As far as i can see, if we are to have manned exploration of space (beyond the moon), our present chemical rockets won’t do. They are too expensive, too dangerous, and too slow. The idea of using nuclear bombs to propel a spaceship was c\developed in the 1960s, it was judged feasible at that time. of course, the idea of setting off nuclear bombs in the earth’s atmosphere is not popular. Suppose the ship was built in earth orbit? Would it then be safe to use?
Well, you could, although the idea of “seeding” the upper atmosphere with lots of highly radioactive dust isn’t much more appealing to me that setting it off in the atmosphere would be.
And putting the thing in orbit to begin with is overlooking one of the things that made the idea so attractive in the first place – it provides a way to lift all of your payload efficiently out of Earth’s gravity well in one big shot. With your craft in orbit, you still have to get your payload up into orbit using conventional rockets. Unless they get that Space Elevator (maybe that newfangled inflatable one) working in time.
Orion-type nuclear lifters figure in some science fiction. Larry Niven and Jerry Pournelle have one in Footfall. And your only-in-space version almost made it into the movies. Kubrick was considering showing the interplanetary craft Discovery (the one with HAL on board) being propelled by nuclear explosions in 2001, but wisely (in my mind) decided against it. It looks classier as it is. When Peter Hyams showed us the engines on the Discovery firing in 2010, they looked decided non nuclear-bomb-like.
In addition, there was concern that if you set off nukes anywhere in space within the Earth’s magnetosphere, the fallout would be channeled to the Earth’s magnetic poles, contaminating those areas.
You’d also run afoul of several treaties, setting bombs off in space. I don’t think those treaties distinguish between peaceful and violent uses.
Another problem is that if you build the Orion in orbit, and fuel it by building the bombs on Earth and lifting them into orbit via chemical rockets, if any of those chemical rockets suffer a catastrophic failure in the lower atmosphere, the radioactive payload of the bombs will be scattered around. Rocket launches are far from 100% reliable.
CalMeacham is right on. An Orion spacecraft has to be enormous and very heavy, to tolerate the stress from setting a nuke off near the pusher plate. This is very difficult and impractical to put into orbit without using nukes from the ground. If it took, for example, 1000 Saturn V launches to launch all of the components and assembly tools to build the pusher plate, you could build much lighter spacecraft using other designs and go to other planets directly instead with 1000 launches worth of stuff.
Another factor is the pusher plate has to be one homogenous piece to tolerate the stress of each nuke going off, yet it is too big to launch in one place. So you’d have to manufacture it in orbit…which means launching the machinery to do said manufacturing which is very very heavy.
So if you aren’t willing to launch from the ground and just eat the extra cancers and radioactive fallout plume, it’s not a good solution.
Another thing occurred to me – although Electrmagnetic Pulse phenomena from ground nuclear explosions results from interactions with atoms in the atmosphere, you can still get an EMP even with space detonations due to interactions with the Earth’s magnetic field. This isn’t theoretical – it’s been observed in early high-altitude nuclear blasts.
So even if you set off your propulsive nukes in space, you’ll be in trouble, generating EMPs that will affect both ground equipment and satellite systems.
This would make a nice aurora. If I recall correctly, the early communication satellite Telstar was disabled by a high-level test of this sort.
First let me proclaim my ignorance. Now, how would you overcome the G forces associated with the extremely quick acceleration.
To build an Orion it has to be massive…I mean REALLY massive. Like bigger than the biggest air craft carrier. With a huge pusher plate. So, you won’t get extremely quick acceleration or a large G load. It would be more like flying on a V-1 buzz bomb with it’s pulse jet.
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Another thing occurred to me – although Electrmagnetic Pulse phenomena from ground nuclear explosions results from interactions with atoms in the atmosphere, you can still get an EMP even with space detonations due to interactions with the Earth’s magnetic field. This isn’t theoretical – it’s been observed in early high-altitude nuclear blasts.
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Wouldn’t it be directional, since the blast is directional? Also, presumably you could shield the electronic equipment on the ship from the EMP…the military has been able to shield sensitive equipment for a while. The very think pusher plate could be threaded with copper or some other things to protect the electronics and crew. Probably a good idea not to launch the things from the Earth though, as noted. 
I don’t see any technical show stoppers to building an Orion…it’s probably our best option if we ever need something really big to go really fast into space, though I seriously doubt that anything that important will come up before we can build something better.
Not necessarily. The very smallest proposed design for an Orion-type spacecraft weighted in at a svelte 880 tons. That would have been more of a prototype/proof-of-concept test vehicle, but even the “base” design was still “only” 4,000 tons. (One thing, “nuclear explosion” doesn’t have to mean Tsar Bomba, or even Hiroshima–the very smallest-yield warheads had extremely low yields; 1o to 20 tons–not kilotons–TNT-equivalent. I mean, “small” for a nuclear warhead.)
Admittedly, Orion spaceships do scale up really fast; the biggest proposed designs had a diameter of 400 meters and weighed in at a whopping 8,000,000 tons–I dunno how tall it would be (or long, or whatever), but that’s definitely got me humming the “Imperial March” from Empire Strikes Back.
This. I recall Carl Sagan mentioning this regretfully in his book Cosmos. Can’t recall if it was brought up in the TV series.
Good point, though of course you’d scale down the yield if you scaled down the ship, so I think you still wouldn’t get massive acceleration (also, one of the points if making the things really really big is it provides more shielding for the crew, so not sure how well that would work scaling back too much). The point is to create a ship that is usable, not one that is going to turn the crew into paste.
As for EMP, this was extensively researched during the cold war, and a lot of the equipment from that era is EMP resistant. It’s a relatively simple thing to shield against :
- Faraday cage around the electronics
- There’s this wire mesh guarded “U-bend” where the antenna enter the box containing the electronics that somehow blocks most of the EMP.
- Some kind of fuse or shunt so that if the antenna experiences a large voltage transient, it won’t fry the electronics.
As you can imagine, anyone who can build killer robots could shield a robot’s control system using these and other methods. EMP probably won’t harm the killbots of the future.
Really, REALLY big shock absorbers: http://pre10.deviantart.net/f4a9/th/pre/i/2015/216/4/a/michael_by_william_black-d8eudqd.jpg
