Nozzle erosion blamed for Vega C launch failure

Europe plans to return the Vega C rocket to flight by the end of the year after concluding an eroded nozzle component caused the failure of its previous launch last December. The European Space Agency announced March 3 it had completed an independent investigation into the failed Dec. 20 launch of the Vega C on the VV21 mission, which experienced a loss of thrust from its Zefiro-40 solid-fuel second stage. The failure resulted in the loss of two Pléiades Neo imaging satellites for Airbus Defence and Space. The investigation concluded that a component in the motor called a throat insert, made of carbon-carbon material designed to withstand high temperatures, suffered “thermo-mechanical over-erosion” during the launch. That insert regulates the flow of exhaust through the nozzle, and as it eroded the chamber pressure dropped, causing thrust to decrease. By 207 seconds after liftoff, or a little more than a minute after the second stage ignited, acceleration of the vehicle became “quasi-null” and put the rocket on a ballistic trajectory, said Pierre-Yves Tissier, chief technical officer of Arianespace and co-chair of the independent investigation, in a briefing about the report. A fault tree analysis led investigators to rule out other causes of the failure. The erosion of the insert, he said, was linked to higher porosity of the carbon-carbon material, confirmed in other testing of the material but not detected earlier. “The acceptance criteria established for this material were not able to detect such a weakness,” he said. Avio procured the throat insert from a Ukrainian company, Yuzhnoye. Giulio Ranzo, chief executive of Avio, said the company went with Yuzhnoye during the design phase of Vega C in 2015 to 2017 after concluding that other European suppliers could not provide the material in required quantities “on the schedule compatible with the development program” of the rocket.

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

The flaw, he said, was not directly linked to disruptions caused by Russia’s invasion of Ukraine a year ago because they were manufactured before the war. He suggested that lockdowns linked to the pandemic might have been a factor, though.

The erosion was not seen in the Zefiro-40 motor used on the inaugural Vega C launch last July, or in two earlier qualification firings. “The acceptance criteria were not the right ones,” said Giovanni Colangelo, ESA inspector general and the other co-chair of the investigation. In those earlier firings of the motor, the materials exceeded requirements.

“The one for VV21 was exactly in line with specification, so were not as good as the previous one, so that is the reason why there was a failure,” he said.

The investigation concluded that the Yuzhnoye material can no longer be used on the Zefiro-40 motor. It will be replaced with a carbon-carbon throat insert from ArianeGroup, which already produces similar components for motors used on other Vega stages.

Ranzo said that Avio had already purchased several such throat inserts from ArianeGroup last year as a hedge against potential supply chain disruptions caused by the war in Ukraine. “We have secured the next several flights by having procured this strategic stock several months ago,” he said, adding that Avio was looking at longer-term options for the component from ArianeGroup or others.

ESA said that additional analysis and testing of the Zefiro-40 is planned for the coming months, allowing a return to flight of the Vega C tentatively scheduled for late this year. The payload for that mission will be the Sentinel-1C radar imaging satellite.

“Sentinel-1C is indeed a very precious payload,” acknowledged Josef Aschbacher, ESA director general. That satellite will replace Sentinel-1B, whose radar payload failed last year. “We are putting measures in place which are very robust and we have confidence this will all succeed.”

The Zefiro-40 problem does not affect the original Vega rocket, which uses a different motor in its second stage that does not have a throat insert from Yuzhnoye. ESA plans a launch of that rocket, one of two remaining of that version, before the end of the summer.

Stéphane Israël, chief executive of Arianespace, said that Vega launch will carry two primary payloads and several smallsat rideshares. “We will give more information on these passengers in a few weeks,” he said.

In addition to fixing the problem with the Zefiro-40, there will be a broader assessment of the vehicle’s supply chain to look for other potential quality issues. “We will try to improve substantially the monitoring of the performance and supply chain management activities,” Ranzo said.

Both ESA and Arianespace leadership expressed some frustration with the Vega program, noting that the VV21 failure was the third in eight flights of the Vega and Vega C. They are also dealing with delays with the development of the Ariane 6 that have pushed its first launch back to at least late 2023, as well as the loss of the Soyuz rocket after Russia’s invasion of Ukraine.

“We are in a crisis,” Aschbacher said. “For me, this is really a moment where we need to reflect deeply how to regain independent access to space for Europe.”

ESA lays out roadmap to Ariane 6 and Vega-C flights

Vega-C and Ariane 6 are being developed by ESA to assure Europe's independent access to space. The maiden flight for Vega-C is planned to take place in June 2021, that for Ariane 6 for the second quarter of 2022. Solid progress is being made on both Vega-C and Ariane 6 development programmes. Since March, some technical events and the COVID-19 pandemic have both impacted the progress of activities. Uncertainty from COVID-19 still persists globally to date. Vega-C is a more powerful and versatile version of the Vega launch vehicle currently operating at Europe's Spaceport in French Guiana. Vega-C's maiden flight is planned for June 2021. Vega was on track for its return to flight, after the July 2019 failure, with its mission (VV16) in March 2020, but Europe's Spaceport had to be closed due to COVID-19 safety measures. The VV16 launch campaign resumed in May but several further launch attempts were halted due to unfavourable weather. Vega's return to flight, with the new SSMS dispenser carrying 53 satellites, was successfully launched on 2 September. Between February and September no activities for the preparation of Vega-C were possible in the Vega mobile gantry while it housed the P80 solid rocket motor in readiness for flight VV16, due to safety constraints. The qualification at system and subsystems level is currently under finalisation. As from October, all the new solid motors for Vega-C have completed qualification testing. The Zefiro-40 solid rocket motor for Vega-C completed qualification tests in 2019. The final test of the P120C took place successfully on 7 October.

Two Vega flights, VV17 and VV18, are planned before Vega-C. Activities for the modification of the mobile gantry for Vega-C, such as modifications of the fluids networks as well as connection and installation of the new control bench for Vega-C, will have to start after VV18 now planned early February.

Vega-C maiden flight is planned for June 2021.

Vega-C is a project managed and funded by the European Space Agency. Avio is the industrial prime contractor. Arianespace commercialises Vega-C.

Ariane 6
ESA, CNES and ArianeGroup have jointly established a consolidated reference planning for Ariane 6 development and are working as an integrated team in their respective roles to make it happen. This schedule is based on analysis of recent achievements, remaining critical milestones and the impact on the programme caused by the COVID-19 pandemic.

With the successful third static fire test of the P120C solid rocket motor on 7 October, all the propulsion elements of the launcher system have completed their qualification tests.

At Europe's Spaceport, activities for the finalisation of the Ariane 6 launch base are progressing. First integration testing with fullscale 'mock-ups' of the P120C strap-on booster and of Ariane 6's central core took place in the new mobile gantry. Testing of the cryogenic arms that link the launch pad and the launch vehicle are also ongoing at Fos-sur-Mer in France, before shipping to French Guiana.

ArianeGroup is completing the challenging development and qualification of the Ariane 6 Auxiliary Power Unit for the upper stage. This device will allow Europe to offer additional capabilities in satellite deployment for the satellite constellation market.

The first Ariane 6 upper stage has been assembled in Bremen, Germany. Coupling the launcher's tanks with the equipped engine bay of the re-ignitable Vinci engine for the first time. The upper stage is currently undergoing mechanical, fluid and electrical tests, before leaving for further tests at the DLR German Aerospace Center's Lampoldshausen facilities in Germany.

There, the complete stage will be hot fire tested on a new test bench specially developed by DLR for the Ariane 6 upper stage. The Ariane 6 upper stage static fire tests are planned to start in the second quarter of 2021.

In parallel, the first Ariane 6 core stage and the second Ariane 6 upper stage are under preparation. These specimen will be shipped to Europe's Spaceport from Les Mureaux (France) and Bremen (Germany) respectively, for the combined tests campaign.

In the third quarter of 2021, the Ariane 6 launch base will be handed over from CNES to ESA. At this point the Ariane 6 combined tests campaign can start. These series of tests will bring the launch vehicle and launch base together for the first time for integrated tests of multiple systems. This will include a static fire test of Ariane 6 while standing on the launch pad for the first time.

Following the successful combined test campaign and Ground qualification review of the launch system, the first launch campaign, with the integration of the maiden flight hardware, will start.

When all these steps are successfully completed Ariane 6 will be in a position to perform its maiden flight in the second quarter of 2022.

Ariane 6 is a project managed and funded by the European Space Agency. ArianeGroup is design authority and industrial prime contractor for the launcher system. The French space agency CNES is prime contractor for the development of the Ariane 6 launch base at Europe's Spaceport in French Guiana. Arianespace commercialises Ariane 6.

Impact of COVID-19
The measures taken to control the pandemic have seriously impacted the progress of activities both in Europe and at Europe's Spaceport since March 2020, including as a result of social distancing, site lockdowns and reduced capacity at facilities, travel restrictions, quarantines and confinement measures.

This has considerably slowed all working and operational processes for prime contractors and their respective subcontractors around 13 European countries. Ongoing pandemic effects continue to disrupt on-going development and operations.

"We constantly and closely monitor the COVID-19 impact and technical challenges on our ongoing space transportation developments and operations. Together with our contractual partners and participating States, ESA continues to pull together towards our common priority goals which are the maiden flights of Vega-C and Ariane 6," commented Daniel Neuenschwander, Director of Space Transportation at ESA.