Ariane 6

The first stage of Ariane 6 is called the Lower Liquid Propulsion Module (LLPM). It is powered by a single Vulcain 2.1 engine, burning liquid hydrogen (LH₂) with liquid oxygen (LOX).[11] Vulcain 2.1 is an updated version of the Vulcain 2 engine from Ariane 5 with lower manufacturing costs. The LLPM is 5.4 m (18 ft) in diameter and contains approximately 140 tonnes (310,000 lb) of propellant.[12]

Additional thrust for the first stage will be provided by either two or four P120 Solid rocket boosters, known within Ariane 6 nomenclature as Equipped Solid Rockets (ESR).[11] Each booster contains approximately 142 tonnes of propellant and delivers up to 4,500 kN (1,000,000 lb_f) of thrust. The P120 motor is also first stage of the upgraded Vega C smallsat launcher. The increased production volumes through sharing motors lowers production costs.[13]

The first full-scale test of the ESR occurred at Kourou on 16 July 2018, and the test completed successfully with the thrust reaching 4,615 kN (1,037,000 lb_f) in vacuum.[14][15][16]

The upper stage of Ariane 6 is called the Upper Liquid Propulsion Module (ULPM). It features the same 5.4 m (18 ft) diameter as the LLPM, and also burns liquid hydrogen with oxygen. It is powered by the Vinci engine delivering 180 kN (40,000 lb_f) of thrust and enabling multiple restarts.[11] The ULPM will carry about 31 tonnes of propellant.[13]

Ariane 6 PPH cutaway drawing

Following detailed definition studies in 2012,[18] the European Space Agency (ESA) announced the selection of the "PPH" (first stage of three P145 rocket motors, second stage of one P145 rocket motor, and H32 cryogenic upper stage) configuration for the Ariane 6 in July 2013.[19] It would be capable of launching up to 6,500 kg (14,300 lb) to Geostationary transfer orbit (GTO),[20] with a first flight projected to be as early as 2021–2022.[21] Development was projected to cost €4 billion as of May 2013.[22] A 2014 study concluded that development cost could be reduced to about 3 billion euros by limiting contractors to five countries.[23]

While the Ariane 5 typically launches one large and one medium satellite at a time, the PPH proposal for the Ariane 6 was intended for single payloads, with an early - 2014 price estimate of approximately US$95 million per launch.[24] The SpaceX Falcon 9 and the Chinese Long March 3B both launch smaller payloads but at lower prices, approximately US$57 million and US$72 million respectively as of early 2014, making the Falcon 9 launch of a midsize satellite competitive with the cost of the lower slot of a dual payload Ariane 5.[24] For lightweight all-electric satellites, Arianespace intended to use the restartable Vinci engine to deliver the satellites closer to their operational orbit than the Falcon 9 could, thus reducing the time required to transfer to geostationary orbit by several months.[24]

In June 2014, Airbus and Safran surprised ESA by announcing a counter proposal for the Ariane 6 project: a 50/50 joint venture to develop the rocket, which would also involve buying out the French government's CNES interest in Arianespace.[25][26]

This proposed launch system would come in two variants, Ariane 6.1 and Ariane 6.2.[27] While both would use a cryogenic main stage powered by a Vulcain 2 engine and two P145 solid boosters, Ariane 6.1 would feature a cryogenic upper stage powered by the Vinci engine and boost up to 8,500 kg (18,700 lb) to GTO, while Ariane 6.2 would use a lower-cost hypergolic upper stage powered by the Aestus engine. Ariane 6.1 would have the ability to launch two electrically powered satellites at once, while Ariane 6.2 would be focused on launching government payloads.

French newspaper La Tribune questioned whether Airbus Space Systems could deliver on the promised costs for their Ariane 6 proposal, and whether Airbus and Safran Group could be trusted when they were found to be responsible for a failure of Ariane 5 flight 517 in 2002 and a more recent 2013 failure of the M51 ballistic missile.[7] The companies were also criticised for being unwilling to incur development risks, and asking for higher initial funding than originally planned - €2.6 billion instead of €2.3 billion. Estimated launch prices of €85 million for Ariane 6.1 and €69 million for Ariane 6.2 did not compare favorably to SpaceX offerings.[28] During the meeting of EU ministers in Geneva on 7 June 2014, these prices were deemed too high and no agreement with manufacturers was reached.[29]

Originally proposed Ariane A62 and Ariane A64

Following criticism of the Ariane 6 PPH design, France unveiled a revised Ariane 6 proposal in September 2014.[30] This launcher would use a cryogenic main stage powered by the Vulcain 2 and upper stage powered by the Vinci, but vary the number of solid boosters. With two P120 boosters, Ariane 6 would launch up to 5,000 kg (11,000 lb) to GTO at a cost of €75 million. With four boosters, Ariane 6 would be able to launch two satellites totaling 11,000 kg (24,000 lb) to GTO at a cost of €90 million.[31]

This proposal, unlike Ariane 6 PPH, offered a scalable launcher while retaining Ariane 5's dual-launch capability. The proposal also included simplification of the industrial and institutional organisation along with a better and cheaper version of the Vulcain 2 engine for the main stage.[30][31] Although Ariane 6 was projected to have "lower estimated recurring production costs", it was projected to have "a higher overall development cost owing to the need for a new, Ariane 6-dedicated, launch pad".[32]

The Italian, French and German space ministers met on 23 September 2014, in order to plan strategy and assess the possibility for agreement on funding for the Ariane 5 successor,[33] and in December 2014, ESA selected the Ariane 62 and Ariane 64 designs for development and funding.[6]

In November 2015, an updated design of Ariane 64 and 62 was presented, with new nose cones on the boosters, main stage diameter increased to 5.4 m (18 ft) and the height decreased to 60 m (200 ft).[34] The basic design was finalised in January 2016, advancing the development into detailed design and production phases, with the first major contracts already signed.[35][36] Unlike previous Ariane rockets which are assembled and fueled vertically before being transported to the launchpad, the Ariane 6 main stages will be assembled horizontally at the new integration hall in Les Mureaux and then transported to French Guiana, where they will be erected and integrated with boosters and payload.[37]

The horizontal assembly process was inspired by the Russian tradition for Soyuz and Proton launchers – which was more recently applied to the American Delta IV and Falcon 9 boosters[38] — with a stated goal of halving production costs.[39]

The industrial production process was completely overhauled, allowing synchronized workflow between several European production sites moving at a monthly cadence, which would enable twelve launches per year, doubling Ariane 5's yearly capacity.[37] To further lower the price, Ariane 6 engines will use 3D printed components.[40] Ariane 6 will be the first large rocket to use a laser ignition system developed by Austria's Carinthian Research Center (CTR), that was previously deployed in automotive and turbine engines.[41] A solid state laser offers an advantage over electrical ignition systems in that it is more flexible with regards to the location of the plasma within the combustion chamber, offers a much higher pulse power and can tolerate a wider range of fuel-air mixture ratios.[42]

Reorganisation of the industry behind a new launch vehicle, leading to a creation of Airbus Safran Launchers, also started a review by the French government, into tax matters, and the European Commission over a possible conflict of interest if Airbus Defence and Space, a satellite manufacturer were to purchase launches from ASL.[40]

While development was initially slated to be substantially complete in 2019, with an initial launch in 2020, the initial launch date has slipped twice: first to 2021[43] and then to the second quarter of 2022.[5]

CNES began studies in 2010[44] on an alternative, reusable first stage for Ariane 6, using a mix of liquid oxygen and liquid methane rather than liquid hydrogen that is used in the 2016 Ariane 6 first-stage design. The methane-powered core could use one or more engines, matching capabilities of Ariane 64 with only two boosters instead of four. As of January 2015, the economic feasibility of reusing an entire stage remained in question. Concurrent with the liquid fly-back booster research in the late 1990s and early 2000s, CNES along with Russia concluded studies indicating that reusing the first stage was economically unviable as manufacturing ten rockets a year was cheaper and more feasible than recovery, refurbishment and loss of performance caused by reusability.[45] It was suggested that with Arianespace launch schedule of 12 flights per year that an engine that could be reused a dozen times would produce a demand for only one engine per year making supporting an ongoing engine manufacturing supply chain unviable.

In June 2015, Airbus Defence and Space announced that development of Adeline, a partially reusable first stage, would become operational between 2025 and 2030, and that it would be developed as a subsequent first stage for Ariane 6. Rather than developing a way to reuse an entire first stage (like SpaceX), Airbus proposed a system where only high-value parts would be safely returned using a winged module at the bottom of the rocket stack.[44]

In August 2016, Airbus Safran Launchers gave some more details about future development plans building on the Ariane 6 design. CEO Alain Charmeau revealed that Airbus Safran were now working along two main lines: first, continuing work (at the company's own expense) on the recoverable Adeline engine-and-avionics module; and second, beginning development of a next-generation engine to be called Prometheus. This engine would have about the same thrust as the Vulcain 2 currently powering Ariane 5, but would burn methane instead of liquid hydrogen. Charmeau was non-committal about whether Prometheus (still only in the first few months of development) could be used as an expendable replacement for the Vulcain 2 in Ariane 6, or whether it was tied to the re-usable Adeline design, saying only that "We are cautious, and we prefer to speak when are sure of what we announce... But certainly this engine could very well fit with the first stage of Ariane 6 one day", a decision on whether to proceed with Prometheus in an expendable or reusable role could be taken between 2025 and 2030.[46] In 2017, the Prometheus engine project was revealed to have the aim of reducing the engine unit cost from the €10 million of the Vulcain2 to €1 million and allowing the engine to be reused up to five times.[47] The engine development is said to being part of a broader effort – codename Ariane NEXT[48] – to reduce Ariane launch costs by a factor of 2 beyond improvements brought by Ariane 6. The Ariane NEXT initiative includes a reusable sounding rocket, Callisto, to test the performance of various fuels in new engine designs.[49]