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Or what you are going to call it, an unrealized proposal from Aerojet around 1984. PDF Found on NTRS.

The idea was to have two turbopumps (like on SSME), but instead operate on the expander cycle. Two heat exchangers, two turbines, two pumps. One for each propellant.

 

aerojet_cycle

Both propellants go through a heat exchanger and an expander driving a pump

 

This is a LOX-hydrogen engine. Also this means that since there is the same propellant on both sides of the axle, in the turbine and in the pump, no elaborate seals are needed. Original intent for these engines was for in-space reusable stuff, that needs to be operated many times and for a long time without maintenance. Size was in the RL10 class, about 70 kN. (RL10 has grown though.)

aerojet_margin
Simplicity and margin were claimed

Think for example if you let a fired turbopump sit in space for a long time. Will some fuel leak to the oxidizer side through the seals? This could avoid that. (You can use helium purges too though but then you’ve got one more fluids you need to tank.)

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Sandman

Armadillo flying to 600+ meters with a "mod". I say, it looks like the East German Sandman!

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It seems to be such a marvelous rocket engine. A high thrust to weight, high ISP high tolerance design that is still top of the line after sitting forty years in storage – it will be used for Orbital’s Taurus II as a first stage engine.

I drew a diagram on how the engine works internally.

NK-33 Simplified Flow Diagram

NK-33 Simplified Flow Diagram

It’s a full flow oxygen rich staged combustion design. Also note that there’s a separate geared booster pump to raise the pressure of the small fraction of kerosene going to the gas generator. This is most likely because the turbine lowers the pressure, hence the gas generator has to be at a much higher pressure than the chamber.

In the modern launcher business, Russia probably still has the best expertise on first stage engines.

With a modest chamber pressure, the full flow oxygen rich gas generator gas wouldn’t need even to be that hot. I don’t know why specifically these kinds of engines have not been tried more often. Maybe SpaceX can do something, they’re one of the few companies designing new engines anymore. This is the logical path after gas generator engines. Remember that perhaps the best known GG engine, F-1, originated from around 1958… It could be seen as an anachronism that the US companies are still sticking to gas generator cycle engines.

With modern day machining capabilities and turbine / pump computer optimization, one should be able to do quite a lot relatively easily.

Source for the data that I made the graphic with: Liquid Propellant Rocket Engines, lpre.de, in Russian.

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Masten

Made huge strides in the last few days. A half-L1 done. They might be able to compete with Armadillo on L2, though I’m somewhat skeptical since they’re only going to assemble the new L2 vehicle soon.

Suddenly looks like there are two viable big VTVL sounding rocket companies!

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62 mile club has a writeup of a beta “customer qualification program” for XCOR’s Lynx suborbital craft. This highlights the differences and current state of play. Rocketships will not be as safe as airliners in the near future, and they don’t need to be. There are millions of things that are less safe than airliners – scuba diving, ballooning, general aviation, motorcycling, probably even driving a car. And yet people do those things because they have the judgement and can decide for themselves.

The key difference is an informed consent. The suborbital rocket traveler should be told of the risks truthfully so that they can decide for themselves if they want to do it or not. This, I gather, has always been XCOR’s principle.

Airlines are not directed at such customers because they are a mass means of travel – the customer is not briefed specially but is expecting reasonably good safety – and there are thus governmental and intergovernmental bodies regulating the airlines and trying to constantly improve safety.

It would not make the slightest sense to regulate suborbital passenger rockets at this time at airline level – there are only a few passengers and the companies should have the time and resources to screen and brief them very well on what it will be like and what the risks are. (This is a must though – you shouldn’t advertise the service as something as safe as airlines.)

There should be some very simple regulation of rocketships regarding the risk to the uninvolved public of course – most companies deal with this adequately by just flying from remote enough locations. And of course there’s environmental regulation – it’s not cool to put tonnes of methanol into the ground water for example. Yet these are small no brainer issues (I’ve heard stories of over-eager environmental protection agencies though).

Nontoxic (or those that quickly decompose to such in nature) fuels and oxidizers should help a lot in this regard. Suborbital rocketry is not that performance critical anyway – it is a great way to find the lowest investment and operating cost approaches to rocketry – and these drive towards “nice” systems. Safe, easy, nontoxic, nonhazardous, redundant.

Regeneratively cooled LOX-ethanol or LOX-methane engines could be good in this regard – propellant spills and dumps are not that horrible to the environment or to the public, and the engine could in theory run indefinitely without any parts replaced if it is just refuelled.

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By ATK in 2005. Shows how little I know.

EDIT: Spaceref had the details, Mach 5.5.

(Scramjets are still not a space application.)

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Nice video explanation of the SABRE engine by Richard Varvill.

In a sense, it boils down to the problem of changing the hot fast low pressure intake air flow to a cold slow high pressure flow.

In the Sabre engine, techniques somewhat similar to liquid air plants are used: there is a compressor, that is coupled to an expander, the expander runs from the “waste” heat of the compressor. This is efficient, but it is heavy. In Sabre the compressor is the shock cone (the jet engine style compressor only compresses the cooled air).

The heat exchangers are critical, and I wonder how reliable and expensive they will get with the vast temperature envelopes, ice and thin wall problems of the huge number of tubes there are. On the other hand, such heat exchangers could have uses in many other places as well. (Power generation.) The helium in the tubes is especially leak prone.

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In a sense, having low resources can be seen as a good thing. You don’t end investing a huge amount of effort into some architecture, approach or solution, which proves to be a dog, but which you can’t then get rid of since you have so much money sunk into it, people doing it as a job or it has otherwise started a life and advocacy of its own. These effects can be seen in relatively small projects already, but get worse as projects grow.

Organizations (nowadays companies) like Armadillo Aerospace have done tremendously fast advances, then dumped a lot of them to the wayside (tip propelled rotors, high grade peroxide, mixed monoprop, preburners, etc etc) and seemingly repeatedly started from scratch. John Carmack said this in April:

We have built and flown so many different vehicles now that I don’t even count, but lessons are learned from each one.

What they have learned also is a process of developing new stuff. They have not learned one solution. They have learned finding solutions in general.

The whole existence of Carmack’s personal wealth has been one enabling factor behind this. No bucks, no Buck Rogers. But at the same time, since the team has been small enough and probably mostly centrally controlled in the main directions, they have been able to do quick decisions and moves. If Carmack is the leader and controls most of the money (and in the earlier days controlled it all, as, as far as I know, Armadillo Aerospace didn’t have any sources of income), there is less possibility of factions forming wanting to keep carrying on doing something when the leader decides it’s time to do something else. It is very much simpler decision making.

I have witnessed at times, in organizations, sports, or companies how a leader can make a huge difference, by just picking what to do. It doesn’t matter that much if it’s alternative a, b or c, just that one alternative is picked and everyone believes and accepts it as good enough, and starts working on it.

In the fast moving computer game technology world, where id software has been in the leading edge for about a decade and a half, John Carmack learned quick result making early on in his career when doing cover disk games for magazines. Absolute deadlines were set by the regular magazine publishing intervals.

So, what do we have as good examples from following Armadillo?

  • Taking results oriented approaches from other avenues where they have been successful
  • Having small teams
  • Being unafraid to ditch old solutions and to take new approaches
  • Having consistent funding

I don’t have a good view inside the Armadillo world. It is clear, by watching what they have done and listening to their people, that they have a lot of talented folks there and a good culture. It is certainly not a one man show. They have a lot of good approaches, like trying to train at least two persons for every rocket operations job.

So, had a bigger group been involved in a government operation with similar aims, with much more money, would the routes taken have been the same? Would it have been possible to ditch so many technologies in search for a better one? Would progress have been much faster?

I don’t really know. It might be that it could have been much slower in some ways.

In a sense, there is an optimum size for developing technology. You want to keep it small so it is fast to develop and failures are not too costly, so you actually are not afraid to risk hardware. You can do many many iterations with small and simple hardware in the time it takes to build a full size prototype. Why did DC-X have to be so big? When it crashed, there was no other vehicle ready by because all the money had gone to the one, expensive prototype.

So, taking my words somewhat back from the earlier fed up commentary, maybe it is good for the future of rocketry and RLV:s that the teams making the most advances at the moment are small and not very well funded. They actually make *more* progress that way! (If they are not absolutely starved.)

Turbopumps and real first stages can come later. Right now we are still basic operations development where even stuff like tanking has to be developed to work easily and reliably, nevermind more advanced problems landing.

Good pumps and real performance will come later, when it’s time for that. It’s not yet time for them, although of course it’s smart to keep developing them in the labs and on test stands. Just not worth risking them in flight when so much lessons can be learned with the pressure fed “trainers”.

P.S. This blog turned one year today. Total visitor amount slightly below 10,000, and it’s been rising. Thanks to all the readers, linkers, commenters and other people, and thanks to the friendly, smart, visionary and open Newspace community! It’s been exhilarating being a part of all this so far.

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Fascinating videos showing a little how Mazda makes them. Technically the Wankel engine is a simple one but it certainly doesn’t look simple to manufacture. Via Rotarynews.com.

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Truezero is using metric units (I hear liters mentioned on one video)! That must save a lot of trouble, compare that to Flometrics’ engineering students measuring flow rates at gallons per minute. 🙂 Truezero has a quite different approach otherwise too with careful planning and then construction. Interesting to see how they do. I’m surprised they haven’t hit more snags yet, although of course I know very little of what they have done.

Unreasonable rocket on the other hand has chosen multiple paths with the helicopter prototype for navigation and control, which should save a lot of time and cost. If Truezero tries to do that development with a full blown vehicle and crashes (with only one built), then it might be game over this year for them. Nevermind testing being much slower. On the other hand they seem to have built elaborate software simulation.

Also I should be adding more projects to the link bar…

Thanks to Clark at RLVNews for the heads up!

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