Angry scientists may sue those responsible for the loss of the Ariane V rocket which exploded after take-off in June, destroying their scientific payload, Cluster.

The European Space Agency revealed this week that the rocket failed because of a software problem. A major design flaw, not a minor internal problem, was built in from its inception. Scientists also failed to test the system properly.

"From the very first it was never going to work," said Andre Balogh, principal investigator for one of the Cluster instruments and professor of space physics at Imperial College, London. "It is very serious negligence. I'm convinced that it is at a level well within the scope of what the courts deal with in medical negligence."

Jean-Marie Luton, director general of the European Space Agency, said on Monday: "There have been errors of conception, of specification and of verification in testing. There are no individual guilty people. We are all guilty and we all accept guilt."

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The main reason for the explosion was that software used to control Ariane V's predecessor, Ariane IV, had been brought in for use in Ariane V without being tested in relevant conditions.

"It is not just hindsight which says that this should have been done before," said Professor Balogh. "It was a complete failure of management to allow this kind of failure to creep into the system."

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The Cluster scientists had accepted a free trip on Ariane V's maiden launch. The trip was uninsured and probably uninsurable and it has been suggested that the four Cluster satellites would have been too expensive if the launch had not been free.

Professor Balogh likened the error to "a software company releasing the beta version of a software [to the public] for testing" - a reasonable approach for home computer software but not for software for a critical application. "We were customers, albeit non-paying customers," he said.

He said that the principal investigators will meet on Monday, when the possibility of suing the two bodies involved, ESA and CNES (the French government's Centre Nationale d'Etudes Spatiales), will be discussed. The scientists will probably end up demanding a "free and safe launch" of a new version of Cluster on the next Ariane V rocket in compensation, he said.