Project Orion 'What if?' Image Gallery

Date: Mar 16, 2005

RE: Project Orion 'What if?' Image Gallery

Date: Mar 16, 2005

The angular momentum is conserved, so a rotational motion of one part must cause a reaction that generates counter rotation in the other part. The exact degree of these motions is dependent upon the moment of inertia of each rotating part: the greater the moment of inertia, the slower its rotation relative to the other part. The moment of inertia is a function of the mass distribution about the center of mass. It is proportional to the sum of individual mass units times the squared distance from the center of mass of that component. It has units of Kg*m^2. Thus a distantly located small mass can have a greater effect on the system moment of inertia than a nearby larger mass.

Philipum--nice job explaining it (better then me!) The energy expenditure is a function of the system rotational kinetic energy, which could be rather small if we allowed time to act on it. A slow rotation will require little energy to start, and will require little breaking force (here, a mechanical brake like a clutch.)

Although, in all honesty, assuming Orion is a few thousand tons (4000 tons is thrown around a lot, although I personally would love to explore a design for an Orion in the 100,000 ton regime.) I just kind of assume that for large Orions, the ship would possess a nuclear reactor for auxiliary power. I think that it would be safe to assume that during boost phase that for mechanical attitude corrections, possible several thousand horsepower would be required to accomplish this. A small turbine power plant running a hydraulic pump utilzing hydrazine as its propellant could probably supply this (this is the standard APU pack that the Space Shuttle carries for hydraulic power for engine gimballing and operation of wing control surfaces.) However, for a long duration mission, Orion may run out of hydrazine for APU fuel, and thus a nuclear reactor seems more practical. In this case, then the mechanical energy expended in rotating the structure of Orion for attitude control would be insignificant.

I love to discuss engineering details about Orion, because the Project Orion group accomplished so much of the initial groundbreaking work as to convince me that it would work, while at the same time many of those details are still 'up in the air' so to speak. For instance, the pulse unit delivery system was never fully 'fleshed out' nor was the attitude control system. One of the things that apparently was fleshed out very well, and possibly even tested, were the pulse units. However, most details of these intruiging devices are, understandibly, still very much classified. There are hints in George Dyson's book that Ted Taylor was pretty confident about being able to shape the momentum pulses, both spacially and temporaly to just about any desired specification necessary to support Orion. This suggests that even in the late 1950's nuclear explosives' design were pretty advanced. The pulse units could thus be designed with momentum conditioning in mind--directional blast, but not focussed enough to penetrate the pusher plate with a jet of plasma. Just enough to give it a solid whack, and send Orion flying. Perhaps they could be designed to 'miss' the central hole in the pusher plate where the pulse units come sailing through.

Anyhow, Orion is an awesome concept. It is finesse and brute force; destructive forces for a constructive means. It is a flying contradiction: an artful cross between a battleship and a jackhammer which transforms itself into a technological ballet! Orion is still as 'sexy' an idea now as it was in the 1950's.

Date: Mar 16, 2005

I guess the pusher plate of Orion would be rather hot at certain times. Could it be possible to take advantage of this heat for secondary energy supplies?

Date: Mar 16, 2005

I included the spherical shell pushers to show all the variations that were easy to discuss, not because I thought that was what you meant. I also mentioned that in my previous post.

I also mentioned the difference between the total rotation, and the rotation of individual parts, and that the rotation could be caused by internal means instead of external. That is why I suggested that as a use for the gyros, tho electric motors could be used if the Orion is massive enough to have an onboard reactor. At least you wouldn't be throwing fuel overboard with a more conventional RCS.

But there are other things involved, such as how the pusher assembly can be moved around the ship, while still being attached to it. Probably the easiest way to move the pusher would be to have tracks attached to the outside of the main hull with a mobile cariage riding in them, (possibly with a method of clamping on once in position) and then attaching the pusher assembly to the cariage. The cariage could be moved with electric motors and wouldn't be much more than a really strong roller coaster or train car. Tho you still have the problems of the rails getting squashed, or the cariage breaking free during a misfire. At least it allows a standard pusher assembly.

Part of the reason Orion would work is because the pusher wouldn't get very hot. The plasma would be in contact with the plate for such a tiny amount of time, and would be such a material at such a temperature, that the plate wouldn't get very hot, and would cool off before the next impact. Tho the shock absorbers would be getting hot. That was why the possibility of using water (as in Footfall) to cool the shock absorbers, and then using the steam to spin the gyros (or a turbine to get the electricity). It might not be efficient, but even when you have that much mass, recycleing and being thrifty means less resupply stops, and might be worth it overall. And by using the steam to power the gyros, you lower the size the radiators need to be, while also get more manuevering ability with what otherwise would be waste heat.

Admitedly, I enjoy seeing how many different things I can make one device do at the same time, but sometimes it actualy works. And it cuts down on the number of different types of spares needed.

Date: Mar 16, 2005

Good points about using waste heat for power generation--with Orion, there is plenty of energy to be had.

Ashley: I like the idea of tracks and also your pointing out that the tracks and motor-wheel assemblies would likely get 'hammered' pretty bad. I'd have to agree.

Perhaps such a system would work by making the outer part of the spherical habitation shell a 'bearing' surface, then using the contact of the propulsion module as a partly spherical thrust bearing. By placing another smaller 'bearing' on the other side of the sphere, then 'simply' using cables or tension bands attached to the propulsion module would prevent the whole thing from 'flying apart.' If friction is kept to a reasonable level then the thrust bearings could simply be a dense array of plane old 'Goodyear' radials mounted on aircraft syle bogies. Additional shock absorbers on the individual bogies could even provide a tertiary shock mitigation system--you might just get a fairly smooth ride. Hmmm, I'm starting to see more possibilities with this...

The aircraft bogies could actually provide the means of moving the assembly if some of them were driven. A more or less simple hydraulic motor could easily accomplish full yaw and pitch control, and with sufficient preperation could possibly provide roll control as well. Interesting....!

Date: Mar 16, 2005

Ah, I think I understand about a spherical Orion now. Still, if you have a lot of time available in which to rotate the ship, what advantage would it have over using external propellent ? I doubt you'd need a very great deal.

Date: Mar 16, 2005

Interesting. Maybe use carbon nanotube cables so they have a high enough tensile strength? Probably need several extra wheel (bearing) sets spread around the ship to keep the cables from riding directly on it. This would also make it harder to have weaponry on the ship.

"Open the gun ports!" "Uh, sir! Half of the gun ports that could be used on the target on covered by the propulsion module cables." "Oh." lol

And remember that a chain is as strong as its weakest link. It would be interesting to discuss the possibilities, (possibly in a new forum section) but I think this is one of the weaker variants.

Date: Mar 16, 2005

External propellant is used up once fired. Something internal, like gyros, can be reused, only limited by the amount of energy you have available. So the most obvious advantage is that fewer resupply trips would be necessary, so the ship could stay out longer. Also, the amount of fuel needed goes up fast the more massive the object being moved is. For an Orion, no external, propelant using engine less powerful than an NTR would be powerful enough to make carrying the fuel for it worthwhile. I think it was GoogleNaut who did a rough calculation of the quantities necessary, and they quickly ate up even the cargo mass of an Orion. And it gets worse the larger the ship.

Date: Mar 21, 2005

Because angular momentum is more 'easily' concerved, then I would imagine that for small angular corrections, reaction wheels would be the preferred method of yaw, pitch, and roll control. However, for translations, it is necessary to expend propellant to change the momentum of the whole vessel. So for a large Orion vessel, it may even be necessary to come up with three control systems: one based on large reaction wheels; one for small delta-v corrections in the centimeter per second 'vernier' regime (possibly using VASIMR or arcjet thrusters for efficiency;) and then higher thrust chemical RCS. It would be impractical to use small NERVA engine's for direct RCS because of the need for quick startup and fast pulse mode operation--which would just about kill a NERVA reactor! However, a couple of Triton NTR's could serve a useful role with Orion as Orbital Menuvering System thrusters, where moderate delta-v's of tens of meters per second may be needed for small orbital trajectory changes and for putting distance between an Orion and a space station in preperation to a an Orion Main Drive 'Burn.'

Anything more than a hundred meters per second would probably be best achieved by using several pulse units.

It may be advantageous to have a seperate magazine where pulse units of different 'sub momentum' charges are stored. It may be nice to have a hundred or so 1/2 or even 1/4 momentum charges. Or perhaps engineer the pulse units with something along the lines of 'dial-a-yield' (although 'dial-a-yield' is generally used for much larger stategic and tactical weapons to control the yield of the fusion secondary, I think it has been used on smaller weapons such as the later versions of the "Davie Crocket" W54-2 warhead. (This device also ended up in a nuclear version of the Navy's Pheonix missile.) The orginial, unboosted W54 had a yield of only about 18 to 20 tons (not kilotons) equivalent, but with suitable boosting could achieve kiloton range. This gives an idea of just how small the energy producing part of an Orion Pulse Unit could be...

Think of a W54 at the bottom of two 55 gallon barrels welded end to end. This of course isn't precisely the geometry, but it serves well for imaging the scale of the things.

http://www.brook.edu/FP/projects/nucwcost/davyc.HTM

Date: Mar 23, 2005

Ok, you've convinced me on the value of a spherical Orion.

GoogleNaut : That's one scarily small nuke ! Would be useful for small changes of velocity in deep space (no gravity), though you'd need a lot of them.

I think for larger velocity changes you need bigger pulse units, firstly because small ones just don't give enough momentum to the ship and secondly because you need a certain mass to contain the explosion and direct it at the pusher.

Date: Mar 23, 2005

Negative value? At least that's what I was implying. (except possibly for an unmanned longprobe, tho even there it's probably not very good)

I hadn't heard of the 'dial-a-charge' but considering the squirt bombs it makes sense. Squirt bombs were kind of like the Orion pulse units. (they likely influenced each other tho I can't find sure data on that) But they produced laser beams (including gamma and hard xray) instead of plasma jets. They were also supposed to have a 'dial-a-frequency' feature for incase the enemy hardened their stuff against one frequency. And that was supposed to have been part of what made the Orion pulse units not melt the ship, tho they were supposedly hardwired once the right frequency was found. They would be set at a frequency that would be almost completely absorbed by the material that made up the plasma, so that a plasma jet hit the pusher plate instead of a laser beam hitting it. (plasma pushes harder I guess, ;)

Date: Mar 23, 2005

I never heard of a 'dial a frequency' (I suspect that this would be some of that 'fiction' in the science-fiction of the story...

)

Directed energy weapons could use thermal x-ray emmisions from the fission fireball if suitably channeled and collimated, they won't be a laser in the strictest sense, but would still be immensely effective against distant targets.

An Orion pulse unit, I suspect, would use a different but related scheme to channel thermal x-ray emmisions at a flat plate of dense ablater: a manhole cover sized piece of tungsten, perhaps two or three inches thick. The thermal x-ray emmisions would ablate the bomb-side face of the tungsten plate, causing it to jet in the direction of the bomb at perhaps 100-200 km/s. Because of the rocket principle, an equal and opposite reaction within the tungsten plate would create a powerful hydrodynamic shockwave that will almost instantly impart momentum to the remaining tungsten. The shockwave will vaporize the tungsten, but this relatively cool, dense plasma will then strike the Orion's Pusher plate causing it to briefly accelerate at 100-200 g's.

The use of tungsten is really for the benefit of the smaller Orions (with pusher plates 10-30m diameter.) The dense tungsten allows for efficient coupling of momentum from the ablation generated shockwave to the non-ablating part of the plate (commonly called the 'Pusher'.) It also helps to keep the plasma jet fairly well collimated which increases momentum transfer efficiency to the Pusher Plate of the Orion.

Larger Orions with pusher plates 100m or more in diameter could probably use less demanding materials for the reaction mass. A much thinner ablater could be used, and something like powdered rock, water ice, or just about anything else could actually be used for reaction mass.

The size of the nuke is almost irrelevent (which is counter intuitive at first) because the physical size of a bomb does not necessarily scale linearly with energy output or 'yield.' A 25 ton yield W54 nuke would be identical in size to a boosted version of the W54 with 1-2 kilotons, and would only be slightly smaller than a two stage 10 kiloton warhead (the main size difference would be the presence of the radiation 'bottle' containing the primary and the fusion secondary.)

The pulse units however, tend to scale nicely. The pulse units, physically surrounding the 'physics package' contain the reaction mass. Doubling the energy and momentum just about requires a pulse unit of twice the size. I'm sure it's not quite exactly that simple, but it's close.

Date: Mar 23, 2005

I really should have known better than to confuse mass with size. What I meant was, you'd need to make those small nukes quite a bit heavier to get enough momentum transfer (assuming, from their size, that they don't weigh 400-800 kg).

Date: Mar 24, 2005

The one kiloton nukes will still be small--say 20-30 kg, but the reaction mass in the rest of the pulse unit might be 200-500kg. The actual nuclear device will be a surprisingly small fraction of the whole pulse unit.

For a much bigger Orion, say one that uses 10 kiloton pusle units (such as the Michael Archangel of Footfall) the nuclear explosive part of the pulse unit might be only 50-70 kg, while the remaining pulse unit could be as much as 2500 kg (I'm just tossing numbers around, just to give some idea.) The energy producing component (the nuclear device) is surprisingly non-linear, while at the same time the inert reaction mass component of a pulse unit is pretty much linear.

Hope that helps.

Date: Mar 25, 2005

There was one almost dial-a-frequency xray laser pulse bomb developed for SDI. It consisted of taking a nuke, (I forget if there was anything special about the bomb itself tho) and attaching several dozen metal rods to the outside of the bomb with the use of motorized gimbals. (unfortunately I don't remember what type of metal) When the bomb was blown, the heavy radiation travelling through the metal rods would induce them to las in the xray range, tho the exact frequency was based on the length and diameter of the rods, and on the output of the bomb used. So you had to pick what frequency you wanted when you were making it, but it was possible. Admittedly, this was probably a lot different than the type they were using in footfall. But considering the classifications Pournelle held at the time, I wouldn't rule out the possibility of him using something real in the story, especially since he prefers to use real science in his other stories. (Partly to let people know what we could do but aren't for political reasons)

And I knew about the scaling problems, including that they were one of the reasons the Orioneers wanted a larger ship. And that realistically, 1000 1Kt bombs spread out in a saturation pattern cause several hundred times the damage of 1 1Mt bomb. Tho they do cost more and take up more mass and space. (Not that we have an reason to need this little bit of knowledge, right? lol)

Date: Mar 25, 2005

I suspect that you refer to the nuclear pumped x-ray lasers--I am almost certain that I have read an article (many years ago, and I can't remember the source article, although it was most definately NOT classified! Perhaps a Scientific American article...perhaps late 1970's or early 1980's;) the nuclear pumped x-ray lasers in question used single crystal lanthinum chloride rods. No dimensions were given, however I suspect that long thin rods surrounded by a space or radiation channel filled with a low-Z material opaque to thermal x-rays and liner would be surrounded by some high-Z material such as tunsten or depleted uranium that acts as a radiation 'pipe.' Utilizing thermal x-ray emmissions from the hot fireball of the nuclear bomb could cause the lower most shell of electrons in lanthinum to become excited. Dropping back to their ground states, this lowest shell of electrons would emit a powerful narrow band x-ray emmission. You only need a population inversion (total ionization provided by the strong excititations from the nuclear bomb,) and arrange for stimulated emissions (provided by the geometry of the rod shaped 'cavity'.) These are the essence of a LASER (Light Amplification by Stimulated Emission of Radiation.) An x-ray laser able to capture and re-radiate only 1/1000 of the energy output of a 5 kiloton bomb could create an x-ray laser with the energy equivalent of 5 tons of TNT or a pulse of nearly 20 billion joules in a a narrow x-ray band. This is more than sufficient to completely vaporize a satellite sized target. The exact 'frequency' of the x-ray laser will be a function of the energy transitions of the lower most shells of electrons in lanthinum. Such information is readlily available in information sources such as the CRC Handbook. The choice of lanthinum probably has to do with it having just the right balance of 'opacity' to xrays and as well as having high energy transitions in its lower electron shells. Other materials may also be suitable as well.

Selenium fibers also have been made to 'lase' in x-rays by application of strong irradiation from the NOVA laser array at Lawrence Livermore National Laboratory.

Anyhow, this is getting pretty far off topic, but I love the physics involved!