NASA Spaceflight.com by Justin Davenport July 30, 2021
Close to one year after its last flight, the Ariane 5 ECA has returned to service with its first launch of 2021, lifting off at 21:00 UTC on Friday, July 30. The sixth overall mission for Arianespace this year follows a rework of the payload fairing due to vibration issues that could have endangered payloads.
On board the mission, named VA254, were two communications satellites bound for geostationary transfer orbit. This flight is the first of two that precede the launch of the James Webb Space Telescope as early as this November.
The JWST program found that residual air in the telescope’s sunshield could cause an over-stress condition at the time of fairing separation, so the payload fairing was redesigned for a smoother de-pressurization process with new passive vents and sealant to trap air inside the fairing’s honeycomb material, in order to help ensure mission success for this most important payload. RUAG of Switzerland delivered these fairings for flights starting in early 2020.
However, during the Ariane flights in February and August 2020, the separation process with these redesigned fairings induced unacceptable vibrations into the payload stack. While these vibrations did not result in any sort of mission failure, Arianespace stopped flights of the Ariane 5 to investigate the issue.
The investigation also affected certain United Launch Alliance Atlas V flights that use similar fairings.
Although no damage was done to the payloads on board the two flights where these vibrations were observed, they could have damaged the JWST and other future payloads, so a further redesign of the fairing was needed. The reworked fairings were delivered by RUAG to Arianespace and must now prove themselves on two flights before the James Webb Space Telescope can proceed on its long-awaited launch.
More:
https://www.nasaspaceflight.com/2021/07/ariane-5-loft-satellites-james-webb/
