In December of last year, two of Airbus’ Pléiades Neo Earth-imaging satellites intended for a polar Sun-synchronous orbit aboard an Arianespace Vega C rocket ended up in the Atlantic Ocean instead.

The European Space Agency (ESA) announced the cause of the failure, as determined by an independent commission, last Friday: a gradual deterioration of the Zefiro 40 engine nozzle.

“More precisely, the Commission confirmed that the cause was an unexpected thermo-mechanical over-erosion of the carbon-carbon (C-C) throat insert of the nozzle, procured by Avio in Ukraine. Additional investigations led to the conclusion that this was likely due to a flaw in the homogeneity of the material,” said a prepared statement posted by both the ESA and Arianespace.

The commission concluded the design of the Zefiro 40 was fine, but the C-C material didn’t meet flightworthiness criteria and thus can no longer be used in the rockets. Instead, the rocket will use the Zefiro 40 design but with a different C-C material. That material is already in use in two different nozzles made by the same company, Avio, for Arianespace’s predecessor launcher, Vega.

“During the development program it was found that availability of European material in the necessary quantities and on the schedule compatible with the development program was unfortunately not possible. Therefore the other alternative was selected. After such selection a very deep investigation on the suitability of this material was carried out as a part of the qualification program,” Avio CEO Giulio Ranzo
said (VIDEO) in a press conference on Friday.

According to Ranzo, Avio had no reason to suspect the material was inadequate.

The commission offered its recommendations, including additional testing, analysis, and qualification phase with the alternative C-C material, as well as a "set of actions, aiming at guaranteeing a long-term reliable and sustainable launcher production."

The actions set out in the recommendations were said to be underway so that one day Vega-C can fly again, hopefully by its targeted launch data of the end of 2023.

According to a statement from Avio, Arianespace has also updated its launch schedule to reassign a mission to one of the Vega launchers by the end of summer 2023.

The backlog currently sits at 14 flights: 12 for Vega-C and 2 on Vega. As for who will pay for the added associated costs, Avio said:

In Friday’s press conference, European Space Agency director general Josef Aschbacher
said the launch failure represented the third in the last eight flights of Vega and Vega-C.

After calling the situation “a crisis,” Aschbacher said: “This is really a moment where we need to reflect deeply how to regain independent access to space for Europe, both of course for Vega-C, but more in general as well.” ®

https://www.theregister.com//2023/03/06/nozzle_material_determined_cause_of/