3
$\begingroup$

What makes the most sense (real or theoretical) for energy sources to power large spaceships for thousands of years, not renewable

$\endgroup$
6
  • 2
    $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Dec 10, 2021 at 20:13
  • 1
    $\begingroup$ Welcome to worldbuilding! I would definitely recommend searching the site for answers that would suit your question before asking it - this question for example, has a lot of things that could work as answers to your question. $\endgroup$
    – jdunlop
    Dec 10, 2021 at 20:17
  • 1
    $\begingroup$ @jdunlop Thank you, I looked through the exchange but only saw things that were renewable, I did look through that question and the only thing applicable is Antimatter batteries, so I guess I'll go with that. $\endgroup$
    – i773
    Dec 10, 2021 at 20:29
  • 2
    $\begingroup$ RTGs, Fusion, and atomic batteries are all also non-renewable. $\endgroup$
    – jdunlop
    Dec 10, 2021 at 20:34
  • 1
    $\begingroup$ @i773 Nothing has more energy density than antimatter, but it's your answer to answer. quora.com/…. $\endgroup$
    – DWKraus
    Dec 10, 2021 at 22:06

4 Answers 4

3
$\begingroup$

Fusion is renewable if you are going fast enough.

The Bussard Ram Jet can collect interstellar hydrogen as you travel.

From here:

Bussard1 proposed a ramjet variant of a fusion rocket capable of reasonable interstellar travel, using enormous electromagnetic fields (ranging from kilometers to many thousands of kilometers in diameter) as a ram scoop to collect and compress hydrogen from the interstellar medium. High speeds force the reactive mass into a progressively constricted magnetic field, compressing it until thermonuclear fusion occurs. The magnetic field then directs the energy into rocket exhaust, providing thrust.

If you can get it up to a high enough speed, then it can use the scoop from the ramjet to feed the reactor.

However even regular fusion will work for a generation ship or other slow boat. The idea here is that the ship does not thrust once it has been aimed at a target star. So, it only needs store enough hydrogen to power its internal systems for a very long time. This is doable for a reasonably (unreasonably) large ship (1+ km diameter, 5+ km long).

$\endgroup$
4
  • 2
    $\begingroup$ hydrogen is just as renewable as oil. you can scoop up more of it only as long as it isn't exhausted. just because there's a lot of it, the supply isn't infinite. actually, it is less renewable, because more oil can, in principle, be created. $\endgroup$
    – ths
    Dec 10, 2021 at 22:47
  • 2
    $\begingroup$ @ths, the vast majority of our universe is hydrogen. Unless you have hundreds of ships taking exactly the same route, there will be enough hydrogen to get where ever you need to get to. Also, to make oil, you need hydrogen, carbon and a few other things. I think that you'll run out of oil before you run out of hydrogen. $\endgroup$
    – ShadoCat
    Dec 10, 2021 at 23:13
  • 1
    $\begingroup$ correct. it's still not renewable. $\endgroup$
    – ths
    Dec 10, 2021 at 23:25
  • 2
    $\begingroup$ The ram jet suffers from the problem that the friction from gathering the hydrogen is greater than the power that can be generated from it, so it doesn't work. $\endgroup$
    – Mary
    Dec 10, 2021 at 23:43
2
$\begingroup$

The rocket equation strongly suggests that you need to maximise the mass/energy density of your power plant which also means giving consideration to minimising it's volume to save on containment mass etc... For a long trip you also need a power system that can maintain steady output:

  • The most efficient technology currently in general use is nuclear fission but the power:mass ratio doesn't remain steady over time, nor does overall power output so not suitable.

  • Nuclear fusion is currently a near future technology with the potential to be as, or possibly more, efficient as fission. It's input can be increased or decreased on demand, to a point, and it can maintain a steady output as long as the fuel lasts.

  • Matter/antimatter annihilation is the last word in mass/energy efficiency in terms of fuel but we don't really have enough data to look at the efficiency of a large scale reactor. In theory such a reactor would be similar to a fusion device, controlled variable output with steady production as long as the fuel lasts. One of the major challenges of antimatter is that the fuel for a fusion reactor is inert, antimatter is anything but so any leak is actually a ship wrecking explosion.

  • In theory you could use a sub-stellar mass blackhole as an energy source, it is also nearly perfectly mass efficient but its output goes up, to quite alarming levels, as it runs out of fuel/mass. If you wanted to use this you'd need to overstock so the blackhole was still safely massive at the destination which means hauling a lot of extra mass.

  • What David Brin calls a cavitron; in David Brin's Earth he suggests that one can possibly (we don't have the math yet) build a device that gets hold of the fabric of space and twists, and that such a device could be used to create artificial gravitational singularities that produce energy over unity in the form of Hawking Radiation. A power plant using such a device is identical to using a micro-blackhole except you don't have to take the blackhole(s) with you for the trip, you can make one when you need it and jettison it when it gets too light and hot.

$\endgroup$
1
$\begingroup$

A matter of risk

To clarify, energy is not renewable, when..

  • you own a fixed stock of fuels, after using it up you can't replace it

  • you mine something that is rare, e.g. fossil fuels, or methane, lithium, uranium

  • your mining depends on traveling (=using energy), e.g. hydrogen, deuterium

  • replacing the energy harvester costs more energy than the total energy it yields

  • your energy is converted from energy that is not renewable

You want your spaceship to have energy for thousands of years. When you want to use non-renewable energy only, choose one of the above, or some combination you trust, but keep in mind you will always run a risk of being out of fuel.. at some point in time ! The science of modern logistics provides calculations,

https://abcsupplychain.com/safety-stock-formula-calculation/

..to cover some max acceptable risk, by keeping sufficient stock. In space, I'd keep some renewable backup power at hand... just in case !

$\endgroup$
2
  • 2
    $\begingroup$ I imagine the OP is after something that will cause a fuel shortage, hence the request that it be non-renewable. Presumably after thousands of years of operation, the spacecraft in their story will have a crisis. $\endgroup$
    – jdunlop
    Dec 11, 2021 at 1:40
  • $\begingroup$ There's a lot of dangers/risks on the VERY long term.. especially #4, repairing, or replacing the energy harvesting equipment. Batteries get worn out, what if you can't replace them ? It may be impossible to travel 1000 years. Knowledge will get lost. Energy mining that seemed to be renewable turns out to be finite, because no one alive remembers how it works. The crew of a space ship needs to be stand by.. or in hibernation, saving energy. $\endgroup$
    – Goodies
    Dec 11, 2021 at 2:22
-1
$\begingroup$

What about solar energy? There exist various theoretical means of exploiting the energy of a star. For example, I've read about solar sails which could be "hit" by massive mirrors funnelling a star's light towards the sail, propelling a vessel. With sufficient size or various mirror-like stations along the way, it could potentially provide acceleration for the trip.

$\endgroup$
1
  • 1
    $\begingroup$ Welcome to worldbuilding - the OP's major request was that the power source be non-renewable, though, so this is explicitly not what they're looking for. $\endgroup$
    – jdunlop
    Dec 10, 2021 at 23:48

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .