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Model Lightcraft under laser power

While sadly the funding for this research has not been forthcoming, there have been proof of principle flights and open air flights, so this does work. (more about this here)

https://worldbuilding.stackexchange.com/a/103431/27786

Using the same method, could lasers or protons be beamed from a space stations or ground be used to detonate nuclear gas/dust/fuel injected from ports into the thrust chamber. Similar to a piston engine the chamber would fill and then detonated but many times a second?

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    $\begingroup$ You've got a thing for tiny nuclear explosions. What is a "proton beam"? (Hint: all protons are positively charged, and like charges repel.) What is "nuclear gas/dust/fuel"? $\endgroup$ – AlexP Jan 30 '18 at 0:15
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    $\begingroup$ sadly the funding for this research has not been forthcoming Thank you for restoring my faith in grant committees (a little). :-) $\endgroup$ – StephenG Jan 30 '18 at 6:39
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    $\begingroup$ Nuclear "stuff" doesn't just explode - it isn't inherently explosive.You can't just burn the stuff and expect it to go boom, unfortunately. Nuclear explosions happen either because the specific Fission or Fusion process releases vast amounts of energy. Fission basically means that the atoms change into smaller atoms whilst fusion means the atoms fuse into bigger atoms - both processes releasing large amounts of energy. $\endgroup$ – Miller86 Jan 30 '18 at 12:30
  • $\begingroup$ To expand, For nuclear fission weapons you usually have two pieces of nuclear material being smashed together at high speed, whereas for fission power generation its two pieces of nuclear material being held close together to heat water, which is then used in a steam turbine. I'm not sure of the physics behind fusion but I believe weapons basically have extra knobs and whistles to create the fusion reaction, whilst nuclear power generation via fusion is still in its early stages and currently requires far more power to generate the reaction than it creates. $\endgroup$ – Miller86 Jan 30 '18 at 12:34
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    $\begingroup$ This is not a worldbuilding question, it's a physics question better asked as Physics.SE. And, for the record, Mr. Myrabo's idea is fascinating from the perspective of pushing somthing through an atmosphere in a straight line. It works because you don't need to haul the fuel with you. Anything's better once you're required to make space for the fuel. $\endgroup$ – JBH Jan 31 '18 at 4:10
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Why bother?

If you're going to take fuel into space (the fuel being literally 80% of a space craft's weight or more) what's the point of leaving the ignition source on the ground? Combustible fuel burns Just Fine without a laser, ignition is cheap. The same goes for nukes.

Lasers work for an air-based craft because the laser (i.e. the power source) remains on the ground and turns the ambient air (free!) into plasma, which provides thrust.

In space, there is no air. Because there is no air, you get nothing for free.

The only way you can use a ground-based laser to propel a ship through space is if the ship weighs virtually nothing and has a very large light sail. Photons DO carry a very small amount of thrust capability to them, but you need trillions upon trillions of them to get an appreciable thrust.

It's called a photonic laser thruster and it works by bouncing light between two mirrors. You can get a whopping 3.5 millinewtons with a 500 W laser. You need 5,000,000,000 newtons (roughly) to achieve escape velocity from Earth. That's 1,000,000,000,000 (one trillion) times as much power input needed which is on the scale of the most powerful laser ever built (and its still only half as much power as we'd need).

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  • $\begingroup$ It would save weight. Constant mini nuclear explosions to produce thrust without the need of oxygen. More bang per buck. +1 $\endgroup$ – Muze the good Troll. Jan 30 '18 at 2:30
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    $\begingroup$ @Muze It would save like, a dozen kilograms of weight, on a hundred thousand dry weight craft. Its literally a drop. $\endgroup$ – Draco18s Jan 30 '18 at 3:10
  • $\begingroup$ Think bigger like the bottom of a ship..Much of the power would be provided remotely saving more on board power.. What else would be comparable in bang per once? $\endgroup$ – Muze the good Troll. Jan 30 '18 at 5:53
  • $\begingroup$ @Muze Providing power from the ground does not work in space like this. you want a laser to propel your ship, you need a light sail $\endgroup$ – Draco18s Jan 30 '18 at 6:10
  • $\begingroup$ @Muze, I strongly suggest you read up on Project Orion if you're interested in the use of nuclear reactions for explosive propulsion. $\endgroup$ – Catgut Jan 30 '18 at 15:17

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