The Next Generation of Human Spaceflight

[Brian H]

Seems to me Virgin is way behind the "passengers to ISS" curve compared to SpaceX, whose Dragon capsule seats 7 and is designed for re-entry and re-use.

But it's all moot until Virgin can demonstrate any orbit-re-entry capability at all.

[DeltaV]

Copped this TPS info from http://forum.nasaspaceflight.com :

http://ntrs.nasa.gov/archive/nasa/casi. ... 016802.pdf
http://hapb-www.larc.nasa.gov/Public/Pr ... abeigi.pdf

[Diogenes]

Beamed propulsion: It really is hard to beat plain old rocketry, isn't it?

Pumps for liquid propellants: link didn't work. Turbopumps are a pretty mature technology. Xcor Aerospace has a positive displacement pump driven by a waste heat engine for their still-small engines. New rearrangement of some very old technologies, but it seems to work fine for them. I've seen it. Very simple, very robust.

Yeah, the links have all been pulled. Rather peculiar. It seemed like a pretty good idea. It claimed a serious reduction in weight by dispensing with the turbo pump.

Other types of rockets: High pressure tankage that also serves as primary airframe structure is a very good fit with either solid rockets or hybrid rockets, or even simple pressure-fed liquids. Not as structurally efficient, to be sure, but a very tough design approach that is very consistent with long service life and easy reusability.

These issues are not very easily crammed into a single formula or two, but they are of crucial importance if one is trying to design for LEO access at lower cost per payload pound.

The other big issue is what are the true cost drivers. One-shot hardware is expensive, yes, but one of the real cost increasers is a very labor-intensive vehicle checkout and launch crew approach. The battlefield guys "solved" this with their missiles, which are systems a relatively small crew of not-intensively-trained soldiers can launch. They simplified it. A lot.

Another giant gorilla in the tent is a huge logistical "tail" to produce complicated articles, the kind of things needed to push a design "to the edge". You solve that one by backing off a tad on performance demands. That allows the simplification needed to minimize the manufacturing logistical "tail". It is folly to think a launcher will be low cost, if it does not have operational characteristics that, at least sort-of, resemble those of the launch and recovery and re-launch of a Piper Cub.

Compared to these gorillas, propellant costs are almost trivial. Kerosene is cheap, so is LOX. Even the hydrazines are not very expensive. Hydrogen itself is not that bad. And don't forget about ammonia: the X-15's "big engine" used that with LOX and did very well. One of the new rising stars is liquid methane.

Myself, I suspect the only things that might get added to this mix are some turbine or ramjet assist in the lower speed and altitude ranges on steep ascent trajectories (M0-6-ish, and SL-60kft-ish). Stages done as clusters of smaller modules allow far easier recovery of units for reuse. Here is where stowed wings and some sort of landing gear help on 1st stage items. They come back close to launch site anyway: might as well fly the "model airplanes" home and just land them on a runway.

At this point, these ideas seem to be the most feasible improvements. The space elevator notwithstanding.

[Diogenes]

Sorry, I'm not familiar with the pump.

It was a bit difficult to find any trace of it left on the web, but I found this document that covers the idea. It actually seems like a pretty good method to me.

http://www-rohan.sdsu.edu/~sharring/Pistonless_pump_for_CEV.pdf


For what it's worth, they actually did test it with a real rocket.


http://spacefellowship.com/news/art11143/flometrics-rocket-pump-and-student-rocket-update.html

As to my manner of quickly attacking, I can only explain that I've seen this idea dozens of times over the last half decade and posted on it here several times. I'm not a supporter for the reasons stated.

No one likes to repeat themselves and I admit to some self-interest--that it irks me things like this that make no economic sense, get the grant funds and M-E research has not for 5 years now.

Just irks. . .

Now if NASA would revive their M-E research program at Marshall, I'd be happier (though still a little intolerant for economically senseless approaches to spaceflight..

I know how you feel.

[Diogenes]

"I was going to ask your opinion of the Flowmetrics pistonless Turbo Pump replacement, but Flowmetrics appears to have killed all references to it. I suppose that means they discovered why it wasn't practical."

No it works fine. They just discovered they can't enforce their patent--it's been done before. Turbo pump ISPs at turbo pump dry weights, but dirt simple and you gas and go.

But they can't get a royalty.

I can see why they might be no longer interested in developing it if they can't make any money off of it, but it begs the question. If it's such a good idea, why does NO ONE seem to be pursuing it? Surely a royalty free easily (more easily) manufactured rocket pump ought to be attractive to SOMEONE in the rocket business?

Is there something better out there?

[GW Johnson]

Is there something better than turbopumps? I dunno. The answer may be scale-dependent. XCOR Aerospace uses positive-displacement pumps driven by a waste heat engine that is a piston engine. They are down in the few thousand pound thrust range, but with really robust, long-life hardware. I would be unafraid to put it in an experimental airplane and fly it myself. It's that good. Whether that scales up, I dunno.

[kunkmiester]

Has anyone looked at pressure driven designs using gas generators? It doesn't need pumps, but most pressurized propellant systems can't get very big because they use a tank of gas. Gas generators are basically solid rockets contained so that you get output of high pressure gas for various purposes--laser guided bombs get their power from such a system, burning pellets to run a tiny turbine.

This would basically use a large gas generator to keep the much larger tanks for a larger engine pressurized to the point the propellant will flow. To stop, you blow a plug or open a valve to release the pressure. It's not exactly easy to turn off, but a first stage you ideally wouldn't be shutting off anyway.

[Aero]

A related topic on the NASA space flight forum.

http://forum.nasaspaceflight.com/index. ... ic=17008.0

The idea is to dissolve liquid nitrogen in liquid oxygen which gives much better tank pressurization than boiling the LOX and can be handled at much higher temperatures. The mixture still works quite well as an oxidizer so it looks good at a first look. This approach will also eliminate the helium tank pressurization system which is commonly used. Containing boiling LOX for pressurization is not common, I understand.

[GW Johnson]

Gas generators are something I know work well. But, rather than simply pressurize a tank, why not spin a pump with it? Leave the tank low pressure, and therefore lighter weight. There's all kinds of pumps that could be driven by a gas pressure source, and not all of them are turbine-type pumps.

Unless, the tank needs to be very strong for airframe reasons. Then pressure feed is a good option. Gas generators are one way to do that. Other options that match up well with the "airframe needs a strong tank" scenario: do the hybrid or the solid rocket.

The design advantage of the liquid bipropellant system is the lightweight low pressure tank, which you have to pay for with pumping power. That's why liquid rocket engines are as complicated as they are: it is difficult to get them to pump their own propellants.

But, if you need a strong heavy tank for airframe reasons, then the pressure-fed, hybrid, and solid systems look just about as good as the pumped liquid bi-propellant approach, in many important ways: packaging, materials, compact layout, etc.

Isp-wise, liquid bipropellant is the best at 300-450- sec-ish, ranging from kerosene-LOX to LH2-LOX. Hybrids can vary from 200-ish all the way up to 300ish. Rubber LOX at about 300 sec is about as good as it gets with what we know, and is also the most difficult to ignite or to make burn efficiently. There's still work to do developing good hybrids. The ones that work the best right now are comparable in Isp to the solids.

Solids range from under-200 to about 260-ish, depending upon choices. AP-oxidized composites at 260 sec in large sizes and 1000-2000 psi chamber pressures are about as good as it gets from a practical handling and safety standpoint. The real design advantage of the solid is its wooden round characteristics: it just sits there, needing absolutely nothing for years, until you light it. Then it does its thing. No fuss, no muss, no leaks, no checkouts, no nothing.

I guess my real message is that these issues and selections are strongly linked. Any real design will be constraint-driven, not a "free optimization".

[Aero]

I guess my real message is that these issues and selections are strongly linked. Any real design will be constraint-driven, not a "free optimization".

Agreed - What does your experience tell you about these Fizzy oxidizers and fuels introduced here?

http://selenianboondocks.com/2009/05/ch ... d-rockets/

They are new to me but that's not really my field. Are they even a new concept?

[GW Johnson]

Fizzy stuff is a new concept to me. Sounds sort of like a carbonated soft drink. If that's what it really is, then the more you heat it or shake it, the higher the pressure will be.

Not sure whether that is something different, or just a variation on the pressure-fed liquid. Very interesting notion, indeed.

[kunkmiester]

Gas generators are something I know work well. But, rather than simply pressurize a tank, why not spin a pump with it? Leave the tank low pressure, and therefore lighter weight. There's all kinds of pumps that could be driven by a gas pressure source, and not all of them are turbine-type pumps.

Unless high pressure tanks are easier and cheaper to build than pumps. Likely, some of the new pump designs are going to have to be looked at, but even if it's heavier, and thus has less payload, a simpler design might be cheap enough to out-compete more capable, but more complicated designs.

[rjaypeters]

Virgin Galactic Mulls NASA Crew Bid

http://www.aviationweek.com/aw/generic/ ... 102910.xml

Quote: “There’s about four companies that are seriously looking at [CCDev Phase 2],” Branson said in an interview with AVIATION WEEK. “Two of those companies we’re in discussions with about teaming up with. ... Over the next month, we’re going to make a decision as to whether to team up with one of those two companies or go it alone, but we plan to be in orbital travel within the next few years.”

Well, I hope they go it alone, develop and build something great.

[AcesHigh]

sorry, black hole starships are not exactly "next generation" of human spaceflight. I created its own thread.

[GW Johnson]

On tankage: a high-pressure tank is a high pressure tank, whether it's a pressure-fed liquid, a hybrid, or a solid. Such tanks are rather strong. Doesn't matter all that much whether it is a metal or a composite, either.

In those designs where lightweight tankage is paramount, then, having an efficient pump is very important. The liquid rocket engine guys have gotten pretty good at tapping high quality energy out of the combustion and re-introducing the low-quality energy back into the cycle without losing it.

Still, turbomachinery is very sensitive and demanding. You can easily make or break yourself with it. The older piston technologies are more robust in many ways. That's what impressed me about the boys at XCOR in Mojave. They have a piston heat engine drawing heat into a closed-circuit working fluid that drives a piston heat engine. Its shaft output drives a positive-displacement pump-set for their bipropellant rocket engines.

It's not quite as lightweight as turbomachinery, but it's one whale of a lot more robust. We're talking thousands of hours of system life, not unlike current aircraft engines. Very reliable, very safe. I'd feel quite safe putting a thing like that in an airplane and flying routinely with it. That's totally unlike current "standard" liquid rocket engine practice.

But, it's an awful lot like what future "routine spaceflight" operations will require. From a safety standpoint, as well as reusability.