Re: [ERPS] Aerospikes versus entensible nozzles

[Ian Woollard]

Henry Spencer wrote: On Fri, 8 Aug 2003, Ian Woollard wrote: That's unclear to me, extension pieces needn't be heavyweight, and should be uncooled (in most cases aerospikes have to have cooling)... Note that in the real world, uncooled nozzle extensions are normally built out of quite exotic high-temperature materials, e.g. silicon carbide composites. Interesting. I've done a bit more research, and I'm not that surprised. Even though the gas in the extension is only at about 300C, moving at mach 10 or so; but at the edges of the nozzle the gas tends to stagnate and form a boundary layer; (presumably the stagnation temperature can go quite high; but probably not reaching the temperature of the combustion chamber.) I haven't found a model of the temperature anywhere yet however. There's probably no particular reason it can't be actively cooled though, except more weight. I did find some other data on mass on the web, the Ruskies build the NK-33 and NK-43- these engines differ only on the expansion ratio of their nozzle. The mass of the NK-43 engine is about 10% higher. From what I can see the extra ISP and thrust seems to be a win for a SSTO design, inspite of the extra weight. (Frankly, I'm a little surprised that the Shuttle didn't use one, but the SSRBs kind of mean they didn't have to try quite so hard, alas.) NK-33/43 Specs are here: http://www.spaceandtech.com/spacedata/engines/nk33_specs.shtml There's some good photos and diagrams of some japanese research on extendible nozzles here: http://www.nal.go.jp/krc/eng/rocket/nozzle.htm (about halfway down). Henry Spencer [EMAIL PROTECTED]