Nuclear Powered Rocket?

Discussion in 'Architecture & Engineering' started by Sandstorm52, Sep 20, 2013.

  1. Sandstorm52 Registered Member

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    7
    Would it be possible to put a small nuclear reactor on a rocket that weighs, say 20,000 kg and propel the rocket with steam that gives off a thrust force of 30,000 kg? And given that F=ma, how fast would the rocket go after 10 seconds of flight, and it expelled 500 kg of water per second? I feel that water wold be a much more inexpensive fuel than is currently used.
     
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  3. Fraggle Rocker Staff Member

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    It's not the water that is the fuel. That's just the propellant. The nuclear fuel is what provides the energy for propulsion.

    And don't forget that on a long journey you want to keep the acceleration at or near a constant 1G. This is enough artificial gravity to keep the crew healthy, and it will get them to the nearest star in about 40 years--understanding that the second half of the voyage will be a constant 1G deceleration.

    So make sure that your calculations don't end up turning the crew into Spam.

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  5. billvon Valued Senior Member

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    The cost of fuel is a tiny tiny fraction of the overall cost of any rocket.

    Nuclear rockets are definitely practical - although for safety and design reasons they will likely only be viable as on-orbit propulsion.
     
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  7. Username Registered Senior Member

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    I, personally, would rather have nuclear fuel cells to power cars.
     
  8. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    It would cost a lot to get the water from earth, due to gravity.
    But if water can be got from the moon or better still asteroids, nuclear propulsion by heating water to steam would be a viable proposal.
    It could be used to run steam engines for mineral mining.

    This wiki article on asteroid mining might interest you.
    http://en.wikipedia.org/wiki/Asteroid_mining
     
  9. Janus58 Valued Senior Member

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    1,787
    This is basically the concept behind the NERVA rocket developed in the 1960's. However, they weren't designed to use water, but something like liquid Hydrogen instead. The logic behind this is as follows:

    A rocket's efficiency is linked to its exhaust speed. The higher the exhaust speed, the less reaction mass you need to get up to a given velocity. A water molecule is some 9 times more massive than a hydrogen molecule. This means that for the same energy, you would get 1/3 the exhaust velocity from water as you do Hydrogen. This means that a hydrogen NERVA rocket would end up going 3 times faster than a water one with the same reaction mass.

    Now the NERVA rockets tested got something in the order of 8350m/s for an exhaust speed. So let's say we use 10000m/s for our Hydrogen rocket, this means that a a Water rocket would have an exhaust speed of ~3333m/s. This is less than what our best chemical rockets can do.(~4500m/s)

    So let's see how this works out for a rocket trying to leave the Earth, starting in Low Earth orbit and rendezvousing with Mars using the least energy route. This requires a total delta V of ~8500m/s

    With a chemical rocket, this requires ~5.6 kg of fuel for every kg you deliver to Mars. With the nuclear Hydrogen rocket, this falls to ~1.3 kg. And using the Nuclear water rocket, we get ~12 kg. This is 2.3 time more than a chemical rocket would need and ~9 times that needed for the nuclear Hydrogen rocket.

    Also keep in mind that as the mass of the reaction mass goes up, so does the mass of the superstructure needed to hold it, so even a smaller percentage of mass arriving at Mars is useful payload.
     
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    For trip to the stars, at very near light speed so one ages slowing compared to earth, this would seem to be the way to go:

    but don't separate with magnetic field - let the +e & -e stream out from rocket together for needed charge neutrality. I'm too lazy to do it but bet the specific impulse is orders of magnitude greater than any other, even if on average the electron mass particles carry "only" 150Mev each on average.

    It would seem to be OK if once ejected they convert pair-wise back into 2x0.511Mev gama rays. Might even get a little "free" radiation pressure assist. Best if the rocket is a "space tug" pulling the manned ship a few miles behind it as those "photons" from the bremsstrahlung of 1GeV electrons stopping is nothing you want to be near.

    BTW, it would be a "nuclear powered" rocket, but as the energy source for the laser, not the exhaust directly. Of course you need some more convectional rocket stages to get out of the sun's gravity grasp.
     
  11. billvon Valued Senior Member

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    12,718
    Be a pretty big car, given the the smallest nuclear power source they've developed so far weighs tons and puts out 10 megawatts.
     
  12. Grumpy Curmudgeon of Lucidity Valued Senior Member

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    Sandstorm52

    Actually, air is better in atmosphere(you don't have to carry it), outside the atmosphere plasma is much more efficient in the long run.

    As to atomic powered, air breathing cruise missiles armed with MIRV hydrogen bombs...



    http://jalopnik.com/the-flying-crowbar-the-insane-doomsday-weapon-america-1435286216/@barrett

    Grumpy

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  13. kmguru Staff Member

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    We need to find a better system of propulsion...that moves us with respect to space...something like an electro-magnetic that works in space.....since the same process can work in water...
     
  14. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    You need to throw out mass m with velocity v such that mv = -MV, the opposite momentum given to the space craft (Momentum must be conserved). As space, unlike water, has no mass to eject, you will need to bring that m with you.

    Obviously you want to throw out the smallest m possible at very high v as all the mass thrown out was accelerated with the space craft's M prior to ejection.

    That is why throwing out an electron positron pair, created from energy,* each with ~150 MeV as seems possible (see post 7), can't be bettered, unless you can give them even more energy. (No net charge can be ejected for long as if it were more of same charge would be "re-captured" by the growing retarding voltage field.)

    * Don't fall for this verbal trick. That energy came for decreasing mass in the space craft.
     
  15. kmguru Staff Member

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    Then may be we could find some type of wrap drive to manage the space or use the nuclear to make serious lasers out in space? Getting that high V is a problem...unless it is Laser but a lot of it...

    Are there other transmission like neutrons or other particles that we can send at high velocity?
     
  16. Mathers2013 Banned Banned

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    A rocket goes from it's launch site to a target. 'A' to 'B'. Site 1 to site 2. 1/2.

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  17. Grumpy Curmudgeon of Lucidity Valued Senior Member

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    kmguru

    When you say "warp drive" you might as well say "magic spell". While it is a staple of Science Fiction it is actually pure fantasy and likely to remain so.

    Fusion power is the only viable power source for a real spacecraft, water provides both fuel and reaction mass(in plasma form, ejected very near lightspeed). The need for shielding calls for the spacecraft itself to be constructed from or embedded in large quantities of water(in ice form), the need for establishing a self sustaining environment requires large quantities of water. In total, any spacecraft going to another star will be a huge ball of ice that travels at less than a quarter lightspeed(top speed of a Bussard Ramjet is theoretically .99 tau, but that would take centuries to reach, in Earth time anyway). All interstellar trips will be very long, multi-generation one-way trips. Starships are actually lifeboats from a dying star system if they exist at all, nothing less would motivate dismantling your solar system for the resources necessary.

    Concentrate on using the free resources in our solar system, there's almost infinite living space.

    Grumpy

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  18. Mathers2013 Banned Banned

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    Wouldn't it be dangerous to put a nuclear warhead on a STEAM powered rocket? What if someone got burned?
     
  19. river Valued Senior Member

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    Old school thinking , so out of date

    Carry on
     

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