TIM FURNISS / LONDON
Cooling problem identified in Vulcain exhaust nozzle, while 5G mission may miss window
Arianespace hopes to fly the Ariane 5 ECA again within six months, after an inquiry board concluded the launcher's 11 December first flight failed due to a cooling problem in the exhaust nozzle of the uprated Vulcain 2 main engine. The launch provider will have a plan by 20 January to return the Ariane 5 ECA to service in the second half of 2003.
Launch of the European Space Agency's Rosetta asteroid and comet explorer by a basic Ariane 5G is still in the balance, as the inquiry board requested an "exhaustive examination" of the flight behaviour of the Vulcain 1 engine nozzle on the baseline launcher. Verification work is under way, and Arianespace will make a decision on the launch this week. The Rosetta must fly by 31 January or it will miss its target opportunity.
Failure of the improved Ariane 5 ECA on Flight 147 began with a leak in the Vulcain 2 nozzle's cooling circuit, followed by overheating and loss of nozzle integrity. This caused "a major imbalance in the thrust" of the cryogenic engine, leading to "a loss of control over the launcher's trajectory," the board says.
The likely cause was a combination of fissures in the cooling tubes, which degraded the thermal condition of the nozzle, and "non-exhaustive definition" of the loads to which the engine is subjected during flight. The board noted the flight loads would be difficult to simulate during ground tests.
The board recommends modification of the Vulcain 2 nozzle, taking into account experience gained on 12 flights of the Vulcain 1. The cooling tubes, which form the structure of the Volvo Aero-supplied nozzle, are a different shape on the Vulcain 2, and the technology of the nozzle stiffeners also differs.
The board also calls for research into possibilities for ground simulation of the actual loads observed during Flight 157. The quality of flight hardware should also be enhanced, and acceptance procedures made stricter, says the board. Meanwhile, the last Ariane 4 flight is set for 11 February and the next commercial Ariane 5G flight for 24 February.
Failure of a Proton K on 26 November during an International Launch Service (ILS) mission was caused by excess propellant in the Block DM upper-stage engine. This caused overheating and an explosion during ignition of the stage's second burn, which in turn led the Astra 1K satellite to separate in a low transfer orbit from which it could not recover, says a Russian inquiry board.
Source: Flight International
