Consider a near-future situation where humans have begun to explore the solar system, most groups are still working to start a profitable mining operation and only a few ships have gone beyond Jupiter. There is a space station orbiting the Moon, and in a few more years there will be a permanent base on its surface.


-> A satellite constellation in orbit near Venus that is used to collect solar energy.

-> A Fusion Reactor on the Moon.

Both of them are equipped to send energy in the form of microwave lasers to ships and installations around the system.

What of those two would be the better energy generation system?

  • $\begingroup$ you want to lock-on and focus high energy output of microwave at a distant target? that's sound awesome! $\endgroup$
    – user6760
    May 9 '18 at 1:22
  • $\begingroup$ Imagine accidentally travelling through the beam and all the water in your system just instantly boils killing you $\endgroup$
    – Shadowzee
    May 9 '18 at 1:42
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    $\begingroup$ This page about laser beam spread is probably relevant. The practical aspect of this is that in the near future we're not going to be able to transfer power in the way you describe as beam divergence would make this impractical. $\endgroup$
    – StephenG
    May 9 '18 at 5:15
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    $\begingroup$ @Sasha, is this meant to be hard-science or science-based? This question seems a little unclear. You should put in more constraints as to what is "better." $\endgroup$ May 9 '18 at 13:09

Neither of the above.

First, the microwave beams are going to have an incredibly difficult time hitting moving ships unless very detailed flight plans are filed ahead of time (and deviations for any reason are going to be life-or-death decisions).

Second, as planets orbit the sun, their relative location and distance from just about anything not in orbit will vary wildly. Even in orbit, things will have varying distances between them; eg., the Earth/Moon distance, which is pretty small, as these things go:

The actual distance varies over the course of the orbit of the Moon, from 356,500 km (221,500 mi) at the perigee to 406,700 km (252,700 mi) at apogee, resulting in a differential range of 50,200 km (31,200 mi). -- wikipedia

Third, space is vast, so things are going to be extremely far away from each other most of the time.

So, we have beams that are going to be trying to hit a moving target across vast and varying distances. Power per unit area drops off with distance; even with a highly-focused beam, there's going to be some spread, so there's going to be some loss of power per unit area. Then, there's all the "stuff" in space: little though there is, there's going to be dust and asteroids and ships and moons and such in between the beam station and the ship (especially if it's a mining ship), so the ship is going to lose power intermittently and without warning.

Not to mention the question of how many emitters you're going to need, which is going to be at least equal to the number of ships being powered by the system. Or the whole "single point of failure" this sets up for the entire space-based ecosystem. Or the questions of how instantaneous power needs are balanced against multi-second (or longer) communication lags.

It'll be better by far for ships to have their own power generation the vast majority of the time: solar cells, nuclear reactors, even batteries, depending on the assumptions you make about the march of technology.

All of that said, permanent and semi-permanent installations could well take advantage of a satellite network beaming power down/over, especially if said instillation needs to be in a planet/moon's shadow or under the surface or under intense cloud cover (so solar cells won't work). Or, if the installation's in orbit and can't rely on batteries to keep it going for the time it's in its host's shadow. Or, if the installation is just too small or distant to collect enough solar power by itself.

Local ships could also be powered by such a system: shuttles from the surface to orbit or maintenance bots, the ships that don't need to go far from home base. In that case, the better option would depend on the needs of the system, but a satellite constellation is going to give you a lot more redundancy, which is a good thing when you need a flow of power to keep from falling down the gravity well.

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    $\begingroup$ The idea would be for ships moving around the solar system to be a few giant ships that works basically as mobile colonies. They would receive the energy since they would operate near the asteroid belt. The ships themselves wouldn't be allowed to have fusion reactors in them because of legal reasons. $\endgroup$
    – Sasha
    May 10 '18 at 0:58
  • $\begingroup$ @Sasha What about Nuclear Generators? Solar? Recycling the massive amount of heat generated to maintain life support and other operations? It seems to me that a massive colony ship would have a wide variety of options for internal power generation. If anything, a mega-ship should be shooting out microwaves to power the other ships in its fleet. $\endgroup$
    – Kaosubaloo
    May 10 '18 at 19:18

Ships ought to have their own power source

Gathering power from the engines of the ship are a better bet than either of those options. It is entirely dependent upon engine type, a link to just about every engine type ever thought up with the basics of how they work is included here.


Now one thing pretty much any engine does in generate heat, so a sterling engine is a possible low-tech method to extract usable energy from the ships propulsion method. A sterling engine uses heat to cause a pressure differential between two parts of a cylinder which drives a piston. Pretty much any sort of waste heat can be used, and nuclear fission or fusion driven propulsion systems will be generating a very large amount of waste heat to use.

A molten sodium reactor could also be used, you can use the neutrons generated by a fusion engine to ignite a fission reaction in a secondary reactor which possesses a sub critical mass. This means that the regular nuclear reactor is only capable of operating when the fusion reaction is also running so you have a minimal risk of meltdown. Instead of clunky control rods and giant graphite and cobalt bricks you use the less volatile and more easily controlled fusion reaction to moderate your fission reactor. The molten sodium is used to turn a turbine before it is ejected in fine droplets from the craft to cool before being collected at the aft end of the ship by a collector vane. On the surface of a planetoid the molten sodium can simply be re-circulated through normal radiators after being allowed to cool off a bit.

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