Getting to Alpha Centauri

[PixyMisa]

Finally, although we think the Sun is a pretty standard star, since we've never visted any others we really can't be sure.

You mean, apart from centuries of observations using first optical, then radio, infrared, ultraviolet, x-ray and gamma ray telescopes, we really can't be sure?

In fact, we have a pretty good idea. Unfortunately, there's not a whole lot of good candidates close by. If you're looking for a stable solitary G or K-class star with planets, there's Epsilon Indi and maybe Tau Ceti. The rest are a bunch of binaries, variables, dwarfs, and other such undesirables.

Both Epsilon Indi and Tau Ceti are about 12 light years away, so the trip would be a good bit longer as well.

 

[Cuddles]

You mean, apart from centuries of observations using first optical, then radio, infrared, ultraviolet, x-ray and gamma ray telescopes, we really can't be sure?

In fact, we have a pretty good idea.

No, we really don't. We know it's spectrum is fairly standard, but that's it. Things related to activity, magnetic fields, sunspots, solar winds, CMEs, starquakes and so on, we really have not much idea at all about other stars. And it's those things that are relevant to this question. Astronauts really don't care about the exact proportion of elements in a star or where the peak of EM radiation is, they care about whether their going to get smacked by regular massive doses of radiation or if they can afford to ditch tons of shielding because the star isn't doing anything interesting. At the moment, we know very little about even the Sun, and even less about other stars.

 

[shadron]

That said, you've now got me thinking about something which might be more of a problem. Things are usually cooled by conduction and convection, with radiation being basically irrlevevant until you get really hot. However, in space there is no conduction of convection. Any heat produced onboard will stay onboard, and will only radiate away very slowly. I haven't done any calculations, but I suspect this would actually be quite a big problem. I know some sci-fi has covered this sort of thing, with spacecraft needing big heat sinks sticking out the side, but I don't know if even that would be sufficient. A few gigawatts is an awful lot of heat.

Radiation is, indeed, the only way to dump waste heat in space. When the shuttle gets on station in orbit, one of the first duties is to open the shuttle bay doors, because the insides of the doors are lined with radiators - the heat built up during the launch, running all the electronics, mechanical systems and fuel cells - has to be dumped before it cooks the internals. Satellites have gold foil (to reflect off sunlight) and black or gray surfaces for radiating heat away. Does anyone remember the gold foil umbrella that had to be rigged on SkyLab to cool it off?

Radiating heat into space is fairly easy; the side away from the sun is a perfect black coldness, which runs as far down as about 5 degrees above absolute zero, which makes it the ultimate thermal sink. On the other side, radiation is the only way anything can receive heat as well. There is no convection of conduction from outside sources. Managing a thermal balance is one of the many things that has to be done in designing a space probe.