Sänger aerospaceplane gains momentum
Flight international, 12 August 1989 (page 39-41)
West Germany's Sänger spaceplane is gaining international support. Its success will depend on critical technologies only partly mastered in Europe, however, as Tim Furniss reports. “It is the second-largest programme behind the US National Aerospaceplane... we're on full thrust." Behind these confident words from MBB's Dr Dietrich Koelle lies a project involving the entire West German aerospace industry, along with its Government and academic research institutions. The Sänger aerospaceplane programme is locked into a five-year, DM370 million ($195 million) system definition phase, which ends in 1992. At the end of that time, says Koelle, we'll have a pretty good idea if it can be done". The prize, he adds, is re-usability, and drastically reduced manpower needs compared with conventional rockets, leading to a launch cost one-tenth that of the Ariane 5/Hermes combination.
Pic.1. MBB's two-stage Sänger appears less technically challenging than the USA's single-stage-to-orbit NASP
The technologies required for Sänger will test West Germany's research and development strengths to the limit. The vehicle's two-stage design, driven by the 3,500km European cross-range requirement, is less demanding of propulsion technology than the US National Aerospaceplane's single-stage-to-orbit approach. Nevertheless, says MBB's vice-president, Ernst Hogenauer, "airbreathing propulsion is the technology that will make or break the 'plane". Other critical technologies mentioned by Hogenauer are: aerothermodynamics, lightweight, high-temperature materials, advanced avionics, and liquid-hydrogen fuel management. Major emphasis at present is being given to the turboramjet propulsion system, the first major milestone in the technology programme being reached last December with the first hydrogen ramjet combustor test at MBB.
Pic.2. Sänger's flight profile includes a 3,500km, Mach 4.4 cruise A technological development programme, following system definition, could lead to the flight demonstration of a prototype of the Sänger first stage in 1999, says the West German Federal Ministry of Research and Technology. Development of the actual Sänger vehicle could begin in 1996, when Ariane 5 development is complete, providing the next step in European launchers, says MBB. A first flight could then take place in 2006. MBB says that Sänger is the logical follow-on to Ariane 5 and the proposed Hermes manned spaceplane – should Hermes ever reach development. Making six manned launches a year at $15 million to $20 million each, compared with Hermes $200 million cost for each of only two launches a year, Sänger could save Europe $ 1 billion annually, claims MBB. The West German Government is contributing $115 million towards the definition study. MBB leads a team comprising its two space divisions and two aircraft divisions, MTU, and Dornier, and will provide $8-10 million of the $16-20 million being contributed by German industry. The German DLR aerospace research establishment is providing $45 million, and Deutsche Forchungsgemeinschaft and German universities $10-16 million.
Pic.3. First- and second-stage separation is a critical manoeuvre
Phase 1 system definition comprises: in-depth conceptual analysis; development of a small ramjet; definition studies for Mach 7 propulsion; preliminary component development and design of a flight demonstrator; and development of an engine flight testbed. Koelle, Phase I study manager, says that the rationale behind Sänger is quite logical. For real European autonomy, which means the capability to perform launches from Europe, "only the horizontal launch mode is feasible for safety reasons". The main missions required by Europe are transfer to the Freedom space station, and later autonomous Columbus-based manned platforms, in 28.5° orbit, and launches into geosynchronous orbit, which require a 3,500km cruise capability only feasible with Singer's five first-stage air-breathing turbo-ramjet engines, says Koelle. The turboramjet-powered winged first-stage vehicle offers maximum potential commonality with a possible future hypersonic airliner, Koelle says. "The similarity of the lower stage to a Mach 5 hypersonic passenger aircraft could become an outstanding advantage in the two-stage system, if the synergistic effect of joint development can be successfully exploited." A Sänger-derived hypersonic aircraft could carry 250 passengers 10,000km from Frankfurt to Tokyo in three hours, he adds. In contrast to single-stage concepts, such as Britain's HOTOL, "the two-stage concept allows the air-breathing propulsion system to be separated from the second-stage rocket engine, so that the technical risks entailed by a very complex combined propulsion system can be avoided and no dead weight need be carried into orbit," says MBB's Hogenauer. For the lower stage, various combinations of LH2 turboramjet engines are now being examined, because their high specific impulse of over 3,000s at Mach 4.5 seems to be the most promising, says Hogenauer. Knowledge in all the essential technologies—liquid hydrogen, turbojets and ramjets—exists in Europe, but "must be effectively coordinated and synthesised to create a basis for development," he adds. These engines will propel the first stage at a lower speed than the proposed US scramjet-powered X-30, further reducing Singer's technical risk.
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