Europe’s ATV on Track for April 3 Docking with Station

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PARIS — The inaugural flight of Europe’s Automated Transfer Vehicle (ATV) cargo carrier, after an initial hiccup caused by an overly cautious failure-detection system, delivered on its promise during test maneuvers. As a result, the automated spacecraft likely will be cleared for an April 3 docking with the international space station, ATV program managers said.

At three times the size of Russia’s Progress cargo ship, the ATV will be the biggest unmanned machine ever to approach the orbital complex. It is routinely described as the most complex piece of hardware ever launched in Europe.

Launched March 9 from Europe’s Guiana Space Center aboard a specially designed Ariane 5 rocket, the 19,000-kilogram ATV is viewed by its government and industrial builders as potentially opening a vast new terrain in space exploration for Europe.

These officials said it would not take much for the ATV to be modified to become a crew-habitation module, an orbital refueling point or a way station for future planetary exploration missions.

In the shorter term, ATV gives its prime contractor, Astrium Space Transportation of France and Germany, a powerful card to use as NASA determines how it will service the station once the space shuttle is retired in 2010.

“It is always nice to have a demonstrated system in your briefcase when you negotiate, as opposed to great ideas that have never been in orbit,” said one European industry official, referring to the several private-sector efforts in the United States to build vehicles for commercial station-servicing duties.

The European Space Agency (ESA) owes the station’s prime contractor, NASA, the equivalent of an ATV flight every 18 months to compensate for costs that Europe will incur by using station resources for its Columbus laboratory, which recently docked to the station. Beyond this barter arrangement, ATV is available for commercial sale to NASA, whose treaty obligations to the station’s partners – Russia, Japan, Europe and Canada – extend to late in the next decade.

The job of the first ATV, named Jules Verne, will be to deliver oxygen, fuel, water and other supplies to the international space station. ATV also is capable of re-boosting the station into its operational orbit, a function that is regularly needed because the orbital outpost’s altitude tends to drop because of atmospheric drag.

In a key maneuver designed to prove its safety, the ATV successfully completed a key test of its emergency-abort sequence March 14, performing a collision-avoidance maneuver that ground teams hope will never be needed when the time comes to dock with the international space station.

In the maneuver, the vessel was stopped in its tracks and thrown into reverse, firing four of its thrusters to move backwards at a speed of around 5 meters per second to simulate a slow retreat from the space station.

It is this maneuver that will be required if, as it approaches the station for a planned April 3 docking, its speed, approach angle or some other parameter is judged unsuitable for docking.

The March 14 test also demonstrated the ability of ATV to switch to its independent backup computer, which would be required only if there are multiple failures of the main computer system, which has its own backup.

ATV managers say it is a highly unlikely scenario, but one that must be planned for given the delicate nature of having a machine the size of ATV approach the station.

With its main computers shut off, the ATV automatically placed itself into survival mode, pointing toward the sun to continue to feed its four power-generating solar arrays to await further instructions from ground teams.

“Going into survival mode is obviously something we would prefer not to do,” Alberto Novelli, the European Space Agency (ESA) mission director at the ATV Control Center in Toulouse, France, said in a March 14 interview. “But it was an absolute requirement of the station partners that we do this.”

About 95 minutes after the reverse-thrust command, the vessel’s main computers were switched back on. It is expected to remain in its current orbit of some 305 kilometers in altitude until March 18, when it will begin its transition into higher orbit as it prepares its approach to the space station. The station’s current orbit is about 340 kilometers in altitude.

After March 18, the ATV will remain in its parking orbit some 2,000 kilometers in front of the station until it prepares for the final approach and the April 3 docking.

The ATV’s early moments in orbit after a trouble-free Ariane 5 launch were marked by what appeared to be a failure of one of the four propulsion systems, each of which governs seven ATV thrusters.

The computer overseeing this thruster pack shut down the propulsion after reporting a pressure difference between the lines feeding the motor with hydrazine fuel and those feeding the fuel oxidizer. Then the computer shut itself down, as designed, just in case the problem was one of analysis, not pressure.

“What we later found is that there was a slight difference in pressure, but that this is a normal event,” ESA ATV Project Manager John Ellwood said March 11. “Spacecraft in orbit often see these minor pressure differences when first starting the propulsion, but in this case our system reacted immediately, and shut it down.”

Propulsion control was immediately transferred to another of the seven-motor thruster packs. ATV is designed to function with only three of the four systems operational, and a permanent loss of one would not, in itself, have compromised the mission, Ellwood said.