Flight control teams in Moscow and Toulouse combed through International Space Station electrical data on April 2 in a bid to pinpoint the cause of a Russian power system failure that nearly prompted a premature jettison of the European Space Agency’s recently docked Automated Transfer Vehicle-3.

An undocking of the propellant-laden ATV that would have taken place April 2 was averted over the weekend, as personnel at the ATV Control Center in Toulouse, Mission Control-Moscow and Mission Control-Houston teamed to power the 35-ft.-long freighter through a backup Russian Equipment Control System (RECS) channel. Aboard the orbiting science lab, the six-man crew joined the hastily planned March 31 response to the failure by off-loading the ATV-3’s high-priority dry cargo: food, clothing and spare parts.

Though the cause of the failure had not been determined, ATV-3 systems were functioning normally and control teams were proceeding with plans for an April 5 re-boost of the orbital outpost using the supply capsule’s thrusters, according to Rob Navias, a spokesman for NASA, which manages the 15-nation station partnership.

The troubleshooting has not determined whether the primary RECS channel can be recovered, Navias says.

The third of five planned ESA ATVs docked smoothly late March 28, berthing to the aft end of the station’s Russian segment. It is to remain there through late August, serving as a propulsion source for regular station altitude as well as occasional debris-avoidance maneuvers.

Within 24 hr. of the linkup, the primary RECS power feed tripped as fans in the ATV turned on to filter the air prior to crew entry. The air filtration operation was under evaluation as a possible cause for the power problem, Navias says.

By late March 30, there was a new wrinkle as efforts to troubleshoot the interruption and activate the RECS backup were underway. Though the ATV-3 is also solar-powered, the beta angle, or orientation of the Sun on the station’s orbital plane, is increasing. Control teams determined that the freighter’s solar arrays would become too shaded by April 2 to provide a secondary source of electricity, adding urgency to the activation of the RECS backup.

The RECS backup was successfully activated on March 31 shortly after 1 p.m. EDT. In the meantime, station commander Dan Burbank and his U.S., European and Russian crewmates managed to unload 40% of the ATV-3’s 4,800 lb. of dry cargo.

With electricity flowing, the control teams also proceeded with a scheduled 6-min. 51-sec. station re-boost on March 31, using the supply ship’s thrusters at 5:54 p.m. The dual thrusters raised the station’s mean altitude by 1 mi. to 243.6 stat. mi. Though serving as a test of the ATV-3 propulsion system, the maneuver also positioned the station for upcoming cargo and crew transport activities.

Those include the April 20-22 launch and docking of Russia’s 47 Progress supply ship; the April 27 descent of three station crewmembers aboard the 28 Soyuz transport; and the May 15-17 launch and docking of the 30 Soyuz transport with replacements.

Scheduled April 5 operations with ATV-3 propulsion will provide a refinement of the weekend maneuver.