Space Station Fails to Boost Orbit in Engine Test
The Progress 21 cargo ship is tucked into its launch shrouf in preparation for an April 24, 2006 launch.
Credit: RSC Energia.

The International Space Station (ISS) failed to reach a higher orbit Wednesday during a test of two long-dormant engines mounted near a Russian-built docking port.

Russian ISS flight controllers hoped to test two engines along the aft end of the station's Zvezda service module during a 14-second burn planned for 3:49 p.m. EDT (1949 GMT), NASA officials said. The engines have not been fired since Zvezda docked at the ISS in July 2000, they added.

"We were all set for it but the engines never fired," NASA spokesperson Rob Navias told SPACE.com.

The two dormant Zvezda engines are located at the module's aft, a common docking port for Russian Progress cargo ships and Soyuz spacecraft - one of each are attached to the ISS currently - which can also use their own engines to boost the station's orbit. Other ISS engines are also available and NASA space shuttles can also raise the station's orbit during docked operations.

"These are basically a backup to a backup of the prime engines on the module," Navias said of the aft Zvezda engines.

A stuck propellant isolation valve in one of the two engines prevented Zvezda's computers from performing the brief reboost maneuver, which was expected to nudge the ISS just three-tenths of a mile (0.4 kilometers) higher than the station's current orbit of about 213.1 statute miles (342 kilometers).

The reboost scrub does not affect plans for the arrival of Progress 21 - an unmanned cargo ship slated to launch toward the ISS from Baikonur Cosmodrome in Central Asia's Kazakhstan on April 24.

ISS flight controllers at NASA and Russia's Federal Space Agency expect the Progress 21 supply ship to deliver its cargo of food, water, clothes and other vital equipment to the space station's Expedition 13 crew, commanded by Russian cosmonaut Pavel Vinogradov with U.S. astronaut Jeffrey Williams serving as flight engineer. Vinogradov and Williams arrived at the ISS on April 1 after their own two-day spaceflight from Baikonur Cosmodrome. The two astronauts are in the opening weeks of an expected six-month mission.

Earlier Wednesday, Williams sent a short message and video of himself exercising on a stationary bicycle down to Earth to support friends participating in the MS 150, a Texas bicycle race from Houston to Austin this weekend supporting the Lone Star Chapter of the National Multiple Sclerosis Society.

Like the Expedition 13 crew, Progress 21 is also expected to take two days to chase down the ISS before docking on April 26. The Russian space freighter is currently scheduled to dock at the aft end of the station's Zvezda module at 1:52 p.m. EDT (1752 GMT) during a live broadcast of NASA TV. The cargo ship will join a previous supply vehicle already docked at the station, Progress 20, which arrived at the ISS on Dec. 23.

NASA will begin broadcasting Progress 21's ISS approach at 1:00 p.m. EDT (1700 GMT) on docking day. SPACE.com's feed of NASA TV is available by clicking here.