This week's computer problems aboard the International Space Station (ISS) highlight one of the challenges facing station partners as they strive to complete the orbiting outpost by 2010: dealing with aging components and ensuring enough spare parts are on hand to allow prompt fixes to problems that threaten the crew or the station.
On Wednesday, two computer systems on the Russian segment of the orbiting outpost failed as astronauts from the visiting space shuttle Atlantis were reconfiguring solar arrays. The computers help control the space station's orientation in space and run equipment that provides oxygen and scrubs carbon dioxide from the air that crew members breathe.
NASA officials expressed confidence that the problem would be solved quickly. But the computer outage did prompt them to make plans to extend Atlantis's stay at the station for an extra two days. This would give Russian engineers extra time to deal with the problem if they needed it, since the shuttle could be used to help keep the station in its proper orbit.
"We have plenty of resources, so we have plenty of time to sort this out," said ISS program manager Michael Suffredini during a briefing late Wednesday evening.
By Thursday morning, the situation "was looking a lot better than when we went to bed last night," added John Ira Petty, a spokesman at the Johnson Space Center in Houston. The Russians had re-established communications with one of the two systems, which provides overall command and control for the Russian segments. From there, it would be a matter of "cleanup and troubleshooting" to determine why the computers failed to reboot as planned after they went down, he said.
Yet to some analysts, such problems are likely to crop up with increasing frequency as time passes. While much attention has focused on the new elements the shuttle has been delivering to the station, those elements are being bolted to a core whose key components have been in orbit since the late 1990s. Some parts exceed their original design lives.
"In many cases, these things work just fine," says Keith Cowing, editor of the on-line service NASA Watch and a former payload-integration specialist with the space station program. "But the system is aging, and it's not always aging smoothly."
He notes, for instance, that the core of the Russian command module was originally built as a replacement element for the Mir space station, which ended its career in 2001. "It was sitting on the ground years before it flew, and it's been up for six or seven years now," he says. "Computers in the US segments use radiation-hardened 386 processors," which today's computers industry has long since left behind. "Who knows what the Russians are using," he says.
The issue of spare parts – at least as it pertains to the US – came up earlier this year in a report from the International Space Station Independent Safety Task Force. It recommended that the National Aeronautics and Space Administration spend $1 billion more than it currently allocates to ensure the station has an adequate supply of spare parts and the transportation needed to get them there. Shuttle managers have noted that toward the end of the decade, when the shuttle program is slated to end, three missions could be dedicated to delivering large quantities of supplies and spares to the station. In addition, the space agency is spending some $500 million to help two start-up US rocketmakers develop vehicles capable of resupplying the station. In addition, the Europeans have been developing an automated transfer vehicle to ship supplies to and from the station. The first is slated for launch aboard an Ariane V rocket next year.
Yet as the ISS program has been pared back over the years, so has its spare-parts program.
Initially, Mr. Cowing says, the program was intended to have a storehouse of spares available for relatively immediate delivery. As envisioned, "station crew members could call down and replacements would go up with the next shuttle."
Now, the approach has shifted to "we'll make them as we need them," he says.
While station controllers and engineers focused on the computer glitch, shuttle astronauts were preparing to add an in-flight repair task to their own to-do list. During launch, a corner of one of Atlantis's quiltlike heat shields, which cover two large pods at the rear of the craft, peeled up, leaving a small section of one of the pods exposed to the heat of reentry. Mission managers say that the region doesn't heat nearly as much as the underside of the craft or the leading edge of its wings or tail. But similar events on past shuttle missions have led to damage that ground crews had to repair after the orbiters returned.
There are just enough engineering uncertainties on how this exposed area would respond to the heating to prompt a decision to repair the corner. This Friday, astronauts are scheduled to fix the shield during a spacewalk.
While it would be the first on-orbit repair of the shuttle's thermal-protection system, it won't require the elaborate repair materials and techniques the program has developed since the Columbia shuttle accident in 2003, notes John Shannon, deputy director of the shuttle program. Instead, the crew members will use metal staples from the medical kit and a makeshift sewing kit to secure the corner. Ideally, officials would like the repair to hold all the way to the ground, Mr. Shannon says. But as long as it holds through the period of highest heating on reentry, the shuttle could safely lose that blanket segment later on.