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How practical would be a rocket that would use laser light as a reactive mass, given there is a very efficient electric energy source or storage?

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closed as off-topic by JBH, elemtilas, Agrajag, L.Dutch Apr 16 at 11:33

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  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – JBH, elemtilas, Agrajag, L.Dutch
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    $\begingroup$ Depends on what you mean with practical. It does work and it does not require reaction mass but the energy consumption is pretty insane so proposed designs have very low thrust, en.wikipedia.org/wiki/Photon_rocket $\endgroup$ – Ville Niemi Apr 15 at 23:44
  • $\begingroup$ @Ville Niemi does a photon rocket need the same starting mass as any other rocket? Would it be more practical to produce particle-antiparticle pairs out of nothing and accelerate them? $\endgroup$ – Anixx Apr 15 at 23:48
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    $\begingroup$ It appears you haven't done your homework. @VilleNiemi pointed to one article, here's another: en.wikipedia.org/wiki/Laser_propulsion and the parent article is this one: en.wikipedia.org/wiki/Beam-powered_propulsion. Our help center explains that a Q should be specific, answerable, include context, include restrictions/requirements, and should include research. You're missing most of that. VTC OT:NAW until you've done your homework and have a specific worldbuilding problem to ask about. Thanks. $\endgroup$ – JBH Apr 16 at 0:25
  • $\begingroup$ @JBH Thanks for the links, I linked first search hit before actually reading it, and then I kind of lacked the motivation to replace it with better ones. $\endgroup$ – Ville Niemi Apr 16 at 1:02
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Impractical.

The thrust you gain from using lasers in this way would be extremely low. By the way, light wouldn't be reactive mass since it is massless by definition.

How low? From a comment in the physics stack:

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. If lasers were very efficient at delivering power to a target through the atmosphere, the military would be using them as weapons, not just as missile guide markers, as they do now.

Also, if you are generating energy in space through solar panel, you are getting zero net thrust at worst, and double what you would get just from the lasers at best.

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  • $\begingroup$ I was not asking about earth-based lasers and my question implies an effective electricity source/storage, not solar panels. $\endgroup$ – Anixx Apr 16 at 6:02
  • $\begingroup$ @Anixx who mentioned anything about earth-based lasers? $\endgroup$ – Renan Apr 16 at 6:09
  • $\begingroup$ @Renan Your quote. Incidentally using lasers like that is actually more effective than using them from the spaceship itself because the photons get reflected. And you do not need to carry the massive power plant for the laser, indeed you can get plenty of energy from the laser for all your other needs as well. $\endgroup$ – Ville Niemi Apr 16 at 6:41
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    $\begingroup$ Comment in physicsstack quotes Beam-powered_propulsion, which is about using lasers to heat reactive mass. True photon rocket without any reactive mass is even less effective. It would take about 1 GW of power to generate 1 kgs of thrust. $\endgroup$ – Vashu Apr 16 at 6:56

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