The new Alphabus platform recently sailed through a real life shock test. Analysis results show the platform coped extremely well with the launcher shocks, including the explosive “Shogun”.
The Shock Generation Unit or “Shogun” test is a simulation of the shock transmitted to the spacecraft when its protective fairing separates from the rocket´s upper stage. A set of pyrotechnic devices are screwed to the bottom of the launch adaptor. With all staff withdrawn to safe positions, these explosive charges are set off instantaneously. When fired, the segments rupture mechanically and generate a shock wave similar to the one seen in flight. The shock then propagates through the launch adaptor, through the clampband, into the spacecraft and via the structural elements to each unit on the spacecraft.
The end results of this shock testing campaign show that Alphabus fully complies with the launch environment requirement. Its compliance status is considered similar or better than that of a standard telecom platform.
The Shogun test was performed in Intespace facilities in Toulouse, using a combination of resources and personnel from Astrium, Thales Alenia Space, RUAG Space (Sweden), CNES and ESA, under the leadership of Arianespace.
A shock test on the Alphabus platform was initially not foreseen, said Mr. Philippe Sivac, ESA Alphabus/Alphasat Assembly Integration and Verification Manager.
“Alphabus relied on the Ariane 5 low shock fairing (HSS-3) and with the heritage from existing product lines, qualification with sufficient margins could be demonstrated by analysis. The picture changed after the grounding of HSS-3 and the return to the HSS-1 which has a more stringent shock input. With no available short term damping solution for the Alphabus platform, Arianespace issued a higher shock specification for Alphabus. Compatibility could then no longer be demonstrated by analysis alone.”
Performing a shock test on an integrated platform like Alphabus is not an easy task, explained Mr. Sivac. If sensitive flight units remain on the structure during the test they could break, but if too many are removed the platform will respond severely to the shock input with dangerously high levels. Eventually, a configuration was found where a selection of critical units were replaced by representative dummy hardware, however all damping elements such as harnesses, thermal control hardware and piping remained as per flight.
Measurements just above the spacecraft separation plane allowed Arianespace to recalculate the transfer function between the base of the launch adaptor and the bottom of the spacecraft. Based on this, Arianespace released a new, lower shock specification for Alphabus.
Using the measurements inside the spacecraft, the prime team reassessed the qualification of each unit by comparing its qualification test at unit level to the level expected in flight. The positive results of this assessment was delivered at a final meeting on 17 September between the Alphabus Prime contractor Astrium and Thales Alenia Space and ESA/CNES, and will provide the basis for the overall Ariane 5 mission analysis to be performed by Arianespace for Alphasat.
Alphabus, the new European high-power telecommunications platform jointly developed by Astrium and Thales Alenia Space under a joint ESA and Centre National d'Etudes Spatiales (CNES) contract, is a coordinated European response to the increased market demand for larger telecommunication payloads. A wide range of commercial payloads to provide TV broadcast, broadband multimedia, internet access mobile or fixed telecommunication services can be accommodated on Alphabus.
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