[AR] Re: engine life (was Re: Nozzles for Amateur Solids)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Mon, 12 Mar 2018 00:14:39 -0400 (EDT)
On Mon, 12 Mar 2018, rebel without a job wrote:
In space, no one can hear you scream. A consequence of that is that you
don't have a fluid to cool your heat exchanger. The only cooling fluid
and working mass you have is that which you have brought with you...
Which is actually good news in some ways: cooling with liquids is a whole
lot easier and more effective than cooling with gases. If there's a
torrent of propellant going into the chamber, using it for cooling is an
awfully obvious thing to do. (In fact, aircraft capable of sustained
supersonic speed often use their fuel for cooling too, but this works even
better for rockets, cooling a compact chamber with a high fluid flow.)
Chamber cooling is substantially harder when Isp gets so high that there's
no longer enough propellant flow to accept all the heat, but that happens
well above the chemical-rocket range. (Fusion-rocket designs tend to be
extreme cases of this. In the "Firefly" concept for a fusion starprobe,
which has the fusion plasma pretty much out in the open with the vehicle
intercepting as little as possible of the emissions, 3/4 of the dry mass
of the vehicle is the cooling system.)
Henry
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