Tim Furniss/LONDON
THE FAILURE of the maiden launch of the European Space Agency's (ESA) Ariane 5 on 4 June resulted from the booster flying with an Ariane 4 dual-inertial reference system (IRS) untested for use in a new launch environment. The system also had "specification and design errors in its software" (Flight International, 10-16 July).
The conclusion of the official inquiry board, which was led by French space agency CNES, is accompanied by 14 recommendations for actions which include a critical re-appraisal of all software, improved testing in correctly simulated launch conditions, and changes in systems and project management.
The new measures could cost up to $320 million and will mean delaying the next Ariane 5 flight well into 1997. The $7 billion programme is already 20% over budget. A plan of action and its consequences for the programme is due to be released in September.
"We are all at fault," CNES chairman Alain Bensoussan says of the Ariane contractor team, led by his agency and by Aerospatiale. "Somebody should have found the error," says Jean-Marie Luton, ESA's director-general.
The IRS, made by Sextant Avionique, had been flown on 57 successful Ariane 4 launches since 1998, but was not tested to see how it would perform in the Ariane 5's different launch profile. The inquiry board does not elaborate on the reasons for the oversight.
The alignment function of the IRS served its purpose before lift-off, as planned, but remained active during the ascent, as it does for an Ariane 4 launch. It malfunctioned when confronted with an entirely new launch profile which had not been "sufficiently" represented during testing, says the board.
The Ariane 5's faster acceleration and angular velocity, five times greater than during an Ariane 4 launch, exposed the software flaw in the IRS, which shut down both the primary and back-up flight computers, so that the booster was flying blind, travelling at a speed of Mach 0.7 (860km/h) at about 12,000ft (3,700m).
The vehicle was pitched downwards abruptly at T+29.5s after lift-off (36s after the ignition command of the Vulcain first-stage engine), when the nozzles of the two solid-rocket boosters were gimballed to their 6¡ limit, followed by a similar movement of the Vulcain's nozzle.
The Ariane 5 began to break up 2s later: its on-board self-destruct system was initiated by the rupture of the electrical links between the boosters and the core stage, triggering the final disintegration (Flight International, 12-18 June). It is recommended that the IRS' pre-flight alignment function be inhibited for launch.
Source: Flight International
