TIM FURNISS / LONDON
Launch earmarked for November after Arianespace takes action on malfunction
Arianespace hopes to launch the next Ariane 5 commercial booster in November after taking corrective measures following the failure of an Ariane 5 to place its Artemis and B-SAT 2 satellites into the correct orbit on 12 July.
An enquiry board says that the failure was due to a malfunction in the EPS upper stage, described as "a combustion instability" during the Aestus engine's ignition, which reduced thrust and led to the premature shutdown of the engine due to the early depletion of one of the propellants.
The strong pressure variation responsible for the instability, described as a pressure peak or overshoot, was attributed to "a dynamic hydraulic coupling" or interaction between the EPS "propellant feed systems" and the engine's combustion chamber internal circuits.
The board recommends that the upper stage hydraulic conditions should be dynamically modelled mathematically, the EPS stage ignition phases improved to make it steadier and smoother, and "the qualification criteria" be adapted to the modified ignition phase.
The board adds that test benches should be adapted "to more closely duplicate" flight conditions, in-flight operating margins must be demonstrated by an engine test programme, and the next flight engines should be qualified according to these new criteria.
Arianespace, in conjunction with the European Space Agency and French space agency CNES, has defined an action plan based on the board's findings.
As well as engine qualification, there will be a thorough analysis of the data recorded during ground tests and in-flight operations of the Aestus engine and EPS stage, especially data allowing an in-depth analysis of the ignition system.
Dynamic modelling of the propellant supply system will also be conducted, with mechanical modelling of certain combustion chamber parts and analysis of the hydrazine propellant flow control system.
The partners "will define, validate and qualify" the modifications needed for the ignition system and modify the engine test bench to more closely duplicate flight conditions. Production quality, inspection procedures and application and acceptance procedures for Aestus engine modifications will be reassessed for future flights.
The next Arianespace mission will be a launch of the Intelsat 902 communications satellite this month aboard an Ariane 44L.
Source: Flight International
