Space station lights its ‘big engines’

Previous frustrations
The thrusters provide eight times the push that the smaller Progress engines provide, but the acceleration is still so small as to be practically unnoticeable inside the station. There were no known crew reports describing any feelings, or any sound, or sight out the windows, associated with the firings.

An attempt to test-fire the pair of engines on April 18 last year was aborted at the last minute when one of the protective covers failed to open fully, due to physical interference from an antenna placed there by spacewalkers in 2003. Astronaut Mike Fincke, who made that spacewalk with his cosmonaut colleague Gennady Padalka, later explained that the antenna was installed in support brackets that made sure it was in proper position — but the position had apparently been measured incorrectly by engineers at the spacecraft factory.

Late last year, that antenna was moved during another spacewalk. But whether that was the only problem remained to be tested.

Real redundancy
The frustrations and ultimate success of this operation further underscore some key principles of operating a big space station in orbit:

• The station has grown too complex and has undetectably diverged too far from ground documentation to ever expect all ground-planned processes to work as designed. Surprises, and sometimes unpleasant surprises, will occur with growing frequency, and the only workable approach is to make plans based on such guaranteed uncertainties.
• Because the space station is on a long-term series of expeditions rather than a short-term dash, there is usually enough time to react to such surprises with tools and techniques at hand, or quickly developed.
• The long-term certainty of hardware breakdowns and operator errors means that redundancy in critical capabilities — such as an extra thruster system, an extra spacesuit and air lock system, an extra oxygen system — has proven far more valuable than the station’s designers had originally expected. This is especially true when the redundant systems aren’t simply "extra copies" of one design, but are based on different engineering principles, even on hardware from different nations.
• For decades humans have operated in Earth orbit, where resupply is feasible, spare parts and new tools can be delivered, and emergency landing always an option. The transition in operational and design concepts to missions to the moon and beyond absolutely requires developing and trusting hardware for very, very long lifetimes (and multiple repairs) in space. There may be a lot of space out there, but there is only one place where such hardware can receive the required testing and validation: the international space station.

That’s the context of past, present, and future for this otherwise-routine space technology demonstration. Firing these long-unused rocket engines and adding them back into the "hip pocket" of available capabilities at the space station is another step in that direction.

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