Questions about "The High Frontier"

Mike Combs wrote:
I think pretty much everything we do beyond the Earth is going to
necessitate radiators. Would we be that much better off on Mars? There'd
be some small amount of convection, but how effective will convection be
with 1% pressure air?

The winds will help to some extent.

We might try to use the ground as a heat sink, but
that's mostly dust in a near-vacuum, and for an insulator you can't hardly
beat dust in a vacuum. One might mine ice and dump it on heat exchangers,
but that would be a frightful waste of a valuable raw resource.


You can drill down into the surface, and used a closed-loop system to
cycle something through a heat exchanger that dumps internal eat into
the bedrock where it migrates away via conduction.

Ease of construction (inflatable domes - Mars)


Why couldn't one use inflatable domes on an asteroid, or inflatable spheres
in orbit?


The problem with the inflatable domes isn't that we can't make them - we
have materials that are easily up to the job and fairly low in weight-
it's that outside of Earth's magnetosphere there's is the radiation of
the Sun and cosmic rays to deal with.
You are probably going to want the base primarily underground, or at
least have soil covering it for radiation protection, and that will be
easier to do with some gravity on your side to keep it in place.
Transparent inflatable domes might be tough though; there's unfiltered
high-UV sunlight to deal with, as well as radiation degrading of the
dome's material.

Pat

Pat Flannery wrote:

You can drill down into the surface, and used a closed-loop system to
cycle something through a heat exchanger that dumps internal eat into
the bedrock where it migrates away via conduction.

That was supposed to be "internal heat" the internal eat is dumped
outside the habitat, and migrates away inside the cavernous gullets of
the Martian Manure Muncher Monsters. :-)

Pat

Troy wrote:



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


There's some conflict. This is another reason I harp on the Phobos and
Deimos. Not only are they accessible and possibly resource rich, they
may be a way to build a consensus between two schools that have many
common interests.


... asteroids are the way to go IMHO, if only because of
the possibility of 1G environments.

We don't know what gravity's needed to stay healthy. This argument also
works against orbital habs. So long as mammoth O'Neill cylinders are
perceived as entry level orbital habs, people will dismiss them as
implausible science fiction.

Hop

"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.

Perhaps you're right, but your inflatable domes need less radiation
shielding because of Mars' atmosphere (except at noon).

Such a habitat for Mars might could get by with a radiation shield 1/3 as
thick as one required for free orbit, but it would still be necessary and
vital. It might amount to something like a 2-foot-thickness of soil or
rock. Quite a few megatons, even with 1/3 gravity.

But that leads me to a point. Such a 2-foot-thick radiation shield might
weigh 1/3 as much as it would on Earth. But how much would the 6-foot-thick
shield needed in orbit weigh? And of course the answer is...nothing! Even
for a rotating habitat, the radiation shield needn't rotate with the rest of
the habitat in order to do its job.

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.

And the first colonists will
probably originate from that crowd, using whatever economics as an
excuse to get them there.

Yes, but there will have to be a way to make a living once you get there.

Perhaps I should have said "instantly." An inflatable hab in space, to
be a long-term prospect, has to be spun up, have radiation shielding
and so on.

First, operations could start inside the orbiting inflatable prior to
spin-up to final rotation rate. Second, no Mars inflatable would be able to
able to blow off installing a 2 foot thick radiation shield; at least not if
the intention is for people to live inside it for a year or more.

Once you're on the surface of Mars, a lot of problems
are taken care of for you.

I know that's the convention wisdom, but I don't entirely buy it.

Right now, the big money in the private sector is reluctant to get
into the exploration gig (it seems).

Truth is, the private sector does very little exploration of any kind.
They're more interested in producing goods or providing services to some
market. But some of us are convinced that space will eventually stop being
all about exploration. Past a point, exploration may become the smaller
part of the total activities taking place beyond the Earth.

--


Regards,
Mike Combs
----------------------------------------------------------------------
By all that you hold dear on this good Earth
I bid you stand, Men of the West!
Aragorn

"Hop David" wrote in message
...
Mike Combs wrote:

Then don't deposit them in unstable Lagrange points. Use 4 and 5, and
never use 1, 2, or 3.

EML1 (The Lagrange point between earth and moon) is currently my favorite
spot.

Oh, I'm a L-1 enthusiast myself. I was referring only to the parking of
sizeable asteroids (or sizeable fragments thereof) in Lagrange points.

Myself, I'm confident that any competant operation could keep an asteroid
fragment suspended at L-1 indefinitely (and even if it slides off in the
Earthward direction, I was thinking it would whip around the Earth rather
than collide with it). But I was thinking you might be better able to
assure Joe Sixpack if you can say, "Don't worry, it would take a deliberate
application of force to budge it out of L-5," vs. "Don't worry, we promise
we'll stay on top of the situation."

--


Regards,
Mike Combs
----------------------------------------------------------------------
By all that you hold dear on this good Earth
I bid you stand, Men of the West!
Aragorn

"Quadibloc" wrote in message
ups.com...

But the cost of expanding the habitat, while it would still be larger
than costs of Earth habitats - they would have to be airtight -
doesn't involve gallivanting around the Solar System to pick up
asteroids for metals and comets for volatiles.

Pick the right body, and you could get both metals and volatiles from the
same body.

--


Regards,
Mike Combs
----------------------------------------------------------------------
By all that you hold dear on this good Earth
I bid you stand, Men of the West!
Aragorn

Hop David wrote:

We don't know what gravity's needed to stay healthy.

A question which the centrifuge module on the ISS might have answered,
so of course we canceled that.

Pat

Pat Flannery wrote:



Hop David wrote:


We don't know what gravity's needed to stay healthy.


A question which the centrifuge module on the ISS might have answered,
so of course we canceled that.

Pat

ISTR that a centrifuge module would cost nearly as much as the ISS
itself. Still, that would be more worthwhile than what they're doing now.

Hop

On Wed, 17 Oct 2007 11:56:44 -0700, Hop David wrote:

Quadibloc wrote:
Mike Combs wrote:

We won't build orbital habitats because someone has forbidden the moon or
Mars. We'll build orbital habitats because there are significant advantages
to them over same-scale habitats built on either the moon or Mars. People
who insist on living on other planetary bodies will find themselves unable
to economically compete with those located in free orbit.

Yes, asteroids are good sources of mineral resources, and not being in
a gravity well is an advantage.

I think, though, that the Moon and Mars still have a place, because
start-up costs are going to be way lower.

I agree moon habs will have lower start up costs. But why would Martian
habs be less expensive than NEO based habs? There are NEOs that can be
reached with less delta vee than Mars and with launch windows of
comparable frequency.

That's fine if all you're planning to do is send prefabricated habs by
rocket from Earth, with periodic resupply shipments.

But it's probably going to be a *lot* less expensive if you allow for
the inhabitants to build, provision, and resupply their habitat using
local resources. And Mars has a much broader range of useful resources
than any NEO. Than all NEOs combined, probably.

Mars also has gravity, which is quite useful if you want your inhabitants
to remain, like, alive and stuff. Providing gravity on or near an NEO is
rather hard, especially at small scales.


Here's a graphic I made showing relative delta vee distances for
assorted "low hanging fruit":
http://clowder.net/hop/railroad/deltaveemap.html

Right, so, settling Greenland is likely to be less expensive for
hypothetical European explorers than settling North America or the
Carribean?


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On Oct 19, 9:48 am, John Schilling wrote:
Right, so, settling Greenland is likely to be less expensive for
hypothetical European explorers than settling North America or the
Carribean?

True, but look at Hong Kong. The Brits wanted it for its trade
potential; look what became of it. People go where the trade is
happening, so cyclers habitats may eventually become quite large.
Ultimately, an O'Neill scale hab will give you more of an Earthlike
environment than on Mars.

In addition, a passenger ship to L5 can be more like an airliner,
whilst to Mars you're looking at something like a small cruise ship
for the same numbers.

An L5 asteroid can provide a number of services: 1G R&R for lunar base
personnel (you can get away with at least 4RPM and 100m diameter),
light elements production and reaction mass supply, beam solar power
to moon bases, serve as a space hotel, mount deep-space telescopes,
manufacture stuff on demand for other orbital operations, serve as a
skyhook or supply mass for skyhooks and do all the microgravity
research you can shake a stick at. Plus you have a "saving the Earth"
case for stick-in-the-muds. And the habitat does not have to be stuck
to one asteroid; it can be a mobile "mining town." All that, and it's
3 or 4 days away, and no quibbling about 2 year launch windows.

What, economically speaking, can you do on Mars? Yes, colonists can
trade with each other, but what will they be able to send back to
Earth besides data and rock samples? Some people would probably part
with their fortunes to live on Mars, but it's not going to create
massive expansion of the colony. Longer term, it could became a hub of
Belt operations.

Migration nowadays is largely economic; colonists will likely be
contract workers in the L5 colonies; on Mars you're more likely to
stay. But unless there are companies willing to pay for people on
Mars, large-scale colonisation will not happen unless you have really
dirty cheap spaceflight.