ESA delays Vega-C's return after nozzle design fails tests

The Vega-C rocket will not return to launch until late 2024 because a test on a redesigned nozzle failed, the European Space Agency revealed on Monday.

The redesign was recommended after the launcher failed to place two Airbus satellites in orbit last December, thanks to an anomaly in the Zefiro 40 engine nozzle used in the rocket's second stage. Investigations found a flaw in the nozzle material's homogeneity caused a thermo-mechanical over-erosion of the carbon-carbon throat insert. Ain't it always the way?

A new material was chosen and a back-to-launch target was set for the end of 2023.

However, a late June static firing test revealed the thermo-mechanical properties of the new material did not work well in combination with the legacy geometry. The commission of inquiry investigating the failed launch and subsequent tests found damage on adjacent nozzle parts and a "progressive degradation" that led to the nozzle's ultimate failure.

The commission noted that this failure was completely different to the problem in the previous nozzle design.

• The cause of last December's failed satellite launch? Nozzle material, says ESA
• FAA wants rocket jockeys to clean up after their space launch parties
• Bids for ISS demolition rights are now open, NASA declares
• ESA gets the job of building Europe's secure satcomms network

"During the test the general behavior of the engine appeared to be more or less normal. Some anomalies were spotted, but there were no impacts on the pressure, until we reach 39.7 seconds when the throat insert in carbon-carbon was expelled," explained ESA’s inspector general Giovanni Colangelo in a media briefing.

At that point, said Colangelo, bright spots appeared in the camera images and a sudden drop of pressure was recorded. Nozzle pieces were expelled and the engine continued burning in a "significantly degraded mode" until its solid propellant was completely consumed.

Colangelo revealed that further forensic analysis determined local debonding of the nozzle started one second into the engine firing and progressed until the 28 second mark. Between 21 and 39.7 seconds, an increase of temperatures indicated hot gases circulated in the nozzle, with a gas passage through the metallic structure of the mobile ring. As the nozzle was already in a deteriorated condition, the leak led to the final ejections.

The ESA's plan is to improve the nozzle design of the Zefiro 40 motor further, and predict the results through computer simulations before performing two more firing tests.

Vega-C's return-to-flight date has been pushed back an entire year to the last quarter of 2024. In the meantime, the ESA plans a launch of the smaller Vega in the second quarter of 2024.

Unfortunately, not every spacecraft scheduled to fly on Vega-C can be delivered on Vega, as the latter has a smaller payload capacity.

One payload that needs the Vega-C is the radar imaging Sentinel 1-C. According to ESA director general Josef Aschbacher, the European Commission will decide when and where to launch Sentinel 1-C.

"ESA considers the return to flight of Vega-C a strategic priority to secure Europe's independent access to space and will support the necessary efforts drawing from already available resources," the space agency stated.

Delays to the VEGA-C's return to service leave the ESA in a tight spot. Its Ariane 5 heavy lifter has flown its last mission and its successor is yet to fly. ®