(November 17, 2016 at 7:30 pm)vorlon13 Wrote: Ever wonder why the plume coming out of the back end of a rocket gets so big the higher the rocket goes?
Less air pressure up there, so the exhaust fans out more.
Which causes a major design problem for bell shaped rocket engine exhaust nozzles. The design is governed by the expected rate of expansion of exhaust gas. But exhaust gas expands faster in vacuum of space or thin high atmosphere than in dense lower atmosphere. So an engine bell designed to maximize thrust at sea level loses thrust at altitude, and vice versa.
Hence aerospike.
