Launch of the European Space Agency’s Automated Transfer Vehicle (ATV) has been delayed by 12 months, to May 2007, by a major flight-control software rewrite and other technical problems. The software rewrite, which has cost millions of dollars to complete, was carried out after the Russian Federal Space Agency expressed concerns, writes Rob Coppinger.

The rewrite has caused problems for ESA’s flight-simulator software, which has needed modification and reverification – an ongoing process. “It’s so complicated, expensive and important we want to do it right,” says ESA’s head of development, Alan Thirkettle. Nine of the 19,600kg (43,000lb) ATV cargo craft are to be launched by Ariane 5 ECA to supply the International Space Station (ISS).

Other issues adding to the delay include a fault-tolerance problem in a solar-panel deployment drive and failing attitude-control thruster valves. The solar-panel drive was unsuccessful in failure mode tests and had to be redesigned, while a small rod inside the thruster actuator valve kept failing fatigue tests. The decision to remove the rod required assembled and verified sections of the ATV to be disassembled to extract all 48 valve rods.

ESA has fixed-price contracts with its industrial partner for the ATV, so the agency will not have to absorb the extra costs from the problems. The agency had concluded that, with extra shifts and weekend work, the ATV could be ready by the end of 2006, but the proximity to a planned Russian Progress supply-vehicle launch to the ISS persuaded managers to put the maiden flight back a few months.

The unmanned ATV was to have delivered supplies to the ISS from 2003. The date has been steadily pushed back until the decision this year to delay the launch from October to May 2006, and now May 2007.

Source: Flight International