In the words of Looney Tunes' Marvin the Martian.
The European Space Agency's new, small payload booster, the Vega C has been on hold since its December 2022 launch failure that prompted continuing investigations into the second stage engine. An anomaly that took place during a static-fire test of a Zefiro 40 motor June 28 led to another investigation which recently completed and the announcement today that parts of that engine need to be redesigned, forcing a next possible launch back to the end of calendar '24. (NOTE: Zefiro is from the acronym ZEro FIrst stage ROcket.)
Giovanni Colangelo, ESA’s inspector general and chair of the committee that investigated the incident, said at a briefing that the performance of the motor was “more or less normal” until 39.7 seconds after ignition. At that point, a new throat insert made of carbon-carbon material was expelled from the nozzle, along with other pieces of the nozzle. The motor continued to burn, although at far lower pressures, until the fuel was exhausted.
Just between us, parts of an engine being expelled is never a good thing.
This test (June's) was not intended to be a test of the engine itself, but of that carbon-carbon throat insert, which was implicated in the December failure. The investigation of that failure showed that the carbon-carbon material from the original supplier, Ukrainian company Yuzhnoye, did not meet specifications. That led to ArianeGroup taking over production of the throat insert. At the time ESA hoped to resume Vega C flights by the end of 2023 and the June test was to verify their conclusions and that they were back on schedule to fly in the next few months.
The June test anomaly was not linked to that launch failure, ESA concluded. “The failure of the test is related to the design of the nozzle that was not upgraded with the change in the carbon-carbon supplier for the throat insert,” Colangelo said. The geometry of the new throat insert and its different thermo-mechanical properties contributed to the failure. “The effects had not been identified as critical during the redesign.”
He said that as early as one second into the test, debonding of the throat insert from the metallic nozzle had started, which grew progressively worse. Eventually, hot gas from the exhaust got into gaps in the nozzle, causing the ejection of the throat insert and other nozzle components.
ESA recommended that the Zefiro 40 nozzle be redesigned, along with improved modeling of its performance and two static-fire tests of that new design. A joint task force of [engine manufacturer] Avio and ESA personnel has already started that work, said Giulio Ranzo, chief executive of Avio. “We have to conduct, I would say, an adjustment of the design, a modification of the design of part of the nozzle.”
The Zefiro 40 engine. A static-fire test of the motor suffered an anomaly June 28. Credit: ESA/M, Pedoussaut
The redesign plan includes one static firing, in the second quarter of '24. Ranzo said that test will be used to both confirm the performance of the redesigned nozzle as well as the refined numerical models. That will be followed by a second static-fire test before Vega C is ready to return to flight. From the sound of it, I suspect that launch by the "fourth quarter of '24" is on the optimistic side.