The European Space Agency (ESA) is to fit a second attitude control system to the Ariane 5 in a bid to counteract a stronger than planned roll torque, which endangered the success of the second test flight of the new Arianespace launcher.
The extra system will be fitted to the Ariane 503 scheduled to make the final development flight in July.
The attitude control system will double present performances and is designed to counteract a roll torque of 2,000Nm (Newton metre). The roll rate of flight 502, launched on 30 October, rose to 33¹/s (about 5.5rpm) at the end of the firing of the Vulcain core first stage engine, caused by a 900Nm torque generated by the unit.
The original system had been programmed to counteract a roll torque of less than 300Nm. "Additional tests on the engine, and in flight, are needed to define whether this roll torque is inherent to the engine's design", says ESA.
Engineers conclude that the excessive roll torque on the 502 was caused by either "roughness" in the inner surface of the Vulcain's nozzle, or was the breaking of a rod that holds the turbopump outlets attached to the main nozzle.
Source: Flight International