Interesting Orbits Throughout the Solar System

[JoeStrout]

Classically, space settlement design studies have always focused on cislunar orbits — essentially the same orbits already available in High Frontier:

Here are some of the interesting features of each orbit:

• Low Earth Orbit (LEO): deep within the Earth's magnetosphere, and so requires very little shielding; and very quick access to Earth materials & tourists.
• High Earth Orbit (HEO): includes geosynchronous orbit; these are quite stable, useful for satellite maintenance, and possibly as a transportation hub.
• Earth-Moon L4/L5: these are the "classic" space settlement orbits, relatively easy to access from both Earth and Moon.
• Earth-Moon L1: always between the Earth and the Moon, a useful transportation node for things traveling between the two.
• Low Lunar Orbit (LLO): this is one of the few lunar orbits that are relatively stable; cheap materials from the Moon, and great for hosting lunar tourists, scientists, remote surface workers, etc.
  

But now we want to widen our view...

(from Sea and Sky's Solar System Tour)

Each of these worlds has its own local environment, including different moons, magnetosphere, sunlight, and location relative to everything else.

What do you think are some of the more interesting orbits for building space colonies here?

[Sailor Barsoom]

Habitats around Jupiter or Saturn have the advantages of having the rings and moons nearby.  They would also be useful for science or tourism involving the planets and their moons.

In terms of materials it's better than being in the Asteroid Belt because the asteroids are so spread out.  If orbiting Jupiter or Saturn the rings and moons are always (relatively) nearby.  Of course in the Belt you'd be near at least one asteroid, because why would you settle elsewhere, and one is likely to be enough for a while.

Sunlight is less in the Belt and around the gas planets, and in a probe that has to fit in a launch vehicle and be  launched from Earth that's a problem.  But a habitat can bring the sunlight up to Earthly levels (or more!) by building a big honking flimsy mirror which masses less than the habitat itself.  In fact that can be done even into the Kuiper Belt.

Disadvantages are the long communication times and even longer trip times to and from Earth, but perhaps by the time we're building anything out there that won't be so important.  Sort of like if I'm building something in Texas I'm more worried about how far away it is from Dallas and Houston instead of how far away it is from London and Paris.

[JoeStrout]

Those are all really good points.

I hadn't considered how having so much material in a relatively concentrated area makes a difference, but you're absolutely right, for an expanding civilization that's going to be really valuable.  Initially, as you say, habitats in the asteroid belt will always be built next to a good rock.  But maybe one rock doesn't have everything you need — which means trading with others, and that too is easier in something like the Jovian or Saturn system.

I'm not convinced that sunlight really matters all that much; once we start building nuclear reactors in space, solar panels are going to seem like the harder solution, I suspect (especially in the outer solar system).  I'm talking about ordinary fission reactors; but if fusion ever pans out, then that will be even more true.  But it is nice to know that solar energy is always there as an alternative.

And yeah, it's a long trip to the outer planets.  Eventually we'll have fast ships that can make the trip in a reasonable amount of time, but it's never going to be a weekend jaunt — more like a few months out of your life.  This will put a damper on things like tourism, at least while most of the population still lives on Earth.  Eventually, though, I can see some tourism happening between the Belt and the various outer planets.  Just think of the views around Jupiter or Saturn!  I'd certainly take a year off to go see that.

[JoeStrout]

One thing we haven't discussed yet is the radiation environment.  Jupiter is notorious for having one of the harshest radiation environments in the solar system, thanks to its strong magnetic field.

But those are all trapped particles, which have much lower energies (by several orders of magnitude) than cosmic rays.  They're not very hard to shield against.  In the long run, it's the constant rain of high-energy cosmic-ray particles that will slowly kill you.

So I suspect that, because of its great magnetic field, cosmic ray levels around Jupiter may actually be the lowest in the solar system.  I haven't yet been able to find any measurements to verify that, though.

If true, it means the habitats can get by with relatively little shielding — just enough to block the charged particles.  Radiation levels inside the colony could easily be lower than they are here on Earth.  Going outside (for maintenance or survey work or whatever) could be problematic, though.  We might need either teleoperated robots, or some sort of hard-shell suit with integrated shielding.  Maybe it would look something like this?

[Sailor Barsoom]

Yeah, the repair guys would end up looking like mecha from the anime of your choice.

[JoeStrout]

OK, let's go planet by planet!  Starting with Mercury.

Mercury is about 58 million km from the Sun (compared to Earth's 150 million km).  So, if my math is right, solar intensity should be 6.67 times higher.  (Oh, and I just found this handy table, which seems to agree.)  That's very good for powering things with solar power, if you're in a high enough Mercury orbit that you're not passing through the planet's shadow all the time.

It might also mean more difficulty staying cool, though.  But radiators, edge-on to the Sun, should work just as well there as anywhere else; they might just have to be bigger.

As a source of materials, Mercury looks pretty good.  Very rich in iron, with lots of silicates (silicon/oxygen/metal compounds) in its crust.

The sun side gets super hot, of course... over 400°C (or 800°F).  Mining operations could be challenging there.  But it rotates so slowly that one spot on the surface gets about 88 Earth days of sunlight, followed by that many days of darkness.  In the images below, the red dot identifies one point (and the little red line points straight up from the surface).  "Day 58" etc. counts Earth days since sunrise.

So, you could probably have just have two mining bases, and at sunrise, cover and abandon that one, and move everybody to the sunset one.  Work that through the night, and then switch back to the first.

Finally, the surface gravity is only 3.7 m/s^2, or 38% of Earth's (virtually identical to Mars, coincidentally).  So getting that stuff up to the colony would be reasonably cheap, though not as cheap as from a moon or asteroid of course.

So, what do you think?  Good place for space colonies?  What would drive folks to build here rather than somewhere else?

Incidentally, I'm no expert in this stuff; I have a web browser and Google, the same as anybody else.  So if I've missed anything or screwed up somewhere, somebody please say so!

[JoeP]

Mercury is a great place for materials and energy as you point out, but I think the planet's magnetic field is pretty weak. So like many other places you'll need great shielding unless you want to go down underground on the surface for your colony.

Perhaps with the huge solar energy resources, is generating a protective magnetic field around an orbiting colony feasible?

[JoeStrout]

(09-19-2015, 09:39 AM)JoeP Wrote: Mercury is a great place for materials and energy as you point out, but I think the planet's magnetic field is pretty weak.   So like many other places you'll need great shielding unless you want to go down underground on the surface for your colony.

Yes, a surface colony on Mercury would be really hard, I think, not just because of the radiation, but mainly because of the sun — heat rejection could be a real problem.  Radiators wouldn't work well there because anything edge-on to the sun would still be in view of the ground, which is reaching 800° all around you.

(09-19-2015, 09:39 AM)JoeP Wrote: Perhaps with the huge solar energy resources, is generating a protective magnetic field around an orbiting colony feasible?

That's an interesting idea! If it were going to work anywhere, that'd be the place. I know there has been some speculation about that, even back in the 70s, but I don't know that it's ever been studied in any detail. Might be possible.

The other thing is, I would expect that cosmic rays get weaker the closer you get to the Sun (because you're getting deeper within the Sun's magnetic field), and weaker further out. This is something we're going to have to include in the High Frontier simulation, but we haven't yet been able to find any hard numbers about it.

If anybody can find any numbers for cosmic radiation levels at different planets (or distances from the Sun), please let us know!

[William]

How about near-Earth asteroids? Material already there for making space habitats.

[JoeStrout]

(09-20-2015, 09:41 PM)William Wrote: How about near-Earth asteroids? Material already there for making space habitats.

Definitely! And good call, we'll be sure to include those!