Nuclear Pulse Propulsion starship.

Rune · 2012-05-29 09:49:23

AKA Orion interstellar craft. Good stuff. It is, to my knowledge, the only proposed propulsion system ever capable of launching an interstellar mission without some technical miracle involved somewhere. It also comes from the fifties, and the bomb handling mechanisms were supposed to be copied from those in a coca-cola factory (the pulse units would look like metal cans, only maybe bigger). Big pistons, a control room more reminiscent of a battleship... the cool factor in all of this is completely off-the-scale, at least in my opinion, so I just HAD to take a stab at it, even if the information about it is... shall we say scarce. It is unsurprising how difficult it is to get to real numbers about anything related to nuclear bombs. So here it goes, if only to fuel some decently-researched sci-fi story set in a generation ship I probably will never write. WARNING: this is a very big post, written over a few days: I hope you enjoy it, but I don't expect everybody to endure it, even though it would be nice if the people that take the time to read leave some comment, if only to say how nuts I am. Enjoy! ^_^

The best and pretty much only solid source I could draw on, was the paper by Dyson on interstellar propulsion (Here it is, BTW). I figured if I went to the father of the concept, I couldn't really get the basic assumptions that wrong. Of course, the paper is not that technical, and in fact it is intentionally misleading (again, weapons of mass destruction involved). But apart from that, there is surprisingly little to draw on. I could get the isp from atomic rockets' , but to be frank not only are there many listed, I have no idea where he got them from. So I start my ass-pulling early by saying I ended up feeling comfortable by saying sufficiently big (>10mT) almost-pure hydrogen bombs (or as close as we can get to them) in a big-ass plate (greater than 100m diameter, and probably closer to a km) would give an effective isp of about 750.000s. For a frame of reference, that is about 50% of what a perfect deuterium explosion would get if all the debris went either against the plate perpendicularly, or away from it (it would be half that if the bang went in a perfect sphere). With shaped charges and reasonably big and efficient bombs, I figured you could get close to that, but if not, then you have to adjust travel speed and time accordingly, either up or down (I'm not going to be ONLY pessimistic).

Then, set a mass ratio, apply Tsiolkovsky, and you get a travel speed. I went with a mass ratio of 5. Why? Well, mostly because you have to pick one, but also because that works out to about 4% of c as total delta-v, and cruising at ~2% of c you could get 20ly away from Sol in 1000 years. There are a lot of stars inside a 20ly sphere centered on sol (135 stellar objects, in fact), and even if you don't find earth-like planets in those, you will see this ship would need no clone of Earth to colonize a target system (as in establish a self-sustaining human civilization), as long as there are accessible resources. I will bet whatever you want any given star system has sufficient resources to do that in the form of asteroids and comets. And a millennium seems like a good round number to plan for in multi-generational ships, too. I mean, once you can't make it there in a single generation, using tens of them is not that much of a stretch, many countries and organizations have existed for that long in a stable form. Though maybe isolated island communities is a better analogy. Whatever, I figured it could be done. By all means, if you have a more solid argument for other speeds and travel times, or how long could such a mission take, please feel free to share. Or if you just want to point out why I'm wrong, that's cool too

I didn't go much farther than 1000 years in my thinking because I thought that was going to be a big enough engineering problem: build a machine to be used for a whole millennium! Now that's a tall order. That kind of drove the next point in the concept: size. To put it into one sentence, it's got to be big enough to pretty much rebuild itself in flight. I mean, there is no sane person that would expect any machine to work for centuries, but that doesn't mean that new machines can't be built when (and from) the old ones fail. For one, I am not sure about storing nukes for centuries and then expect them to be viable and go off when you want them to. Too much time for unstable isotopes to go away, even if you stored them in perfect isolation from radiation sources and eroding atmospheres. So I guess most of the bombs for deceleration, or at lest their fissile detonators, will be built (or significantly re-built) as they are needed during the final years of the journey. Which in turn means that the ship has to be capable of supporting a nuclear industry on it's own from the supplies it carries. It would have to anyway, since I am guessing the power for the long interstellar voyage would be provided by nuclear reactors, and they can be very long lived, but even so they would need to be refueled , maintained, and such. Same goes for ECLSS (though I expect most of the work there will be done by the agriculture/waste management systems) and every other thing on the ship: you can't expect it to work forever, so you have to be able to build the replacement, preferably from the materials of the original.

So to set up a truly independent colony you have to send something very close to a truly independent colony. At least big enough so you can maintain a sufficient pool of skills to run everything, maintain anything, and build the replacement parts you will need in the future. How much people is that? Honestly, no idea. I mean, the amount of different skills that go to make a sophisticated society... They will have access to virtually unlimited amounts of data in the ship's library, but access to an engineer course or manual does not make you an engineer able to service a nuclear reactor or build pieces for one... In the same vein, the ship will be built so all pieces are fairly low-tech and easily replicable, but there is only so much you can simplify the design of a guidance computer, for example, or the firing mechanism of a nuke, or an antibiotic, or a thousand other things. To keep on the theme of a nice, round number, I went with an average crew of one thousand. A few hundred people are a viable genetic sample, especially if augmented with frozen embryos from earth, and it seems like a reasonable minimum number to have the necessary skill set. It seems a bit on the low side of things, considering the construction job ahead of them during the trip (at the very least, thousands of H bombs, or at least their fission fuses), but I used such big margins everywhere else, that I imagine you could probably fit several times more people in the same mass budget. But hey, the reasonable thing would be to send these kind of ships in groups anyway (say, three ships providing support and backup to one another), so you could just build a fleet of them in the worst case, and specialize each one on one aspect of production. See where I was going with "these ships don't need planets to colonize"? They are colonies themselves, so to settle a target system they just have to use the capabilities they already have to build copies of themselves without the propulsion systems. Landing and/or terraforming can come later if planetary chauvinism is still a big thing for them (which I suppose it will).

A hab for one thousand people for what essentially amounts to forever... small thing to design, right? First, let's start with the artificial gravity requirement: 1G provided by rotation sets the usual 100m minimum radius for 3rpm's. Having rotational stability means we can not make it much longer than that if we want it to rotate stably on it's own without adding another cylinder (a fact often overlooked when designing these things), so let's play a bit with areas next. This paper (a fascinating read on space habitats on its own right) states the maximum ratio between cylinder length and radius is 1.3, so let's start small: a 100m radius, 130m long cylinder has an exterior surface of a shade over 80,000 square meters. Each of the two endcaps have about 31,500 more. And here is where the second requirement, radiation protection, quicks in to simplify the problem considerably. Let me explain further: in order to protect humans from radiation long-term (as in, generations), you need, basically, a lot of material between you and the radiation. Sources claim anywhere between 5mT per square meter behind the Van Allen belts, to 40mt wherever you put it, to more or anything in between. That is HUGE!! It means, pretty much, that you can forget about structural weight: whatever mass you need of structure is both going to count towards your radiation protection, and be completely insignificant compared to the rest of it. After much thought on this, I picked a more-or-less average number of 10mT/m2, and afterwards decided to double it, just to be extra safe. I figure if you have 10 meters of water and another 10mT of structure, machinery, supplies, soil, and everything else covering every square meter of the exterior of the habitat section, the passengers are going to be safe from just about everything imaginable. Plus, the interior atmosphere, even in this tiny design, does its small part as additional protection peaking on the cylinder inner surface (it may seem weird, but it's just like on earth, where the ground shields you very well from half of the sky). When you go to the big cylinders like O'Neill colonies the atmosphere starts getting so massive that you can actually use almost no shielding apart from structure, but I figured in this case I would ignore that effect since it would be both much less and I wanted to leave as much margin as I could.

And how many square meters per person anyway? Well, again you have a source for every taste, anything from to 100 to 200 square meters or more, varying a lot depending on whether or not you count arable land towards that or not. To make an efficient use of all that radiation protection, I am going to put the interior to good use adding reduced gravity inner cylinders for agricultural production and industry and such (including a 0-g recreational/industrial area right in the middle). So I figure I could get away with a low number, but use a reasonably high one anyway. Let's say more than 150 square meters for every person (low-density city-like), 160 so it fits nicely with the hull area into a round number (remember? 80,000m2). That would work out to about 500 people in the smallest cylinder I could think of, with generous margin everywhere. And I mean generous, 3 inner cylinders starting a healthy 50m up and spaced 10m, give you another 96,000 square meters to grow stuff in. That is several times what is required in terms of food production, and I imagine it can work as oxygen supply. I figure you will still need air filtrations systems, but perhaps air circulation and humidity control can be ingeniously designed to be passive and mechanics-free.

So for our crew of one thousand people, I am going to add a final barrier of redundancy and safety by picking two separate, independent cylinders of just those dimensions: 130m long, 100m radius. By counter-rotating them you give the ship both no net angular momentum and at the same time stability, and they can also be spun up and kept there by electrical means having one push on the other. Technically they don't even have to be physically joined between them and with the propulsion section, they could detach once on cruise, but I imagine some kind of rigid axis would exist, if only for transportation purposes. That would turn out to about 160,000 meters of usable, 1g shielded surface, plus 2 shielded endcaps (you can save two whole endcaps if you keep the two cylinders in line), plus more than 25,000m2 in margin, 'cause I like both margin and round numbers, which comes up to some 250,000 square meters in total. Since area dictates total mass, we are taking about 5 million metric tons of habitat in total, the vast majority of it in plain radiation shielding with perhaps a double use like being a lake or raw materials for future production of stuff. Said shielding could rotate with the habitat sections or stay put, saving some structural weight, but considering the mass budget, I think just spend a bit more in structure that you can certainly afford, and save on complexity and failure modes. Some external ballast running on cables on the exterior could compensate for the irregular and changing mass distribution on the inside (otherwise, prepare for the equivalent of quakes as the ship wobbles).

Thermal control for such a closed system is going to be about getting the power not used by the plants out, mostly, but by happy coincidence the pusher plate is a stupendous and gargantuan conductive radiator in case the huge external surface is not enough. I mean, lighting up the place at a healthy 72W/m2 in LED's needs a bit over 25MW, and providing and additional, I don't know, 50kw/person (a huge overkill by at least a factor of 5 based on current US consumption), another 25MW. Pitifully low numbers when you stop to think about the rest of the project. Rejecting that much power with ISS-like radiators would need about 250,000m2 of them. By coincidence, wink, wink, the same as our shielding area. But I still think making the pusher plate do double duty is a neat solution. Besides, generating that energy has probably generated at least as much in waste heat from the powerplants in the first place, so the total area may need to be up to three times bigger (that's 33% efficient thermal-to-electric conversion, which seems reasonably good and feasible with simple high temperature turbine systems). But who cares, a big, efficient pusher plate (1km diameter? why not, the bigger the better) would have much more surface than that. The fact that we are talking about cold interstellar space versus "hot" inner system operations also eases things here, since any radiator should work much better than at Earth's orbit.

So things start to take shape. The "payload" is about 5 million metric tons of radiation shielding with a bit of structure, piping, and machinery keeping it together, and a touch of human and plant flavor inside, in the form of two counter-rotating habitat cylinders set up in line. All this in front of a non-rotating magazine section containing the "fuel", with the shock absorbers coming afterwards (good place to put the power reactors, too, if they don't need gravity to work) and the 1km diameter pusher plate completing the picture at the end where the fun stuff happens. Total length, anything from ~300m (you keep the bombs around the habitat section) to perhaps 500-600 depending on magazine size. Width, well, you have the 1km wide plate, but the rest should fit within 200m, which is the diameter of the habitat section.

A few more notes on the propulsion system to complete the picture. I have no idea how the diameter of the pusher plate affects the overall propulsion efficiency, so I had to pick a radius out of thin air, mostly. Basically, because it depends on the bomb collimation factor and its power, and to know those I would have to start by designing the pulse units, something which I am very poorly equipped to do. By applying the weight fractions Dyson also pulls out of thin air for pusher plate mass and shock absorbers, I get 3.33 million mT for the plate and 0.2 million for the shock absorber system. By picking plain steel for the plate (7.85g/cm3), and assuming it is a perfect cylinder 0.5m tall, I get a radius for the plate of about 500m. The plate is not going to look anything like that, of course, but the exact geometry is not going to be spherical either with well-collimated shaped bombs. The most I assume about the bombs is that they are more than 1MT per metric ton, BTW, and powerful enough to provide the quoted isp. Which basically means that they are a lot of deuterium, and one bomb weighting 20mT explodes every 3s to propel the ship at a minimum of 0.05G at full weight and 0.2G with the last bomb. That translates to an effective jet power of... wait for it... 96x10^6 freaking terawatts, which should provide an acceleration time of 230 days to ~2% of c. Must make a bright star at departure.

Oh, and BTW, I finish up with a total ship mass of 50 million tons. 40 in pulse units, 5 for payload, 5 for the propulsion system. I know, 3.33+0.2 doesn't come up to 5, but you will need some sort of magazine, and a lot of auxiliary equipment like nuclear reactors and radiators. Call that additional margin, structure, whatever you want.

As a final addendum, you should note that a bit more than a fifth of the total ship's weight, about 12million metric tons of bombs, which is mostly deuterium, stays with the ship until the deceleration "burn". That is the part of the bombs that might have to be manufactured during flight in the probable case that you can't guarantee nukes working hundreds of years after production. You may also note that that would be a much more than decent radiation shield, and that using it as such and dispensing with most of that would instantly multiply several times the payload capacity in terms of people. But, you know, I like to provide a robust starting point on what is feasible. If it turns out you can put ten times as many people in a bigger, lighter hab section, then great: just increase radius and length, and see where structural fractions to handle the loads get you. But this is definitely doable, and retains radiation shielding the whole time, even after arrival at the target system, which seems to be a safe bet.

Phew, that was a really, really long post. Must be the exams inspiring. What do I get out of this, as a final conclusion? First, that the ship is so dirt-simple in technological terms, that this is actually doable, just a matter of price. But more importantly, that someday, when a project of this size is within our possibilities economically speaking, is is perfectly viable to settle other stars if we put our mind to it. It doesn't even take that much. And simple economics and compound interest says that point in time is not really that far away... Hope you enjoyed!!

Rune. Ad astra... right?

Last edited by Rune (2012-05-29 11:03:09)

GW Johnson · 2012-05-29 15:26:57

Rune:

You did a really good job thinking about a lot of really tough issues on that one.

There's a lot of pulse propulsion information buried in George Dyson's book "Project Orion: The True Story of the Atomic Spaceship". George is the son of famous physicist Freeman Dyson (who did work on old USAF "Orion"). The "cover" to get funding as a USAF project was an "orbital bomber". But that team clearly had deep space exploration travel as their goal, the whole way.

There's a whole slew of famous folk who worked on that project who couldn't talk about it until recently. Who they were and what they did will really surprise you. What eventually happened to it will disgust you. As it did me.

You're exactly right about the nuclear "shaped charges", that's exactly how to get a spindle shape of EM radiation pulse from the explosion. In space there is no blast wave at all, just that pulse of intense EM radiation. If it's spindle-shaped, your pusher plate can be made to intercept one end (half) of it, at the design detonation distance. It's a diameter-at-range thing (constant angle).

Until one looks at actual nuclear test results from Nevada in the 50's, one would think this radiation pulse would vaporize the steel pusher plate, but it does not. If you grease the plate, the steel is completely un-eroded even for multiple explosions (sacrificial very thin layer of grease, replenished after the "burn" to be ready for the next one).

Your L/D proportions for spin about the longitudinal axis matches old Orion's typical ship shape and dimensions. It was my long Mars "stacked module" ship that spun the other way: end over end. Both are dynamically stable, and extremely simple. Short and fat works best with pulse propulsion.

I'm guessing that the shaped charge effect can be done with thermonuclear devices (all they did back then was fission). If so, then gigantic pulse ships like yours become easy to build. We already know it works. The old Orion guys flew a 1-meter model just fine with ordinary explosive charges long ago. Even though they weren't supposed to.

The only real problem would be EMP wave effects from the explosion damaging electrical stuff near enough by to be hurt (it is a 1/r^2 decrease with range, like ordinary radio). I doubt very seriously we would really want to start one of these from low Earth orbit routinely. But maybe a few thousand miles up would work fine. 10 times more r is 1/100 times the EMP intensity.

Even with fission devices, the fallout from surface-launching a fairly big ship is about like popping one typical ICBM weapon warhead in the atmosphere. Spread over a period of a few years, I think we could easily afford the radiation fallout from launching a half dozen of these. The real problem is EMP during the launch. The "shipyard" needs to be very isolated, like way out in the Pacific, maybe. I dunno.

Imagine what we could do with anywhere from 1 to 6 of these in the 10,000-100,000 ton range of size: plant major colonies anywhere in the solar system, in a single trip. And your 10,000,000-100,000,000 ton size range actually could be a slowboat multi-generational starship.

The hardest thing about your starship isn't the ship or its propulsion, it's the closed ecology life-support, and the organized "miniature industrial society" setup to maintain all the technologies and hardware and pulse "fuel" for centuries. We get those items down right, and multi-generational interstellar flight becomes a realistic thing to consider doing. We may even have some reliably-identified more-or-less-Earthlike target exoplanets to visit, by the time we get that support stuff "right", if we started right now and worked on it (but, we are not doing those things).

I think you're much younger than I am, being bothered by "exams". That's over 4 decades ago for me. You might actually live to see one of these pulse ships built, if the politics changes to support it. I probably won't. I'll be lucky to live to see a manned Mars mission of any sort. Maybe not, the way things are going right now.

But hope springs eternal....

GW

Last edited by GW Johnson (2012-05-29 15:31:35)

Mark Friedenbach · 2012-05-29 22:55:15

Is there any way you can reasonably work the numbers to get it down to a century or less (0.2c)? Any longer than that and it is possible that regular technological progress would allow a later generation to leave after you and get there first (using, say antimatter propulsion).

Last edited by Mark Friedenbach (2012-05-29 22:56:16)

Glandu · 2012-05-30 03:27:49

waow. That's the kind of things I'm not equipped to understand. I just want to know if I read it right : 40 million metric tons of atomic bombs?

el_slapper. You Rune & GW Johnson are really tough guys.

Rune · 2012-05-30 07:36:38

Thanks for the replies, guys! Good to know all that writing got read.

Glandu wrote:

waow. That's the kind of things I'm not equipped to understand. I just want to know if I read it right : 40 million metric tons of atomic bombs?

Yup, you read right. The ship has a mass ratio of 5, and the propellant is comprised of the pulse units themselves, so 4 tons of bombs for every ton of ship. And by the efficiency figures I quoted, most of that is Deuterium turning into helium before impacting the plate. I know, it sounds insane, but look at that jet power! This is what interstellar propulsion looks like in the real world.

Mark Friedenbach wrote:

Is there any way you can reasonably work the numbers to get it down to a century or less (0.2c)? Any longer than that and it is possible that regular technological progress would allow a later generation to leave after you and get there first (using, say antimatter propulsion).

I think I already went as far as you could go maximizing parameters. Mass ratio looks already absurd enough when you consider the fuel... you know how the rocket equation works, I'm sure, so you can see how you might need a mass ratio in the millions if you can't improve on the isp. And remember that the maximum theoretical debris velocity in a pure D-D reaction is only twice the one needed to get my effective isp... if that is the only efficiency loss. I'm sure you know that translates to an exhaust speed of some 7,500km/s, and I see it as very difficult to increase that number by a factor of ten.

Theoretically, yes, you could go even bigger and faster than that with antimatter, after all I am only converting a tiny percentage of the mass into energy. But not without first finding out a way of producing and storing that much antimatter. And I'm talking millions of tonnes of antimatter here to manufacture these "advanced pulse units". And you also run into the problem of a significant fraction of the energy being released as weird particles like muons and pions that don't care much that the pusher plate is on their way.

Any other drive runs into the problem of the jet power: efficient as you can be, I am talking about a hundred Petawatts (with a "P", yes). No matter how little leaks from the drive system, it is more than enough to melt any ship. In the case of pulse propulsion, however, the magic of open systems and nanosecond detonations solves both: whatever little fraction gets deposited on the ship as heat goes into ablating a few microns of plate, nothing else. Consider this: going by jet power, the bomb exploding every three seconds behind the ship is the equivalent of some 72 megatons of TNT, which would make it bigger than the Tsar bomba, the most powerful nuclear test ever. Any other drive system has to match that energy at least, and improve on energy density if it wants to increase the specific impulse. BTW, if you can't make bombs big enough for the thrust required, you could increase the frequency. As long as you get the equivalent of a 24 megaton bomb going off every second. And also, you'll have to forgive me, but I caught a typo, the effective jet power should be ~90.2x10^15 watts, so quite different than I last wrote (If I haven't screwed with the decimal points again).

GW Johnson wrote:

You're exactly right about the nuclear "shaped charges", that's exactly how to get a spindle shape of EM radiation pulse from the explosion. In space there is no blast wave at all, just that pulse of intense EM radiation. If it's spindle-shaped, your pusher plate can be made to intercept one end (half) of it, at the design detonation distance. It's a diameter-at-range thing (constant angle).

I know, it's some kind of lensing effect produced by the plasma distribution at the beginning of the blast, originally thought up for the Casaba Howitzer, right? Or something similar, my particle physics are not what I would like them to be. It only depends on the bomb composition and mass distribution, so I figure you can get the same effect on H bombs. Lucky, too, otherwise efficiency drops by a huge factor.

GW Johnson wrote:

The hardest thing about your starship isn't the ship or its propulsion, it's the closed ecology life-support, and the organized "miniature industrial society" setup to maintain all the technologies and hardware and pulse "fuel" for centuries. We get those items down right, and multi-generational interstellar flight becomes a realistic thing to consider doing. We may even have some reliably-identified more-or-less-Earthlike target exoplanets to visit, by the time we get that support stuff "right", if we started right now and worked on it (but, we are not doing those things).

Yeah, we completely agree on that point, this is the critical point in the concept. But the way I see it, most of those problems also need to be solved for independent orbital settlements anyway. So perhaps building the passenger section and testing it as the first orbital city is a way to build confidence that keeping a few thousands humans living for hundreds of years in a completely closed artificial environment is something feasible. You know, just like Earth but artificial and as tiny as we can make it. Once you know how to do that, then it's a matter of starting to assemble bombs and building pusher plates, and we are set to start seeding the galaxy with humans.

GW Johnson wrote:

You did a really good job thinking about a lot of really tough issues on that one.

Thanks! You'll get me to blush. I am a big fan of orbital settlements and pulse propulsion, so I have been thinking about this kind of things for a long time. I think that shows, I only referenced a tiny fraction of the sources I used because, honestly, I don't remember where I saw most of them, they have become general knowledge stuck in my brain.

GW Johnson wrote:

I think you're much younger than I am, being bothered by "exams". That's over 4 decades ago for me. You might actually live to see one of these pulse ships built, if the politics changes to support it. I probably won't. I'll be lucky to live to see a manned Mars mission of any sort. Maybe not, the way things are going right now.

Yeah, I'm in my twenties trying to finish my engineering degree in aeronautics one of this days. Hopefully it'll be next year? One can try. But I don't think any of this is happening in the 21st century, it needs a huge solar system economy to be feasible, and the solar system will keep us busy for a long time yet. Enough to develop the habitat technology, by the way, and test it thoroughly. But, you know, perhaps significant life extension IS achieved during my lifetime (or yours), so why not?

Rune. It was fun to think it up, at the very least.

Last edited by Rune (2012-05-30 07:37:44)

Glandu · 2012-05-30 08:46:43

I'm still trying to get the concept(my mind is well-trained, but not to that point). There would be one explosion every 3 seconds(or I misread?)? How tough would it be for people inside? I mean, if it's too strong, people will just end up as tomato sauce at the end of the ship. How many G's will they receive?

El_slapper, overwhelmed.

Rune · 2012-05-30 10:27:48

Glandu wrote:

I'm still trying to get the concept(my mind is well-trained, but not to that point). There would be one explosion every 3 seconds(or I misread?)? How tough would it be for people inside? I mean, if it's too strong, people will just end up as tomato sauce at the end of the ship. How many G's will they receive?
El_slapper, overwhelmed.

Hehe... I can see how you might be, a little. Yes, you are exactly right: one pulse every three seconds, and each pulse is a 72 megaton thermonuclear explosion. But this is a big ship, you must remember. The shock absorbers even out the thrust over the three seconds between each pulse, and the resultant acceleration turns out to be a gentle 0,05G (more or less) when the ship is fully loaded, 0,2 with empty magazines. Surprising, right? Think that no matter how energetic the reaction, individual bombs mass 20mT, so they cannot really impart that much momentum to a million-ton spaceship.

Dyson actually limits momentum exchange for practical reasons like material strenght, and also 1G maximum thrust, to about 30m/s for each pulse. This would actually be significantly less.

Rune. Hope that helps!!

GW Johnson · 2012-05-30 14:18:20

The old 1959-ish designs from the original Project Orion were smaller. If memory serves, their big one was a 10,000 tonner for going to Saturn and back in (only!!!) 3 years, stopping off at the moon and Mars along the way! It used shaped-charge fission devices, at about 1 per second.

You use low-yield fractional kiloton devices for surface launch, where the blast wave helps push you, then a few kilotons each, once out in space where it's pure radiation pressure. Again, if memory serves, that design was in the 2-to-4 gee range during the "burn". Then in coast, it just spun about its longitudinal axis for artificial gravity. A 2-to-4 gee "burn" measured in a day or two, is quite doable for some very high interplanetary travel speeds. Months instead of years to Saturn, for example.

Myself, I'd be afraid to try to land a thing like that directly upon a planetary surface. Launch, yes. Land? Jeez, how do you keep it controlled that fine? If it were me today, I'd have rocket landing craft aboard, to make the surface visits. Being nuke anyway, I'd just use a hell-for-stout-built single stage "boat" powered with a close variant of the old NERVA solid core nuke thermal rocket. That's good enough for single-stage two-way on Mars, Mercury, or any of the outer moons. At 10+% payloads.

GW

Void · 2012-05-31 22:25:28

I thought this might fit in here:

http://en.wikipedia.org/wiki/Antimatter … propulsion

Granted it is not even an infant yet, but a real exciting potential version of the pulsed method described in this thread.

I like the original Orion concept also though. Big bombs. That is K*** **S. Sort of a no fooling around approach. Lots of Testostorone in that.

Just in case you think I am a Kreep;

http://www.lunarpedia.org/index.php?title=KREEP

Thorium - Useful as a fuel in some nuclear reactors, as well as an ingredient in some super alloys
Uranium - A nuclear power source

More about mining on the Moon;
http://www.thelivingmoon.com/43ancients … ining.html

Quotes from the above;

Thorium Deposits
Information on the distribution of radioactivity on the lunar surface was one goal of Lunar Prospector. This map shows that the element thorium is highest on the front side of the Moon, mainly in the highlands south of Mare Imbrium. The correspondence with the Imbrium Basin suggests that the basaltic lavas that filled it were enriched in Th. Note that corresponding highland surfaces on the farside are lower. - SOURCE - NASA
Again you will notice that the richest deposits are in the vicinity of Copernicus Crater.
Thorium is a chemical element in the periodic table that has the symbol Th and atomic number 90. As a naturally occurring, slightly radioactive metal, it has been considered as an alternative nuclear fuel to uranium.
When pure, thorium is a silvery white metal that retains its lustre for several months. However, when it is contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and eventually black. Thorium dioxide (ThO2), also called thoria, has one of the highest melting points of all oxides (3300°C). When heated in air, thorium metal turnings ignite and burn brilliantly with a white light.
Thorium as a nuclear fuel
Thorium, as well as uranium and plutonium, can be used as fuel in a nuclear reactor. Although not fissile itself, 232Th will absorb slow neutrons to produce uranium-233 (233U), which is fissile. Hence, like 238U, it is fertile. In one significant respect 233U is better than the other two fissile isotopes used for nuclear fuel, 235U and plutonium-239 (239Pu), because of its higher neutron yield per neutron absorbed. - Source - Wikipedia

So, I guess that is why I think telepresence/telerobotics on the Moon could be big for getting machines and people to Mars.

There is latency issues, but I think that if a computer were put on the Moon and another one in a "L" location, then the intentions of the human living on Earth could be modified by those computers where those computers would work to prevent the human from making a reflexive mistake that could damage the robot on the Moon.

This could be a big way people on Earth could participate in the work on the Moon, to support the Mars effort. If it were me, perhaps I could enter a virtual reality environment, and suddenly be "On the Moon". Then take a coffee break, and then back on the Moon. Why not hone such skills?

Last edited by Void (2012-05-31 22:55:36)

GW Johnson · 2012-06-03 11:17:43

I thought the old 1959 fission designs were remarkable in and of themselves. Their 10,000 tonner, surface-launched, was estimated to leave fallout in the atmosphere equivalent to the atmospheric test of one single 9 megaton bomb.

In the decades since, we have learned there is less fallout per unit yield (by far!!!) with thermonuclear devices. So a fusion update of pulse propulsion is radiologically intrinsically cleaner. The real side effect, unrecognized at the time, is EMP with each pulse. You don't start one of these in LEO. You could surface launch from out in mid-Pacific, I guess. Or maybe Antarctica.

I'm not sure U233 bred from Th232 can be made to explode. I was always told that a U233 bomb was not feasible. But it can be made into very good reactor fuel.

GW

Void · 2012-06-03 13:59:29

[I'm not sure U233 bred from Th232 can be made to explode. I was always told that a U233 bomb was not feasible. But it can be made into very good reactor fuel.

I know far less about it than you do. However, I think that there could be U238? on the Moon with the Thorium.

Maybe an antimatter trigger (Very futuristic), with a U238/u233 mixture could explode? As I said I don't know.

Rune · 2012-06-03 15:44:37

Well, if I recall what little I know of nuclear fuel, thorium can be used for a breeder reactor, and a breeder reactor can enrich uranium to any grade, including weapons grade. You get horrible efficiencies and lots of energy as a by-product, which is why stuff like centrifuges to filter out the natural concentrations ended up having an economical advantage in output for weapons. As for a bomb on uranium 233, I guess it's not that it is impossible, it's that it is impractical. The minimum mass would be much greater, and the efficiency lower.

And about the antimatter "catalyst"... sure, the more efficient the bombs are, the greater the isp. But before jumping in joy and start calculating isp advantages, I would give some thought as to how you expect to produce a sufficient flow of antiprotons in flight to have meaningful thrust. I think storing them for such periods of time as I consider here is out of the question for obvious reasons, but if you have some other idea, I'm all ears. Just the usual reminder that antimatter is not a source of energy, it is a storage medium. And with the current magnetic bottle storage, a pretty inefficient one at that.

Just one final note for GW. You keep mentioning EMP's as a problem for launching an Orion from LEO. Well, EMP's are only produced if you blow a bomb inside the upper atmosphere, and are completely non-existent in a vacuum where there is no gas to be ionized by the initial burst of gammas. So if you restrict that objection to ground launch, I have no discrepancy. If not... well, I will scold you for not doing your homework.

Rune. And, you know, I'm all for telepresence. Spacesuits have a though competition coming.

Void · 2012-06-03 22:34:56

Rune,

I did not set out to be a jerk on this, so please forgive me if it would now seem that is what I am doing. I did not have time to research it before now, and I feel a bit nervous that what I have found may not entirely agree. Please accept it or correct it as you feel needed. I entirely intend to be polite.

Anti-Matter
http://en.wikipedia.org/wiki/Antimatter … propulsion

The current (2011) record for antimatter storage is just over 1000 seconds performed in the CERN facility, a monumental leap from the millisecond timescales that previously were achievable[1].

An infant technology, but preuming a consirvative intrepreation of an improvement from 100 ms to 1000 seconds, isn't that an improvement on storage of 10,000/1?

It is easy to get me to slip on a bananna peel in the world of math, but I see that as being 16.67 minutes (1000 seconds). At least one bomb could be set off with that. (Delivering the antimatter to the bomb? Well, I said infant technology. I am just trying to judge if there is any hope at all, and I think there is).

What if another improvement of 10,000 times for the storage could be achieved? 16.67 minutes * 10,000 = 115.74 days (I think). Go to Mars and collect $200.00.

Starships? Not likely in my lifetime, but perhaps if an on board source of anti-matter could be created? It would be quite fantastic if the Bussard Ram Jet could be coupled to this concept. I know that fusion of regular Hydrogen is much harder than Heavy water and Helium3, but perhaps with antimatter triggering?

Anyway as I said I am interested in a planetary transport, not a starship, except for speculation fun.

I was looking for an article where a person had indicated that large amounts of anti-matter could be created in orbit with a machine, but I did not find it but I found this stuff, very interesting: The Van Allen belts have anti-matter in them that might be captured some day.

http://forums.liveleak.com/showthread.php?t=83679
http://www.pcmag.com/article2/0,2817,2390638,00.asp
http://www.centauri-dreams.org/?p=19198

Anyway I am not so stuck on anti-matter that I would want to depend on it. It is most likely for some considerable time in the future, and in fact when it does come, I think that perhaps heavy water and Helium 3 would be the prefered use for an anti-matter triggered explosion.

But for now, back to Thorium and U233 and other Uranium:

http://uranium-news.com/2010/09/11/yes- … m-uranium/

Yes you can make nuclear weapons from thorium, as well as from uranium
Uranium 233 is fissionable, and you can make bombs out of it. And the best part of all is that it can be purified chemically out of the spent fuel of the thorium reactor.
Nuclear Weapons for the Masses . The Greenroom August 31, 2010 by Steven Den Beste“.……Thorium reactors use natural thorium, which is isotope 232. There are a lot of neutrons running around in there; it’s how reactors work. If an atom of thorium 232 absorbs a neutron, it becomes isotope 233. Some will fission, but some won’t.
Thorium 233 beta decays (HL 22 minutes) to proactinium 233, which beta decays (HL 27 days) to uranium 233.
Uranium 233 is fissionable, and you can make bombs out of it. And the best part of all is that it can be purified chemically out of the spent fuel of the thorium reactor. You don’t have to mess around with gas diffusion or centrifuges.
If, as some propose, there’s a thorium reactor buried in every backyard, you could face the possibility of pretty much any dedicated extremist being able to build nuclear weapons

http://www.americanscientist.org/issues … ium-future

U-233 is an excellent fuel for a fission weapon. It has a considerably smaller bare critical mass than U-235, about 15 kilograms versus 45 kilograms. This can be made significantly smaller—perhaps halved—by use of a lightweight beryllium tamper. Unlike the plutonium present in spent fuel, U-233 is immune to predetonation problems in even a crude gun-type bomb due to its low rate of spontaneous fission. It is a fairly copious alpha decayer, a property that can lead to premature detonation if the core is contaminated by light elements. But because the rate of alpha decay is only about one-sixth of that of Pu-239, this might not represent an insurmountable purification problem for would-be bomb makers. Perhaps liquid-fluoride thorium reactors could be engineered to enhance production of U-232 as a nonproliferation measure even if that produced a performance penalty.

http://kevinmeyerson.wordpress.com/2012 … ear-bombs/

http://en.wikipedia.org/wiki/Uranium-233
http://en.wikipedia.org/wiki/Uranium

It is interesting that there are potential sources of Thorium on Mars as well.

Among the other things I have read in the other links I posted is that with U233 you will have some U232 which is very dangerous. However as suggested in the quotes above, extracting U233 might be done by a chemical process, which I interpret as being favorable.

I have to add that in order for this technology to be safely used I think that our global culture will have had to evolve a trust system of some kind sufficient to maintain reasonable control of all of these processes. After all it is fission bombs in orbit isn't it.

Sadly there is likely still quite a few control freak groups who have always wanted to modify the human race before we go into space (Superman dreams), both communist, and fascist, and also religious.

I think it stems from a internal projection of the inadiquate nature of the members of such groups on to the rest of the world. It is easier to try to make other people be better than to try to be better yourself. No matter who you have to kill.

Last edited by Void (2012-06-03 23:28:29)

Rune · 2012-06-04 06:21:17

Void wrote:

I did not set out to be a jerk on this, so please forgive me if it would now seem that is what I am doing. I did not have time to research it before now, and I feel a bit nervous that what I have found may not entirely agree. Please accept it or correct it as you feel needed. I entirely intend to be polite.

Don't sweat it, you are being more polite than I am, and we are all here for fun! Discussions are better when both parties can present pointy arguments without any getting personally offended...

U-233 is an excellent fuel for a fission weapon. It has a considerably smaller bare critical mass than U-235, about 15 kilograms versus 45 kilograms. This can be made significantly smaller—perhaps halved—by use of a lightweight beryllium tamper. Unlike the plutonium present in spent fuel, U-233 is immune to predetonation problems in even a crude gun-type bomb due to its low rate of spontaneous fission. It is a fairly copious alpha decayer, a property that can lead to premature detonation if the core is contaminated by light elements. But because the rate of alpha decay is only about one-sixth of that of Pu-239, this might not represent an insurmountable purification problem for would-be bomb makers. Perhaps liquid-fluoride thorium reactors could be engineered to enhance production of U-232 as a nonproliferation measure even if that produced a performance penalty.

...and it seems it is is me who needed the scolding. I thought it made for a bad nuke! Doing a proper job and looking up the bare minimum in looking up things I retract what I said: Thorium reactors would make for great fission detonator production. A second stage of deuterium/lithium (for tritium production during the blast), which is stable so we can store it indefinitely in principle, and that looks like a good pulse unit production scheme, or as good as I can think up with my civilian knowledge of nuclear weapons.

Void wrote:

Anti-Matter
http://en.wikipedia.org/wiki/Antimatter … propulsion
The current (2011) record for antimatter storage is just over 1000 seconds performed in the CERN facility, a monumental leap from the millisecond timescales that previously were achievable[1].
An infant technology, but preuming a consirvative intrepreation of an improvement from 100 ms to 1000 seconds, isn't that an improvement on storage of 10,000/1?
It is easy to get me to slip on a bananna peel in the world of math, but I see that as being 16.67 minutes (1000 seconds). At least one bomb could be set off with that. (Delivering the antimatter to the bomb? Well, I said infant technology. I am just trying to judge if there is any hope at all, and I think there is).
What if another improvement of 10,000 times for the storage could be achieved? 16.67 minutes * 10,000 = 115.74 days (I think). Go to Mars and collect $200.00.
Starships? Not likely in my lifetime, but perhaps if an on board source of anti-matter could be created? It would be quite fantastic if the Bussard Ram Jet could be coupled to this concept. I know that fusion of regular Hydrogen is much harder than Heavy water and Helium3, but perhaps with antimatter triggering?
Anyway as I said I am interested in a planetary transport, not a starship, except for speculation fun.

Yeah, if we go by the recent advances you quote and we extrapolate a more-or-less linear increase (always a tricky thing to do, nature usually doesn't work that way), then interplanetary ships fueled before departure start to look very feasible. Not that you need the isp on interplanetary travel, but you could use tiny sub-kiloton clean fusion nukes while lifting off a planetary surface, for example. Don't bother with Helium 3, we don't need that to blow up hydrogen bombs.

Always remember that the containment system will take an appreciable percentage of the total ship mass, of course, though how much it is very difficult to say at this point. And it will likely need some power of it's own, which presents the usual problems (if you start needing a fixed percentage of your jet power as electrical energy to sustain your propulsion scheme, however good your efficiency at producing it is, when you scale things up to interstellar the waste heat problem becomes astronomical). That is what I don't buy about inertial confinement schemes: a very important part of your jet power is going back and forth though a whole electrical system on each pulse, so efficiencies being what they usually are, I don't see how you can work that out to interstellar travel without radiators the size of moons, never mind antimatter storage or production.

So, you know, it may be that in the end the "mercury orbit power station" for antimatter production gets built to provide fuel for the whole solar system and the interstellar arks at departure. As a sci-fi fan, I can see the appeal, believe me. But if I had to go by economics... I have to say I never much liked antimatter. One of those start trek thingies I never bought as happening in the real world. The way I see it, someone will figure out the materials problem for a space elevator sooner, and then we can move the messy "nuclear rocket of mass destruction" stuff out of the gravity well and shut every greenie up without invoking stuff like practical fusion or practical antimatter economy. Just unobtanium cables

As to proliferation concerns, there is pretty much only one thing that I can say with certainty: we are going to have to solve those, or stay confined to the inner system. The energies involved in serious space travel, and Jon's Law ("Any interesting space drive is a weapon of mass destruction") conspire to make any race stupid enough to blow up itself very capable to do so as soon as they start fiddling with merely interplanetary speeds. I mean, try dropping rocks at 100km/s, and you don't even need the nuke on the pointy end. So an ion propulsion system can be just as dangerous as the meanest ICBM. We better get a handle on how to solve our differences of opinion without blowing stuff up.

Rune. It's weird how Orion is technologically simpler the more you ask of it. Bigger is better!

GW Johnson · 2012-06-04 09:40:08

Hmmm. Back in the 50's and 60's we were told a U233 bomb was not possible. It seems things have changed.

I like it. There's more thorium than uranium, just about everywhere we have looked, and by far. Sounds like a thorium breeder plant is needed somewhere "out there" to make the U-233 for reactor fuel and pulse propulsion devices. I'd put it on the close-by moon for now. That pretty well keeps it out of the hands of terrorists and other infantile idiots. Plus, it's way far easier to launch the charges into space for use by a pulse ship, too. Some sort of catapult could do it.

U-233 triggers on an ordinary lithium-hydride fusion, all configured as a shaped-charge for propulsion. I like it. Cleaner than straight fission, and easily scalable into the 1-50 megaton range for really big ships.

There's got to be at least some EMP from these things in vacuum, because of the expanding cloud of bomb debris. There's a lot more during surface launch in the atmosphere. You launch with very low-yield devices, since the shock wave assists thrust. As the air thins, you increase the yield. Out in space, you use much larger-yield devices.

I certainly wouldn't put the shipyard and launch site for these things anywhere near a populated zone with a power grid and electronics. But we really don't need to build very many of them. So the risk is low. Ships built like this could serve for centuries, periodically updated to the "latest and greatest".

Talking about propulsion like this is fun, because, for guys, there are few things more fun than converting perfectly good fuel into fire, smoke, noise, and thrust. There's drag racing.......

GW

tahanson43206 · 2022-02-21 08:10:57

In the Recruiting topic, GW Johnson and Calliban recently took up the subject of atomic/nuclear propulsion.

This occurred in the context of Large Ship ... I asked FluxBB to show me topics already created with the word "propulsion". There were plenty, but fewer than 25. I decided this one is a good match for Calliban's proposed hybrid fission/fusion BB sized pulse power pellets.

I am quoting GW Johnson here because he was talking about the problems and challenges of large scale propulsion in 2012 and probably well before that.

(th)

GW Johnson wrote:

Rune:
You did a really good job thinking about a lot of really tough issues on that one.
There's a lot of pulse propulsion information buried in George Dyson's book "Project Orion: The True Story of the Atomic Spaceship". George is the son of famous physicist Freeman Dyson (who did work on old USAF "Orion"). The "cover" to get funding as a USAF project was an "orbital bomber". But that team clearly had deep space exploration travel as their goal, the whole way.
There's a whole slew of famous folk who worked on that project who couldn't talk about it until recently. Who they were and what they did will really surprise you. What eventually happened to it will disgust you. As it did me.
You're exactly right about the nuclear "shaped charges", that's exactly how to get a spindle shape of EM radiation pulse from the explosion. In space there is no blast wave at all, just that pulse of intense EM radiation. If it's spindle-shaped, your pusher plate can be made to intercept one end (half) of it, at the design detonation distance. It's a diameter-at-range thing (constant angle).
Until one looks at actual nuclear test results from Nevada in the 50's, one would think this radiation pulse would vaporize the steel pusher plate, but it does not. If you grease the plate, the steel is completely un-eroded even for multiple explosions (sacrificial very thin layer of grease, replenished after the "burn" to be ready for the next one).
Your L/D proportions for spin about the longitudinal axis matches old Orion's typical ship shape and dimensions. It was my long Mars "stacked module" ship that spun the other way: end over end. Both are dynamically stable, and extremely simple. Short and fat works best with pulse propulsion.
I'm guessing that the shaped charge effect can be done with thermonuclear devices (all they did back then was fission). If so, then gigantic pulse ships like yours become easy to build. We already know it works. The old Orion guys flew a 1-meter model just fine with ordinary explosive charges long ago. Even though they weren't supposed to.
The only real problem would be EMP wave effects from the explosion damaging electrical stuff near enough by to be hurt (it is a 1/r^2 decrease with range, like ordinary radio). I doubt very seriously we would really want to start one of these from low Earth orbit routinely. But maybe a few thousand miles up would work fine. 10 times more r is 1/100 times the EMP intensity.
Even with fission devices, the fallout from surface-launching a fairly big ship is about like popping one typical ICBM weapon warhead in the atmosphere. Spread over a period of a few years, I think we could easily afford the radiation fallout from launching a half dozen of these. The real problem is EMP during the launch. The "shipyard" needs to be very isolated, like way out in the Pacific, maybe. I dunno.
Imagine what we could do with anywhere from 1 to 6 of these in the 10,000-100,000 ton range of size: plant major colonies anywhere in the solar system, in a single trip. And your 10,000,000-100,000,000 ton size range actually could be a slowboat multi-generational starship.
<snip>
GW

SpaceNut · 2022-02-21 10:34:35

Calliban wrote:

GW Johnson wrote:
Some scaled-up form of electric propulsion might serve well enough in the nearer term. What I identified for the longer term was that one or another of the gas core nuclear thermal concepts might work, and also possibly the nuclear explosion propulsion concept, given a workable solution to EMP effects.
GW
The EMP effects of a fission detonation are the result of gamma rays interacting with upper atmosphere producing free electrons and then free electrons getting caught up in the Earth's magnetic field. The resulting electric field gradients cause power surges, especially in long exposed power lines. Surge protection trips out breakers, which must then be manually reset.
Smaller fission pulse units produce proportionately smaller EM spikes. Fusion bombs tend to release more neutron radiation but less direct gamma. So EM pulse effects are less pronounced. The concept I am presently working on uses milligrams of fissile material to produce a hot spot at the centre of an imploding lithium deuterium fuel pellet. EMP effects will be negligible, as will fallout. A bigger issue, which is far more difficult to solve, is that a drive like this will pump the Earth's Van Allen belts with high energy plasma radiation. This may damage satellites and imperil any humans in low orbit. The only solution would be to surround a pulse unit with inert material that reduces the average energy of the propellant ions. Unfortunately, that also dilutes ISP. Any decent performing space drive is a weapon of mass destruction in the wrong hands.

Again the equation of motion of mass is the equalizer for the flavor of propulsion to be used to make a large ship move from LEO to Mars low orbit.

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#1 2012-05-29 09:49:23

Nuclear Pulse Propulsion starship.

#2 2012-05-29 15:26:57

Re: Nuclear Pulse Propulsion starship.

#3 2012-05-29 22:55:15

Re: Nuclear Pulse Propulsion starship.

#4 2012-05-30 03:27:49

Re: Nuclear Pulse Propulsion starship.

#5 2012-05-30 07:36:38

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#6 2012-05-30 08:46:43

Re: Nuclear Pulse Propulsion starship.

#7 2012-05-30 10:27:48

Re: Nuclear Pulse Propulsion starship.

#8 2012-05-30 14:18:20

Re: Nuclear Pulse Propulsion starship.

#9 2012-05-31 22:25:28

Re: Nuclear Pulse Propulsion starship.

#10 2012-06-03 11:17:43

Re: Nuclear Pulse Propulsion starship.

#11 2012-06-03 13:59:29

Re: Nuclear Pulse Propulsion starship.

#12 2012-06-03 15:44:37

Re: Nuclear Pulse Propulsion starship.

#13 2012-06-03 22:34:56

Re: Nuclear Pulse Propulsion starship.

#14 2012-06-04 06:21:17

Re: Nuclear Pulse Propulsion starship.

#15 2012-06-04 09:40:08

Re: Nuclear Pulse Propulsion starship.

#16 2022-02-21 08:10:57

Re: Nuclear Pulse Propulsion starship.

#17 2022-02-21 10:34:35

Re: Nuclear Pulse Propulsion starship.

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