Saenger (spacecraft)

Development

During World War II, German engineer Eugen Sänger drew up early plans for a two-stage rocket-powered aircraft. Designed for military use, the craft was meant to fly at roughly 17,000 kilometers per hour, cross the Atlantic, and drop a one-ton bomb load on US East Coast cities like New York. It was never built, but the idea later inspired further development. In the 1960s and 1970s, the German firm Messerschmitt-Bölkow-Blohm revived the concept, calling it Saenger. The German Aerospace Center took notice and made it a reference design for a West German hypersonic research program. Saenger was imagined as a passenger plane bigger and faster than the Concorde, and also as a way to send payloads into low Earth orbit. Another planned role was as the first stage of a two-stage launch system, paired with a crewed spacecraft called Horus or an uncrewed cargo module called Cargus. Proponents claimed it could cut launch costs from $3,500 per pound to $500 per pound, a strong economic reason to pursue it. In the mid-1980s, official interest grew. In June 1985, the Saenger launch system was formally presented to the European Space Agency council. At that time, ESA was weighing three competing projects: Saenger, the French Hermes, and HOTOL. From the start, securing ESA funding looked tough, given the agency’s tight budget and a lack of strong political backing. Although Germany supported Saenger, many within ESA wanted to downplay independent crewed space programs and instead focus on using existing systems and other space research.

Design

The Saenger was a hypersonic aircraft concept designed with highly aerodynamic features, comparable in size to a Boeing 747 and able to take off like a standard plane. In its passenger role, it was expected to reach speeds of Mach 4.4, cover 11,000 kilometers, and carry roughly 230 people—more than twice the speed, range, and capacity of the Concorde, the only supersonic airliner in long-term service. Power would have come from six hybrid turboramjet engines, and according to Flight International, the project’s success hinged on the development of very advanced jet engines for the mothership. The Saenger was also planned for space missions, serving as a mother ship to launch payloads into orbit. It would have carried a smaller piloted orbital spaceplane called Horus (Horizontal Upper Stage), intended mainly to service and supply space stations, transporting between 4,000 and 6,000 pounds of cargo and up to six astronauts to a 270-mile orbit. Other upper stages were considered, such as the uncrewed, expendable Cargus (Cargo Upper Stage), which would deliver 5 to 15 tonnes to low Earth orbit, reusing propulsion elements from the Ariane 5 rocket. In a space launch configuration, the Saenger would take off conventionally, climb to 100,000 feet and Mach 6, then release the second stage for its own powered ascent to orbit. Extensive studies also examined the Saenger as a hypersonic passenger airliner. Its high-altitude flight would have greatly reduced ground-level noise, a major public issue for the Concorde. The first stage of the launch system was aerodynamically similar to the airliner model, allowing shared development work.

Variants

The Saenger I spacecraft was designed around a two-stage setup, much like the American Space Shuttle. The first stage, carrying the second stage on top, would take off horizontally from a runway. It would use airbreathing ramjet engines to ascend to 30 kilometers. At that point, the second stage would separate and fire its LOX/LH2 rocket engine to reach orbital speed and altitude. The key benefit was that the first stage could take advantage of the higher specific impulse of airbreathing engines until the air became too thin and the speed too high for them to work effectively. The second stage measured 31 meters by 12 meters and was meant to hold two astronauts. There was also a different concept called the RT-8 "Raumtransporter-8," or "Space Transport 8," which would use a steam rocket to push both stages along a 3-kilometer track, reaching a release speed of 900 kilometers per hour.

The Saenger II project evolved from Saenger I in the late 1980s. It was planned as a European launch vehicle meant to match the idea and abilities of the Space Shuttle program. The West German aerospace firm Messerschmitt-Bölkow-Blohm (MBB) handled the development. As planned, the vehicle would take off from a runway using ramjet engines, climb to 30 kilometers, and reach Mach 7. The second stage would then detach and use its rocket engine to accelerate to orbital speeds and altitudes, while the first stage flew back to the original runway. This spacecraft could deliver a payload of 10,000 kilograms or a crew module to low Earth orbit. Saenger II was also envisioned for passenger service as the EHTV (European Hypersonic Transportation Vehicle) MBB HST-230, carrying 230 passengers over a range of more than 10,000 kilometers—for example, from Frankfurt to Tokyo—while cruising at Mach 4.4 at an altitude of 24.5 kilometers.