Vega-C Launch Failure Investigation Requires New Zefiro40 Nozzle Design

In December 2022, the Vega-C launch VV22 ended in failure, prompting the formation of an Independent Enquiry Commission. Their task was to uncover the root causes of the failure and propose recommendations for a dependable return to flight and a robust exploitation of the Vega-C launch system.

A Vega C lifted off Dec. 20, only to suffer a failure with its second stage about two and half minutes later. Credit: Arianespace webcast — *Vega-C VV22 lifted off on Dec. 20, 2022. It will then suffer a failure with its second stage about two and half minutes into the flight. Credits: Arianespace Webcast*

In the world of space exploration, reliability and safety are paramount. When things go wrong, meticulous investigation and swift corrective action are essential to ensure the future of missions.

Initial Recommendations

One of the key recommendations made by the Commission was to undergo a (delta-)qualification of the nozzle, introducing a new Carbon-Carbon throat insert material distinct from the one previously utilized in the Zefiro40, the solid rocket booster for the Vega-C’s second stage.

Vega-C Mission VV22 Lifting Off the Pad. Credits: ESA-Arianespace-CNES-Optique video du CSG-JM Guillon — *Vega-C Mission VV22 Lifting Off the Pad. Credits: ESA/Arianespace/CNES/Optique video du CSG/JM Guillon*

The modified Zefiro40 engine underwent a crucial static firing test on June 28, 2023, at the Salto di Quirra test bench in Italy. However, during this test, the engine nozzle experienced significant damages, raising further questions about the Vega-C program.

To get to the bottom of this issue, ESA Director General Josef Aschbacher established an Independent Enquiry Commission chaired by the ESA Inspector General, Giovanni Colangelo. This commission comprised experts from organizations such as CNES, ASI, ESA, Arianespace, and academia, all dedicated to understanding the anomaly and providing valuable recommendations.

The New Findings

The Independent Enquiry Commission’s findings pointed to a critical issue within the nozzle design.

They identified that the combination of the geometry of the Carbon-Carbon throat insert and the differing thermo-mechanical properties of the new material caused progressive damage to other adjacent nozzle components. This gradual degradation ultimately led to the nozzle’s failure. It’s important to note that this particular phenomenon was distinct from the issues observed with the previous Carbon-Carbon material used in VV22.

Transfer and integration of the Zefiro 40 second stage for Vega-C. Credits: ESA - M. Pedoussaut — *Transfer and integration of the Zefiro 40 Second Stage for Vega-C. Credits: ESA/M. Pedoussaut*

To ensure the future reliability and safety of the Vega-C launch system, the Commission formulated a series of recommendations. Among these is the imperative need to enhance the nozzle design of the Zefiro40 Engine and to calibrate numerical models capable of predicting the material’s behavior under extreme conditions. Additionally, two more firing tests are scheduled to verify the performance and reliability of the redesigned nozzle.

Task Force and Next Launch Date

To expedite the implementation of these recommendations, a task force has been assembled, overseen by ESA and Avio.

Vega-C is currently undergoing critical design modifications for the Zefiro40 nozzle and technical reviews, along with the planned firing tests. The anticipated return to flight for Vega-C is set for the fourth quarter of 2024, but in the meantime, another Vega (the initial version of the launcher) flight is scheduled for the second quarter of 2024.

*A render of the Zefiro40 Engine. Credits: AVIO*

ESA recognizes the return to flight of Vega-C as a strategic priority, as they stated, ensuring Europe’s independent access to space. The organization pledges its full support and allocation of available resources to make this happen.

Avio, in its role as the Design Authority, is fully committed to implementing the Independent Commission recommendations and taking responsibility for the successful return to flight of Vega-C.

Many Questions – Few Answers

During the Press Conference held by ESA on Oct. 2, a lot of questions were asked to the panelist, but very few of them were properly answered.

The speakers of the Press Briefing were:

Josef Aschbacher, Director General, ESA
Giovanni Colangelo, Inspector General, ESA
Giulio Ranzo, CEO, Avio
Stéphane Israël, CEO, Arianespace

The bottom line was made clear since the beginning: AVIO and ESA are working hard on the redesign of the nozzle, but a return to flight is definitely impossible before Q4 2024.

The Press Conference held on Oct. 2, 2023 about the Independent Commission Findings on Vega-C. Cresits: ESA — *The Press Conference held on Oct. 2, 2023 about the Independent Commission Findings on Vega-C. Credits: ESA*

Asked by Space Voyaging about the launch cadence expected after a safe return to flight, AVIO’s CEO Giulio Ranzo said that they expect to launch two times in 2024, a Vega and the Vega-C return to flight Mission, increasing this number to four launches in 2025, all with Vega-C.

They also expect to increase the yearly launch capability to up to six in the following years: “We’re already working with our European suppliers and ESA about that… It’s a joint and collaborative effort”, Ranzo stated.

In a collaborative effort, ESA, Avio, and Arianespace, each playing crucial roles in the Vega launch system, will continue their joint endeavors to achieve the common objective of a robust exploitation of the Vega launch system. This commitment, according to them, serves not only their institutional interests but also benefits the broader community of commercial customers relying on Vega-C for their space missions.