could use some technical checks

On 7/4/14 10:46 AM, Al Globus alglobus@... [spacesettlers] wrote:

> The bottom line is that reboost of settlements in LEO is no big deal
> using solar electric propulsion. The mass requirements are negligible.

Yes, this is an important result.

> Putting a settlement in LEO has a huge affect on the required shielding
> (Im working on a paper on this), multiple tons per square meter.

Absolutely, that's exactly what I found last week when I went through
the numbers. Radiation (both solar and cosmic) in LEO is about 1/200th
of what it is beyond, and that makes an enormous difference in
shielding. In LEO, if you've got a pressure vessel and enough soil to
grow stuff in, you're more than covered, radiation-wise. Outside of
LEO, you need to add another 4-5 meters of heavy stuff (or a much deeper
layer of light stuff). The difference in the cost is tremendous.

(If you're in the mood for a collaborator on that paper, I'd be delighted!)

> The limiting factor on the altitude of the settlement then is time to
> impact with Earth if all control is lost (all sats below GEO will
> eventually impact Earth).

Really? I would think that a lot of orbits below GEO would have such a
long decay time as to be essentially "never." (Not LEO, though, and
since we're not going to park a settlement in the Van Allen belts, I
guess this is academic.)

> heres a question for the group: how long should we require a
> settlement to impact Earth if there is total loss of control? 50 years?
> 100 years? 1000 years? ?????

I'd think 100 years would be fine. That's enough time for us to enter
and recover from a great depression. And if civilization actually
collapses, we'll have bigger problems than a habitat falling (and most
likely hitting ocean).

Best,
- Joe