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John Creighton

Member

From: Nova Scotia, Canada

Registered: 2001-09-04

Posts: 2,401

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Re: Nuclear Transfer Vehicle Design

it's just that when you are dealing with gasses at this high a temperature, it becomes a negligable factor.

Maybe but for an http://md.chem.rug.nl/~mark/Courses/Kin … html]ideal gas viscosity is proportional to the square root of the temperature does not dependent on pressure. Therefore viscosity is very much a factor for any long tube but I presume these things use short nozzles so the losses are minimal. The real question is how quickly does the viscosity increase the entropy, does it increase it fast enough to mitigate any advantage from expanding the gas further.

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GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Nuclear Transfer Vehicle Design

Another reason the engineers might of not thought the optimal solution initial is that computational fluid mechanics is very computationally extensive.

P.S. Someone has to think of something first. I am not saying I ever had an original idea but maybe maybe I will implement it before the other guy...

Unlikly. The engineers would start with the fundimental physical principles behind rocket propulsion, which is what your "plumbing trick" is aimed at, and would certainly not have ignored the idea if it would have given a big performance increase.

Although CFD has come a long way, fluid dynamics themselves aren't too complex in a rocket engine like this, and I doubt that the refinements in today's models would yeild a big increase compared to those of the NERVA program.

The extreme temperatures of the Timberwind upper-stage engines plus the high fuel burnup rate makes them only good for one shot. But, they don't weigh much, don't need any acessory systems, and provide reasonably high thrusts. If you want a throw-away TMI stage, which is what NASA has in mind for the later revision for DRM, thats the ticket. Such a stage would increase payload by around 33-50%, or permit a MarsDirect/DRM sized payload to be launched on a 80MT launcher instead of a 120MT heavy.

As far as getting you there faster, I don't know, and it should also be figured what a faster transit would do to surface stay times.

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Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Nuclear Transfer Vehicle Design

With 1,000sec Isp why even bother with electric propulsion except for deep space probes and station keeping?

The JIMO mission has a delta v requirement of about 30 km/s.  That is high enough that it would be impractical even for an NTR with 1000s Isp.  There many other missions, especially ones with multiple targets, that would also need electric propulsion to become practical.