned. The unit is scaled to provide enough oxygen for a seven-person crew, and for 10 during visits from other spacecraft. Unlike the Elektron, with its troublesome fluids, it uses a solid polymer for electrical conduction. ”OGS hardware is being expedited for flight [in December],” he announced.

The refrigerator-sized OGS rack, installed in the Destiny science lab module, still needs some work. A dump line to get rid of waste hydrogen gas must be installed, requiring several hours of spacewalk time. The water supply lines must also be delivered and installed. But although original plans called for water to come from a special urine processor not due for delivery for two more years, a recent redesign now allows for getting water from a special tank filled by visiting shuttle missions. If the equipment showed up and work time were found on three planned U.S. spacewalks in January, OGS could ease the breathing crunch soon afterwards.

The Catch-22 is that only a shuttle flight can reliably restore enough oxygen capacity for the station to host a stranded shuttle crew, yet without that capacity, no shuttle can safely fly.

The backup stranded crew option was put under further strain by delays in fabricating the redesigned external fuel tanks, which contributed to the decision to let the schedule for the next shuttle flight slip from February to March. However, the ”long pole in the tent”--the element that did the most to slow things down--was the imperative to keep a stranded crew breathing for another month in space, while waiting for a rescue mission.

Examining even more far-out alternatives, Suffredini added, ”negotiations are ongoing with the Russians on crew rescue.” Last summer the Russian Space Agency announced that it could accelerate its three-seat Soyuz launch rate to pick up stranded astronauts, and many reacted with skepticism. But the plan was feasible, and Suffridini’s comments show that he takes it seriously.

Meanwhile, the Russians have told NASA that they can get a completely new ’Elektron’ unit aboard their next scheduled supply drone, set to launch in February 2007, a job they had earlier said would take until spring 2007. Reportedly they have also removed other cargoes and manifested 350 new-design oxygen candles, which use Sodium Perchlorate rather than Lithium Perchlorate; these would suffice to keep three people breathing for three months. But because even these reserves won’t be delivered until after the shuttle is supposed to launch, they can’t be relied on for emergency use.

Meanwhile, NASA is considering returning the broken Elektron on the December shuttle flight, for repair and re-launch as soon as possible.

The continuing struggle to maintain sufficient reserves of breathable air has, space experts insist, a silver lining, because it allows engineers to spot and fix problems now, so that the hardware will be truly reliable on later flights beyond low-earth orbit, which will be well out of reach of spare-part shipments. The shakedown may well be the best way to ensure that future space travelers will breathe easy.

Update, November 1:

On Oct 31, cosmonaut Tyurin switched on the repaired unit, and a spokesman for the Russian Space Agency declared that "we can safely say that is now operating normally." The next morning, however, NASA's website had a different account: "An initial attempt to turn it on failed, but a second attempt did activate the unit. It ran for a short period before failing to its backup pump, where it now continues to run." Soon afterwards, NASA commentator John Ira Petty disclosed that the unit had been "deliberately" turned off again to allow Mission Control in Moscow to "perform more troubleshooting."

The crew continues to use bottled oxygen from the newest Progress freighter, and the saga of the space oxygen supply goes on and on.