Air Repair Cares

During the week last month when two crews were still aboard they had tried another tack. The 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. And 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.