# What is the best way to exploit the energy from a red dwarf and send it to other systems?

Scenario:

• Earth men colonized Alpha Centauri.
• Barnard's Star is at range.
• There is a huge fleet of fission bomb pulse propulsion cargo ships. Given Enough time and space they can reach 0.8C.

Question:

Barnard's Star has no planets to colonize. Would it be possible to use it to collect energy? If so, how? How could they send energy back to Earth? What about to Alpha Centauri?

• Yes I think it's possible to do by using a Dyson sphere and about beaming energy worldbuilding.stackexchange.com/questions/3372/… – Vincent Mar 14 '15 at 0:33
• Barnard's Star is a red dwarf, not a brown dwarf. They two are very different. – HDE 226868 Mar 14 '15 at 0:50
• Alpha centauri is a triple star system, why not just build a dyson sphere around Proxima Centauri? It's only 0.23 ly from the other two stars in Alpha centauri. – Samuel Mar 14 '15 at 0:53
• assume that there are plans to do so in proxima centauri and wise 1049-5319 and wise 0855-0714 – Jorge Aldo Mar 14 '15 at 0:58
• Why do they need the energy? What are they using it for? I am asking because for using interstellar power transmission to make sense you would have a very big need. And that need would have a big impact on pretty much everything they do, including, especially including, how they go about generating and transmitting power. – Ville Niemi Mar 14 '15 at 13:45

## Build a Matrioshka Sphere

The standard setup for stellar energy capture is currently accepted to be a Matrioshka Sphere, a set of concentric Dyson spheres where each recycles the energy output of the immediately preceding layer. Now the problem would be if you want to do something useful with the energy elsewhere.

Now, my caveat is that transferring energy or mass around is a poor use of reaction mass/energy. Our galaxy has plenty of energy and mass lying around all over the place, so schlepping atoms across interstellar gaps is a remarkably cost-ineffective maneuver. More likely, once you properly 'Matrioshkate' a star, you simply send the computing substrate running locally on that energy a particularly difficult sub-problem you need to solve as part of your larger optimizing goal, and only transfer back the sets of solutions and additional problems.

Regardless, let's assume that for some reason you really, really, really need more energy than a single M, K or even G-type star is able to provide. The logical thing to do would be to go capture a bigger star, or build yourself a few Hawking-radiation-blasting micro black holes. Let's assume that's out of the cards for some reason. What are you to do?

## Beam Energy

Laser light can carry surprisingly large amounts of energy, but will tend to lose coherence and diffract over interstellar distances, so you'd need massive refocusing arrays sprinkled along the way, somehow coordinating their positions to maintain a direct link between source star and the ultimate destination.

$$RT = 0.61 \times D \times L / RL$$

where:

RT = beam radius at target (m)
D = distance from laser emitter to target (m)
L = wavelength of laser beam (m, see table below)
RL = radius of laser lens or reflector (m)

A properly focused X-Ray laser can maintain decent focus over distances in the range of a solar system, so you'd still need plenty of refocusing stations.

## High density energy storage, with cargo ships to schlep it around

The highest density energy storage in the works (aside from micro-black holes, which would render going all the way to red dwarf star pointless) is currently reckoned to be antimatter. Of course there are (currently unsolved) issues of efficient generation and confinement, but a civ capable of interstellar travel can probably confine a few megatons of antimatter on a freighter. If your ships are properly built (i.e. without a human crew) you can achieve 1000g accelerations and get to your destination in short ship-subjective time.

Unfortunately, unless your propulsion methods are entirely unconventional by our current physics, you'll likely be using orders of magnitude more energy to get your cargo of antimatter from point A to point B than you're actually transporting in your cargo-hold.

Still, if you're trucking in the goods from a sufficiently large number of nearby stars, you might be able to achieve another sun or two worth of energy output ($$10^{26}J$$ each second).

• Example in point, plugging an electric car into an electrical outlet powered by coal-fired, steam-driven-turbine power plants to drive to work everyday (unless you have to drive more than a half hour on the highway of course). No problem. – Starrdaark Jul 14 '17 at 17:28

Here's an unconventional idea (which however assumes you are able to build large space constructs): Put a gigantic parabolic mirror around Barnard's star which concentrates the energy in a focal point near earth (or wherever else you need the energy), where you put a receiving station (which may simply be an object that gets heated up as "secondary star").

Now you may ask, how do we keep the parabolic mirror stay in place? This has two points: Hindering it from floating away or falling down to Barnard's star, and hindering it from changing its direction.

To address the second point, you simply make it rotate around the paraboloid axis; angular momentum conservation will then make sure that the direction of the mirror doesn't change.

Now to the harder part: Keeping the mirror in place. Let's start with making a massive ring around Barnard's star, with the same axis as the parabolic mirror, and attached to it. That ring should contain the majority of the mass of the construct (which means making the actual mirror as light as possible; given its size, you'd want to do that anyway to save cost/material). That will certainly take care of one dimension (because the ring will be attracted to the star, it will always be moved back so that the star lies in the "ring surface").

I'm not sure whether the gravitation/centrifugal force acting on that ring also would take care about the perpendicular direction; indeed I don't think so. But given the symmetry, in the perfect position there's no force perpendicular to the axis, so even if the forces when drifting away go in the wrong direction, they should be small, so corrective forces need only be small either. Maybe one could use the stellar wind to ensure the parabolic axis to always be aligned with the star (it has the right properties: it goes outward and is the stronger the closer you are to the star).