Engineers assess problem aboard Jules Verne craft
BY STEPHEN CLARK
Posted: March 9, 2008
An electronics box on Europe's first cargo ship shut down a propulsion system command chain responsible for a quarter of the space-age delivery truck's maneuvering thrusters, officials said Sunday.
"We really don't think it's anything serious, but we're studying it prudently," said Alan Thirkettle, the European Space Agency's international space station program manager.
During the propulsion system's activation sequence moments after reaching orbit, Jules Verne's computers noticed a slight pressure difference between the ship's hydrazine fuel and nitrogen tetroxide oxidizer being fed through valves. The suspect chain controls seven of 28 attitude control jets and one the ship's four main engines, according to Nicolas Chamussy, ATV program manager for contractor EADS Astrium.
"This is something we're looking at in a lot of detail now," said John Ellwood, ATV project manager. "I think the very good news is that all the failure detection and recovery action all went perfectly. It measured a small anomaly, immediately went onto the other chain, which is working perfectly."
Jules Verne's main engines are positioned at the back end of the spacecraft, while the smaller thrusters are scattered across the exterior of the ship.
The system is certified to work with three electronics chains, but officials want the cushion of a backup system, particularly during precise maneuvers near the space station.
"There is an off-nominal situation somewhere in one of the four propulsion chains, and that's what we now investigate," Thirkettle told Spaceflight Now.
In the meantime, managers ordered controllers to temporarily halt plans for the vessel's first major engine firing later today. The maneuver was the first in a series of burns designed to raise the ship's altitude, culminating in the craft's arrival in a parking orbit about 1,200 miles in front of the station by March 19.
"We will be a bit cautious now because we're now on a redundant chain, so we don't want to go on another redundant chain," Ellwood said.
ESA and EADS Astrium engineers are devising a plan to reintegrate the electronics that ordered the switch into the propulsion system's command structure over the next few days. Ellwood said he expects the reconfigured electronics will help engineers determine what happened in the first propulsion chain.
The electronics system is designed to turn itself off after switching chains in case the problem lies within the electronics box itself.
The issue could be due to an electronic fault or a problem within a maze of propellant and helium gas lines leading from Jules Verne's tanks to the ship's thrusters, Ellwood said.
A command box called Propulsion Drive Electronics, or PDE, controls the extensive network of tanks, pipes, valves, and thrusters.
"What happened last night was the PDE detected there was some difference in the pressures between the (nitrogen tetroxide) and the (hydrazine), said this is an anomaly, and as planned, the software took over and put it onto the other chain," Ellwood said.
If engineers are able to resolve the issue, the chain could be restored to operational capability after extensive testing, Chamussy said.
Officials said engineers have ample time to diagnose the trouble. Jules Verne was to have loitered ahead of the outpost for more than a week to wait out the shuttle Endeavour's assembly mission to the complex, scheduled to wrap up with an undocking March 24.
Plans then called for the ATV to move toward the station, conducting two "demo days" to check out its rendezvous capabilities before pressing ahead with docking April 3.
"We have the 10-day margin before we need to start going into demo days at the end of the month," Ellwood said.
The electronics snafu is the first glitch in Jules Verne's mission, which began smoothly at 0403 GMT Sunday (11:03 p.m. EST Saturday night) with blastoff from the French-controlled spaceport in Kourou, French Guiana.
The heavy-lifting Ariane 5 rocket, specially modified for the ATV mission, released Jules Verne at about 0510 GMT (12:10 a.m. EST). Telemetry from the nearly 43,000-pound spacecraft confirmed it unfurled its four solar array wings and deployed a critical communications boom within the first three hours after launch.
"We can simulate until the cows come home, but this is the first opportunity the control team has to work a real off-nominal situation," Thirkettle said.