This remarkable design was called the Silbervogel ("Silverbird") and would have relied on its fuselage creating lift (as a lifting body) to carry it along its sub-orbital path. Sänger was assisted in this design by mathematician Irene Bredt, whom he married in 1951.[3][4] Sänger also designed the rocket motors that the space-plane would use, which would need to generate 1 meganewton (225,000 lbf) of thrust. In this design, he was one of the first to suggest using the rocket's fuel as a way of cooling the engine, by circulating it around the rocket nozzle before burning it in the engine.