Sänger was a concept for a reusable launch system by Eugen Sänger. It was under development from 1961 to 1974 by Junkers as part of a study about gliders that could reach space.
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Concept
The concept consisted of two stages. The first stage was supposed to be a glider that would takeoff horizontally. It would carry the actual space shuttle about 30 km high into the stratosphere. The first stage would had been equipped with an airbreathing jet engine. The first stage would then be separated at around 1000 km/h and the second stage (space shuttle) would then use its rocket engine to reach its destination in orbit. The main advantages over a conventional rocket design are that the first stage does not need to carry oxidant, making it lighter. Due to the horizontal flight the impact of atmospheric friction is much lower and the first stage is more maneuverable, allowing a more flexible target orbit.
The first stage's wing spread was 31m x 12m. Sänger should had been able to carry two astronauts into orbit. Sänger was never built, but the concept was reused in a new project called Sänger II.
Sänger II
Sänger II was planned to be a European space shuttle. At the end of 1980 the West German company Messerschmitt-Bölkow-Blohm brought up the concept of a two stage reusable launch system.
Like Sänger the second stage would separate at 30 km altitude but this time at a speed of Mach 7. While the first stage would glide back to the ground the second stage would accelerate to its orbit.
The second stage would had had to different optional configurations. "Cargus" = Cargo Upper Stage for 15000 kg cargo or "HORUS" = Hypersonic ORbital Upper Stage as a crew transport for two astronauts and 3000 kg cargo.