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Ideas for a power source of the future

This is quite a general question, so I suppose I should add some context; The ships that I have envisioned are pretty big. The flagship is about 1km long. They are very typical sci-fi, with large engines at the back, and one pointing in every direction on the nose to control speed and direction. My question is, what power source could these behemoths use to power engines, weapons and other necessary systems, and how large would it have to be?

I'm pretty open to most zany sci-fi ideas, but every time I write one down myself it seems stupid and hole-filled. It is also worth mentioning that the elements available in the written universe are the same as the ones as our own, but compounds can be created if you wish. Laws of physics however can be altered to fit any ideas, as it's set much further in the future where humanity has made many more scientific discoveries.

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    $\begingroup$ What is wrong with nuclear or thermonuclear power? $\endgroup$ – MolbOrg May 30 '17 at 17:40
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    $\begingroup$ It's generally a good idea to wait at least a day before accepting an answer to encourage people from every time zone to have a chance to answer. $\endgroup$ – sphennings May 30 '17 at 19:51
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    $\begingroup$ Make it super-retro and have them burn coal. Or, better yet, peat bricks. $\endgroup$ – user535733 May 30 '17 at 21:14
  • $\begingroup$ that depends; Did you like Star Trek vs (new) Battlestar Galactica? In Trek they explained everything which is boring. In BG, it works, use it, cut to the action. $\endgroup$ – dcy665 Jun 3 '17 at 23:00
  • $\begingroup$ How much energy are need the ship to work? I mean, 180 MW (little nuclear reactor) are not the same as 5 GW (one of the biggest nuclear reactor made by man). $\endgroup$ – Ender Look Jun 4 '17 at 1:45
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Nuclear power

Modern battleships as well as submarines carry nuclear reactors for power. This gives you a good idea of the size of them. When you can build a starship that size you're likely to have better ones too. So either smaller or more powerful.

So also don't need a single reactor for everything. It makes much more sense to split the load on your ship over several with the option to rerout power. They could also power things like railguns and lasers.

No matter

Now if you want to move beyond (thermo)nuclear power you can look at antimatter reactors. Their principal isn't that different from a nuclear reactor. You create a reaction and then harvest the energy of the 'explosion'. For antimatter reactors this is done by combining matter with antimatter.

More mundane would be nuclear fusion. We're not there yet but it's been one of those "In a decade" for the last few decades. This would create a self sustaining reaction much like a star. It would create almost limitless power, it's output would rely on size, bigger is more power.

Fusion reactors would probably be similar in size to a regular nuclear reactor. From the size of a fridge up to a small house. Again you can go for many smaller ones if you prefer.

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  • $\begingroup$ And why in the hell don't so many authors understand that smaller distributed power solutions might well be cheaper and more easily protected. Nope, power is offline and nothing works. $\endgroup$ – dcy665 Jun 3 '17 at 23:02
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    $\begingroup$ Because it creates high stakes and most writers have no background in military strategy :P $\endgroup$ – Mormacil Jun 4 '17 at 9:37
  • $\begingroup$ Minor nitpick: There are no battleships currently in service, and none of the ones that were built ever had nuclear reactors. Aircraft carriers and submarines are the vessels that may be nuclear-powered today. $\endgroup$ – Brian Mar 2 '18 at 17:40
  • $\begingroup$ I guess battleships was the wrong word, non native speaker here but the US has nuclear cruisers for sure. $\endgroup$ – Mormacil Mar 3 '18 at 19:00
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Depends on how handwavy you want to get.

Nuclear fusion is probably your best bet. It uses abundant elements, is generally considered to be clean, and if you're willing to handwave in 'cold' fusion then you can ameliorate some technical issues (like having to vent the heat of a miniature sun from a really well insulated tube).

Other than that, antimatter mining abd annihilation might be a good choice, but would require a reasonably abundant source of antimatter nearby, and you'd need to be ridiculously well prepared for mining it.

If you're willing to go the full 'magic handwave' you could posit that some of the laws of conservation are breakable under certain conditions (as determined by Future Science) and skip the antimatter annihilation step to jump straight from matter to energy. Or throw around some terms like 'zero point energy' or 'harnessed singularity', keep the technical details very light, and accept that if you're discussing power systems for hypothetical kilometre long space battleships the science probably isn't going to be too hard.

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  • $\begingroup$ Well. you could use solar power to make antimatter at 'fueling stations'. A few million square kilometers of solar panels could feed a pretty decent antimatter production rate. $\endgroup$ – Andrew Dodds Jun 5 '17 at 11:35
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Before star I want to note this:

  • 1 PW = 1,000 TW, 1 TW = 1,000 GW, 1 GW = 1,000 MW, 1 MW = 1,000 KW
  • This can also be used with PJ, TJ, GJ, MJ and KJ.
  • Also note that to convert Kelvin to Celsius you have to substract or sum 273.5.
  • m^3 or m3 and m^2 or m2 are the same.

Solar Panels

Solar panels could be very useful like a renewable source of power. It's a pity that solar power always have to be a secondary source power and you must to have batteries to store emergency power.
Comercial solar panels have efficiencies of 20% - 25%, investigation solar panel have 40% - 50%, and new theorical panels have reached 58%. You said that we can make our own physical laws so I think it won't be a problem have a 95% efficiency solar panel.
For expample:

  • If the ship is in Earth orbit it would produce an amount of 1,296.75 Wh/m^2 aproximately, knowing that you have 1 km^2 of surface >>> 1,29675 GW/h. In Mercury's orbit (closer to the sun) it would produce 8.66 GW/h.

Nuclear Power

Nuclear reactors could be a perfect soltion, they doesn't need light, they only need a little amount of uranium-235 to work, remember that uranium have 83.14 TJ/kg equal to 23.0944 GWh/Kg, 19 times the energy generated by one hour in the Earth's orbit with solar panels, in a setting were nuclear reactor have been mastered you could have an almost 100% efficiency and even use low enriched uranium, plutonium, etc. Also you could use remaints of fuel to make weapons...
Also, if you don't want to spend water in the nuclear reactor (remember that nuclear reactors heat water used to produce energy in a turbine) you can have a dozen of littles radioisotope thermoelectric generators (their use pellets of 238PuO2).

Fusion Power

Who want fission power with uranium when you can simply fuse a drop of water!
Maybe your are not familiarized with the term so I will quote this:

Fusion reactions occur when two or more atomic nuclei come close enough for long enough that the strong nuclear force pulling them together exceeds the electrostatic force pushing them apart, fusing them into heavier nuclei. For nuclei lighter than iron-56, the reaction is exothermic, releasing energy. For nuclei heavier than iron-56, the reaction is endothermic, requiring an external source of energy. Hence, nuclei smaller than iron-56 are more likely to fuse while those heavier than iron-56 are more likely to break apart.

In this page there are a lot of different fusion reactor if you want to use them.
Fusion can be made with a lot of materials, water (H2), deuterium, tritium, helium, litium, etc. For example a large power station generating 1,500 megawatts of electricity would consume approximately 600g of tritium and 400g of deuterium each day.

  • Fussing 1 kg of helium-4 (Alpha particules) could produce 16 TWh. See triple-alpha-process.
  • Fussing 1 kg of deuterium could produce an amount of 2 PWh. See proton-proton chain
  • Fussing 1 kg of deuterium and helium-3 could produce 362 PWh.

Solar Fusion Power

I have marked this in cursive because it's a compound energy generation system. This idea come from the Destiny, Do you know what I am talking about? If not put in your browser: Stargate Universe: Destiny Recharge Power.

The idea of this system is to collect solar energy with a new way. This system is only suitable by armored or shielded ships (for the high temperature). The idea is come closer the ship to the Sun's Photosphere and steal a little part of Sun's gas.

The photosphere is compound of 74.9% Hydrogen and 23.8% Helium at 4,500 K and 6,000 K with a density of 2×10^−4 kg/m^3 (0,2 g/m^3), so each cubic metre of photosphere have 13,35 GWh only in Hydrogen.

If you use the material of a star to produce energy you can make a stellar nucleosynthesis like the CNO Sun cycle witch produce 177 TWh per kilograme of hydrogen (CNO means Carbon - Nitrogene - Oxigen but their are catalyst, hydrogen is the fuel). There are a lot of more reactions.

Bussard Ramjet

Basically is a ship who produce a very big magnetic field to capture hydrogen atoms of the space and produce nuclear fusion. Because there is only a little of hydrogen per m^3 of space this ship must to travel at a minimal speed of 1% ligh speed (I would put the link of this but I found this information 1 or 2 years ago). Maybe you could be interested in this answer.

Antimatter Reactor

Did you know that 1g of antimatter produce 180 PJ equivalent to 50 TWh when it touch 1g of matter?.
Well, It speak by itself. I don't know how to get an important amount of antimatter (neutron stars produce some thousand possitron per second) but for a sci-fi setting you could say that black hole produce antimatter.

Others

Well, am tired of write so I will only write their names and a link. Their are taken of Stargate

EDIT

I found this useful answer, basically you could have a room filled with radioactive diamonds. (How to make them).

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I see 3 possibilities. Antimatter and Nuclear fusion have already been mentioned. Fusion seems the most likely as hydrogen accounts for the bulk of known matter, and occasional restocking of a lithium supply would allow breeding deuterium (heavy hydrogen) for higher energy output. A third possibility would require some serious advances in pure and applied science. Freeman Dyson wrote a paper that proposed harnessing the entire energy output of a star by enclosing it inside a sphere. Assume that a Dyson sphere has been built and that ERP or wormholes can be artificially made and moved, then a Dreadnought warship of a very large size could be built that is propelled by the light output of a star being channneled through a wormhole to strike a reflecting plate in the rear of the ship. Max velocity would probably be about .25C after long accelerations. The same mechanism would account for some serious beam weapon capability of the ship.

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