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A third way for rockets?



 
 
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Old January 12th 05, 04:45 AM
Steve Harrington Steve Harrington is offline
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First recorded activity by SpaceBanter: Jan 2005
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Quote:
Originally Posted by Jordin Kare
Remy Villeneuve wrote:

Found interesting things on the Web tonight:

http://www.flometrics.com/rockets/ro...rocketpump.htm

Very, very interesting approach... I'm even tempted to say that it's
too good to be true, to have the possibility of "best of both worlds"
applications.


We looked at this type of pump for Mockingbird (LLNL concept for a small
SSTO vehicle), and as I recall Mitch Clapp also looked at it for his
Bricklifter (slightly earlier version of the same thing); as with many
ideas, it's been around for a while. It was probably invented by
Tsiolkovsky; everything else was :-).

We found that for our size vehicle, a small, rapid-cycling piston pump
was better than a large, slow-cycling pistonless configuration such as
Flometrics is describing. Among other things, the piston separates the
pressurant gas from the propellant, allowing the use of a much hotter
pressurant, and by using a differential piston (gas end larger diameter
than liquid end), you can make the system self-pressurizing. And the
piston maintains propellant flow in zero-G, so it's better for a
restartable engine; no need to settle propellants before you can
restart.

[color=red]

The pistonless pump can easily accomodate a float to separate hot gas from the propellant. The fact that the pressure of the gas is the same as the propellant is not a big factor, unless your are using the catalyzed propellant to drive the pump as John Whitehead did. It is much easier to loosely seal a float to a pump cylinder for propellant management than to seal a piston at 300-1000 psi. Calculations of system mass show that the pump mass is much less of a factor than the mass of the pump power supply and the pistonless pump system mass is the same or less than that of a turbopump system
see http://kahuna.sdsu.edu/%7esharring/LVpistonless.pdf
for the calculations.
The piston pump is most useful for smaller engines, especially maneuvering missiles.



How big do you thing such a design can be scaled?


There's no obvious upper limit, but "reciprocating" systems tend not to
scale up as well as rotating systems; at some point the cost and mass of
the valves required for this system will exceed the cost and mass of
turbopumps. The crossover for our approach was around 50,000 lbf total
thrust. [color=red][i]

We think that the pistonless pump can be scaled up to the million lbf thrust level.

Can it be used for low-tech liquid-fueled boosters in the near term?


Possibly, but actually making a complex set of valves work reliably is
not trivial; note that many pressure-fed liquid and hybrid vehicles have
failed because of valve failures even though they have only one or two
valves that only need to operate once. As another example, John
Whitehead at LLNL, the guru of piston pumped propulsion, was never able
to get electrically-operated valves working reliably for propulsion
pumps despite a couple of years of effort; he eventually switched to
mechanical valves.

Making a complex set of valves work reliably is familiar to us, we have designed medical ventilators, where a valve failure means the patient may die.


Jordin Kare
Kare Technical Consulting
[color=red][i]
Check out the update page at www.rocketfuelpump.com

Steve Harrington
Flometrics
 




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