Troubles of an old space station

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.

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