The CFRP tank has proven its structural load-bearing capacity and tightness over several pressure cycles at cryogenic temperatures around 20 K (-253°C), despite the fact that it comes without an additional internal coating (linerless). "The test result is a groundbreaking success in Europe; after all, fuel tanks are safety-critical elements in any propulsion system," explains Hans Steininger, CEO of MT Aerospace AG. "We have provided proof that a high-performance pressure tank made of CFRP can withstand cryogenic stress. In the future, the use of CFRP high-performance tanks should not only enable safe rocket launches, it can also exploit the advantage of significantly lower mass compared to metallic tanks."

Comprehensive tank test campaign
The test campaign was carried out in several stages, as hydrogen has to be specially treated and stored: Hydrogen only assumes a liquid state at a frosty 20 K (-253.15 °C). The test specimen, a tank with a diameter of 400 mm, was first subjected to a helium leak test at room temperature and at about 77 K (-196.15 °C). It was then filled with liquid, i.e. cryogenic hydrogen (LH2). After filling, the tank was even pressurized beyond the supercritical LH2 pressure in order to achieve a stress condition that is to be expected when used in a rocket flight. MT Aerospace was thus able to successfully demonstrate that the CFRP tank it developed and manufactured meets the specified requirements in terms of LH2 tightness along the entire load history, even when exposed to a combination of cryogenic thermal loads and simultaneous, high mechanical loads. Further filling and emptying cycles also underlined the excellent behaviour of the tank.

Can the tank also withstand liquid oxygen?
To confirm the tank's quality, a further helium leakage test was completed. This gave MT Aerospace AG the go-ahead for another test, which will focus on the tank's reaction when filled with liquid oxygen (LOX) under cryogenic conditions. This second test campaign is intended to prove that the CFRP material selected is suitable for use with both media - i.e. liquid hydrogen and liquid oxygen - in a future upper stage.

Encouraging test result
For MT Aerospace AG, the test result forms a solid foundation for the upcoming material decisions within the framework of the PHOEBUS upper stage demonstrator project, with which ArianeGroup GmbH was recently commissioned. The project aims to define, manufacture and test tanks with a diameter of two metres by the end of 2022, in preparation for near full-scale structural upper stage demonstrator.
"The test result is very encouraging for us, also and especially in view of our recent investment to expand the company's CFRP manufacturing environment," adds Dirk Lanuschny, Head of Launcher Programmes at MT Aerospace AG, referring to an Automated Fibre Placement facility that will enable the production of tanks with diameters typical of launch vehicles from early 2022. "As part of the PHOEBUS project, we intend to manufacture the two cryogenic tanks (LH2, LOX) as well as the primary structures of an upper stage demonstrator with a diameter of 3.5 metres."

MT Aerospace AG
MT Aerospace AG is an aerospace company with around 600 employees at its sites in Augsburg, Cagliari (Italy), Santiago de Chile and Kourou, French Guiana. MT Aerospace develops and produces key components for the European Ariane launcher, the Airbus aircraft fleet, spacecraft and satellites. MT Aerospace is a technology leader in lightweight structures made of metal and composite materials. With an order volume of ten percent, MT Aerospace is the largest supplier for the Ariane programme outside France.