Space exploration takes flight in Bremen
AerospaceUpper stage of the Ariane 6 launch vehicle to be built in Bremen
Production of the upper stage of the new Ariane 6 launch vehicle will soon begin in a new production hall near Bremen Airport. The upper stage is the heart and the brain of the rocket, whose maiden flight is scheduled for July 2020.
Tolerances in the range of tenths of a millimetre
The size of the building on the edge of Bremen Airport is impressive. Just over a dozen tennis courts could be accommodated under the roof of the structure, which rises five storeys into the sky. But there is only a single machine in the hall – about six meters high, four meters wide, and weighing just over 40 tonnes. It is hard to believe that this colossus is designed for intricate work. “We work with tolerances in the range of tenths of a millimetre,” says Ralf Schleith, who manages production of the tanks for the European Ariane 5 launch vehicle at MT Aerospace. This vast hall in Bremen is his latest workplace – the machine will soon produce the first tanks for the upper stage of the new Ariane 6, which is set for its maiden space flight in 2020.
Centre of excellence for rocket manufacturing
The upper stages of the Ariane launch vehicles have been manufactured in Bremen for over 20 years. “We refer to it as integration, as it is here that all the components from around Europe are put together into a complete system,” Schleith explains. The expertise acquired by the engineers and technicians in Bremen secured the contract for the successor model Ariane 6. The upper stage is the heart and the brain of every launcher: after a successful launch into space, it provides the necessary thrust to get the satellites on board into the desired position in orbit. It also contains the control systems that keeps the rocket exactly on course.
“Ariane 6 is a completely new system”
The Franco-German ArianeGroup, which develops and builds the rocket on behalf of the European Space agency (ESA), is in charge of the project. Its most important German partner is MT Aerospace based in Augsburg. 70 per cent of the company is owned by Bremen-based OHB Systems AG and 30 per cent by the Bavarian entrepreneur Hans Steininger. In addition to manufacturing the tanks and other metal structures for the main and upper stages, MT also has a key role in the construction of the launch facility in Kourou in French Guiana. MT has delivered pre-assembled upper stage tanks to Bremen for the 100 Ariane 5s that have launched so far; in the future, final assembly will take place in Bremen. Despite the decades of experience gained since 1996, MT and ArianeGroup cannot rest on their laurels: “The Ariane 6 is a completely new system, and its production has also been developed completely from scratch,” Schleith says.
40 per cent lower costs and double the number of units
It has only been four years since the ministers for economic affairs and for science and research of the ESA member states commissioned the European Space Agency with building a new launcher. They specified that Ariane 6 must cost at least 40 per cent less than the current Ariane 5. Furthermore, production had to be doubled from currently five to at least eleven units a year. The ESA ministers also transferred the financial risk of marketing the rocket to the industry and committed only to the purchase of five units a year at a fixed price of €70 million per rocket. “This was a very ambitious commission,” Schleith says. “After all, we had to develop the rocket and the manufacturing process at the same time, and within a very tight time frame.”
A piece of European space history
The project has obviously been a success so far – while the production plant for the Ariane main stage is still under construction in Les Mureaux in France, MT and ArianeGroup are already gradually ramping up the integration of the upper stages in Bremen. The two partners literally work side by side in Bremen’s Airport City. MT manufactures the hydrogen and oxygen tanks at its factory and then hands them over to ArianeGroup next door, where the tanks are finished, insulated and cleaned before they are assembled. Although the hall complex looks brand new, it is actually a piece of European space history: “It was built for the construction of Ariane 5 ME, which was originally planned as the successor to today’s Ariane 5,” says Schleith. The MT hall was already fully equipped with machines, but in the end only a single tank was built as a prototype. Before series production could begin, the European Space Agency rejected the 5 ME plans and replaced them with Ariane 6.
Automated manufacturing process uses new welding technique
The isolated blue machine in MT’s huge hall is symbolic of the kind of innovations that the change of course demanded by the policymakers has inspired in the space industry. When a car manufacturer revamps its model range, it usually replaces the tools, but not all of its machinery. The Bremen-based aerospace engineers, however, had to part with the equipment installed for the Ariane 5ME – some of them maybe with a heavy heart, as the new machines had only been switched on a few times. But it does mean that the technicians can now work with a particularly sophisticated manufacturing process for the Ariane 6. “Parts prefabricated in Augsburg are welded together in Bremen to form complete tanks,” explains Schleith. The welding method used for the Ariane 6 is friction stir welding. “The sheets are welded under very high pressure, with heat generated by friction and a rotating tool ‘stirring’ the sheets together,” he explains.
Quality is paramount in space travel
While conventional welding always requires the addition of material, friction stir welding is performed without additional welding wire. The seam is of consistent quality from start to finish and the entire welding process is fully documented by recording all parameters such as pressure, friction speed and temperature. Quality is paramount in space travel: “Rockets must be extremely reliable,” says Schleith. “That’s why we have to document every step exactly.” There is a special reinforced area in the floor of the huge hall where each tank is checked for its durability at full operating pressure.
The cap of the hydrogen tank is 5.4 metres wide
The reason why the decades-old technology of friction stir welding is only now being used in the aerospace industry is the same as the reason as why the hall at Bremen Airport is so large: “We are dealing with very large components that cannot simply be clamped into a vice,” says Schleith. The cap of the hydrogen tank, for example, is 5.4 metres wide, and the tank itself has a volume of 70 cubic metres. The oxygen tank is also anything but small – it measures 4.6 metres in diameter and has a volume of 30 cubic metres. “You have to somehow be able to move items with such dimensions,” says Schleith, looking up for a moment at the ceiling of the hall. “Well, OK, so we’ve probably got enough room here,” he says with a chuckle. Whether he is right or not will be revealed in a few weeks’ time. Once the largely automated integration in the neighbouring hall at ArianeGroup is complete, production of the new Ariane 6 will start in Bremen.
OHB Systems, Günther Hörbst, head of corporate communication, Tel.: +49 421 2020-9438, E-Mail: guenther.hoerbst@ohb.de
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