Laser arrays for propelling spaceships can also be used like nuclear cannon weapons

A powerful 70 gigawatt laser propulsion system that could accelerate an 100 kilogram object over 122 seconds to 2% of light speed (6000 kilometers per second) would also be able to fire kinetic projectiles at nuclear weapon power.

The goal of the Breakthrough Starshot program (which has $100 million in funding) is to send wafer chip spacecraft to 20% of lightspeed to probe exoplanets and other star systems. The initial $100 million would not reach that goal but a follow on program for a few tens of billions of dollar could achieve it.

A 100 kilogram object accelerated to 2% of light speed (6000 kilometers per second) would have a kinetic impact of 430 kilotons of TNT.

Battleship naval guns can fire metal projectiles with 5000Gs of acceleration (49000 meters per second per second).

It would take 367,347 kilometers of distance to accelerate at 5000Gs to reach 2% of light speed.

The moon is 384,400 km away from the Earth.

A large moon based laser array for accelerating spaceships and probes to Mars or on interstellar missions could be pointed at the earth and about every 2 minutes be able to fire a kinetic shot to medium sized nuclear bombs.

Initial space based laser arrays should therefore start with installations on the dark side of the moon to minimize geopolitical issues by being positioned to only launch away from earth. Any ship with its own propulsion and relativistic speed capability would have vast destructive potential.

Powerful manufacturing capability in space to print large solar arrays are also powerful. Every square kilometer of solar array would be receiving about 1 gigawatt of solar power. There would then be inefficiencies converting the solar power to laser power and then inefficiencies to kinetic acceleration.

Note: This is why science fiction and science fiction movies are highly inaccurate with their portrayal of weapons. Kinetic weapons for Star Wars and Star Trek would be far more powerful than what is usually shown.

29 thoughts on “Laser arrays for propelling spaceships can also be used like nuclear cannon weapons”

  1. One thing I would point out is that such kinetic energy “weapons” have a major problem, namely what are you going to shoot at? At 6000 km/s, a projectile exceeds not only Earth’s escape velocity (by a multiple of over 500) and solar escape velocity (by a multiple of over 100) but also *Galactic* escape velocity (by a multiple of more than 10), so you can shoot at (thus far non-existent) aliens or (thus far similarly non-existent) rebellious space colonies with this, but not anything on Earth so long as the launching system is based on Earth. OTOH, as a propulsion system this thing is intriguing, provided you have a way of slowing down at your destination, otherwise your payload is going on a loooong one-way trip out of the Galaxy.

    • You could also shoot at any asteroids or comets that are currently on an inconvenient trajectory. Such as one that intercepts the Earth’s orbit.

    • This is the fault of your English teacher who did not teach you the alternative meanings of the word “dark”, not the fault of the person using a perfectly cromulent term.

  2. Something is wrong with the math here. This thing would violate conservation of energy — the projectile somehow gets 2 orders of magnitude more energy than is spent on accelerating it.
    70 Gigawatts over 122 seconds is 8540 Gigajoules.
    1 kiloton of TNT equivalent is 4184 Gigajoules.
    Therefore unless projectile somehow gets energy from source other than the lasers it can’t have more than about 2 (two) kilotons of TNT equivalent. That is close to 2 orders of magnitude less than 430 kilotons.
    That is also not counting that instead of accelerating the entire projectile, without damaging it, the lasers would likely vaporize most of it. Only a small fraction of initial 100 kilograms would get to 2% c, if any.

  3. Putting it only on the dark side of the moon is still a problem. As the dark side of the moon is still “Visible” during half the month.

  4. Strangely enough I am the creator of this applied technology. I gave the schematics and project idea to a Brentwood NASA scientist who said “that’s a really good idea…”, got my name and said we’d name it the “Dilleydrive”. Call me Brentwood NASA scientist! I am awaiting the recognition I deserve for imparting this technology upon Mankind.
    Sincerely, Your blue eyed friend from afar.

  5. In the case of bombarding things at Earth-Moon distance, where the acceleration distance is comparable to the range to target, the projectile is redundant; Only a tiny fraction of the laser energy ends up as kinetic energy in the projectile, and you’re pointing the laser at the eventual target.

    The target gone by the time the projectile arrives.

    It would be interesting to analyze just how far away the target has to be, before the projectile delivers more energy than the accelerating laser.

    • This would probably use Bae’s photonic thruster approach, which bounces photons many times between the ship and the laser source to extract a lot more momentum from them.

      So the figure in Newtons per watt is probably quite higher.

      And no, such a thing doesn’t violate any physics nor conservation laws, being already being tested in the lab.

  6. At 2% the speed of light, nuclear reactions would occur between the projectile and whatever it hits. So it might be just the same as using a nuclear bomb.

    It might be a better idea to use a heavier/slower projectile — would deliver the same destructive energy but without the radiation.

    • Or… and it could just be the tequila talking here… or maybe, just shooting the target with a 6 GW laser array in the first place could also cause a bit of damage???

  7. On this, old style chemical rockets have a clear advage: that of having way less chance of being perceived as a threat.

    Interplanetary ships made of BFS modules and tankers with comparatively slow, deliberate trajectories for specific missions are way less scary than Death Star analogues.

    Thankfully, I’d say, because the thing private space settlement efforts need the less is yet another political motivation to nip them in the bud.

    • On the contrary. Telling your leader that you can build him a deathstar is a strong political motivation to get more funding.

      Only when it’s finished does he notice that it’s permanently pointed out to space.

    • All that you touch
      All that you see
      All that you taste
      All you feel.
      All that you love
      All that you hate
      All you distrust
      All you save.
      All that you give
      All that you deal
      All that you buy,
      beg, borrow or steal.
      All you create
      All you destroy
      All that you do
      All that you say.
      All that you eat
      And everyone you meet
      All that you slight
      And everyone you fight.
      All that is now
      All that is gone
      All that’s to come
      and everything under
      the sun is in tune
      but the sun
      is eclipsed by the moon.

      “There is no dark side
      of the moon really.
      Matter of fact
      it’s all dark.”

    • dark
      adjective: dark; comparative adjective: darker; superlative adjective: darkest
      with little or no light.


      hidden from knowledge; mysterious.

      (of a region) most remote, inaccessible, or uncivilized.
      “he lives somewhere in darkest Essex”

      Meaning 4 is the relevant one here. It has nothing to do with how much light is there.

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