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Is making photon Engine possible ? :A different thought to power space craft

  1. Dec 22, 2012 #1
    Is making photon Engine possible ? :A different thought to power space craft!!!

    Now a days Scientists are working on photon engine. They are trying to power engine from light. Thought is looks great but there is practical engineering problems with it.
    Ya it is true that photons have momentum (But very small)...Because what is a photon, It is just an light energy particle. Which carry light energy. ok
    so if photon have momentum then what is the practical problem in making Photon engine.
    The problem is, photon have very very small momentum. So you need a gigantic lager system to propel a small engine and a big lager system is directed toward chemical reactions.
    so it is impossible to make a photon engine but this idea can be useful in different way...

    Think for a moment if we can reduce the mass of rocket then it is very easy and low cost method to go in space. 90% mass of rocket is just because of its fuel. Means a rocket needs power to lift his fuel also. We can eliminate this 90% fuel mass if we can supply energy from outer side to rocket. And the only solution is LASER beam.
    We need to establish a Laser system on earth to focus on space craft and space craft will be full of water. this water will be heated by laser and the water vapor will provide thrust to push the craft.

    this idea can reduce the cost as well as efficiency of space shuttles.
    thanks
    paramTV
     
  2. jcsd
  3. Dec 22, 2012 #2
    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    A laser would provide better directionality than a regular beam of light such as that from a flashlight beam sent through a series of lenses, but one would have to also consider the difference in desired momentum between the two systems versus the electronic payloads required for either system to make a qualified choice.

    The water would then be the fuel and the question to ask then would be "What % of the rocket mas iwould need to be water?"

    Perhaps your idea deserves some merit, especially when you mention fuel cost, though I am not so sure about the efficiency. Bear in mind, there is also a cost to operate the laser beam from the earth.
     
  4. Dec 22, 2012 #3
    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    Why operate the laser from Earth? It would be more efficient to do it from space - none of that nasty atmosphere to get in way (even with beam correction).
     
  5. Dec 22, 2012 #4
    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    There really is nothing to be gained by using water as reaction mass. You can take the same mass of oxygen and hydrogen and this will contain the energy needed to heat it and push it out of the back of the rocket. No need to bother with a laser.

    The efficiency of a rocket will depend on the speed on the exhaust gas, and this depends on the temperature wich can be as high as 3500kelvin. This temperature will be only reached inside the engine, and the walls of it will be cooled (by the fuel itself).
    A large tank of steam or any gas at this temperature isn't possible.

    If you would want to try this you'd have to aim the laser at the mouth of the rocket engine itself, and if you miss slightly you will start to melt the rocket. I think the exhaust plume will get in the way.

    To get at least theoretically better than a chemical rocket, you could use hydrogen as fuel, since lighter molecules will move faster at the same temperature, and hydrogen has the lightest molecules, so you get the highest possible exhaust speed.

    Another idea is to make the bottom of the rocket from some soled material that will evaporate. You could heat this to a much higher temperature with a laser. It will be hard to steer tough.
     
  6. Dec 22, 2012 #5
    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    thanks to share your views.
     
  7. Dec 22, 2012 #6
    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    Lighter particles have less momentum for the same velocity, providing less thrust. What you want is a fuel which results in the highest momentum of the propellant. Ion and Plasma engines have been considered by NASA for this reason, but those don't work in the atmosphere and would have to be launched the old fashioned way.


    The only "Photon Engines" I've ever heard of basically consist of a big reflector that bounces light back the way it came, gaining 2x the momentum of the "photon" in the elastic collision. I think at one point this was considered a viable method of thrusting space craft around in space, but not for taking off from earth. I'm not sure if its still popular though or ever was. This would not be able to overcome the gravity of earth.

    In terms of efficiency, you must remember that lasers are pretty inefficient by themselves, like 1%. It probably gets worse and worse as the power goes up.

    I am also reminded of something else I saw on one of those UFO TV shows... again it was a small object with a reflective tail end, but shaped in a way to focus all the light into a point close to the tail, or into like a ring close to the tail. The focused light causes the air to explode, propelling the thing forward. This could work in the atmosphere, but not in space. I guess this would get more thrust since the light is first reflected back, transferring the momentum of the light into the vessel, and then getting a little more from the puff of exploding air? Maybe it would work in vacuum too.. I didn't take it too seriously considering the source.

    Launching anything of significant mass into orbit requires a pretty ludicrous amount of energy. I'm holding out for the space elevator, but everyone says it'll never happen. Well they used to say flying would never happen too so who knows.

    Heating a tank of water to produce steam for thrust this is an idea 2000 years old, haha. Heating a tank of water vapor to thrust a space ship into orbit is not very plausible in my opinion.. sorry.
     
  8. Dec 22, 2012 #7

    sophiecentaur

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    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    Lasers are not very efficient. A ship based photon drive would not need the beam to be 'particularly' parallel - the loss of drive from a small spread would be negligible so why not use a more efficient light source?
    The big advantage of a photon drive is that you don't need to lose any propellant mass from the ship and you don't need to take any with you. I'm ignoring the mass of the energy source, of course but, if you were doing a star hopping journey, you could pick up energy on a near fly by of each star you visited. (Massive PV panels to accumulate the 'solar' energy over tiny fractions of the total journey time.) In fact, I'd assume that we'd need to wait for Fusion power for this to be worth while, actually.
     
  9. Dec 22, 2012 #8
    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    The only way to get energy from near by star is using PV panels. But We need hug amount of energy to propel space craft in space. SO we need big amount of panels. Means more mass and big system. It would be very hard for us to push out from earth gravitational field.
     
  10. Dec 22, 2012 #9
    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    but below one person is saying NASA is using ion and plasma fuel because of their heavy mass particle. because at the same speed massive particle produce more momentum. So it provide more thrust to propel the rocket.

    i am confused NASA is using light particle fuel or heavy particle fuel
     
  11. Dec 22, 2012 #10

    sophiecentaur

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    Re: Is making photon Engine possible ? :A different thought to power space craft!!!

    The choice between photon and ion drive will be based on detailed engineering choices, I imagine. Either way, you either need to carry all your energy with you oe harvest it on the way. PV would be one way of harvesting. I can't think of another solution that is available at the present stage of tech.
     
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