Arianespace restored some confidence with the successful launch of its proven Ariane 4 on 17 December, carrying New Skies Satellites' NSS-6, less than a week after the failure of the Ariane 5 ECA on its maiden flight. The Ariane 44L launch of the Lockheed Martin-built communications satellite was the 73rd consecutive successful Ariane 4 flight, and the penultimate mission for the booster, which is being phased out in favour of the larger Ariane 5.
On 6 January, an Arianespace, European Space Agency (ESA) and French space agency CNES inquiry board will report its findings on the 11 December failure of the uprated Ariane 5 ECA. The company still plans to launch ESA's Rosetta comet explorer between 13 and 31 January using the basic Ariane 5G, as the probe into the loss of flight 157 focuses on changes incorporated in the improved ECA model.
The Ariane 5 ECA's core stageuses the Snecma Vulcain 2 cryogenic engine, which produces 20% more thrust. Reports suggest the Vulcain 2's longer and wider nozzle, developed by Volvo Aero, may have been damaged during the period of maximum dynamic pressure. This could have resulted in a thrust asymmetry that only became apparent after separation of the solid-rocket boosters, which provide 92% of take-off thrust.
Cooling-circuit pressure on the Vulcain 2 core-stage engine reduced at T+96s, 24s after maximum dynamic pressure. The twin solid-rocket boosters were jettisoned after a further 41s and, starting at T+178s and lasting for 8s, "engine speed changed and a significant flight control perturbation occurred", says Arianespace. Payload fairings were jettisoned at T+187s, but the launcher's attitude was not correct and the vehicle demonstrated "erratic behaviour".
Control was lost at 150km (93,000 miles) altitude and the vehicle began falling back to Earth. By T+455s the vehicle had descended to 69km and was 800km downrange when it began to break up and was destroyed by the range safety officer, with the loss of two communications satellites, Eutelsat's Hot Bird 7 and CNES's Stentor, jointly worth $600 million. The new ESC-A cryogenic upper stage was never used. The Vulcain 2 was apparently underperforming during the whole ascent. The uprated engine burns a mixture with 20% more liquid oxygen under higher pressure, which required development of a new turbopump by Fiat Avio.
The Ariane 5 has suffered two launch failures in 12 flights, including its maiden mission in 1996, and two failures to reach the correct orbit.
Source: Flight International
