One topic that is sometimes mentioned in alternate histories of the 20th century is Orion. Orion was a spacecraft propulsion concept first thought of in the US of the 1950s, which would drive a spaceship by having it pushed by the shock wave of exploding nuclear bombs. The singular benefit of the Orion concept is that such an engine would produce a large amount of useful propulsive energy, allowing the craft to achieve much higher velocities than a conventional rocket with a given amount of fuel. An Orion spacecraft could thus afford to devote a much smaller portion of its total mass to fuel than a conventional rocket, and more to payload and the spacecraft systems. The benefits of this would be that Orion spacecraft could carry very large payloads into orbit, or when loaded with fuel could travel interplanetary distances much more quickly than conventional rockets. Since the spacecraft would not have to be almost entirely fuel, an Orion would not need to use the sort of very expensive lightweight components needed by conventional rockets.
For these reasons, many people see the Orion system as a sort of missed glory of the space program, which could have allowed fast, cheap, and massive space travel decades ago. Many alternate history scenarios have been presented in which an Orion is constructed fairly cheaply in the early days of space flight, and is used to dramatically increase human presence in space. Orions have featured in several works of fiction, including the novels Footfall (Larry Niven and Jerry Pournelle) and The Stong Dogs (S.M. Stirling). Some of the more extreme advocates of the Orion system present it as the holy grail of space travel, which could have taken mankind into a new age of space travel in the 50s or 60s were it not for misplaced fears about nuclear technology, "tree hugger" environmentalists, or whoever the Orion advocate's favorite bogeymen are.
Unfortunately, the reality of the situation was rather different. Not only did the Orion propulsion system have a great many flaws, but its advocates have tended to dramatically overstate its potential benefits.
First, let's look at what some of the actual Orion proposals promised. There were actually several different proposals throughout the lifetime of the Orion project, but they fall into two classes. Note that the Orion project was originally classified, and some of the specifics of the research into some Orion technologies remain classified to this day. The proposals and the estimates of their capabilities, however, are now publicly available. Before we look at the proposals I should mention that one way to define the efficiency of a rocket is a value called its ISP. ISP is essentially a measure of the efficiency of a rocket. A higher ISP means that the engine can produce more acceleration for a given amount of fuel. Thus a higher ISP rocket can take the same payload from point A to point B using less fuel, or (typically) in less time. Orion engines also have a high thrust, which means they can produce a lot of acceleration quickly rather than just over a long period of time. This is useful for escaping the Earth's gravity.
The origin of the Orion idea was in a classified 1955 paper by Stanislaw Ulam and Cornelius Everett. It involved a spacecraft with a large pusher plate connected to its aft end by shock absorbers. The craft would periodically eject nuclear bombs behind itself, followed by disks of a solid propellant material. The bombs would explode, turning the disk of material into a plasma which would hit the pusher plate and thus propel the craft. Project Orion itself began in 1958 at General Atomics (a subsidiary of General Dynamics), funded with a million dollars a year from ARPA. The project was driven by Theodore Taylor, and Freeman Dyson was heavily involved. Taylor modified Ulam's idea to combine the bomb and propulsion mass into a single unit. The propulsion mass was to be a plastic, similar to styrofoam (perhaps styrofoam itself). Such materials are good at absorbing the neutrons released by a nuclear explosion, and break down into lightweight atoms that transform most absorbed heat into translational kinetic energy (ie rapid movement).
In November 1959, the researchers first succeeded in testing a small proof-of-concept craft which flew a few hundred feet using conventional explosions. Testing was also done to determine the necessary structure of the pusher plate.
The first proposal was for an Orion spacecraft which would launch from the ground. This spacecraft was envisioned as being extremely large, with plans calling for craft massing anywhere from 10,000 to 40,000 metric tons. One design called for a craft which would mass roughly 20,000 tons of which half was fuel and the rest was spacecraft structure and payload.
Tayler's original proposal was for a vehicle 16 stories high and with a pusher plate 135 feet in diameter. The launch pad would have consisted of eight stabilization towers, each 250 feet high. The vehicle's initial mass would have been 10,000 tons. The bomb units ejected on takeoff would have yielded 0.1 kiloton, initially at an ejection rate of one per second. As the vehicle accelerated the rate would slow down and the yield would increase until 20-kiloton bombs would have been going off every ten seconds. A total of 2000 bombs would have been required, making up approximately half of the spacecraft's mass. These would have allowed it to reach escape velocity. Since the payload would have been several thousand tons, it was proposed to man the craft with a crew of 150. The original cost estimate for the construction of this craft, from Dyson, was 100 million dollars per year for 12 years. Since the vehicle could not land using the pulse drive, the designers probably anticipated that a conventional vehicle would be available to shuttle crew and material between the ship and planetary surfaces.
At around that point, US space efforts were reorganized so that all military projects were funded by the Air Force and all civilian projects by NASA. When the Air Force was approached, it repeatedly refused to fund Orion because it could not find any military use for Orion. Its only potential use to them was as an orbiting nuclear weapons platform, an idea which was falling out of favor as the advancement of ballistic missiles made such concepts irrelevant.
Orion's only chance for funding at that point was NASA (apart from the entirely nonexistant nature of a civilian market for space launch capability at that time, the project was classified). A new design was produced, for a smaller Orion which would be launched into orbit using Saturn V rockets. The vehicle would have centered around a 200,000 pound propulsion module with a 33 foot pusher plate. At least two Saturn V launches would have been required to lift the craft into orbit, where its pieces would be attatched. The main proposed mission profile was a flight to Mars. The craft was to carry eight astronauts and 100 tons of equipment, with a round trip time of 125 days. The Orion planners predicted that it would cost 1.5 billion dollars, half of that for the Saturn V rockets to launch it into orbit.
In 1964, aspects of the project were finally declassified, a year after the nuclear test ban treaty made its launch technically illegal. The signing of the treaty did not actually result in the project being cancelled, but eventually NASA made its decision to cut all funding to the project and the Air Force then announced that it would not fund the project any further without NASA contributions.
Dyson estimated at one point that the most extensive ground-launched Orion plan would have added no more than 1% to the atmospheric contamination at the time (from atmospheric nuclear testing). It was even estimated at one point that pulse units (bombs) for the original concept could have been obtained for as little as 10,000 to 40,000 dollars, although other estimates within the project assumed 500,000 dollars.
The Orion workers had produced a new, "first generation" design that abandoned groundlaunch and instead would have been boosted into orbit as a Saturn V upper stage. The core of the vehicle was a 200,000-pound "propulsion module" with apusher-plate diameter of 33 feet, limited by the diameter of the Saturn. This design limitation also restricted Isp to from 1800 to 2500 seconds
The performance of an Orion craft would actually vary considerably depending on its mass. This is because nuclear fission bombs have a minimum "critical mass", which produces a 20 kiloton explosion at full efficiency. Decreasing the power of the explosion below that point does not reduce the weight of the pulse units, and so would merely decrease the efficiency of the craft. This means that larger craft are more efficient because they can absorb more energy from any given explosion (if a craft absorbs enough energy to accelerate it by more than about 30 meters per second from a single pulse, this puts tremendous stress on its structure).
For comparison, a conventional chemical rocket has an ISP of 450. The ISP of the small, orbit-launched Orion designed for NASA would have been in the range of 1800-2500. A very large Orion, massing around 40,000 tons would have had an ISP as high as 6000. ISP values of 10,000 are sometimes mentioned in conjunction with the Orion project, but would have required extremely massive craft. Around the time when Orion was originally being developed, there were few ideas that could easily have led to engines more efficient than chemical rockets. Foremost among them was the NERVA engine, which relied on heating a gaseous exhaust with a nuclear reactor, and would have delivered an ISP of around 850.
Of course, there are several problems with both the Orion concept itself, and many of the "facts" that are commonly said about it.
The biggest environmental problem associated with Orion is radioactive contamination from a ground launch. The people working on Orion produced some very rosy estimates of atmospheric contamination, roughly 1% of that produced by all atmospheric nuclear testing. Unfortunately, they based these figures on fission-free fusion bombs, a technology that they expected was just around the corner but which turned out not to be. Nuclear fission releases quite a lot of contamination compared to nuclear fusion. Since fusion bombs need a fission bomb to start their explosion, this means that actual nuclear weapons all tend to be fairly dirty. A fission bomb is nearly as dirty as a fusion bomb because most of a fusion bomb's contamination comes from its fission "trigger". The people working on Orion assumed that it would be able to use fusion bombs without a fission trigger, which would be extremely clean. Such a technology did not, however, arrive like they expected it would.
This means that their original estimates of Orion contamination were off by an extraordinary amount. The launch of an actual Orion based on fission bombs would involve more than a megaton of fission explosions in the atmosphere, from perhaps 350 fission bombs (many would have an artificially reduced yield, but that doesn't reduce the amount of radioactive plutonium needed for them). While most of the explosions would not be near the ground and thus would not create direct fallout, the radioactive remains of the bombs themselves would be spread across the Earth.
The radiation release from this would actually be very high. It was high enough that the US government of the 50s and 60s, which was conducting regular atmospheric nuclear testing, had serious misgivings about the amount of contamination Orion would produce. We are not talking about some stereotypical 90s "tree huggers" here, we are talking about the US government in the 50s and early 60s and even it was willing to concede that there was a limit to the amount of radiation that should be spewed into the atmosphere.
Of course, if the Orion engine was not used until the spacecraft was fully in orbit, this would not be a problem. However, that would mean that large and very expensive chemical rockets would be needed to carry it into space. Even the original Saturn V-launched concept called for the Orion to use its engine before actually reaching orbit. A version that did not use its engines until safely in orbit was proposed, but the mass the Saturn V's were required to launch was approximately 1100 tons.
Orion's side-effects would not be limited to fallout, they would also include EMP and X-rays. EMP, or Electro-Magnetic Pulse, is essentially a powerful charge differential that will destroy nearby electronics (unless they are specially shielded). It is produced by explosions at ground level and in the stratosphere. While Orion's small fission bombs would not produce large amounts of EMP, they would produce some of it especially while passing through the stratosphere.
X-rays are even more destructive. They are absorbed effectively in the atmosphere, but travel long distances in space. The nuclear explosions in space created by an Orion spacecraft would release large amounts of X-rays. The effect of those X-rays would be to cause severe damage, even destruction, to the electronics of anything else in space within a significant distance of the spacecraft (up to thousands of miles or more). When Orion was originally proposed, there was very little in space. Within a decade, however, satellites were already beginning to appear. Many of those satellites would be destroyed by operating an Orion in Earth orbit. If an Orion was launched today, it would cause tens of billions of dollars in damage to commercial and military satellites from many countries.
Orion advocates are very quick to mention how simple Orion supposedly is. The concept itself admittedly sounds quite simple - you just throw nuclear bombs behind you, ride the blast, and get propelled at great speed. Often mentioned is the fact that an Orion craft would have such tremendous lift capacity that its builders would not have to spend large amounts of money on expensive weight-saving measures. An Orion could easily be built with the technology of the 60s, let alone today. It could be "built like a battleship" rather than like an expensive weight-optimized spaceship, so that even such a very large craft would not cost much compared to spacecraft driven by chemical rockets.
Or could it?
Most importantly, there are two aspects to any space program - the propulsion technology, and what that technology is used to propel. Ignoring for now the expense or difficulty of developing the Orion propulsion system, what of the craft's mission payload? If you can send thousands of tons into orbit, what are those thousands of tons going to be and how much will they cost? Let's take, as an example, the common proposal of using surfaced-launched Orions as interplanetary explorers in the 60s or 70s as an alternative to the Apollo program.
It turns out that there are some fundamental technology and cost obstacles to doing this. First, you have to support a significant human crew in space for long periods of time. Even an Orion would take months of travel to get to nearby planets like Mars, and a mission to the outer solar system would take years. The crew would also want to spend significant periods of time at the destination planets, so as to conduct exploration. This doesn't sound like such a big deal today - after all, we've had people in space for over a year, we've landed on the moon, and we've done a great deal of study of conditions on other planets. It was a much bigger deal back in the 60s and to some extent the early 70s. Until the mid to late 70s, nobody had ever lived in space for any extended period of time. Mission durations were measured in weeks on a space capsule, not months on a space station. Humans had never set foot on another planet till 1969, and at that point even robotic probes were quite primitive.
Surviving in space for long periods is hard, and has been the subject of a fair amount of research for the last three decades. We have reached the point when we can be confident that crew survival is a rapidly solvable problem for interplanetary travel. Someone wanting to launch interplanetary Orion missions without having the benefit of all of this research would have to go to quite a bit of effort and risk to compensate for that. A lot of research would have to be done on human survival in space and on other planets, research which would take time and cost a fair bit of money. If it was decided to launch such an Orion exploratory vessel without having somehow gained actual experience in living in space for long periods, a substantial risk would be taken. To help overcome that risk, the designers of the ship's crew systems would have to be quite conservative. At any rate, this constitutes a significant difficulty for any space program regardless of propulsion systems.
Next, there are secondary vehicles. One of the problems with the Orion propulsion system is that it cannot land. Once launched, it can come no closer than orbit to any planet. Using it to explore the solar systems thus requires a seperate means of getting to and from planets. Something which is, at a minimum, functionally equivalent to the lunar module (which could carry a crew of two to the surface of the moon along with minimal scientific equipment for a short stay, and then return to lunar orbit). An Orion planning serious exploration would need multiple landers, capable of carrying more stuff down to planets, supporting a longer stay, and preferably having more powerful engines to escape the gravity of bodies larger than the moon. While the Orion weight advantage allows a lot of landers to be carried, it wouldn't make them significantly cheaper. The landers themselves can't be built like battleships, because they have to be able to escape planetary gravity wells under their own chemical power. Development of the lunar lander was actually quite an expensive component of the Apollo program, and an Orion exploration program would tend to require even more expensive developments. We are talking about many billions of dollars in research, development, and production. Of course you can't really use the same lander for any arbitrary planet, as they have differing conditions, and you may need additional secondary vehicles to shuttle crew between Earth and the ship, and if desired to refuel it in Earth orbit.
Another difficulty is the exploration equipment itself. The crew would need equipment to explore planets with, and to survive on planetary surfaces with. This would also require a significant and expensive program of development. Again, the Orion's carrying capacity allows a lot of this equipment to be transported, but it does not reduce the cost of the equipment itself to triviality. The equipment must still be taken down to planetary surfaces by lander vehicles, and must still contain some fairly advanced scientific instrumentation and survival equipment. Regardless of how much lift capacity is available, the solar system cannot be explored with compasses and binoculars. This would all require significant time and money outside of the costs for developing the propulsion system. Whatever you put in the ship, if it was build in the early days of space exploration it would require lots of research and development to be of much use.
Next, there is the issue of the propulsion system itself. The concept is simple to describe, but not necessarily simple to implement. In fact, Orion advocates often gloss over how much research the people running the actual project felt was necessary. Remember, their plans called for over a decade to get things going, and even then outside observers invariably reported that their projections seemed overly optimistic. Some of the fundamental research was done when the project itself was going, but much was not completed. Much of the stuff that would be necessary for an Orion interplanetary ship, such as guidance systems, did not exist at the time though it has been developed and refined since then by the conventional space program. Guidance at the time was primarily the responsibility of ground control, even for space probes. A manned Orion on an extensive journey would have to be responsible for its own navigation and piloting without having timely assistance from ground control (due to communications delay imposed by light speed). Independent spacecraft navigation would not have been trivial to develop back then, as they lacked our advanced computer technology and decades of experience with interplanetary robot probes.
The ship's structure itself would take some design work. It has to be able to take the stress of sitting next to a bunch of exploding nuclear bombs. Even with shock absorbers, it would be under repeated stress of a type not experienced by any vehicle we have ever built. The ability of a battleship to survive the strain of firing its own guns was the subject of a considerable amount of development efforts in the early 20th century, and that strain would be dramatically less than the strain experienced by an Orion. Building such a ship would be more than just welding together big hunks of steel. One of the big problems would be the repeated nature of the stress. Certainly an Orion could be built that would withstand a dozen explosions, even a hundred. But it has to withstand thousands of shocks over the course of a significant period of operation in space. It would take a non-trivial amount of work to design a structure to do this, especially without the benefit of modern CAD techniques. It would be an essentially new area of development, because nobody has ever built such a thing before. None of our knowledge about building vehicles and structures would easily translate into building such a ship.
In short, Orion was not proven technology. It's not even something that we could be entirely confident of getting working in the near future. While many of the individual components had been developed, the problem of ensuring that they would all actually work together as a system to produce an effective spaceship was not solved. The closest the designers came to any sort of test was a proof-of-concept test of pulse propulsion in general, involving a small model which flew a short distance using conventional explosives. Various accounts of Orion have stated that there was substantial work still to be done on the design of the pulse units, with special bomb designs being called for. Even in the early research, significant effort was directed toward research in this area, although it is mostly still classified so we don't know exactly what was being developed. The project's advocates said that integrating all of these components into a fully working design would be straightforward and cheap, but outside reviews were done on the project and they invariably said that major technical problems remained unsolved. They also said that the estimates of the time and money necessary to develop the project seemed extremely optimistic.
Another concern is, of course, cost. For any Orion mission, a significant amount of research and development would be required as outlined above. In addition to this, there would be the time and money required to actually build the ships themselves, plus whatever payload they were to carry. Orion advocates (then and now) tended to tout extreme cheapness of the system as the overriding reason to adopt it. Orion would supposedly allow space travel on a budget.
First, let us note for historical purposes that the Apollo program is generally reported to have cost in excess of 25 billion 1960 dollars. The main work on the project itself took under a decade, and it put a man on the moon less than twelve years after the US launched its first craft into space. Also note the Orion project's own estimates for its requirements - twelve years, and total funding of about 1.2 billion dollars. Both of these estimates were referred to as extremely optimistic by outside reviewers who examined the project.
One of the major things to note about Orion is the cost of the fuel. The designers at one point estimated that they could get each "pulse unit" for at most 500,000 dollars, and at some point that they could probably be had for less than a tenth of that. They are noteworthy, however, for grossly overestimating the development of nuclear technology in at least one respect, when they assumed that small fusion bombs would be developed that did not require a fission trigger. If we went with the estimate of 500,000 1960 dollars, which was probably based at least loosely on how much it actually cost the military to construct fission bombs, the 2000 pulse units of the ground-launched Orion design would cose one billion dollars. This already takes us roughly to the estimated budget limit for the entire project, just for buying the fuel for one craft. It is worth noting that fission bombs really are quite expensive devices, and that there were not much more than 20,000 such devices in the US arsenal at its peak. Launching even a few Orions would require a significant increase in US bomb production (and because off-the-shelf bombs weren't suitable for the Orion mission profile, they'd couldn't just roll off an existing assembly line).
This does not, in itself, make Orion tremendously expensive. A few billion dollars for fuel is not that big a deal if you can launch thousands of tons of payload into space. This is mainly intended to illustrate how dramatic the difference was between the cost estimates often quoted for Orion, and what a plausible minimum cost would actually have been (given our hindsight in regard to technological development). It does mean that Orion wouldn't save as much as some people think, though. A Saturn V rocket, costing several hundred million dollars at the time, could lift roughly 100 tons into orbit (it varied depending on where in orbit you wanted the payload). An Orion that could lift 10,000 tons into orbit would probably pay a minimum of a billion dollars for fuel and other launch-related costs. This is still, however, as much as 50 times less than the cost for the Saturn V.
Of course, there are two factors worthy of note. First, that the Saturn V was quite expensive as chemical rockets go. Someone willing to develop something as big and dirty as an Orion could put that sort of effort into developing chemical rockets that, while requiring lots of risk, investment, and technological development could put payloads into orbit for many times less money than Saturn Vs. The Orion would also cost more than just its fuel, from a standpoint of lifting stuff into orbit. Since the ship cannot land, it is "expendable" in the context of a launch vehicle, and in general would have associated costs much more significant than just its fuel.
It should be noted that these concerns apply to an even greater extent if you don't launch the Orion from the surface. Their big cost advantage would be as a launch system with an unusually low cost per unit of mass lifted to orbit. If you remove that, then Orion just becomes an interplanetary vehicle that is quite speedy but does not scale down well at all. While chemical rockets are still the only main alternatives for launching from Earth, because of their high thrust, there are plenty of non-chemical alternatives to Orion for interstellar flight. Ion drives for example, which as of now have been successfully tested in interplanetary space, are more fuel efficient than all but the largest Orions. An Orion interplanetary vehicle would inevitably cost a lot because it has to be fairly large, and would have to be launched by chemical rockets. The chemical launch phase would cost over a billion dollars (1960 dollars) even for the most modest space-launched Orion. It would have cost several billion dollars to launch the larger thousand-ton design.
The ship itself wouldn't be all that cheap either, in absolute terms. Orion advocates are quick to claim that it could be built like a battleship, but that doesn't mean exactly what the average person might think. Battleships were, by the middle of the twentieth century, a highly refined technology which the world had an extraordinary amount of experience building and using. They were about as well established as a technology could get, they were heavily refined so that the designs were highly effective, and they were produced by industries which had experience in churning out many battleships effectively and for a reasonable cost. Despite all of this, the average battleship took three to four years to build even under the urgency of wartime conditions, and cost quite a bit of money.
Structurally speaking, there is an analogy between building an Orion hull and a battleship. Both of them would be heavily reinforced metal structures, very large and designed to take a fair amount of stress. The analogy between Orions and battleships ends there, though. Orion's hull structure would be a fundamentally new design that would require new construction facilities, new techniques, and a cautious approach. An Orion would be filled with advanced technologies and equipment to allow it to travel in space and conduct its mission. This technology would be new, to a significant extent it would be untried, and it would be in general much more expensive and difficult to construct than anything put in a battleship. The Orion design would be anything but the cheap kludge some advocates insist it could be. While it would not have to be weight-optimized like a conventional spaceship, its components would be finely crafted and of the highest reasonable quality. For a project with the high absolute cost of an Orion (which really is a "put all or most of your eggs in one basket" approach to launch capacity), and with all the detrimental side-effects and risks of an Orion, its backers would not be willing to risk cutting too many corners in the construction.
In general, I would expect the cost of building a single ground-launched Orion in the suggested range of 20,000 tons loaded weight to be quite high. First, a substantial amount of R&D would be required to produce an actual design, and confidence that the design would in fact work. Beyond the work done up to the point when the project was historically cancelled, this would take several years and cost hundreds of millions of dollars just for the propulsion technologies and hull design. Then you have to actually build and launch the ship, which would probably take as much as a decade (definitely at least five years even at a very rushed pace). Construction of the ship itself, especially the first ship, would range into the billions of dollars. Plus the fuel, which would easily reach one or two billion. Plus the payload.
The payload is the big thing. Orion has a low cost per unit of mass to orbit, but you can only get that low cost by doing a lot of research and construction. Developing and building the first few Orions would easily match the time and cost requirements for the entire Apollo program, and possibly even exceed them. And that's before you've paid for actually doing anything with the ship(s). What if you want to do some interplanetary exploration with them? Well, as mentioned above you are going to be spending many billions of dollars to develop and build additional equipment. You need to navigate the ship, support the crew in space, carry scientific instrumentation, develop and build landers to explore planets with, develop equipment for living on and exploring the surfaces of other planets, and more. In that case you aren't just developing a propulsion system, you're also developing an entire space program to wrap around the propulsion system. That costs a lot of money. Even ignoring the other problems with the Orion technology, actually building (for example) one or more large exploration Orions in the 70s would cost substantially more than has ever been spent on any program of space exploration.
The general point is that whatever you are building an Orion for, it's payload is not going to be cheap in absolute terms. You have to fill the ship up with thousands of tons of useful stuff in order for it to be worthwhile to build the ship in the first place. Building Orions is thus a de facto commitment to a large space program. Financially speaking, their launch cost advantages don't start to exist until you've already decided that what you want to do in space involves launching a substantial amount of stuff, and spending a substantial amount of money.
An Orion project would encounter numerous political obstacles. Nuclear detonations in the atmosphere and in space are banned by several major treaties, ever since the Nuclear Test Ban Treaty was signed in 1963. At the present post cold war time it might be possible to renegotiate them, but in the 60s and 70s those treaties were with the hostile and unforgiving USSR. With no nuclear pulse program of its own, at least in the short term, it would balk at renegotiating the treaty to allow the US to start launching nuclear spacecraft. By the mid 60s and after, launching a spacecraft powered by throwing nuclear bombs out the back end would be incredibly unpopular for the US government from a PR standpoint. Both with its own people, and with the rest of the world. The contamination produced by an Orion ground launch, of course, would be unacceptable to just about everybody even back then.
Considering that the historical Orion project didn't even get started until 1959 and even its own (probably overly optimistic) plans didn't project launch of a craft until 12 years after approval of funding, an Orion wouldn't realistically be launched until the early 70s. By that time satellites will also be becoming a useful space asset, and anybody whose satellites were destroyed by an Orion launch would be very displeased.
If an Orion was launched without successfully easing the Soviets into the idea that it was going to happen and was essentially peaceful, the Soviet command would be incredibly nervous at the launch. They would probably assume that it was intended as a military craft, since that would seem the most likely explanation for the US going to so much trouble and risk. They would have a strong incentive to destroy the craft, and if they did not they would still be quite nervous and liable to act unpredictably.
So the question is, what is that much launch capacity good for? Especially considering that Orion's main attraction is that you can fly all over the place with it - it's not just a glorified booster to orbit, especially since it can't land once it has taken off. You could do it purely for exploration, in which case you would get a lot of exploration done - but in a fairly expensive manner. It's not all that urgent to do scientific exploration of the Solar System, and few people would argue that getting lots of exploration done ASAP would be worth spending lots of time and effort on an Orion, and risking the negative side-effects.
Orion is basically nothing more than a cheap per unit weight, but high in absolute cost, option that is best used to get lots of stuff off Earth with a lot of nasty side effects. It is a propulsion system, nothing more - it puts stuff into space, and into places around the solar system. Granted this would be nice, but you still have to research and then build the useful stuff, and for any continued operations in space, you have to get more stuff up there somehow to supply it. And in most applications it helps to have a lot of experience before you actually ship all the stuff into space. Orion can't carry a space program by itself - in fact the only real sense of using it is as the major lift component of a _much_ larger and more extensive space program, which has very concrete long term plans and is very prepared, in which case costs of lifting to Earth orbit aren't so high a proportion anyway, and the budget is big enough that better propulsion systems than Orion could be researched.
Orion isn't a "magic bullet" that produces a cheaper better space program. It would have to be part of a space program with much greater funding than our space program historically had, within which it could save money or expand capability in very large-scale operations.
Many people have suggested that the cheap (per unit weight) launch costs of an Orion could pay for themselves by spurring early commercialization of space. Unfortunately, in the 50s through 70s, the technology did not really exist to get financial return from a permanent manned presence in space. Even with the cheap launch costs of a working Orion system.
There are four methods, in general, with which a presence in space might generate financial return with known technology.
1. Commercial value of Earth-orbiting satellites.
2. Manufacturing in space of components that are easier to produce there than on Earth.
3. Commercial application of various technologies developed from space-oriented research.
4. Extraction of valuable materials from bodies in space.
Let's take a look at these, and which of them could be satisfied by an Orion program in the 70s or before.
#1 is unlikely. Not only does Orion make a bad satellite launching platform (they're not the sort of thing it's best to take tens of thousands of tons of to a single orbit, all at once), but it tends to fry all unshielded satellites already in space, and the technology of the time isn't really up to making lots of profits from satellites. Satellite technology itself is simply very primitive at this point. In order to be useful as a satellite launch platform, you have to use ground-launched Orions, the biggest and dirtiest kind.
#2 is likewise unlikely. It would require substantial technology to be able to produce goods in space, and they would have to be returned to Earth via a non-Orion means of propulsion (Orion cannot land). This would be a very long-term project, relying mostly on non-Orion technology anyway. Technology isn't really up to it by the 70s, at least not without a huge initial investment other than Orion. As an addendum, it's historically been found to be cheaper to develop newer, better manufacturing techniques on Earth than it would have been to simply move likely-looking processes into space.
#3 can be rejected out of hand. The entire point of Orion is to be a cheap heavy-lift vehicle without requiring very long term, ultra-intense research programs. Most of the money spent on any large-scale Orion program would be in capital investment, not research and development. In general, Orion's money would be spent taking known technologies and integrating them into a complex working whole, rather than by developing entirely knew technologies. The spinoff potential of such an approach is low.
#4 is possible but again, the problem is that while Orion would provide lift system and in-space propulsion, everything else would have to be developed (for example technology to mine an asteroid in space in the first place). There would be a substantial investment beyond Orion, and in the 70s it would be fairly unlikely that enough revenue could be produced to make a competitive profit from all the required investments. The essential problem is that if a space investment doesn't produce an average 10% annual return, then it isn't competitive with investment here on Earth. It would be quite difficult for something like space mining to provide that level of returns with the technology of the era.
Like it or not, even with a cheap ultra-heavy lift system, the space technology of the 70s is not really up to making enough profit in space to pay for Orions. Massive Orion launches are not something that could continue indefinitely, and the 70s is just not an ideal time to establish one's primary space infrastructure. The only real uses are military and exploratory. Militarily, Orion really isn't all that great, and as far as exploration goes... sure Orion could do much more than the major programs of the time (probably for at least the same cost, though), but it'd be cheaper still to wait a few decades and use robotic probes.
There are many alternatives to using Orion, and they get more and more attractive as time passes. Foremost among them of course is conventional rocketry. It's more expensive per unit of payload weight than a fully developed Orion program... but it's safe, clean, obvious, effective even for small individual payloads, and requires less in the way of technology to get started. It has many applications outside of heavy lift and fast interplanetary travel.
Around the time of Orion, there is NERVA. It's also safer, cleaner, and works in small sizes. It's ISP is far less than a large Orion, but nearly half that of more reasonably sized orbit-launched Orions. In any situation where Orion is attractive, NERVA will also be attractive and much easier to sell.
Further into the future (ie by the 90s) several other technologies present themselves. Ion engines are more efficient than all but the larger Orions and suffer none of their problems. They have low thrust, meaning that they cannot launch from the surface or make ultra-fast trips to other planets, but they are excellent for getting payloads through space cheaply. More advanced Nuclear Thermal propulsion systems (NERVA successors), such as Gas-core systems, promise Orion-like thrust levels. Developing them at this point would not likely be harder than developing an Orion, and again, they don't have to mass thousands of tons to work.
In the "radiation-spewing atomic rocket" category, there is the Nuclear Salt Water Rocket. It is a concept for a rocket whose fuel is a solution that undergoes fission. This system would be just as polluting as an Orion rocket, but it would also produce an ISP even higher than that of the Orion design. An ISP of 6700 for an initial low-efficiency design has been projected. Unlike Orion, the NSWR does not generate satellite-frying X-rays or require a ship massing thousands of tons.
Except for the ion drive, these systems are presently untested concepts that would require much development... but so would Orion. While Orion was the highest-performing option back in the 50s, by the present day that is not the case.
Further into the future, there are other concepts that are relevant to today's planners. A long-term project aiming at producing a high-efficiency craft in 20 years (a reasonable time period for any project started in the near future), has several attractive options. Magnetic sails, for example, could allow ships to sail across the solar system without requiring the inconvenience of fuel (the solar wind moves at over a hundred kilometers per second). Antimatter propulsion may soon be a reality (the US military for example has recently decided to fund a project), because small quantities of antimatter can be used to catalyze a fusion reaction. Proposals for this technology start with ISP figures of 10,000 at the low end, and range up to heights that Orion can only dream of. Antimatter catalyzed fusion is an efficient, in-space propulsion technology scalable from tiny probes to massive spacecraft, that is actually fairly safe and clean.
This essay has made the case that the US would not be very likely to build Orion. What, then, about some other country? First and foremost, historically Orion was a minor and classified US project and it is unlikely that anyone else knew or cared about it before it was declassified. The USSR does not seem to have had an Orion project of its own. Most of the same problems apply to other countries, of course. The necessary research and funding are even bigger obstacles, since nobody else had as much wealth as the US or as many scientists.