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Author Topic: Could we ever make a nuclear spaceship engine?  (Read 4524 times)

Offline acecharly

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Could we ever make a nuclear spaceship engine?
« on: 04/06/2013 18:48:39 »
Could we use the power from a nuclear weapon as an engine how small could it be made obviously a Hiroshima jobby wouldn't leave much behind so something smaller, how small could one be made before it would not work and how could it work? maybe use a strong magnetic field to push against the blast.

Cheers
Ace
« Last Edit: 10/06/2013 19:10:56 by chris »


 

Offline CliffordK

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Re: Could we ever make a nucear spaceship engine?
« Reply #1 on: 04/06/2013 23:05:21 »
Check out Project Orion

It was an idea of using nuclear bombs as a pulse propulsion for very large rockets, initially proposed in the late 40's to early 60's. 

The advantage is that the rockets or vessels can be very large.  However, today they would never be allowed to lift off from Earth using nuclear pulse propulsion, although potentially it could be used once in space.

=====

Several of the deep space probes use nuclear thermoelectric generators for powering onboard equipment because solar power is less efficient as one travels further from the sun.  This doesn't provide propulsion though.  I don't know of current work for direct nuclear propulsion.  Potentially one could use a nuclear fission plant, similar to the ones now being used for commercial power to generate energy for an ion plasma engine (probably most applicable for spaceships already in space).  Power could be very high, but it would eventually need to have the rods replaced, unlike the thermoelectric generators that can last for decades.
 

Offline evan_au

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Re: Could we ever make a nucear spaceship engine?
« Reply #2 on: 08/06/2013 02:36:29 »
Much of the energy from a nuclear explosion is in the form of electromagnetic radiation (including gamma rays, X-Rays, visible & infra-red) plus neutrons and general radioactive isotopes carried in the shockwave from the nuclear explosion.
  • Visible and infra-red can be shielded fairly efficiently.
  • Neutrons can be reflected by light isotopes like Lithium and Beryllium - but both are likely to be boiled away by the electromagnetic radiation
  • Absorbing enough neutrons to keep humans safe would require a fairly heavy barrier of high atomic mass (like lead) or low atomic mass (wax contains a lot of hydrogen which absorbs neutrons, and/or slows them down).
  • Gamma & X-Rays could probably be absorbed in the neutron shield.
  • The shockwave could be reduced by shock absorbers - or just being far enough away.
  • Unfortunately, most of the momentum is delivered by the shockwave, so further away=less speed.

You would not want to crew such a vehicle by people who were intending to become parents one day!

As for the minimum size of a nuclear weapon, that is a state secret, but there has been mention of nuclear weapons small enough to be carried by one person, and some small nuclear devices were developed for MIRV weapons during the cold war.

You would not want to use such a rocket anywhere near the earth, as the gamma rays would produce an EMP event on Earth.

A more gentle form of nuclear fission propulsion has been proposed, where a propellant is heated by passing it through a nuclear reactor. But the temperature of the reactor is limited, which limits how much force you can extract from the propellant. Generating electricity to power an ion drive makes much more efficient use of the propellant.

If and when we can master controlled hydrogen fusion on Earth, we may be able turn that into a practical space rocket - with some hope that the raw fuel (mostly hydrogen) could be collected in space.
 

Offline Pecos_Bill

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Re: Could we ever make a nucear spaceship engine?
« Reply #3 on: 08/06/2013 17:27:34 »
I believe the ion thruster used in some space exploration uses a nuclear device for power.

It having been found that AA batteries just don't cut the mustard -- even alkaline energizers.
 

Offline PatLogan

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Re: Could we ever make a nuclear spaceship engine?
« Reply #4 on: 21/06/2013 15:41:31 »
A few different classes of nuclear "rocket" have been considered over the years:

 - there's the "big and dramatic" - basically, "Orion" - a pulse system powered by exploding nuclear against a big, strong plate and using the reaction to accelerate the ship.  On the upside, it could generate lots and lots of thrust without much reaction mass needed - ground to orbit looks possible, or acceleration to measurable fractions of lightspeed.  On the downside, it involves lots of nuclear bombs, and it'll be a horrible environment in terms of vibration, etc.

 - there's the "small and subtle" - use something like a thermoelectric generator to power an ion rocket.  It doesn't produce much thrust but it makes amazingly effective use of reaction mass.

 Both of those have been touched on on the thread so far. 

What's been missed so far is the one that probably (IMHO) looks most feasible.  Compared to the first two, it's relatively conventional.  Basically, take a smallish graphite moderated nuclear reactor (of a type that uses ceramic fuel in solid elements, ideally integrated with the moderator), then pump liquid hydrogen in.  Out of the other end comes extremely hot hydrogen as a conventional rocket exhaust.

Several were built as experiments in the 1960s - google "NERVA" and "Slowpoke". The Soviets had an equivalent project called RD-0410.

You'd probably not want to use one in the atmosphere (although in reality, the exhaust isn't much activated), but it'd be a very effective "engine" for interplanetary flight.  It makes much more effective use of reaction mass than chemical rockets, and could conceivably used for burn of many hours, producing respectable thrust.  To give an idea of just how powerful even an early design was, it was mooted as a replacement third-stage engine for Saturn V.

There'd doubtless be some neurosis about getting the reactor to orbit in the first place, but the fuel (a concept called "TRISO") is inherently tough and all but impossible to damage through blast or temperature.
 

Offline evan_au

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Re: Could we ever make a nuclear spaceship engine?
« Reply #5 on: 24/06/2013 21:25:00 »
One of the challenges of nuclear fusion research is how to get rid of the nuclear "ash": Helium plasma at millions of degrees and high pressure=ideal reaction mass for a rocket.

In nuclear fusion, the hydrogen fuses to Helium - and then you need to remove the hot helium so you can inject more hydrogen fuel. You don't want the hot helium to touch the walls, so having a magnetic portal into space makes a natural rocket jet.

Magnetic-confinement fusion researchers are looking at making the toroidal (doughnut-shaped) plasma more stable by creating localised magnetic fields which can extract some of the hot ash.

See http://omegataupodcast.net/2009/12/22-nuclear-fusion-at-mpi-fur-plasmaphysik/
Media includes a podcast interview of 1.7 hours on status & directions of fusion research.
« Last Edit: 24/06/2013 22:14:53 by evan_au »
 

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Re: Could we ever make a nuclear spaceship engine?
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