Terraforming Mars

2008/5/24 bonello_joseph :
> In adition to abundant minerals and ores, Mars has vast suplies of
> what we need most-water.

I don't like this idea, but it would work. Mars also has a deep,
fairly awkward gravity well.

I'm thinking that going out to the asteroid belt, beyond the snow line
is probably a better idea. You could pick up water there, and separate
it using a solar still, shovel it in, cook it up.

The delta-v from the snow line to Earth transfer is only about 5km/s;
11 km/s if you want to avoid aerobraking at Earth orbit. That sounds
like a lot, but it's not really, the actual thrust needed is very low,
so you can use a high Isp drive.

Let's just say what you don't want to do. You don't want to launch
propellant from the Earth's surface to return the water from the belt.
So you really want a scheme to use some of that water via ISRU as
fuel.

To do that, break down the water into hydrogen and oxygen using
electrolysis and then just sling the oxygen out the back in a hall
thruster, and optionally sling the hydrogen out in some other kind of
highish Isp drive (e.g. solar thermal); the overall Isp is plenty good
enough. With a Hohmann trajectory (which you should be able to
approximate even with a Hall thruster in this case) the trip will take
a year or a so, but the costs are pretty low overall, it's all
reusable. You could just aerobrake the water into LEO, but leave the
engine on a free return trajectory back up to the belt to pick up some
more water. The engine would need some propellant to circularise its
orbit again, but it's much lighter without the water, so it's only a
small penalty.

The other advantages of mining the snow line is that the synodic
period (i.e. launch windows) are rather more frequent (1.6 years,
compared to 2.6 for Mars), and unlike Mars there's more than one
target out there, so you could expect several deliveries per year,
whereas with Mars you get one big delivery, and then nothing for
almost 3 years.

The only downsides I can think of is that Ion drives tend to wear out,
but it might be possible to avoid that by spraying the inside of the
engine with ice or something and use it as an ablative. The Isp would
suffer due to ablation and sublimation, but it might not be that bad
in practice if you keep the inside surface cool enough and only use a
thin layer of ice.

> Joe Bonello

--
-Ian Woollard

We live in an imperfectly imperfect world. If we lived in a perfectly
imperfect world things would be a lot better.