Arospike engine efficiency in a vacuum

[Tommygun]

Does anyone know what a real arospike's engine efficiency is in a vacuum compared to a traditional bell type motor?

[SargeRho]

All I know is that Aerospikes generally are about 25-30% more fuel efficient, and have the same Isp at all altitudes.

[Apotheosist]

From memory of something I read a while ago, (or possibly complete rubbish I'm making up) I think aerospikes had about 90% the efficiency that a bell nozzle would have for a specific altitude. However, the aerospike kept it's efficiency through all altitudes, whereas a bell nozzle rocket would lose it's efficiency with changes in altitude. So, it's 90%. But don't quote me on that.

[Letum]

The idea with an Aerospike is that it is efficient at a wider range of altitudes than a bell engine, which is designed for maximum efficiency for only a small altitude range.

Aerospikes manage this because whilst a bell engine compresses gases by the shape of the bell, the airospike uses atmospheric pressure to constrain the gasses dynamically.

Aerospikes have no efficiency benefit in a vacuum vs a bell engine designed for a vacuum, but will be more efficient in a vacuum than a bell engine designed for atmospheric and vacuum use.

[opticalshadow]

i know they look way more cool, so thats got to count for something.