How does an aerospike engine work?

Aerospike engines work based on the principle of reversing the standard engine design. In a traditional rocket engine, the combustion occurs in a chamber and moves through a throat, expanding out into a nozzle where the walls contain the pressure. In an aerospike engine, however, the pressure from the combustion is on the outside and pushes inward against a spike, somewhat like squeezing an ice cube to propel it forward by applying inward pressure.

The aerospike engine's design allows it to operate efficiently both at sea level and in the vacuum of space, thanks to its ability to maintain a large expansion ratio—the ratio between the throat area and the nozzle exit area. This ratio is crucial as it helps transform the high-pressure, high-energy gases into faster-moving, lower-pressure gases along a specialized "spike" surface. Unlike traditional engines where atmospheric pressure may disturb exhaust flow at sea levels, the aerospike’s unique configuration prevents flow separation, extending engine efficiency across varying altitudes.

Despite these advantages, the practical challenges associated with aerospike engines involve their cooling due to an increased surface area of the throat, which is more difficult to manage due to the reversed flow. Moreover, no aerospike engine has yet been flown on an orbital rocket 1 2 3.