Diversification

From: Ian Woollard [mailto:ian.woollard@...]

It seems to me that if we build stuff from lunar or asteroidal
material
reentering it is probably very cheap.

>I must allow that returning material to the Earth is probably going to be much cheaper than
>lifting things up from the Earth, due to aerobraking. But one must still place the payload on
>an atmosphere-intercepting trajectory. That still takes a certain amount of delta-V, which is
>going to be expensive. Aerobraking is a discount, but it's not a free ride.

If aerobraking is used on a large scale you have to start worrying about
modifications to the upper atmosphere. The high temperatures of reentry
cause a lot of chemical reactions. It might not be a problem, but if it
is we need to know about it in advance -- an atmosphere is a terrible
thing to waste. The first step is a more thorough understanding of the
upper atmosphere, followed by modeling of the effects of various levels
of traffic. It won't be easy or glamorous, but its an essential step
towards large scale colonization.

--
Al Globus
CSC at NASA Ames Research Center
aglobus@..., (650) 604-4404
http://www.nas.nasa.gov/~globus/home.html

The dinosaurs weren't spacefaring. We are. I don't think that's an
accident. Maybe we are life's taxi to the stars.