Ariane 6 maiden: A good but not flawless flight as two of its payloads did not get to where they wanted to go

by | Jul 10, 2024 | Launches, Reliability Info, Satellites, Seradata News

Criticised for its very long development time, its ‘out of date’ non-reusable technology, and for its still too high launch price, nevertheless, Ariane 6, Europe’s new launch vehicle, has been finally launched from the Kourou, French Guiana launch site.  There was initial relief as the ignited rocket lifted off at 1901 GMT on 9 July 2024, clearing the tower upwards into the cloud punctuated blue skies over the South Atlantic coastline.

The flight initially went as planned with the P120C solid rocket boosters (SRB) separation occurring at two minutes 16 seconds after launch, followed by a shut down of the main liquid hydrogen/LOX core stage Vulcain 2.1 engine at seven minutes 35 seconds.  After separation of the main stage, the upper stage was then fired for the first of three burns, with most of the spacecraft released after the second burn.

Ariane 6 maiden flight lift-off showing the bright glow of its Solid Rocket Booster’s efflux. Courtesy: Arianespace

The French Air Force, now called the Armée de l’Air et de l’Espace, the latter part of its name to reflect its increasing involvement in space, even mounted a Rafale fighter chase plane to follow the rocket upwards on its climb.

The Ariane 6 maiden flight streaks into orbit – followed for part of its climb by a French Air Force Rafale fighter jet. Courtesy: Armée de l’Air et de l’Espace

Aboard were 11 payloads.  The largest was actually an instrumented mass simulator – a dummy payload designed to measure the accelerations and vibrations that a typical large satellite would experience on a standard flight.  Attached to this are a number of hosted payloads: YPSat, Peregrinus, PariSat, SIDLOC, LiFi.

The other spacecraft payloads were much smaller: 3Cat4 is a Spanish technology demonstration 1U Cubesat  to demonstrate the capabilities of nano-satellites for Earth Observation (EO) using Global Navigation Satellite System – Reflectometry (GNSS-R) and L – band microwave radiometry, as well as for Automatic Identification Services (AIS); Curie A and B were two 5 kg US spacecraft designed to study radio burst emissions from solar eruptive events; Curiumone (Major Tom) is a technology demonstration microsatellite. The 2U Cubesat GRBBeta’s primary mission is to detect and study gamma-ray bursts and similar high-energy events occurring at the edges of our Universe; ISTSat-1 is an ADS-B equipped technology demonstration 1U Cubesat for aircraft tracking; OOV-CUBE is a 10 kg IoT (Internet-of-Things) technology demonstration communications satellite for agricultural use; Replicator is a 5 kg spacecraft to demonstrate 3D-printing in orbit; ROBUSTA-3A is a 3U Cubesat from University of Montpellier for testing GNSS reflectometry techniques for mapping atmospheric water vapour.

Tracking data soon showed an altitude shortfall at the end of the flight. Courtesy: CNES

Ariane 6 maiden flight delivered the above nine payloads to their correct orbits. However, APU (Auxilliary Propulsion Unit) failure on the upper stage briefly ignited and then stopped. This prevented the third ignition of Vinci engine & deployment of Bikini Demo (NYX) & SpaceCase SC-X01 re-entry test payloads at their correct altitude. It was immediately decided to passivate the upper stage to prevent the risk of explosion. This meant that the upper stage and its still attached satellites will now have an uncontrolled re-entry, albeit not for some years given its altitude.

One major difference between the Ariane 6 and its Ariane 5 predecessor was the introduction of the new APU technology which is used to pressurise the tanks for multiple reignitions of the cryogenic expander-cycle Vinci engine (the Vinci’s HM-7B cryogenic gas-generator cycle predecessor was not restartable). The APU achieves this pressurisation function by drawing a small quantity of the liquid oxygen and hydrogen from the tanks which it heats up by means of a gas generator. This heated and pressurised propellant is then injected back into the tanks.

Exhaust from the APU gas generator burns also have an ‘ullage’ function in accelerating the upper stage slightly to settle its propellants towards the bottom of the tanks to ensure optimal operation of the Vinci engine’s turbopumps. Before the flight, analysts noted that if a failure was to occur, it was likely to be on the APU given that it was new technology.

Comment by David Todd: Arianespace can be congratulated for what was mainly a successful flight.  However, Slingshot Aerospace’s Seradata database team  does regard this launch as a partial failure – albeit a minor one. We judge all launches in the following way: if a single payload on a launch does not achieve its correct orbit in an undamaged condition we mark the launch down as a ‘raw total failure’. However, we then modify this by taking into account how many payload spacecraft on board actually achieved their correct orbits.  Of those that did not, we even make an estimation of life or capacity left and modify the failure via a “capability lost” function.  For example, a spacecraft may be able to recover itself using on board propellant, albeit at a loss of some of half of its design life. This would result in a ‘spacecraft capability loss’ of 50 per cent.  After summing up, we will come up with a figure of the percentage failure of the launch.  In Ariane 6’s case, two of the 11 spacecraft failed to achieve their orbital drop off in a non-recoverable way. Thus, the Ariane 6 maiden launch in this incidence is regarded as an 82 per cent success.

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