Project Orion Revisited. - Why not an Earth Launch?

mauk2 · 2002-12-18 16:28:43

Soph: Fusion as currently being researched is not any better (cleaner) than a modern PWR design, and is actually WORSE than an Accelerator Driven system like the Energy Amplifier designed at CERN.

See, the easiest fusion reaction to ignite is Deuterium - Tritium. It is also VERY energetic. Unfortunately, the huge majority of that energy is represented by neutrons emitted at the blazing high energy of 14Mev. (To compare, the energy of neutrons emitted by Uranium fission have energies of 2 Mev.)

So, fusion as it is currently being developed gives off most of its energy in super hot neutrons.

The problem is that converting those neutrons to heat is TOUGH, and neutron bombardment is going to be very, very high. Huge absorbers will be needed to soak up those neutrons, and inevitably, they will become riddled, embrittled, and activated. Nasty.

Add in the fact that tritium doesn't exist in nature and has to be bred from lithium jackets, AND that tritium is very radioactive AND is very easily absorbed by humans, and you have a very unpleasant combination.

Tritium is VERY nasty stuff, folks. Think of it as gaseous plutonium. Sad, but true.

Basically, we should build new PWR's as fast as we can to phase out coal, then build Energy Amplifiers once we get them perfected. We should not start using fusion until we mature it to the point that Deuterium - Helium3 is possible, then we should mine He3 off the Moon.

If we ever run the Moon out of He3, we just mine it from Uranus. We should have enough energy to last us literally MILLIONS of years, at consumption levels FAR higher than we have now.

It's just a matter of getting over this irrational fear of the "Ebil Nooklure!" we have been brainwashed into.

Nuclear is natural.

RobertDyck · 2002-12-19 02:00:59

Actually, there are more ways to make tritium than from lithium jackets. The deuterium in heavy water of a heavy water reactor is bombarded by neutron radiation. Some deuterium is converted to tritium. Heavy water becomes even heavier. That is why a CanDu reactor is the most efficient producer of tritium, and why a coolant leak is nasty.

This is also why I think helium3 will never be an exported from the moon for fusion fuel. Once we do have fusion technology we can either use double-deuterium fuel, or make tritium from deuterium. One part in 7,000 of very drop of water on Earth is heavy water, and there is a lot of water in the ocean. Tritium-deuterium is a richer fuel mixture than helium3-deuterium, and tritium can be made from neutron bombardment of deuterium.

mauk2 · 2002-12-19 09:00:09

robert dyck:

Actually, there are more ways to make tritium than from lithium jackets.

Yes, but breeding in lithium blankets is the system that is almost always mentioned by our esteemed fusion developers.

That is why a CanDu reactor is the most efficient producer of tritium, and why a coolant leak is nasty.

You have just pointed out the single reason that I would never use a CANDU design. It's a real pity, too, the CANDU is a GREAT design, if it wasn't for that darn tritium. Tritium is just too nasty to fool with, in my opinion.

Once we do have fusion technology we can either use double-deuterium fuel, or make tritium from deuterium.

While I agree a D-D fuel cycle greatly lowers the tritium problem, D-D still has an enormous neutron flux. How are we to convert those highly energetic neutrons into power we can use? Unless there is a VERY fundamental breakthrough, that will remain a severe problem.

He3-D is aneutronic in itself, although a D-D side reaction still produces a lot of neutrons. He3-D produces about 1000 times less neutrons than D-T or D-D. (I think thats right, I should go look that up.... )

Preston · 2002-12-19 15:45:25

With a 50/50 D-3He fuel at 50 keV, the reaction rate is ~21 times greater for D-3He than it is for D-D. There are two reactions with an equal chance of occuring for D-D:

D + D => n(2.45 MeV) + 3He(0.82 MeV)
D + D => p(3.02 MeV) + T(1.01 MeV)

Charged products heat the plasma and are 'filtered' out, but the neutron is about the energy of one you'd get from fission.

So 1/40 of the reactions will give a 2.45 MeV neutron at this mean temp when you do D-3He.

and FYI, D + 3He => p(14.68 MeV) + 4He(3.67 MeV).

The D-T reaction is D + T => n(14.07 MeV) + 4He(3.52 MeV).

Slightly less than half of the reactions will make tritium in a D-D reactor.

I should think that a space reactor only would need neutron absorbers (high Z material) for the direction that is toward the crew (..?). The rest can just be moderated with light or heavy water. I'm thinking heavy water doesn't absorb neutrons as well as a chunk of heavy metal.

mauk2 · 2002-12-19 17:28:35

Why, thank you Preston! That saved me the trouble of digging that stuff out.

With a 50/50 D-3He fuel at 50 keV, the reaction rate is ~21 times greater for D-3He than it is for D-D.

This is correct! Using a 50/50 ratio, He3-D has one fortieth the high energy (14Mev) neutron flux of DD. Most proposals I have seen for running He3-D aneutronic has consisted of running the plasma very helium rich, so the aneutronic reaction has the best chance of happening. If there are 100 heliums for every deuterium, it stands to reason the DD reaction will be suppressed. I will see if I can't find the article I read that stated the 1000 fold drop....

D + D => p(3.02 MeV) + T(1.01 MeV)

This reaction is the fly in the ointment for both DD and D-He3. That tritium snaps up a D very easily and BANG, you have one of those hot neutrons to deal with.

I should think that a space reactor only would need neutron absorbers (high Z material) for the direction that is toward the crew (..?). The rest can just be moderated with light or heavy water. I'm thinking heavy water doesn't absorb neutrons as well as a chunk of heavy metal.

Actually, I think the best material to shield neutrons, hands down, is liquid hydrogen, of all things. The fast neutron Mean Free Path in liquid hydrogen is only about 60 centimeters, and every collision saps an average of 63 percent of the neutrons energy.

LH2 is very light, so carrying a few meters of it as a shield is not a huge hardship. Put a healthy dose of boron in it to mop up the thermal neutrons after they're moderated and voila, you have a very effective and pretty lightweight neutron shield. You would place it as far from your reactor as you can get, and let the majority of the neutrons escape into free space, so that the thermal load on the LH2 doesn't make it boil too fast. In other words, the side of your crew section that faces the reactor has a ten meter thick borated liquid hydrogen tank on it, and the rest of the ship just lets the neutrons zip away into space.

The escaped neutrons decay pretty fast into a proton and an electron, and render themselves harmless, so shielding against them is not needed.

soph · 2002-12-19 17:31:05

didnt zubrin say something about using the speeding neutrons to provide the power need to keep the reaction going in Entering Space?

soph · 2002-12-20 13:51:12

well, with all the new research in genetics, couldnt we, theoretically, do an experiment in which human cells in a lab, with normal genes, are subjected to nuclear-plant level radiation? you could observe effects for as long as you wanted. wouldnt this at least give us a better understanding of the issue?

RobertDyck · 2002-12-20 14:38:49

A successful nuclear fusion reactor, at least here on Earth, requires a means to use the energy of the neutrons. An exotic fuel mixture that requires shipping helium3 from the moon will never be commercially viable. The moon guys will not want to hear that, but they need to focus on products they can produce on the moon which have a market now.

Liquid hydrogen to moderate neutrons is a great idea. The trick is then to extract energy from them. As neutrons are slowed, energy would be transferred to the liquid hydrogen so that heats it. How do you use that heat? Liquid hydrogen must be kept very cold; re-liquefying requires active cooling, so I don't see how to use that heat. Since the process is moderation, a commercial reactor for Earth could use heavy water as a neutron moderator instead. That heavy water could be run through a heat exchanger, and the light water which receives the heat could drive a turbine. This would operate just like any heavy water fission reactor. Heat collection would just be a thick jacket of water.

This permits a fuel of pure deuterium to produce tritium and helium3 as by-products, which are contained and act as fuel for both D-T and D-3He reactions. You could argue that the D-D reaction is a breeder reactor to produce T and 3He fuel. The only question is what will absorb the protons and neutrons.

Slowed protons could be captured by a magnetic field and further slowed to reduce it to hydrogen. Neutrons can also be captured with a magnetic field, although it's more difficult. If neutrons can be contained they will decay with a half-life of 10.3 minutes into protons and electrons. That would avoid radioactive contamination, or "activation", of a neutron absorber. Capturing neutrons in this way would probably require moderation, so a small quantity of deuterium in the heavy water moderator would be converted into tritium. That could periodically be replaced, and the spent coolant/moderator could be electrolysized so the deuterium and tritium could be fed in as fuel. Alpha particles could similarly be moderated then captured by a magnetic field so it could be slowed into normal helium.

The fusion reaction itself could be fed through a giant torus with a constriction. The constriction would increase the pressure and temperature to enable fusion, rather than attempting to maintain fusion throughout the ring. The constriction would be designed as a ram-jet so the reaction itself would accelerate the plasma through the ring. Magnetic fields would retard that plasma flow and use the energy so gained to power the containment field. A quantity of high speed plasma would be injected into a mass separator that would extract hydrogen and helium4, while injecting deuterium, tritium, and helium3 back into the reaction torus. Power for the mass separator would be provided by excess power from the torus containment system.

Fuel for this reactor would be pure deuterium; waste would be pure, non-radioactive hydrogen and helium. Of course you would have to watch the reactor operators to ensure they don't skimp on efficiency of the mass separator.

soph · 2002-12-20 14:48:23

This would be safer, cleaner, and produce more power than your average fission plant?

Preston · 2002-12-20 22:17:42

Robert, I'm not certain about what the numbers would actually look like but I think you'd need a pretty massive magnetic field gradient to stop neutrons -- the force on a dipole such as a neutron is proportional to the magnetic field gradient. Given the size of a tokomak, the gradient would be small. F=m grad B, I think, where m is the dipole moment, B is the mag field. So unlike what we have for a proton or electron, it won't radiate it's energy away so easily. And even thermal neutrons go around 1000 m/s, so they'd zip right out anway.

RobertDyck · 2002-12-21 10:59:24

There is more than one way to tackle the neutron problem. First is to produce one hell of a magnetic field using a superconductor. Another is to reduce the speed of neutrons with a moderator. If all fuel is derived from electrolysis of the heavy water moderator then a large quantity of tritium would just enrich the fuel. Another approach is to find a way to promote neutron decay faster than 10.3 minutes. Would a radio signal of a certain frequency promote neutron decay before it leaves the moderator? Would an electromagnetic signal carried in the outer wall of the heavy water tank cause neutron decay when the neutron passes through?

The advantage to a superconductor is once power goes in, it stays in; additional power increases the strength of the magnetic field, you don't have to continuously supply power to maintain the field. Radio waves have to be maintained. An efficient power plant must use the waste from one component to power another; for example, the waste heat after the secondary coolant has passed through the turbine could be used to distil heavy water from tap water. The light water produced as a by-product of distilling tap water could be sold as bottled water. If heavy water is only used to supply the primary coolant/moderator, then the only source of fuel would be electrolysis of spent primary coolant. That ensures deuterium fuel is enriched with tritium.

Oxygen shouldn't be a problem; 99.757% of oxygen is 16O, 17O and 18O are the others. Neutron absorption of 16O would just create 17O which is a natural isotope. Similarly 17O would become 18O. Only 0.205% of oxygen is 18O, and 19O has a half-life of 26.9 seconds releasing a beta particle to become fluorine 19F, which is the naturally occurring isotope. That means neutron bombardment of heavy water would produce trace quantities of fluorine, but it wouldn't be radioactive.

RobertDyck · 2002-12-22 13:06:03

I just talked to a friend about the fusion reactor design. He pointed out that radio waves could not affect neutrons the way I speculated. It has been demonstrated that a fast moving electron hit by a photon from a laser at a particular frequency will flip the electron into a positron. However, a neutron is much greater than an electron so the frequency of a photon would have to be that much higher. A proton is mass is 938.2723 MeV, a neutron is 939.5656 MeV, and an electron is 0.510999 MeV, so a neutron is 1838.68 times as massive. A photon of frequency that much higher would be gamma radiation. The energy yield from neutron decay is traditionally represented by the symbol Q, and it is 0.7823 MeV. Not all that energy is kinetic energy of the proton and electron, an electron antineutrino is created. Attempts so far to measure an electron neutrino have estimated the mass at less than 30 eV. (eV = electron-Volts, MeV = Mega-electron-Volts)

Ok, so is there a way to use the gamma radiation from the fusion reaction itself? Could we slow the neutrons in a moderator so they are delayed at a positioned close to the fusion reaction that it is soaked in gamma? Would the gamma radiation from fusion be the right frequency to break down free neutrons?

Calculating the frequency of a photon is E=hv where E is energy, v is frequency, and h = Planck's constant = 6.626*10^-34 Joules?second = 4.136*10^-15 eV?s. If you assume a photon to trigger neutron decay is roughly the same energy as the energy released (resulting in double that release), then the photon would have to have energy of 0.7823 MeV. Since 1 MeV = 10^6 eV, the frequency of such a photon would be 0.7823*10^6 / 4.136*10^-15 = 1.891*10^21 hertz. That is very high gamma rays. Is that right? Did I screw up the calculations? Could a lower photon trigger neutron decay?

Preston · 2002-12-23 16:11:46

Could you lead me to some material where electron-positron flipping has been demonstrated? The closest thing I can find on the subject is pair production of electrons and positrons from high energy electrons incident on heavy nuclei -- very intense lasers are used to heat the electrons.

The fusion reaction itself won't give gammas, I believe, but basically they do indirectly because gammas come from inelastic collisions of neutrons with deuterons and reactor materials.

mauk2 · 2002-12-24 17:28:18

I will second that request for info on photon-generation of antimatter.

If we could use a more energy efficient process to produce anti-protons, that would make ACMF and other anti-matter using designs much closer to reality.

Oh, and even positrons in bulk would be a very useful thing, I have seen designs for positron-fueled SSTO spaceplanes powered by positron-generated gamma rays in tungsten ramjets and using air as reaction mass.

Anything that makes volume and inexpensive antimatter is a positive development for space travel.

John_Frazer · 2002-12-31 23:03:03

Plenty of fans for ground launch. Little information now, and what we have doesn't seem hopeful -towards eradicating fallout from a ground launch.
Even neutron bombs have some lingering radiation, and if you're using a couple kilos of Pu or U per bomb, and several hundred bombs to get above the atmosphere, it doesn't look good.
EMP is a myth in this circumstance (I'll bet $ now). Everything we've seen on EMP states that it's produced in extremely large blasts -above 2mt- or in "much smaller blasts which are specifically designed to maximize" EMP. (paraphrasing T. Taylor)
Orion pulse units are not large, and may be designed to minimize EMP (gammas) though I suspect that it's enough that they're not specifically designed to produce EMP.

I like to point out that ground launch isn't necessary to get full use out of Orion. I've written in several places at nuclearspace.com boards about space asembled NPR stages, and I'm pretty sure I put it here too.
One thing I recently found in the Orion fan's 'bible': "Project Orion- the True Story of the Atomic Spaceship", by G Dyson rings out: Either the ground launch or the high-toss launch (The NPR stage lifted high by a booster stage, where it fires off above the atmosphere) is fraught with many places where a single-point failure means disaster.
A string of several hundred bombs tossed out the ass end of the ship, all of which must go off perfectly as planned or else the ship is junk -along with much of the surrounding countryside.

Build the ship out of parts lifted to LEO by an HLV. Shuttle or Energia parts lift ~100 tons each. Sea Dragon or similar booster lifts ~500 tons per shot.
Once the basic propulsion package of the ship is together, fire a small bomb to test things out. Build a little more on it, then fire a bigger shot. Fire a few shots for the next test.
Do a shakedown cruise out around the Moon & back before you commit to a crewed fully loaded ship with a long drawn out series of blasts (which are up to 20 seconds apart instead of .75 seconds for the ground launched ship).
One prime reason the original Orion workers decided against a ground launch was the inherent difficulty in testing it out, and the unforgiving environment.
Much more forgiving when you don't rely the entire mission on any one of a few hundred blasts...

Note that we're not talking about the tinkertoy ISS. These are large 500 ton segments of heavy steel, fitted together with big forged steel nuts & bolts. Ever worked a carnival? I've done that, as well as a MASH unit. Every day stuff to place heavy parts together with precision in a time crunch in heavy rain & wind. Doing the asembly in space suits won't be that much harder, if it's built right. Zubrin criticized the NASA large ship plans because they required pressurized hangars and lots of little finicky bits -just like the ISS, it's prone to trouble and high costs.

These first space assembled ships place the space infrastructure Ideally at NEAs or maybe Mars' moons) to build bigger ships. By the time the first mission to Mars has gone out & back, we're ready to build space-going luxury liners of several hundred thousand tons for the tourist and colonist trade to Mars!

soph · 2003-01-01 00:38:06

using a space elevator, theoretically:

1. send a central or end piece up, capture it to the space station counterweight.

2. Attach the subsequent parts, using overlapping vacuum seals and computer controlled screws and bolts, that can be double checked later, and monitored by computers.

3. Once the ship is assembled, send up all supplies that are not prone to rotting. Tools, computers, etc. Now, astronauts can put things in place.

4. Send up propellant and sensitive gear, along with long-lasting foods.

5. Send up crew, perform final checks, launch.

RobertDyck · 2003-01-03 10:16:55

I tried to get some references on electron flipping. My friend doesn't remember, he though I told him about it. I had breifly read about an experiment where an electron beam was subjected to a high-intensity laser, and the result was an electron-positron pair. I ignore the electron as an irrelevant byproduct of producing positrons. I thought medical PET scanners had required a cyclotron to produce a high intensity electron beam which was rammed into a tungsten foil target to generate positrons. A relatively low speed electron could be generated by the same electron gun as Cathode Ray Tube (CRT); that is the picture tube of a television or computer monitor. A laser coupled with an electron gun would be a lot smaller and more energy efficient than a cyclotron.

However; my study has shown the original electron is retained and the photon is converted into both the electron and positron of the pair. This doubles the energy required to produce the pair. Furthermore, most papers I found use atomic nuclei to catalyze the reaction between two photons rather than an electron. One reference does state that two photons with enough energy to create the electron-positron pair must react within an electric field (such as a nucleus or other charged particle). The energy for the electron-positron pair does not have to come from two photons, it can work with a photon and a virtual photon. That is, the virtual photon comes from part of the momentum of the charged particle. To gain enough energy this may require a linear accelerator rather than an electron gun. All references I found do use a linear accelerator (linacc).

TJohn · 2003-01-30 07:35:11

I don't want to upset anyone and be accused of being narrow-minded but, since we know that nuclear engines can be made and have been tested before, why not focus on developing that technology first? From what I've gathered, VASMIR is still a more efficient propulsion but we seem to have a problem with containing the plasma.

I feel that once we get the ball rolling on nuclear propulsion, the technology will develop naturally until we get to VASMIR type propulsion systems.

soph · 2003-03-09 18:15:51

Development of liquid and gas core nuclear thermal rockets could greatly improve our space capabilities, outside of orbit.

Perhaps a hybrid NTR/VASMIR spacecraft would be an ideal planetary cruiser until more advanced propulsion methods were developed.

The problem today is that we are really focusing on one option or another, instead of approaching a few different systems. For example, a single shuttle design is not the best approach. As others have said, scaleable vehicles should be designed for specific purposes.

Perhaps R&D will eventually lead to plasma sail/fusion/GCNR/solar planetary cruisers, if we let it.

Ad Astra · 2003-03-09 20:00:01

As George Dyson pointed out in his book, Orion may not be technologically or socially acceptable until the 2050-70 time period. Clearly, we will develop NTRs and nuclear-powered plasma rockets before then. But there is hope that Orion will eventually come to fruition, because it is more practical than solar sail or mag sail propulsion.

Each propulsion system will eventually find its niche, rather than one propulsion system replacing the previous one. Chemical rockets are good for transport to earth orbit because of their benign (in the case of hydrogen) environmental effects. NTRs are preferred for lunar transport because it will enable 24-hour transits. Plasma engines, like the tortoise who defeats the hare, cannot sprint to the moon but they allow 90-day transits to Mars. I predict Orion will be the preferred engine for flights to Jupiter, Saturn, and perhaps the outskirts of the solar system. Travel to the stars will be enabled by antimatter or fusion ramjets.

On an unrelated tangent: If any of the "Axis of Evil" nations are still up to their games by 2050 (the odds of Iraq making it that far are the same as a snowball's chance in Hades,) an international Orion mission to Europa will give the nuclear powers an opportunity to disarm multilaterally and deplete their nuclear stockpiles in an effort that benefits all mankind. It's something I hope to see.

soph · 2003-03-09 20:25:58

A fusion engine, in the 20-40 ear future, may allow 1 week to a month trips to Mars.

Orion, I just don't see the need for. It's inefficient, perhaps useful for speed bursts in space, but you need a huge pusher plate for it, which means that you really can't make it a hybrid. It is a rather restrictive design.

NTRs provide the advantage of providing a power plant for the spacecraft. So would fusion drives.

John_Frazer · 2003-03-10 19:11:35

soph Mar. 09 2003
> A fusion engine, in the 20-40 year future, may allow 1 week to a month trips to Mars.

The problem there, is that fusion has been 20-40 years in the future, just about for the last 40 years. We don't even know for certain if a sustained fusion reaction is possible short of a star.
Orion uses atom bombs. The hardest parts of a space-use Orion ship are a giant grease mist sprayer, to coat the pusher plate between pulses!

Compare that also to VASIMR... NTR may be more readily buildable, because every part of it has seen use in a rocket motor to date.
NTR and VASIMR both suffer compared to Orion in performance. Nothing else as close to coming off the drawing boards is as realistically feasible as Orion -and has anything like the incredible performance.

> Orion, I just don't see the need for.

No need for big strongly built ships, built with updated 1960s technology, that outperform anything else as easily built, as well as just about everything else that's only now theoretically possible as a lab curiosty?
What do you look for in a ship?

> It's inefficient

It's simple. The fuel production is a bit of a problem in the far future, when we've already used up the extra decomissioned warheads. I'm prepared to say we'll deal with that when we get there.
Also, projections show that the bigger space-only ships have potential for isp of between 10,000-1,000,000 seconds. That's in the range of ion propulsion, vastly better than NTR, better thrust and much simpler than VASIMR.

> perhaps useful for speed bursts in space

Uh, yeah, speed bursts with huge robust ships, with over 45% of the initial mass being cargo. Like a battleship able to cross the Atlantic at 35+ knots, carrying thousands of tons of cago, with the crew in big roomy luxury-class quarters, with ltl or no fuel being burned from its bunkers. Sorry, but passenger liners are out of business...

> but you need a huge pusher plate for it

Maybe not what you mean, but I actually like this detraction of Orion I've heard: "It needs a big huge pusher plate made of steel, and it needs lots of heavy structure to hold together. Lots of waste mass in all that"
Correction: The pusher plate & heavy structures aren't mass penalties, but enablers. They let us use the raw simple power of the atomic bomb, and at that, they have plenty of power left over for a vast proportion of the ships mass to be useful payload sent on quick trajectories.
I like the (ability to use/requirement for) strong battleship structure. Throw in lots of other "waste mass" in the form of redundant sysems, alternate pathways & conduits, tools, spare parts, machine & repair shops.

> which means that you really can't make it a hybrid. It is a rather restrictive design.

Wht else do you want? Extra power production? Toss in a couple or RTGs and some solar panels folded up in the 30 tool lockers spaced throughout the ship. Add batteries in (each primary and the 3 redundant separately placed) power junction boxes, with computers dedicated to power handling built in. The ships' 4 primary redundant fission plants can be provided with parts commonality and lots of extra space to work around them via telerobotics.
What- it's too much mass? We only have 6000 tons of payload left of our 10,000 ton ship built up in HEO from NEA materials... What to do? Add more tools!
All this is survivability, which is the primary payload.

Saw something on this tread about the radiation hazard to the crew.
They placed the crew at the top of the stack, with all the mass f the ship in between them and the blasts. Fallout isn't a problem when you're going away from the blast site at high speed.
NASA took a newer look at nuclear pulse recently. They seem to have avoided bad PR by calling it "Externally Pulsed Plasma Propulsion with no mentio of nuclear pwer. Their ship was called Gabriel, and the simplest cheapest version was a 10 meter module boosted into space via chemical HLVs (just as the 10 meter Orion). It was the least efficient, but it outperformed everything else we could build.

Interestingly, they said that the fast transit times available meant that the exposure to space radiation was so brief that EPPP meant less radiation exosure for the crew.

soph · 2003-03-10 19:24:06

isp is lower than an NTR, and thrust is higher. Your resupply ships can run better on NTRs-40% fuel mass to launch, and higher isp. NERVA was built, Orion wasn't.

A crack in your pusher plate, and you've got a problem. Your pusher plate is no more of an enabler than a NTR reactor.

I'd like to see figures on the exhaust velocity and thrust of Orion, if you could provide them.

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#51 2002-12-18 16:28:43

Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

#60 2002-12-20 22:17:42

Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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Re: Project Orion Revisited. - Why not an Earth Launch?

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