aero spike.

While sketching I wondered what would happen if you built a solid
rocket booster that had an aero-spike ( an inside out rocket engine ).

One of the advantages of an aero spike engine is that the engine does
not loose efficiency as the external air pressure changes. A 'normal'
rocket engine like the space shuttle engines looses efficiency (
specific impulse ) between ground level and vacuum. The aero spike is
designed to maintain efficiency at all heights.

The kinds of engines which are commonly transfer between sea level
pressure and vacuum are solid rocket boosters. These are the boosters
which are very common on many space rockets ( space shuttle/Ariane).

The idea was that you build a solid rocket booster with a aero spike engine.

Nasa got there first
http://www.nasa.gov/missions/research/aerospike_rocket.html

So I want that but bigger.

more info
http://en.wikipedia.org/wiki/Aerospike_engine

http://www.orbitalvector.com/Orbital%20Travel/Aerospike%20Rockets/Aerospike%20Rockets.htm

Excellent detailed info.

http://www.aerospaceweb.org/design/aerospike/main.shtml