Discussion A REAL Delta Glider (well, almost)

[T.Neo]

In the past few months (as I have been dealing with other projects :dry, I have become increasingly interested in a spacecraft built for access to low Earth orbit, particularly a reusable single-stage spaceplane.

Integrated with the interest in the Orbiter community in the Delta Glider and related addons, and questions as to whether said spacecraft could be constructed in reality, I am beginning to set my sights on a "real-world" Delta-Glider. :thumbup:

The foremost requirements for such a craft would be an SSTO vessel, that can place 5 people in space. In the interests of realism, certain aspects of the Delta Glider that are more focused on gameplay rather than design in reality, such as hover engines, retro-rockets and the nosecone docking port will be omitted.

The spacecraft will only have a Delta-V for flights to an acceptable LEO; going anywhere beyond the Moon in such a small cabin would be highly impractical regardless. Possibility for a sixth crew member (co-pilot) would be included. Other design requirements are:

- A potential small cabin payload capability (max. 3 tons).

- Use of nuclear thermal propulsion, as opposed to chemical/scramjet, or Quantum-Handwavion flux accelerators. Both solid core and (enclosed) gas core designs must be considered; I would consider solid core to present a lesser engineering challenge.

- Liquid or potentially slush hydrogen propellant.

- Use of advanced composite materials for a light (yet still realistically plausible) airframe.

- Seperate thruster system for on-orbit manuvering (integrated to RCS).

- Potential for use of solar power during on-orbit activities.

I currently have no fancy meshes to show for this, nor do I have a fancy .dll (I wish ). I have come up with some preliminary (and rudimentary) mass and power figures however.

Comments, suggestions, advice, and constructive criticism (or harsh criticism, if you wish :lol are welcome.

Cheers,
T.Neo

 

[Grover]

i cant wait, im thinking, is this going to be a more realistic XR-2?

i always wanted solar power intergrated into vessels, coz the excuse (nuclear power) is a bit tired (need i mention how big and heavy a whole nuclear system is?)

thanks
-=Grover=-

 

[T.Neo]

i cant wait, im thinking, is this going to be a more realistic XR-2?

No, it's going to be a more realistic Delta Glider. The XR-2 is actually a very different spacecraft capability wise, and besides, it belongs to Coolhand and Doug. If I were to do something that derived from the XR2, I'd only do it with their wishes.

i always wanted solar power intergrated into vessels, coz the excuse (nuclear power) is a bit tired (need i mention how big and heavy a whole nuclear system is?)

Don't bash nuclear power, it can be advantageous. Solar power isn't massless either.

I actually have a nuclear power plant onboard, but I'd prefer not to leave it running, or associate mass and complexity with a power generation system linked to it. I'd also imagine engines with an output of several gigawatts producing a measly kilowatt or so would be hopelessly overkill.

 

[Grover]

well a nuke plant is far bigger than you could fit in a DG, especially with our current or near technology.

its more realistic to imagine a whole range of energy sources, solar to the max (try finding a way to get them on the entire wing surface for realism), backup batteries, conventionally fuelled APUs (Hydrogen, possibly carbon based fuels) and if youre going into future settings, then add nuclear.

and when i said XR2, i meant a complete craft, that does every role within its quota (itll do anything in LEO in this case)

 

[T.Neo]

well a nuke plant is far bigger than you could fit in a DG, especially with our current or near technology.

Not really. TOPAZ massed about a ton, and I have a feeling it was not the size of a house.

its more realistic to imagine a whole range of energy sources, solar to the max (try finding a way to get them on the entire wing surface for realism), backup batteries, conventionally fuelled APUs (Hydrogen, possibly carbon based fuels) and if youre going into future settings, then add nuclear.

Putting solar panels on the exterior is a generally bad idea due to thermal stresses during reentry; that is likely covered by some sort of thermal protection system. It is more efficient to have a seperate structure with the panel on a swivel, so it can make use of sunlight as best as possible.

APUs are another story entirely, necessary to operate stuff like control surfaces... I'll see. I'm not going to run the craft on them while in orbit, obviously.

I already have nuclear power, I'm just not going to use it on-orbit.

 

[jedidia]

You really should think twice about putting a nuclear PLANT into an SSTO. *Very* optimistic expectations for power/mass ratio are about a kw/kg, which most probably won't cut it in an SSTO. Add to that that for an SSTO it has to be fully shielded, and you're getting yourself into even more trouble. (Thermonuclear engines are another matter, but they work totally different than a nuclear reactor).

Also, you'll get heating problems. Working with a built-in power plant means having to dispose of about 80% of the heat (yeah, we can't have much more than lousy 20% efficiency from a nuclear reactor. Heat-to-electricity conversion is a rather inefficient aproach). The upper atmosphere isn't enough of a cooling medium, but prevents you from deploying radiators, and the radiator mass might get rather large too. It depends on how much power you really need from it, I guess.

There's also the question what you actually need it for... I can't think of anything that would need more than a fuel cell to keep going. If you want to use it for the thrusters, that's a no-go: The only thing you could work with is an electric engine, which have nice ISPs but lousy thrust values. Our best bet for interplanetary drives currently, but utterly useless for earth take-off. If you want to use nuclear power for the thrusters, you'll have to go with thermonuclear thrusters, which as mentioned already are a completely dufferent kind of animal and might actually make sense.

i always wanted solar power intergrated into vessels,

While solar power reaches a similiar energy/weight ratio, what you have here is trouble with the energy/area ratio. Anything sporting solar panels big enough to produce any meaningfull energy has way too big a surface area for being an effective atmospheric vehicle.

 

[Wishbone]

Please forgive my ignorance, could you consider tethers for current generation while on LEO?

One more request, if you don't mind: could you also outline the sequence of your sizing decisions (e.g. what iterative scheme you use and what the driving factors are)? It will be of great interest to spaceflight & design newbies like me.

 

[Sky Captain]

You really should think twice about putting a nuclear PLANT into an SSTO. *Very* optimistic expectations for power/mass ratio are about a kw/kg, which most probably won't cut it in an SSTO. Add to that that for an SSTO it has to be fully shielded, and you're getting yourself into even more trouble. (Thermonuclear engines are another matter, but they work totally different than a nuclear reactor).

Also, you'll get heating problems. Working with a built-in power plant means having to dispose of about 80% of the heat (yeah, we can't have much more than lousy 20% efficiency from a nuclear reactor. Heat-to-electricity conversion is a rather inefficient aproach). The upper atmosphere isn't enough of a cooling medium, but prevents you from deploying radiators, and the radiator mass might get rather large too. It depends on how much power you really need from it, I guess.

I think in this case engines are suposed to be nuclear thermal like NERVA so there is no need to generate electricity. If your reactor is only a bare core with chanals to run LH2 through everything becomes much simpler, lighter and easier to construct. NERVA had power to mass ration ~100 kw/kg and that was only a prototype built 40 years ago. I'm sure with modern materials even better performance could be achiewed.

 

[jedidia]

Oh, I just noticed that T.Neo was actually proposing thermo-nuclear propulsion, which got turned into a nuclear power plant by Grover, which are two completely seperate things. Unfortunately I didn't read the initial post carefull enough, my bad.

@T.Neo: Yes, I think thermonuclear propulsion is a possible solution to the problem.

 

[TMac3000]

The space shuttle is borderline-SSTO as the ET is the only part of it that can't be recovered. The SSMEs are way more powerful than the DG-IV's engines. In fact, the Shuttle could theoretically take off from a runway if not for the size of the ET (though it couldn't reach orbit like that).

My point is that the technology certainly exists to build an SSTO (I think the Skylon is our best bet). All we're really missing is the $$$

 

[T.Neo]

STS isn't an SSTO, it's effectively a two-stage rocket with detachable, reusable engines.

The SSMEs are ignited from launch, yes, but during the portion of the flight when they are attached, the SRBs essentially act as a first stage... they account for something like 80% of the thrust of the entire stack.

The interesting thing about a runway takeoff is it means you can have a far lower thrust (it really does take a lot to accelerate at just 1 G). The lower thrust means that even though my engines have an exhaust velocity more than twice that of the SSMEs, they have around the same power output.

Please forgive my ignorance, could you consider tethers for current generation while on LEO?

I'm not sure. I think their flimsy-ness would be disadvantageous, unfortunately.

One more request, if you don't mind: could you also outline the sequence of your sizing decisions (e.g. what iterative scheme you use and what the driving factors are)? It will be of great interest to spaceflight & design newbies like me.

I wish I knew- you tell me!

Currently my iterative process is forwards, backwards, up, down, left, right... it is not the best to be confused. :shifty:

I'm sure with modern materials even better performance could be achiewed.

Indeed, improved mass figures is always a good thing but I'm also trying to get more exhaust velocity from these engines as well.

Currently I'm in a bit of a spot... hydrogen requires very large tanks (more mass and difficult to fit into an airframe), but has the best exhaust velocity, whereas methane is something like more than 6 times the density and offers an acceptable exhaust velocity; even with the ISP decrease and inevitable mass ratio increase, I end up with a far smaller volume- one that is far better than LH2 (edging into plausible territory to be fitted into an airframe).

The problem is though, not only do I get a decrease in exhaust velocity (which is accceptable but still not nice), but methane also dissasociates into hydrogen and carbon in the engine... if this means soot buildup, it is not a good thing (rebuilding an SSME is bad, but rebuilding a nuclear engine is even worse).

Furthermore, how close can I come to the theoretical ultimate for a solid-core nuke thermal engine? Atomic Rockets gives a theoretical ultimate of 12 000 m/s, and my own experimentation with propep/GUIpep seems to corroborate that... obviously there are material limitations and inefficiencies, but how high could it potentially be pushed with modern technology?

 

[jedidia]

If you go with a solid core, I think you'll need at least oversized JATO-style boosters to get the thing a good start...

You might have to consider liquid core. (gas-core would be nice, but still requires premium amounts of handwaving).

Then again, having a liquid core blasting off at ground level might be rather unhealthy for the launch site, which makes a classical runway start questionable too.

 

[T.Neo]

The low thrust you're talking about is really intrinsic to NERVA; DUMBO, a competing design to NERVA, had a far superior thrust- 3.5 MN (NERVA had only 49 kN), at an engine mass of 5 tons. That is comparable to the SSME, which has about 2.28 MN (vacumn) at an engine mass of 3.177 tons- the thrust/mass ratios are very similar.

Liquid core offers higher exhaust velocity (presumably due to higher operating temperatures), not higher thrust (well, it potentially could, but thrust increase isn't intrinsic to the design). The exhaust velocity increase is always welcome, but not at the cost of the release of radioactive materials into the environment (and increased complexity).

 

[jedidia]

but not at the cost of the release of radioactive materials into the environment

A liquid core doesn't need to do that, as far as I know.

DUMBO, a competing design to NERVA, had a far superior thrust- 3.5 MN

Nice, I never heared of that design before. If the ISP is superior enough to the SSME, it might work.

 

[T.Neo]

A liquid core doesn't need to do that, as far as I know.

It doesn't need to, no. Rotating the reaction chamber encourages the fuel (heavy) to be centrifuged to the walls of the chamber, rather than exit the nozzle. I'm having trouble believing that it would prevent all radioactive material from exiting.

And if the rotation system fails, it will do so painfully... add to that the lack of crash/explosion protection that is inherent to a solid core design.

Nice, I never heared of that design before. If the ISP is superior enough to the SSME, it might work.

It should be comparable with NERVA, but my point was more that by utilising an appropriate design (such as that found in DUMBO), one need not be limited to the low thrust of NERVA.

I imagine that it would not be impossible to increase the exhaust velocity somewhat with more tweaks and modern technology and materials.

 

[Axel]

The simplest way is the use of an XR1 with realistic settings. Rocket mode to Isp 4500m/s, scram jet realistic and here we go! Theres still only the front docking port.
Liquid and gas core nuclear thermal engines are inacceptable for flights inside the earth atmosphere. To mutch nuclear waste. A solid core is hard at the limit, but tests of NERVA showed - radiation too, but low. I suggest a starting/landing point at an old atomic test side, this areas are already contaminated :lol:.
But i guess a nuclear surface to LEO vessel is unrealistic, because our politics. Think about an accident near a city, a nightmare! :facepalm:
You have to put him inside a black box for that case, the critical components of the reactor. But then it would be heavier. A solution could be a very small reactor inside a security box. As propellant you use three-component-fuel, which burns alone with higher ISp than two-component, the reactor gives some extra heat to the reaction and pushes the Isp alot more, to maybe 6800-7200m/s.
But best way i see is Skylon-style spaceplane. Clean and relativ simple with only a single engine working in two modes.

 

[T.Neo]

No... that is just a DG (well, an XR1) with some of the values changed. Aside from all of it's other problems, I doubt there is enough internal volume for propellant, and the craft is still made of unobtanium (at least, the SCRAMs are, though I don't know what their operating temperature is when at "realistic" mode). The density of the vehicle is almost half that of the shuttle, without a gigantic hollow payload bay making up a large amount of the craft...

A properly designed solid-core engine is perfectly clean (fuel is contained within the reactor structure), and during a forseeable accident, no radioactive material should be released- during the Rover tests, an engine was destructively tested with no release of radioactive material. Considering that the internal components of the engine withstand high temperatures and pressures as a course of their operation, this is not too surprising.

Nuclear propulsion is not unlikely due to politics, it is unlikely due to stupidity. The reality of such technology is different from what is envisioned by the layperson when you merely utter the word "nuclear".

As propellant you use three-component-fuel, which burns alone with higher ISp than two-component, the reactor gives some extra heat to the reaction and pushes the Isp alot more, to maybe 6800-7200m/s.

You really want to piggyback chemical onto nuclear (like LANTR, to utilize the full potential), rather than the other way around. And that leads to an increase in thrust, anyway- at a decrease in exhaust velocity, obviously.

Three-component fuels are a bad idea. At least one of them that burns with an impressive exhaust velocity, is hydrogen and lithium as fuels, with fluorine as oxidiser. Which is problematic, because hydrogen needs to be kept at extremely low temperatures (at least -252 C), Fluorine is extremely reactive (and needs to be kept at least -188 C), and lithium needs to be kept at over 180 C.

A strikingly easy engineering "challenge".

But best way i see is Skylon-style spaceplane. Clean and relativ simple with only a single engine working in two modes.

It is the most forseeable way (politically), but chemical SSTO attempts are by far not the best... you end up with a painful mass ratio, and coupled with the low density of liquid hydrogen, you end up with a painful tank volume.

You get a lot of interesting gains by flying the beginning of your ascent in airbreathing mode, but the role of the engines in rocket propulsion mode is not trivial. They still have to accelerate the craft to 60% of orbital velocity.

The engine(s) of Skylon are not nuclear reactors, but I don't think they could be classified as "simple". A jet engine is not simple, and I seriously doubt a hydrogen precooled jet engine (combined with a rocket) is anything near simple.

 

[jedidia]

Have you checked possible propelants? STS doesn't have that huge tank for nothing... propellant density might be a real pain when trying to fit enough of it into such a small craft like the DG.

 

[Sky Captain]

I think the biggest issue with nuclear engines would be ground handling and maintenance. Shadow shield would protect only the vessel from irradiation. Any maintanance on the engines would have to be performed in specially designed facility with extensive use of robotics. Even powered down reactor would be too hot to allow people to work on it.

When taking off the unshielded reactor would irradiate surroundings with gamma and neutron radiation which again would recquire dedicated launch facility far from populated areas. You won't be flying this thing from normal airports.

 

[T.Neo]

Have you checked possible propelants? STS doesn't have that huge tank for nothing... propellant density might be a real pain when trying to fit enough of it into such a small craft like the DG.

I have. I was just mentioning the methane conundrum I'm in; it allows me to have a far smaller propellant tank, but I'm unsure of carbon deposits fouling the engine.

It won't be as small as the DG; not by far, regardless of what propellant I use.

I think the biggest issue with nuclear engines would be ground handling and maintenance. Shadow shield would protect only the vessel from irradiation. Any maintanance on the engines would have to be performed in specially designed facility with extensive use of robotics. Even powered down reactor would be too hot to allow people to work on it.

Well, they will certainly emit less radiation when they aren't operating.

For maintainence issues we can potentially look to the maintainance of nuclear power stations, and nuclear powerplants in marine vessels. Obviously they do not have the other intensive maintainance demands of a rocket engine, but potentially a system can be devised where the reactor core itself is easily removable leaving the engine to be repaired safely and easily.

When taking off the unshielded reactor would irradiate surroundings with gamma and neutron radiation which again would recquire dedicated launch facility far from populated areas. You won't be flying this thing from normal airports.

That is nothing exceptional, considering that current launch vehicles are launched from dedicated facilities far from populated areas. Indeed, launching any 20 gigawatt-output rocket from a normal airport would probably be a no-no, regardless of any radiation.

Shadow shields will be thickest facing the crew, yes, but I see no reason for thinner shields on the sides of the engine to protect surrounding areas, despite the inevitable mass increase.

And the spacecraft structure, although thin and undedicated, also provides a degree of shielding.