01 Ariane 6

Each booster, technically known as an Equipped Solid Rocket (ESR), is 22 metres long, with a diameter of 3.4 metres. It consists of a P120C engine loaded with 142 tonnes of solid propellant delivering an average thrust of 357 tonnes (3,500 kN). The lower part of the engine is fitted with a rear cylindrical skirt, which is designed to support the booster when positioned on the launch table pallets. A conical skirt at the front of the booster is where it is joined to the inter-stage structure of the Ariane 6 central core (main and upper stages conjoined). This connection supports the weight of the central core and transmits the booster’s thrust to it.

The boosters are ignited a few seconds after the central core’s Vulcain® 2.1 engine, which enables the launcher to lift off. The boosters provide most of the launcher’s thrust at lift-off and operate for 130 seconds, before being jettisoned once all the solid propellant has been burned, at an altitude of 60 kilometres. 

At the heart of the boosters is a P120C solid fuel engine 13.5 metres high and with a diameter of 3.4 metres. This is the same engine as that used for the Vega-C rocket first stage. The P120 is built by lead contractor Europropulsion, a 50–50 joint venture between ArianeGroup and Avio, and comprises two main sub-assemblies: a wound carbon-fibre structural body produced by Avio and a nozzle manufactured by ArianeGroup. This latter enables the extremely hot gases generated by the engine to be ejected at very high speed. It is made up of various composite materials, including woven thermostructural carbon/carbon for the nozzle throat, which must be able to withstand high-speed gases at 3,000°C.

The P120C engine is loaded with 142 tonnes of solid fuel at Europe’s Spaceport by Regulus, an Avio and ArianeGroup joint venture.

Evolution

Europropulsion is developing an upgraded P160C version of the P120C solid fuel engine, under an ESA contract. The P160C is one metre longer and its propellant load will be increased to 156 tonnes, raising the booster’s operating time to 135 seconds. This will expand the range of Ariane 6 missions by increasing the launcher’s payload performance to low Earth orbit (LEO) by more than two tonnes, and by offering significant performance gains for geostationary, scientific and exploration missions.

This modification changes neither the external dimensions of the booster, nor the interfaces with the central core. Ariane 6 will therefore be able to use boosters equipped with either the P120C or the P160C.

The main stage, technically called the Lower Liquid Propulsion Module (LLPM), is 32 metres long, with a diameter of 5.4 metres. Its final assembly is carried out on ArianeGroup’s Les Mureaux site near Paris in France. It is powered by the Vulcain® 2.1 cryogenic engine which delivers about 140 tonnes (1,370 kN) of thrust.

The stage consists of two structural aluminium alloy propellant tanks, joined together by a metallic inter-tank structure. The upper tank contains 25 tonnes of liquid hydrogen (LH2) at -253°C and the lower tank contains 125 tonnes of liquid oxygen (LOx) at -183°C. New-generation refuelling modules are located on either side of the stage so that the tanks can be filled with propellant from the umbilicals on the ground. These modules disconnect at lift-off. The stage is covered with sprayed-on thermal protection which enables the liquid cryogenic propellants to be kept at extremely low temperatures in the tanks, while insulating them from the ambient temperature in French Guiana, which frequently exceeds 30°C.

For an Ariane 6 launch, the Vulcain® 2.1 engine is ignited on the ground and the main stage then functions for about 470 seconds until an altitude of 270 kilometres is reached, at which point it is separated from the upper stage. The Vulcain® 2.1 engine uses a system of gimbaled thrust actuators, so that the launcher can be controlled during the second part of the flight, in other words after the boosters have been jettisoned.

The inter-stage structure joins the launcher’s main stage and upper stage together to form the central core. It consists of two identical parts made of carbon fibre-based composite: an upper part (IFS-U – InterFace Structure – Upper) and a lower part (IFS-L – InterFace Structure – Lower) interconnected by metal flanges. A pyrotechnic ring is placed at the top of the inter-stage structure and separates the two stages when the main stage is jettisoned. The lower part contains some of the launcher avionics.

The upper stage, technically called the Upper Liquid Propulsion Module (ULPM), is 12 metres long, with a diameter of 5.4 metres. Its final assembly is carried out on ArianeGroup’s Bremen site in northern Germany. It is equipped with the Vinci® cryogenic engine, which can be re-ignited in flight and delivers 18 tonnes of thrust (180 kN), and with an Auxiliary Propulsion Unit (APU). 

The APU is an innovative system that is crucial to the performance and versatility of Ariane 6. It is used to pressurise the upper stage’s tanks and prepare for Vinci® engine re-ignitions by settling the propellants in the tanks in weightless conditions. When required, the APU can also provide additional thrust in orbit, and it can be used to de-orbit the upper stage at the end of the mission. 

The stage consists of two aluminium alloy tanks, joined together by a metallic inter-tank structure which contains some of the launcher’s avionics equipment. The upper tank is structural and contains 25 tonnes of liquid oxygen (LOx) at -183°C. The suspended lower tank contains 5 tonnes of liquid hydrogen at -253°C. New-generation refuelling modules are located on either side of the stage so that the tanks can be filled with propellant via the retractable arms on the launch tower. These interfaces disconnect when the arms are retracted at lift-off. The stage is covered with sprayed-on thermal protection which enables the liquid cryogenic propellants to be kept at extremely low temperatures in the tanks, while insulating them from the ambient temperature in French Guiana, which frequently exceeds 30°C. 

The upper stage provides the additional velocity needed to place the payloads in orbit. It starts up after separation from the main stage, at an altitude of 270 kilometres. The Vinci® engine is ignited in a vacuum and can be re-ignited several times for up to a total of 900 seconds. Depending on the mission profile, the Vinci® engine can be switched off and re-ignited in flight up to four times and it operates in parallel with the APU. 

Once the flight is over and depending on the mission requirements, the stage is either placed in a parking orbit, or de-orbited by means of a final ignition of the Vinci® engine or thrust from the APU, so that it burns up during atmospheric re-entry.

Evolution

Under an ESA contract, ArianeGroup is currently developing a version of the Vinci® engine with a thrust increase to 200 kN, enabling the launcher’s performance to be further enhanced. 

Under its Future Launchers Preparatory Programme (FLPP), ESA has also tasked ArianeGroup with management of the Phoebus demonstrator programme, which aims to develop and build structures and tanks made of carbon fibre based composite compatible with cryogenic propellants. The goal is to develop technologies capable of significantly reducing the weight of launcher upper stages for use in a future lightweight version of the Ariane 6 upper stage.

The upper composite is an assembly with a diameter of 5.4 metres containing the payloads to be deployed into orbit. It consists of the two half-fairings, the Launch Vehicle Adapter (LVA), which joins the launcher to the upper composite and to which the two half-fairings are secured, the payload and various devices supporting the payloads. 

Ariane 6 uses two different fairing lengths depending on the mission. A short one of 14 metres and a long one of 20 metres for the Ariane 64 version. Depending on the payloads, the upper composite can accommodate different devices. The composite-material Dual Launch System (DLS) enables two satellites to be launched simultaneously. It houses and protects a first satellite in the lower position, while supporting a second satellite in the upper position. Its dimensions vary according to the size of the satellites to be launched. For multiple launches, composite-material carrier structures can hold and then eject several satellites into orbit. These deployments can be in pairs, or in fours, as for the Galileo navigation satellites, or up to several tens at a time for larger constellations. 

Lastly, the Multi-Launch System (MLS) offers a ride-share capability to launch groups of smallsats and micro-satellites, in addition to the main payloads.