F026@CPC865.UEA.AC.UK (08/25/88)
> > What is an aerospike? What is meant by its being (or not being) > "plugged"? > The business end of a conventional rocket engine is a bell shaped nozzle. This has some disadvantages, among which are the fact that (for best efficiency) it should be narrow in dense atmosphere and wide in vacuum, and you can't re-enter with it pointing forward because it won't be there when you've landed. Some company (can't remember which) started experimenting with ways round this, and came up with the idea of turning the nozzle inside out, so you have a thing shaped [ ABS(COS(X)), X=0,PI ] (ha! that solves the problem of no graphics!) with a ring of fuel injectors round it. In atmosphere, the air acts as the 'other side' of the pseudo-nozzle, making it narrow. In vacuum, it's infinitely large. You still can't re-enter with this thing, but if you cut most of the spike off to leave a thing shaped like [ MAX(.5,ABS(COS(X))), X=0,PI ] and then blow a small jet of gas down through some holes in the flat bit, which is now called a "plug", you can create a spike, hence "aerospike". If the plug is made of suitably solid material, or covered with replaceable ablator, you can use it as a heat-shield when you re-enter. It's also lighter than a spike. If you keep a small reserve of fuel on board, you can re-ignite your engine and slow the craft down enough to soft-land without a parachute (a la LEM descent stage). Because the engine is efficient you now have a small, 100% re-usable VTOL spacecraft. That company made some research models in 1966, and declared the whole thing viable. A man called Gary Hudson designed an aerospike-driven craft called PHOENIX (presumably cos it lands in flames, then can be refueled and take off from its own ashes) for which he needed $300M development. Nobody took it on, so he set up the Pacific American Corporation, and started building conventional engines to raise the money for PHOENIX. You may have heard of the LIBERTY booster, which has just got a demonstration contract from the SDIO. They're already bending metal for it, so hopefully it won't be too many years before PHOENIX rises. For a better description of aerospikes, read Bono & Gatland's "Frontiers of Space". * Mike Salmon, Phone +44 603 56161 x2875 Time GMT+1 * * Climatic Research Unit, JANET m.salmon@uea.cpc865 BIX msalmon * * University of East Anglia, BITNET f026@cpc865.uea.ac.uk * * Norwich, Norfolk, ARPA f026%cpc865.uea.ac.uk@cunyvm.cuny.edu * * United Kingdom Elsewhere f026%cpc865.uea@ukacrl.bitnet * * - - - - "How far can you comfortably spit a mail gateway?" - - - - *