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A third way for rockets?
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. How big do you thing such a design can be scaled? Can it be used for low-tech liquid-fueled boosters in the near term? |
#3
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A third way for rockets?
One nice thing about that pump design that I don't see mentioned on the
website is that, although you need as much pressurant as you would if the main tanks were pressurized to the pump delivered pressure, you vent most of that pressurant on the way up, and don't need to accelerate it. Oxidizer tanks especially have significant pressurant weights at burnout. The large pressurant requirements for a design like this pretty much means they are going to have to boil something if they are going to orbit. Whatever they boil is going to have to be supplied or boosted to high pressure. Whatever contains or boosts that pressurant is going to weigh something, and I don't see that factored into their mass calculation. But I still think it's a great idea. |
#4
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A third way for rockets?
Remy Villeneuve wrote:
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. How big do you thing such a design can be scaled? Not that I'm an expert, but I don't see any reason it can't be scaled up to an arbitrarily large size. It would also be possible to have multiple pumps, if necessary. Or pumps with more than two high-pressure cylinders. Can it be used for low-tech liquid-fueled boosters in the near term? Practically speaking, only if the company is very liberal (and cheap) with his patent licensing. The big aerospace companies aren't going to change their designs for this. The existing engineering teams will find plenty of reasons not to give it a try. So his only hope (in the near term) of seeing this fly is to convince one of the X-Prize teams to try it. Not that it would be a factor for the competition itself. But some of the teams like Armadillo will (I believe) continue working, even if they don't win the race. Flowmetrics will have to get some good flight data though, before other people will be willing to experiment with it. At any rate, I have some doubts about the amount of pressurant needed. I haven't yet read all the info on the site, but it seems to me (intuition can always be wrong) that they would need a lot more pressurant than a traditional pressure-fed design. That's because you're blowing out large quantities of it with each pump cycle. They're talking about heating it, which should reduce the amount needed. Perhaps I need to run some numbers. James Graves |
#5
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A third way for rockets?
This design has to heat the pressurant. The hot pressurant cycles
through the pump chambers with the propellants. If the propellants are cyrogenic, there is going to be a fair bit of heat transfer to the propellant. More than you would see in a comparable pressurized main tank, since a big tank can use diffusers and stratify the pressurant in the tank. That means more, maybe a lot more pressurant will be needed, since the colder pressurant will contract. |
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#7
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#8
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#9
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#10
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A third way for rockets?
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. 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. 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. Jordin Kare Kare Technical Consulting |
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