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Okay, so while I'm fairly certain this is possible to do, I wanna know if it actually makes sense to do so. Imagine you have a fleet of ships, each of them so large it takes megatons of antimatter to get the fleet moving at anything resembling a decent speed. Even for antimatter, carrying that much fuel is gonna cause problems. If not in weight, then in the inherent dangers of storing enough volatile antimatter on your ship to cause a planetary extinction event. Anyone could tell you that despite the pressing need to get the ship moving, this is still a terrible fucking idea.

So here's the solution I came up with. Build another huge ship that's completely unmanned and is basically a giant antimatter-catalyzed fusion reactor strapped to the universe's largest RC car, situate it in the middle of the fleet a few AU from every other ship just to be safe, and have it use tightbean lasers to transmit power wirelessly across multiple AU to receivers on the hull of all the other megaships in the fleet. Or at the very least, build a ton of smaller generator ships that'd serve the same purpose as one huge one.

Does this make sense as a means of keeping the fleet going without risking having a bunch of exploding murder-fuel aboard your starship or is it less safe/efficient than just keeping your means of generating power confined to the ship?

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    $\begingroup$ How are the manned ships going to use the power? Unless you're using Handwavium-powered engines that can generate motion from electricity, those ships would still need propellant to accelerate. $\endgroup$ – Werrf Oct 26 '16 at 19:27
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    $\begingroup$ Perhaps all you really need is a tug boat. Connect the inhabited ships to the tug or tugs with a really long thick chain during periods of acceleration and when slowing down again. Disconnect the chain while at cruise speed and put some more distance between the fuel reservoir and the inhabited ships. Ship operations like life support could be powered separately with small nuclear power plants. A tug boat configuration would also allow the temperatures within the tug to be much hotter than they could be on a manned ship, saving $$ on cooling systems. $\endgroup$ – ohwilleke Oct 26 '16 at 19:58
  • $\begingroup$ You can transmit electricity through microwave... But yeah, propulsion is gonna be tough without reaction mass. You might have to look at using the "Impossible Reactionless Space Drive" as a way to do it using just electricity. $\endgroup$ – AndyD273 Oct 26 '16 at 20:00
  • $\begingroup$ @ohwilleke Just a nitpick... even in an automated power tug, you will most probably need a cooling system. Heat dissipation in space is very slow (only through radiation), so unless your use of the power tug is very sporadic it will quickly overheat too much even for an unmanned spaceship. $\endgroup$ – SJuan76 Oct 26 '16 at 22:04
  • $\begingroup$ I don't think there's an issue with propulsion. Yes, each ship will need mass to propel. However, there's no reason that mass has to be dangerous. They might have the space-faring equivalent of bags of sand, which is quite inert until accelerated by the engines (which use the energy provided by the reactor ship) $\endgroup$ – Cort Ammon Oct 26 '16 at 22:59
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Bad Idea

For sake of argument lets assume you have a way of transmitting a pure energy beam of power directly to friendly ships, and said pure energy could be converted to meet all of their energy needs. Congrats you have also made a very effective energy weapon (with a range of a few AUs). This also very dangerous since you are essentially shooting an energy weapon at your friendly ships but either the beams are hitting a special receiver that can handle the energy or your ships are outfitted such that the energy never can damage your ship.

There has to be an amazing degree of coordination between the ship sending the energy and the ships receiving it. At two AUs it takes light roughly 16.6 minutes to cover that gap. So unless you have FTL communication there is going to be a 16 minute delay between each communication back and forth. What this means is that if you want to change direction you have to tell the energy ship your expected course change, otherwise you will lose power, or worse the beam of energy will hit part of your ship not capable of handling the power.

This assumes all ideal conditions, I am a bad guy and I am out to cause mischief with your fleet. Those lovely beams of energy with a huge delay in communications provide me your adversary with several advantages:

  • If I were to jam all communications in the area, or your communications were simply slow, all your ships would no longer be able to make any quick course changes, and so I can use a wider range of weapons, like rail guns, which normally you could easily and quickly dodge.

  • Space is big [citation needed], and finding ships in space can be hard if they do not want to be found. Well if I spot your energy ship I can follow the beams of energy directly to where your fleet is trying to hide.

  • If I compromise your communications I can send false information to your energy ship and have it accidentally destroy every single ship in your fleet or stop sending energy to where your ships are at.

  • If you had gone the route where the energy beam had no way of damaging your ship, then I would be sure to outfit my ship with the same feature. I would then park my ship in between you and your power source. There is no reason why I cannot hijack your power supply, and use it to power my weapons.

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I think it makes more sense to keep your fusion reactors aboard each ship for a couple of reasons.

  1. Building any craft, the normal operational stresses tolerances and dangers present during operation are factored in to the design, so your ship builders would be unlikely to construct a ship which couldn't move itself. Rather they'd have to reach some compromise between ship size and stability/reliability of the propulsion system.

  2. Catastrophic failure of one huge power generation ship would possibly kill the whole fleet regardless of their distance from the blast as the rest of the fleet will now have no way to generate power and be dead ducks floating through space. Even if they remained on their current trajectory, they would have no way to speed up or slow down once they got to their destination.

So even if having your huge megaton reactor "is still a terrible fucking idea", if you're going to go with it then I think it's only prudent to have some kind of redundancy to allow for multiple failures on board individual ships while still keeping the fleet going wherever they're headed.

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In a way you have a bad concept for a good idea.

Beaming power to spaceships and starships is actually considered a good idea, since you leave the heavy power plant and even a lot of the fuel behind, making your ship far less massive and thus needing less energy to accelerate or decelerate.

Robert L Forward popularized this idea as far back as the 1970's, with designs like "Starwisp" and laser driven starships using monster lightsails illuminated with terawatt powered laser beams. Other variations of the idea have matter beams transferring momentum to the ship, or fuel pellets being sent in a stream towards the target, and the ship gathering these pellets in flight somewhat like an air to air refuelling mission. Other proposals exist as well.

In virtually all these cases, the driving power is held "at home" on the Moon, an asteroid or a collection of solar power plants orbiting Mercury, rather than a spaceship travelling with the fleet. This provides a means to provide power (usually though solar energy), periodic maintenance and the ability to upgrade the system. Free flying spacecraft in interstellar space lack all these requisites.

So large and small spacecraft can be propelled by beams of matter or energy, but preferentially the beam generator and all the equipment remains in the home solar system while the beam riders travel along the paths marked out by the beam.

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