Space station lights its ‘big engines’

James Oberg NBC News space analyst

HOUSTON - For a routine orbital boost last week, the international space station pulled off a new trick that significantly enhances the outpost's operational flexibility and safety. Experts at Russian Mission Control successfully ignited a set of maneuvering thrusters that had not been used for seven years — and that had refused to fire in several previous attempts.

Mission Control's Nikolai Kryuchkov said controllers decided to use the station's main engines on the Russian-built Zvezda service module for last week's boosts —rather than following the usual routine, which relies on the smaller thrusters on a docked Progress cargo craft. The big engines were previously used when Zvezda docked with the station's earliest modules, back on July 24, 2000.

"The fact that the Russian engines operated well now proves their high reliability and long service life,” Kryuchkov said.

Having those main engines working will be increasingly important in the years ahead, Susan Brand, NASA’s manager for the current space station expedition, told MSNBC.com in an e-mail.

She acknowledged that the station's orbit could get a boost from Russian Progress ships as well as the European Space Agency's Automated Transport Vehicles, which are due to enter service this year.

“However, in the process of managing and planning all of the vehicle traffic to the ISS, there will be more frequent and longer time periods that no vehicle will be docked to the aft end of the service module,” she continued. “During these time periods, reboost capability will be available using the service module thrusters. These service module reboost tests reconfirm the performance of these engines to support future operations.”

Why those boosts are neede
Reboosting is performed both to line up the station’s orbit for future visits and on occasion to dodge a too-close predicted space debris fly-past. In the past, docked shuttles used surplus maneuvering fuel to push the station upward, but changes in the station’s size and location of docking ports have basically eliminated that option.

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Firing these two engines, which are positioned 180 degrees apart near the outer rim of the Zvezda's service module’s aft end, was made possible by the absence of a transport vehicle docked to the port there. A Soyuz carrying the station's returning Expedition 14 crew and space passenger Charles Simonyi had undocked a week earlier, and the next robot supply ship is scheduled to arrive on May 15.

Both engines were first test-fired for 30 seconds last Wednesday. That cleared the way for an 80-second firing on Saturday.

The previous “oldest engine” firing had been 20 years ago, when thrusters of the same design were installed aboard the Salyut 7 space station, launched in April 1982. They were last used four years later during a joint maneuver with the just-launched Mir station.

Requalifying the engines for continuing use on the international space station, and conducting operational firings over the next five to 10 years, will extend their certified lifetime significantly. For Earth orbit missions, alternative thrusting is almost always available from docked supply ships, but it is reassuring to now have the ability to perform an “anytime” debris avoidance burn when such a ship is not docked to the station.

The biggest benefit has to do with developing long-term certification for such thrusters on interplanetary missions of the future.

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