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To me at least, beam-powered propulsion seems like a great idea. High specific impulse, non-negligible thrust, and no heavy nuclear reactors on board. It's even been successfully tested by Escape Dynamics and Freeman Dyson is a proponent. Why has no launch vehicle used this technology? Why does there seem to be not much research or development in this area? What are its limitations?

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    $\begingroup$ How much propulsion can be delivered relative to the mass of the vehicle? $\endgroup$ Sep 13, 2018 at 0:03
  • $\begingroup$ @DonBranson I don't know myself -- that's largely the sort of thing I'm asking the question to find out -- "What are its limitations?" I guess that if the microwave / laser emitter was not providing very much power then you could simply use more microwave emitters, so the thrust producible should be limited by the rocket itself, right? If the microwave / laser emitters are capable of heating a surface on the rocket to several thousand degrees, and if the energy of the material can be passed on to the energy of the propellant, then you could get significant thrust from that, no? $\endgroup$ Sep 13, 2018 at 0:08
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    $\begingroup$ It is very difficult to produce a beam with gigantic power. Overall efficiency would be very small. Due to the rotation of Earth, one beam station could be used for a very short time interval, a lot of stations is needed. To place them around the equator, a lot of stations has to be placed within the oceans. $\endgroup$
    – Uwe
    Sep 13, 2018 at 9:04
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    $\begingroup$ For the same reason that we don't have Mr. Fusion yet, which according to this documentary film, we should have had three years ago. $\endgroup$ Sep 13, 2018 at 12:48
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    $\begingroup$ @uhoh I imagine you are thinking of space.stackexchange.com/a/13443/4660 $\endgroup$
    – kim holder
    Sep 13, 2018 at 13:18

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From the Wikipedia article:

The rule of thumb that is usually quoted is that it takes a megawatt of power beamed to a vehicle per kg of payload while it is being accelerated to permit it to reach low earth orbit

Laser efficiency is on the order of 25%. Then there are atmospheric losses, at low altitudes this can be as much as 30% to an altitude of 6 km and distance of 40 km. The most powerful continuous laser available has an output on the order of 1 MW.

So you'd need ~10,000 of the world's most powerful lasers to launch a 1-ton payload into orbit.

At low altitudes, you can use the lasers to heat the atmosphere, but above ~30 km, you need to start supplying propellant, which reduces your payload.

While this idea has some potential, the initial investment is massive. I think that's why beamed propulsion is not used yet.

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