Why they are terrible for SSTO. They may still have some promise for space-based systems, though.
58 thoughts on “Nuclear Thermal Rockets”
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Why they are terrible for SSTO. They may still have some promise for space-based systems, though.
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Dueling scenarios.
Although not perhaps a NTR, it seems to me the original Orion was a battleship sized SSTO. Good to know, if we ever need it, it’s there.
Ah, Orion. If we had some ham, we could make ham and eggs, if we had some eggs.
Paul, there was no technical obstacle to Orion. The obstacles were purely political.
Ken,
Political as in releasing massive amounts of radiation into the environment, killing all satellites in orbit by pumping up the van allen belts, and frying most modern electronics. Opposition to RTGs is political, opposition to Orion seems a little more…well…solidly founded?
~Jon
The environment gets massive amounts of radiation already, which is a good thing since without sunshine we’d all be dead.
Radiation can be tuned or even canceled. Radiation can be dealt with. Irrationality is a much bigger problem.
Let us also not forget the purely technical issue of inability to static test the monstrosity in any meaningful (let alone economical) way. And no, Rube Goldberg concepts involving putting large sheets of chemical explosive onto an inverted pusher plate don’t count.
Ordinary chemical rockets can be static tested. It’s one of the nice things about them.
Weellll, ya could… but you wouldn’t want to. Not all up in any case.
It’s an external combustion engine. Much simpler than the car you currently drive. It happens to use lot of really big bombs (actually, small bombs by nuke standards.)
We used to be able to build things. Now we play video games.
They built a model. It flew. The real thing would just be bigger.
But if we ever need to put millions of tons into orbit; we have a way.
The really nice thing is the bigger you make it, the better it works. Passengers would experience less vibration than ANY chemical rocket.
Ok, you want to put passengers on a vehicle whose engine cannot be meaningfully tested, and whose operation involves complex interactions between the pulse units, their delivery system, and the surrounding environment.
You don’t like passengers very much.
Nuclear pulse propulsion will only ever be developed once the vehicles can be assembled and tested in space, for use in space.
The designers planned to ride it themselves. Yes I do like passengers. Great CAN’T do attitude ya got there. Typical of our times.
I don’t expect it will ever be developed. As for use, putting a great deal of mass into orbit would be the main reason for doing it. There are other useful ways of moving around once you get to orbit.
Ken,
I love the Heinlein SSTO nuclear powered rocket as much as the next guy, but this just isn’t practical for atmospheric flight. For deep space flight sure, but anywhere near people is a bad idea.
Here’s an interesting single stage application. http://www.astronautix.com/lvs/yardicbm.htm
I saw something similar, more recently. That’s all I’ll say…
Actually, I’ll say one more thing. ITAR may be onerous, but the rules concerning anything nuclear are downright draconian. Working on the simplest part of even the commercial nuclear fuel cycle requires a DoE clearance whose name I won’t mention. DoD Top Secret (with tickets) doesn’t guarantee you admission into this club.
anywhere near people is a bad idea
Right, which is why I would recommend an ocean launch variation. Imagine a big doughnut with the mass of a dozen aircraft carriers.
rules concerning anything nuclear are downright draconian
Right, political. I really do not expect it ever to be done.
YaRD ICBM
1960s – can do. 2010 – can’t do. 2060s – will do.
Static testing of nuclear pulse devices is being done today. Examples include NIF and Z-machine. The problem is nuclear devices of their kind presently require a very heavy detonator, so to speak. Also the efficiency for those devices sucks, since you get less energy out of the nuclear pulse than the one originally provided by the detonator…
The neat thing about fission triggers is that they are lightweight in comparison. Plus you (obviously) get more energy out of such a fusion reaction than the one provided by the fission trigger. Otherwise no one would be using fusion bombs.
a vehicle whose engine cannot be meaningfully tested
Testing is why they ABSOLUTELY KNEW IT WOULD WORK AND WERE PREPARED TO RIDE IT. Yes, it had to be tested in parts. All the parts were testable. It is a relatively simple machine. The hard part was getting the bombs small enough.
Timing tolerances were extremely loose and easy to accomplish.
Distance tolerances were extremely loose and easy to accomplish.
The ablative surface could be both passive (graphite) and active (oil) being extremely fail safe.
The mechanisms needed were simple and due to scale (bigger being better) VERY EASY to accomplish. Your car is a pulse drive. Does it rattle your teeth loose? Orion would be much smoother. If not told the passengers wouldn’t even know nukes were involved.
inability to static test
Now that I think about it, you could easily static test. It would be a very big test stand. It would be expensive. But it could be done.
But static testing is not required because… it is an external combustion engine. A very simple machine. Tolerances are loose.
It would work, first time and every time. No hard start possible because it’s an EXTERNAL combustion engine. The mechanism for delivery can be extensively tested before ever being used.
Are we capable of making a nuke explode the moment we want it to? I think so.
Would the ship blow up? Nope. That’s the first thing they figured out.
The tolerances are less than any chemical rocket. No worries about mass fractions. Did I mention the tolerances were ridiculously loose?
It’s only the psychological impact of using nukes that prevents us from doing it.
Now that I think about it, you could easily static test. It would be a very big test stand. It would be expensive. But it could be done.
At it would not tell you what you need to know.
The behavior of the engine changes as the air pressure changes (for chemical rockets, the behavior of the internals of the engine are independent of external pressure). And each explosion alters the environment the next charge must travel through and then explode within.
No, testing the function of the engine is going to be impossible short of a full-up flight. You think expendable chemical rocket testing is arduous? This would be nightmarish.
Testing is why they ABSOLUTELY KNEW IT WOULD WORK AND WERE PREPARED TO RIDE IT.
Wait a minute… you think they tested all the parts of a vehicle they could ride in? Ridiculous! They tested some things related to the basic physics of the concept. Extremely important systems, vital to the operation of the vehicle, existed only on paper (charge delivery system) or at very reduced scale (pusher plate, shock absorbers). Essentially all the detailed engineering for producing a working vehicle hadn’t been done.
They knew there wasn’t some basic physical reason it wouldn’t work. That is all.
Godzilla, didn’t see your post. I’m sure they do the static testing in a better way than I imagined it.
You think expendable chemical rocket testing is arduous? This would be nightmarish.
Paul, I keep repeating it, but apparently not enough for it to sink in. LOOSE. TOLERANCES.
A chemical rocket needs to operate almost at it’s limits to work. A nuke rocket doesn’t because you’ve got plenty of everything to spare. A chemical rocket needs extensive testing because the tolerances are so tight. A nuke rocket doesn’t. By being very conservative you can build a paper rocket that will work first time, every time. Because of
LOOSE TOLERANCES and a very simple machine.
Essentially all the detailed engineering for producing a working vehicle hadn’t been done.
Very true. We are talking about a machine that is simpler than the engine in your car. One that would work with much less engineering required. Forget the nukes for a second. Nothing else comes anywhere near difficult. Nothing. Add the nukes back in. That introduces basically two issues… ablation and radiation. Ablation is what got the project started. Radiation can be mitigated. There are no show stoppers for a system that gives us unequaled capabilities.
It’ll never happen, but it’s not because it would work.
Well, you get the idea.
An example of the difference in tolerances. Max Q.
Chemical rockets are thin shelled and high acceleration.
A nuke rocket could have a foot thick iron shell and accelerate at just one G all the way to orbit.
They wouldn’t even talk about max Q for a nuke because it wouldn’t be an issue.
Ken,
I’m with you. It might be noted that the first test of the uranium bomb was its operational use on Hiroshima and a lot of other problems go away when instead of Boeing building your spaceship you give the contract to the Electric Boat Company.
Nice little naval nuke for on board power? I like it.
Kirks numbers are a bit *baked*. Firstly, NERVA 2’s T/W of 7.5 is pretty acceptable. The NTR Kirk was using for comparison is the Triton reactor meant only for in space use, so its as inappropriate as comparing the T/W of Three Mile Island.
Secondly, if you took NERVA 2, and put an air augmented ram ejector nozzle around it, you could boost the Isp significantly higher for the first 20km of flight, as well as the thrust, so you’d break through the 10 T/W ratio limit Kirk imposes and have a higher flight averaged Isp.
Thirdly, NERVA2 doesn’t spew radioactive pieces and parts of itself in its exhaust plume, so its pretty clean, compared to, say, DUMBO. Kirk needs to run the numbers again without rigging them to reach a predetermined outcome.
Jonathan
“…releasing massive amounts of radiation into the environment, killing all satellites in orbit by pumping up the van allen belts, and frying most modern electronics… opposition to Orion seems a little more…well…solidly founded?”
There may be plenty of good reasons for opposing Orion, but the ones you cited are two parts fantasy and one part exaggeration. By what mechanism would the Van Allen belts “pump up” and kill ALL orbital satellites? And how are the puny kiloton class pulse units of an Orion Drive supposed to generate an EMP that could fry most modern electronics?
Launch of Orion would contribute to worldwide fallout, but even so much much less than a single one of the megaton class airburst H-bomb tests that were conducted prior to the nuclear test ban treaty. In fact, I bet radioactive elements released from current worldwide coal burning in a single year contributes more radiation danger to the public than a single Orion launch would.
But in a world where the barely detectable release of radiation from the Three Mile Island power station incident was enough to effectively shut down future nuclear power development in the United States for decades, it doesn’t surprise me that reasonable risk analysis of nuclear energy for space propulsion seems beyond hope.
Paul, I keep repeating it, but apparently not enough for it to sink in. LOOSE. TOLERANCES.
Kirk, repeating idiocy doesn’t make it any less idiotic.
Having loose tolerances doesn’t mean the system doesn’t need testing, or can’t have complex interactions that will be very hard to simulate or debug.
Orion is a complex Rube Goldberg device, much more complex than a conventional chemical rocket engine. Unlike a rocket engine, where you have steady flows of fluids, in Orion you have much more complex mechanical systems — the pulse unit feed system itself is a nightmare — as well as interactions driving materials closer to their limits (nowhere in a conventional rocket are you driving frickin [b]shock waves[/b] through solid structural elements.)
And yet, despite the layers of complexity, you think this will not require extensive testing. You have the engineering insight of a stone.
Oops, meant Ken not Kirk.
How much for a one-way tiket? ObamaWorld holds no appeal.
Orion is a complex Rube Goldberg device
Saying it doesn’t make it so. For example: A car engine is such a Rube Goldberg Device. It’s got these cams that open and close these valves with fuel being pumped into these constantly exploding chambers that would melt if not limited in RPM which is only limited by a human with no backup. Not simple like a rocket engine that doesn’t pulse.
They made a working model using conventional explosives and that ‘Rube Goldberg’ device worked fine. Now if that’s not a ‘Rube Goldberg’ device, explain how increasing the yield of the explosives makes it such?
You have the engineering insight of a stone.
And you make a false accusation when you say, “you think this will not require extensive testing.” Just read what I’ve said above to know that’s not true. Do you have the same argument against the F9/Dragon. Many, many people have accused them of not doing the proper testing… Oh, the parachute didn’t work, they failed! Rubbish.
You continue to not appreciate that the abundance of excess performance boom-boom gives you allows you to build something that is so forgiving you can be assured it will work, first time, every time. All the objections you’ve raised have been thought of and they are not the huge problem you suggest they are. ‘Rube Goldberg’ is a slander of a very simple device known as an external combustion engine. A very, very well understood device that is actually simpler than anything but the simplest type of rocket. Rocket launched by NASA, SpaceX, etc are not of that simple type. They aren’t bottle rockets.
Every component of Orion has a much more complicated analog in general use today. A soda bottling plant is much more complicated by comparison. It’s just the fact that the high explosives are nukes that makes peoples brains shut down.
My engineering insight goes back decades. You might learn something from a stone.
They made a working model using conventional explosives and that ‘Rube Goldberg’ device worked fine. Now if that’s not a ‘Rube Goldberg’ device, explain how increasing the yield of the explosives makes it such?
It is comments such as this that demonstrates how inane your position is. The device you are referring to bore about as much resemblance to a real Orion as an Estes model rocket bears to an orbital launch vehicle. Less, even: absolutely vital physical effects (interaction of the hypervelocity jet with the pusher) are entirely missing.
And yes, internal combustion engines are complicated. They can also be tested incrementally, at bench scale. When delivered into production, they are typically small and inexpensive. Herbert York pointed out that these are the qualities of successful technologies, technologies that can be incrementally improved, by small, inexpensive steps. In contrast, he noted: “Orion involved putting together simultaneously a number of novel technologies, most of which could not be meaningfully tested in insolation from each other or on a small scale.”
Why are you all arguing over Orion-drives when the article was about NTRs for SSTO?
Because I mentioned Orion in my first comment and it took off from there??? In my defense, I did link to an NTR.
Um, maybe you guys could take your Orion arguments to another thread.
Orion can and to some extent has been tested incrementally and it can be incrementally improved. Like most all technologies.
[Herbert York] noted: “Orion involved putting together simultaneously a number of novel technologies, most of which could not be meaningfully tested in isolation from each other or on a small scale.”
Paul, I happen to have a high regard for your opinion, bringing in the opinion of York doesn’t really add weight to your argument for me. But let’s examine his comment.
putting together simultaneously a number of novel technologies
This is called complexity. As a computer programmer that has worked in manufacturing and materials engineering I know a little bit about complexity. Hand waving is not a good argument against. What makes a tech ‘novel?’ Most of today’s tech would be considered novel in the 1950s, but not so much today.
most of which could not be meaningfully tested in isolation from each other or on a small scale
Note that most of which is not all of which. Assuming something can’t be tested in isolation only means it has to be test together. So?
So it means the testing will be expensive. Nobody said it wouldn’t be. But without facts, you could claim it to be prohibitive. You continue to disregard a most important point about tolerances. If you don’t understand that point, you can never accept my assertion that you can have a successful first flight. Somebody argued here on this blog that ‘rockets always blow up on their first attempt’ or similar nonsense.
How can I be so sure they could build it and it would work? Because you can’t point to one thing that would be a show stopper or HAVE SUCH A TIGHT TOLERANCE that we wouldn’t know until we did it. Raise any specific objection and I can show why it’s not a big deal and I’m just an ignorant rock.
absolutely vital physical effects (interaction of the hypervelocity jet with the pusher) are entirely missing
In the model, yes. However, they were tested separately.
It is comments such as this that demonstrates how inane your position is.
Paul, your argument has been that Orion is a ‘Rube Goldberg’ device. Let’s not change the goal posts. Was the model a R.G.D?
If it isn’t, then you must acknowledge that, that part of your argument must be discarded.
Re: Orion
The feed mechanism for the bombs needn’t be Rube Goldbergian. Just off the top of my head, a scaled-up, fewer-barrelled, much-slower-firing version of the Gatling-style mechanism employed in the GE GAU-8 cannon used in the A-10 Warthog would seem a reasonable place to start. Round-to-round timing is very consistent and the mechanism has been demonstrated to be reliable under much greater vibration and g-force loads than it would need to accommodate in an Orion application. Firing rate would be in seconds/round instead of rounds/second.
Re: DUMBO
While contamination of the exhaust stream with radioactives from the fuel elements might make this general approach dodgy for surface-to-orbit application as a reaction engine, I wonder if it mightn’t be just what the doctor ordered as the power core of a lightweight nuclear-electric generating package for running VASIMR engines. Instead of heating and expelling hydrogen as an exhaust, the core would heat a noble gas as a primary circuit working fluid in a closed cycle that runs a very high-temperature turbine. This would dump heat into an intermediate circuit using some other suitable working fluid to run an intermediate-temperature turbine. This, in turn, would dump heat into a low-temperature working fluid like ammonia to run a low-temperature tertiary turbine. Remaining heat would be dumped to radiator fins. Kind of a nuclear-powered, triple-expansion turbo generator, as it were. The radioactive contamination stays in the primary working fluid circuit.
Holy crap! I never realized the size of the Warthog cannon and I lived near Davis-Monthan for years.
For the Orion pulse unit projector, a closer analog than the 30mm cannon of the A-10 would be the Swedish AMOS 120mm automatic mortar system.
http://www.patriahagglunds.fi/amos.html
As Dick points out, the delivery system would be a detuned version of existing designs…
the final reference design used a simple gas gun to shoot the devices through a hole in the center of the pusher plate.
Interesting factoid…
Danger to human life was not a reason given for shelving the project – those included lack of mission requirement (no-one in the US Government could think of any reason to put thousands of tons of payload into orbit), the decision to focus on rockets (for the Moon mission) and, ultimately, the signature of the Partial Test Ban Treaty in 1963. The danger to electronic systems on the ground (from electromagnetic pulse) is insignificant from the sub-kiloton blasts proposed.
Can we think of a reason to put thousands of tons of payload into orbit and beyond?
You might be surprised by these design goals…
The Orion workers wanted a spaceship that was simple, rugged, capacious, and above all affordable.
Which they felt were not achievable by chemical rockets.
Ken,
Of course we can:
mining equipment
nuclear power reactors
electromagnets for mass drivers
lots of power cabling
water distillation equipment
regolith smelting equipment.
solar power sats
laser frikken battle stations
Just to be clear, I wasn’t suggesting use of an actual GAU-8 gun to poop out the ORION nuclear propulsion charges. I doubt it is possible to build a fission charge of sufficient yield into a 30mm form factor – at least not using U-235 as the fissionable material. A friend once told me that it is theoretically possible to build a fission device that could be fired from a pistol or rifle chambered for .22 LR if Americium is used as the fissionable material. I lack the nuclear physics background to be able to confirm or deny the accuracy of this assertion, but it certainly suggests that not all possible ORION implementations would necessarily have to be of battleship scale.
Anyway, the W48 warhead of 50 years ago fit into a 155mm artillery shell casing and yielded the equivalent of 72 tons (that’s tons, not kilotons) of TNT. Doubtless, modern design capabilities could boost the sub-kiloton yield, if needed, while staying within the same dimensional and weight envelope. A scaled-up version of the GAU-8 mechanism seems a good candidate for an Orion charge ejector because it has proven very reliable in its 30mm form at a very high rate of fire and has the inherent Gatling advantages of being externally powered, very finely controllable as to firing rate, virtually jamproof and tolerant of misfires by individual rounds – the firing of round N+1 is not compromised by lack of combustion gases from a misfired round N.
The AMOS mortar is certainly closer to the needed caliber, but it is a twin-barrelled design. An advantage of the Gatling design is that, though multi-barrelled, it fires one barrel at a time at a consistent “clock point” of the rotating barrel assembly. I assume that having only a single hole in the pusher plate through which to eject the propulsion charges is preferable to requiring two or more, but I am willing to be persuaded otherwise on this score.
Sorry about the bad link in my preceding post. Here’s the W48 link.
The reference design wants about 150 tons, so 72 is in the ballpark. I understood you meant a reliable mechanism properly scaled, like the GAU-8 but not the GAU-8 itself.
I actually think they should go with slightly larger bombs which means they need fewer of them. The trade off is shock absorber design and rate of fire. The reference design was a redesign to fit as a second stage to a Saturn V first stage and I think that was a mistake, politically motivated. The original, better design in my mind was a fat squat bullet. Bigger bombs give you a slower rate of fire (say 3 seconds rather than 1.1) and a longer stroke on the shock absorbers. The ablation requirements and pusher plate doesn’t change much if at all.
The delivery system doesn’t have to be a gatling design, seven separate delivery systems would do the same thing (seven holes instead of one, which they considered but rejected.) If your rate of fire needs to be 3 seconds, each individual ‘gun’ would have a 21 second rate of fire. It shouldn’t be too hard to come up with a reliable jam proof mechanism with that rate.
Now another reason loose tolerances benefit. They launch from one of the poles… a remote sight so nobody is around to catch whatever radiation they can’t tune out of the system.
If we ever get serious about colonizing, there isn’t anything that competes with Orion and the more you look at it the better it looks.
My 2000 cubic meter spaceship would be about 300 tons. A small version Orion could put a dozen of them, ready to go, fully supplied, fueled and crewed into orbit. Each spaceship is it’s own launch escape system. That would be in addition to Mike Lorrey’s list of items. Now that would be going into space in style.
I once held a million dollar check for an FAA radar installation in my hands. I think seeing a rack of a thousand 200 ton nukes all lined up would be a bigger thrill with the added advantage of making an enviro-wackos head explode.
“BUT THE RADIATION” eh, go get a sunburn.