Mike Combs wrote:

"Troy" wrote in message
oups.com...

Try telling that to politicians and hysterical anti-asteroid campaign
groups!


I'd have to allow that public education would be a hurtle to overcome.
Similarly, I think SBSP is the best long-term energy solution (and might
lead to space settlement), but that will require extensive public education
that no, there's no cause for concern from the microwave beams.

I think what we might call "Deep Impact hysteria" might rule out aerobraking
asteroids through Earth's atmosphere, but I would hope we won't be prevented
from depositing a fragment of an asteroid perhaps the size of an apartment
building into either L-4 or L-5.

It's desirable to have a near earth perigee not only for aerobraking but
to exploit the Oberth effect.

I don't think hysteria is the right word. Large payloads would be harder
to control and a tiny error could change aerobraking to lithobraking. I
would call it "Deep Impact sensible fear". Again, I advocate payload
mass ceilings well below Tunguska size.

Given plausible methods of delivering payloads, we won't be bumping into
that ceiling for some time to come anyway.


Isn't there a big fight between the L5 crowd and the Zubrinites?


Yeah, and I find it significant that we L5'ers tend to emphasize things like
servable markets, exports, balance of trade, and return on investment, while
the Zubrinites say things like "those who colonize Mars will go for hope,
not for cash". But I think they say that because they have to.


You'll probably wind up with both.


Yeah. I've decided it would be wrongfully dogmatic for me to say that Mars
will never be settled by anybody. Some will do it out of nothing other than
a stubborn love of the planet.

I believe colonization of Mars will come as naturally from the
development of Phobos and Deimos. The Martian moon colonies will
probably need resources that are more easily supplied by Mars than other
sources. The inhabitants of the Martian moons will want to explore and
enjoy their neighbor.

Phobos and Deimos enjoy substantial advantages over most other small
objects. Their proximity to Mars reduces the delta vee budget -
aerobraking and the Oberth effect can be used.

There's a nice launch window to Phobos and Deimos every 2+ years.

Given an eccentric elliptic orbit (as most NEOs have), a nice, low delta
vee Hohmann transfer launch window only opens up when the NEO has a near
earth perihelion. If the NEO's orbital period isn't resonant with the
earth, such launch windows will occur very rarely.

Some examples: Given an asteroid with a 3/2 year period, it's possible
to have a near earth perihelion every 3 years. An asteroid with a 5/4
year period can have a near earth perihelion every 5 years.

Given an earth resonant asteroid with periodic near earth perihelions,
high delta vee but very short duration sprint trajectories between the
earth and the asteroid are also possible.

http://clowder.net/hop/railroad/HohmSprin.jpg

These considerations make earth resonant asteroids much more amenable to
human bases, in my opinion.

But, sadly, resonant NEOs with near earth perihelions are a small
fraction of the total population.

Non resonant asteroids may be exploited by one shot missions (possibly
Kuck mosquitos) but they don't lend themselves to human settlement.

So, after the Moon and the Earth-Moon Lagrange points, Phobos and Deimos
hold spots near the top of my list.

Hop