

Project Orion (nuclear propulsion) - shaaaaawn
http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

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Symmetry
One interesting bit that was in George Dyson's book but not the Wikipedia
article (that I saw) was that for sustained thrust the idea is to keep the
pusher plate in resonance with the atomic bomb detonations. You use a half
sized bomb to get things going then detonate full sized bombs when the plate
is heading away from the main compartment.

The real problem with an Orion drive is launching the thing. Simple atomic
bombs don't generate that much fallout (relatively speaking) by themselves.
There wasn't any noticeable fallout in Japan after the explosions at Hiroshima
and Nagasaki. The big source of dangerous fallout is when neutrons from an
atomic explosion are captured by nearby materials and transmute them into
radioactive ones. For an explosion high up the surrounding hydrogen, oxygen,
carbon, and nitrogen don't turn into anything nasty. But if the explosion is
near the ground there are all sorts of horrible things that can easily be
produced.

If you wanted to launch an Orion into space with relatively little fallout you
would need to either have boosters that lift it a kilometer up before it
engages it's main drive or launch it a large area you've covered completely
with graphite (see again carbon-14 not being dangerous).

The reason that the bombs the US and USSR have stockpiled produce so much
fallout is their third stages. First you have a regular atomic bomb that sets
of a fusion explosion. But surrounding these is the bomb's shell made out of
the Uranium-238 that was left over after the process of separating out the
uranium-235. You can't create a chain reaction with U238 but it does fission
and produce a lot of energy (but no neutrons) when you hit it with a neutron
and about half the energy of a bomb can come from the case. You can easily
make the case out of lead instead and have a relatively clean nuclear bomb but
the military considered the fallout a feature rather than a bug.

In the end project Orion was a cool idea and not so crazy as you might think
at first. But I'd much rather people use conventional nuclear thermal rockets
where you use a normal reactor to heat a bunch of propellant. It doesn't offer
the same combination of power and efficiency as Orion but if you switch your
reactor to generate power and run a VASIMR then you can have at least one or
the other and you don't have to deal with _any_ fallout.

EDIT: Oh, there's also the problem of EMP as Orion passes through the
ionosphere. The bombs it uses are much smaller than an H bomb so they
_probably_ won't cause problems but nobody knows for sure.

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mrfusion
You could always construct it in orbit too? That might be the safest option?

~~~
Symmetry
Yes you certainly could. But once you're in orbit you don't really need high
thrust anymore, you might as well connect a normal nuclear reactor to an
electric drive of some sort. I suppose there are still other places in the
solar system you might want to land. Venus and hypothetical floating platforms
on Saturn, Uranus, or Neptune might make Orion worthwhile. Orion might also be
required to take off from the surface of Jupiter (which has much stronger
gravity than the other gas giants). But for other bodies the gravity is light
enough that I'd just use nuclear thermal and leave the pusher plate at home.
For most space travel the journey is going to take a long time so it doesn't
matter if you get up to cruising speed in 15 minutes with your Orion drive or
a week with your nuclear electric.

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Yizahi
I recommend to read this story by Charles Stross "A Tall Tail":
[http://www.tor.com/stories/2012/07/a-tall-
tail](http://www.tor.com/stories/2012/07/a-tall-tail)

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Freaky
Medusa seems like a better approach, since it doesn't require detonating as
close to the spacecraft and can forgo the big heavy pusher plate:
[http://www.centauri-dreams.org/?p=23754](http://www.centauri-
dreams.org/?p=23754)

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alcima
People forget that Kennedy's actual request was: First - "before this decade
is out, is landing a man on the moon and returning him safely to earth"

Second - "acceleate development of the Rover nuclear rocket"

Third - "accelerate the use of satellites for world wide communications"

Fourth - "a satellite system for world wide weather observation"

Too bad we only got 3 out of 4 and are still stuck with cans of flammable mud.

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Maakuth
See also Tintin's moon rocket's propulsion:
[https://en.wikipedia.org/wiki/Explorers_on_the_Moon#Rocket_e...](https://en.wikipedia.org/wiki/Explorers_on_the_Moon#Rocket_engine)
and [https://en.wikipedia.org/wiki/NERVA](https://en.wikipedia.org/wiki/NERVA)

~~~
Symmetry
People have come up with a lot of ways to use nuclear energy to power rockets.
Most are less crazy than Orion but one, the nuclear saltwater engine, even
more so. Here's a good source of info.
[http://www.projectrho.com/public_html/rocket/enginelist.php](http://www.projectrho.com/public_html/rocket/enginelist.php)

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4ad
George Dyson (son of Freeman Dyson) speaks about project Orion here:
[https://www.ted.com/talks/george_dyson_on_project_orion](https://www.ted.com/talks/george_dyson_on_project_orion)

