Tim Furniss/LONDON
THE EUROPEAN SPACE Agency (ESA) plans to proceed with the second launch of an Ariane 5 in September as scheduled, despite the loss of flight 501 on 4 June. The demise of the first Ariane 5 over the skies of Kourou, Guiana destroyed its payload of four Cluster science satellites.
Two days after the loss, ESA and French space agency CNES were pinpointing the cause as an "electrical and software" malfunction. The findings of the ESA and CNES joint accident-investigation board will be released on 15 July, and there is likely to be relief that the failure was not, apparently, caused by an inherent design fault.
The failure of the Ariane 5 launch took just seconds to unfold. The 501 experienced intense aerodynamic loads and broke apart 31.5s after lift-off. The nozzles of its twin solid-rocket boosters had been incorrectly commanded to swivel sharply to their 6¡ limit 2s earlier, to control thrust vector. The launcher tipped over in flight.
The errant command, from a computer in the launcher's vehicle equipment bay (VEB) electronics and attitude-control system, was caused by an electrical or software malfunction which informed the computer that the vehicle's attitude was incorrect. It appears that the incident occurred as the redundant inertial-guidance system failed.
The Matra-Marconi Space-built VEB, in the launcher's second stage, contains the Sextant Avionique ring-laser gyro inertial-reference system and the Daimler-Benz Aerospace flight-programme and attitude-control-system computers.
Telemetry data indicate that the boosters and the Ariane 5's Vulcain first-stage engine were functioning perfectly as the vehicle entered its final moments, travelling at Mach 0.7 (857km/h) at an altitude of 3,500m (11,500ft).
As the vehicle broke up, the onboard self-destruct system was operated, with a duplicate command being made from the launch-control centre. Debris showered the area, some pieces coming down 1h later.
The launch of the 52m high, 730t, 5,800kN-thrust 501 had been delayed for 58min, to allow rain clouds to clear over the Devil's Island remote-camera-tracking site and to ensure that there was no risk of lightning in the murky skies at 09:33 local time. The conditions for the camera were only 60%, however, and the views of the launch and accident are not clear.
Source: Flight International
