# Is is possible to create a nuclear fusion reactor on a satellite and use it to produce heat

I am not a physicist but I would really like to know what trained physicists think about this problem that came up in conversation the other day.

I have been reading about the search for habitable planets for a little while and about the conditions it takes for a planet to be habitable. I understand that the right amount of heat is important for ideal conditions. Then I caught an interesting documentary on Oppenheimer, Heisenberg and the race for the atomic bomb in world war II. The documentary said something to the effect that a nuclear detonation or any nuclear reaction is very much like a small, very temporary star on earth. It got me thinking that nuclear reactors must also be analogous to mini-stars or suns so I started wondering what it would take to create a nuclear reactor that could make a planet (or moon) more habitable by allowing the heat produced to escape the reactor and warm the planet's surface.

As an example, once the technology exists for a nuclear fusion reactor, could it possible to assemble one outside our atmosphere, send it into orbit around, for example, Jupiter's icy moon Europa in order to heat the surface and create more habitable conditions for life?

• Besides the physical challenge of producing enough energy to be useful, you also have the engineering challenges of building a working fusion reactor (components of which must be kept cool to work properly) in space (where keeping things cool is very hard). – Asher Apr 16 '16 at 22:10
• Thanks Asher. I'll have to research this more but since the focus is projecting the heat toward the surface couldn't we just ventilate the heat in the direction of the surface to keep the reactor cool? – Aaron Pennington Apr 16 '16 at 22:36
• "ventilate" is something you do in an atmosphere. In space, your only option to transfer energy is by radiation, and if the outside of your reactor is hot enough for the radiation to significantly warm the moon's surface from orbit, you'll have to deal with some, ahem... material failure. – Asher Apr 17 '16 at 5:20

Not realistically. Ignoring other considerations, it's worth looking at how much power you would need to produce. The Sun produces about $1400$ watts per square metre at the top of the atmosphere: so let's assume we wanted to produce $1000$. Europa's radius is about $1.56\times 10^6$ metres, so we would need to generate $1000\times\pi\times (1.56\times 10^6)^2$ watts, if our system was completely efficient -- all its power output was directed at Europa. This is about $7.65\times 10^{15}$ watts, or a seven million gigawatts. That's not very practical.