Questions about "The High Frontier"

On Oct 21, 1:12 am, Hop David wrote:
Mike Combs wrote:
"Troy" wrote in message
roups.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.

I'm still curious whether there might be a way to increase payload
mass and reduce terrestrial hazards by delivering asteroid-derived
payloads to Earth orbit in the form of large spherical shells of
material. As I've probably mentioned in this forum before, I was once
asked to look at an RFP for "demisable tanks" -- i.e., satellite fuel
tanks guaranteed to burn up on reentry. That inquiry went nowhere,
AFAIK. Which underscores a point: maybe you don't need ablative
shielding or heat-soaking tiles to bring stuff down intact. After
all, LEO satellite fuel tanks have been found in desert regions with
little more than scorch marks and dents from hitting the ground (at a
relatively low terminal velocity, obviously.) Maybe that's a bug for
satellite fuel tanks, but it's arguably a feature if you're interested
in aerobraking or aerocapture of resources delivered from cislunar or
interplanetary space.

Now let's say you want to deliver a lot of asteroid-mined metal to an
L-point, using aerobraking in the Earth's atmosphere. Blow the metal
up into a big, relatively thin-walled sphere. Maybe store some
asteroid-derived volatiles inside, which would coat the interior as
they freeze down to the point where you get into equilibrium with
sublimation losses. Then push it off toward Earth. Now let's look at
the shipment failure modes.

CLOSE, BUT NO CIGAR

There's a navigation error: it misses aerobraking, and you lose a
shipment. You've blown a lot of capital, but not much life/limb risk
here. (Except crew loss if manned; see below.)

TOO CLOSE

There's a navigation error: it flies past Earth at or somewhat below
its aerocapture threshold. Well, then, maybe it makes it all the way
down. BUT, if it has a very low mass/volume ration, maybe it just
falls to a certain altitude in the atmosphere and ... floats. Even
with all the volatiles inside, boiled off, it might enclose a lot of
relative vacuum compared to some point in the atmosphere. And a thin
IR-reflective coating on the exterior of the sphere might give it more
thermal load toleration during atmospheric entry, as the radiative
heat losses during the long transit would reduce the temperature of
the internal volatiles to some very low equilibrium point. If the
volatiles mix is mostly H2O, so much the better: H2O has a lot of heat
capacity.

DIRECT HIT

There's a navigation error: it enters the Earth's atmosphere at a high
angle. This is by far the most worrisome scenario, and I would only
hope that a large, thin-walled sphere would simply vaporize much more
easily, at much higher altitudes, than any chunk of rock of the same
mass.

Some things I like about this idea, if it could be made to work:

(1) Gradually scalable. Relatively small spheres might be returned to
Earth just for starters, with relatively high value payloads (e.g.,
those platinum-group metals some talk about.) You could get people
used to the idea that stuff can arrive ballistically from space
without serious hazard to people on Earth.

(2) Testable elsewhe one initial use for a Venus cycler might be to
perform small-scale experiments on the idea, prototyping it by
watching what happens in the TOO CLOSE and DIRECT HIT modes. Likewise
for a Mars cycler. The results might have some scientific value for
studying upper atmosphere composition on those planets -- assuming
much more work needs to be done in that area (I wouldn't know.)

(3) Putting terrestrial uses first: building a space economy might
depend on first exploiting space material resources for use on Earth.
And there might be a case for that. Digging up ore from the Earth's
crust, transporting it by ship, processing it into steel -- these are
all energy-intensive, with all the environmental issues that are
raised by generating the required energy on Earth. A big ball of
mostly-pure iron appearing in the atmosphere, ready to be aerially
towed to steel mills with an assist from prevailing winds, might offer
all kinds of financial and environmental economies, maybe enough to
offset the costs of making it possible.

(4) Water, water, water: if H2O proves to be the most valuable of
volatiles for improving the heat load tolerance of such spheres, you
might end up with a net surplus of water for use in space. As I've
conjectured elsewhere, how we do things in space might change a lot if
assume a relative abundance of water. Even payloads slated for
delivery to Earth might offer a way to deliver water to cislunar space
-- initial aerobraking passes might require the most water, and if so,
you might jettison the vapor into balloons at the perigee after each
pass, and use a little more vented vapor to propel the balloons to
highly elliptical orbits that don't graze the upper atmosphere, or
that aerobrake them more gently for delivery to LEO.

(5) Human return vehicle: while I lean toward unmanned, automated/
teleoperated asteroid mining operations to keep costs down, human
presence might turn out to be necessary for a while, and those people
will probably want to come back. A big metal sphere would have
obvious debris-strike protection value; one with lots of frozen
volatiles inside might provide the foundation for a reasonable cosmic-
ray-shield habitat as well. Well, it would be hellishly cold in
there, though, right? But perhaps the process of applying a uniform,
highly IR-reflective coating to the exterior could wait until late in
the return journey.

Do I know what I'm talking about? No. Is anybody else talking about
this? Not that I've heard. If nobody else is talking about it, maybe
it hasn't been shot down yet. My clay pigeon for the day, the product
of little more than an afternoon's idle thought.

-michael turner

John Schilling wrote:

On Fri, 19 Oct 2007 13:10:07 -0500, "Mike Combs"
wrote:


"John Schilling" wrote in message
. ..


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 there's every reason in the world to expect an asteroidal settlement to
be doing this.


Except for the critical shortage of local resources that aren't steel or
coal or glass.



And Mars has a much broader range of useful resources
than any NEO. Than all NEOs combined, probably.


I'm not sure why you would say this. What resources would be available on
the surface of Mars that you couldn't find in a well-selected CC-type
asteroid?


"CC" meaning "Carbonaceous Chondrite" generally?

OK, let's see: How about useful concentrations of Helium, Lithium,
Beryllium, Boron, Nitrogen, Fluorine, Neon, Sodium, Aluminum, Chlorine,
Argon, Potassium, Titanium, Chromium, Manganese, Copper, Zinc, Arsenic,
Bromine, Krypton, Strontium, Zirconium, Niobium, Molybdenum, Silver, Tin,
Antimony, Iodine, Xenon, Barium, Hafnium, Tantalum, Tungsten, Gold,
Mercury, Lead, Bismuth, Thorium, and Uranium.

While CCs may be poor in some those materials, there are other asteroids
that aren't.

I acknowledge that one asteroid containing all these resources would be
rare. It would be hard for colonists on a metallic asteroid to use
nitrogen from an NEO on a different orbit.

On the other hand, there's no superhighways, oceans or rivers that can
be used for transportation on Mars. Transportation will be a substantial
barrier to self sufficiency on Mars as well as among the NEOs.



Mars definitely has some of those in abundance , and almost certainly has
useful ores of the rest on account of having experienced the same geologic
processes that produced such ores on Earth.

I seem to recall Peter Tillman saying uranium ore was concentrated via
biological processes. There's certainly some ore concentrating processes
on Mars, but I don't regard it as a given Mars would have all the same
ores earth does.


Carbonaceous chondrites, based on the meteoric evidence, do not.

Meteoric evidence is biased. Some meteorites are much more perishable
than others. If they're not discovered within hours or days of impact,
they're gone. More durable objects are more likely to reach the earth's
surface and become meteorites.

They're
just raw primordial dust, slightly baked.

Some carbonaceous chondrites may be homogenous aggregates that haven't
experienced any ore concentrating processes. But this isn't the case for
all asteroids. Metallic asteroids are believed to come from the interior
of large asteroids that were massive enough to have differentiated layers.

I also believe there can be ore concentrating processes going on in
objects that outgas when they're closer to the sun.


Asteroids, are where you get steel and coal and glass, and maybe magnesium
and platinum for the export markets, and that's really about it.

I believe water, ammonia and other volatiles not at the bottom of a
steep gravity well and not far from the earth would be valuable.

On http://clowder.net/hop/railroad/asteroidresources.html I give a list
of reasons (with some web cites) why I believe volatile rich NEOs exist.


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.


I wouldn't so much say "hard" as "requiring a certain minimal scale". If
one has two counter-rotating structures of equal mass, nothing is required
to spin them up and keep them spinning other than an electric motor between
them.


Making them useful requires more than just keeping them spinning, as you
ought to know by now.

Could you elaborate?

And the minimal scale issue is critical, because
the first outposts are going to be small and the first big colonies are
going to be where the outposts already are.

Minimum gravity to maintain health is still unknown. Human tolerance to
angular velocity given a gradual transition is still unknown. So minimal
scale is still unknown.

Hop

Damien Valentine wrote:

On Oct 20, 11:08 am, Hop David wrote:


This is like saying if modest log cabins were good enough for the
pioneers then why should their descendants bother with high rise buildings.


Because building things in space (whatever those things may be)
doesn't automatically lead to either log cabins or high rises.
Someone mentioned oil rigs a few posts back; we may have 24-hour crews
on them, but the crews don't stay on the rig for their whole lives and
raise kids. There are no "oil rig cities", so far as I know.


Many cities have sprung up around oil fields in formerly desolate, hard
to reach areas. Same with mining towns.

So far as I know, most long duration off shore drilling rigs aren't far
from land and it's not a major investment for a worker to make a trip to
a coastal settlement. But if it's very hard to access coastal
settlements, I believe service industries would grow around a long
duration rig. Eventually there'd be schools, churches, etc.

Hop

On Oct 23, 2:36 am, Damien Valentine wrote:
On Oct 20, 11:08 am, Hop David wrote:

This is like saying if modest log cabins were good enough for the
pioneers then why should their descendants bother with high rise buildings.

Because building things in space (whatever those things may be)
doesn't automatically lead to either log cabins or high rises.
Someone mentioned oil rigs a few posts back; we may have 24-hour crews
on them, but the crews don't stay on the rig for their whole lives and
raise kids. There are no "oil rig cities", so far as I know.

But there are such things as mining towns. Oil rigs are extremely
dangerous and rather unpleasant places, plus they run out of resource
eventually. They also have to be towed out in one piece. Johannesburg
was once a mine, now it's South Africa's largest city.

As Dr. Schilling pointed out when he kindly took the time to rip my
argument to shreds, a bunch of small scattered habs is not going to
make a decent permanent settlement. Mars does lend itself to permanent
settlement because of the availability of resources and infrastructure
concentration of a base of operations.

If you have a single large base of operations which processes towed-in
asteroids, support infrastructure will spring up around it, requiring
more and more human presence. Trips back Earthside may happen every 6
months or so, but if you close your resource loop, it's effectively a
permanent settlement. As the habitat becomes more... habitable, people
may stay longer.

Michael Turner wrote:



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.


I'm still curious whether there might be a way to increase payload
mass and reduce terrestrial hazards by delivering asteroid-derived
payloads to Earth orbit in the form of large spherical shells of
material. As I've probably mentioned in this forum before, I was once
asked to look at an RFP for "demisable tanks" -- i.e., satellite fuel
tanks guaranteed to burn up on reentry. That inquiry went nowhere,
AFAIK. Which underscores a point: maybe you don't need ablative
shielding or heat-soaking tiles to bring stuff down intact. After
all, LEO satellite fuel tanks have been found in desert regions with
little more than scorch marks and dents from hitting the ground (at a
relatively low terminal velocity, obviously.) Maybe that's a bug for
satellite fuel tanks, but it's arguably a feature if you're interested
in aerobraking or aerocapture of resources delivered from cislunar or
interplanetary space.

Now let's say you want to deliver a lot of asteroid-mined metal to an
L-point, using aerobraking in the Earth's atmosphere. Blow the metal
up into a big, relatively thin-walled sphere. Maybe store some
asteroid-derived volatiles inside, which would coat the interior as
they freeze down to the point where you get into equilibrium with
sublimation losses.

Asteroid mined metal would come from a metallic asteroid which is
unlikely to have volatiles.

There may be exceptions to this. One scenario I can think is an object
from Jupiters' Trojans. Objects drift in, stay awhile and then drift out
(I believe). See the NEC apohelion graphic on
http://clowder.net/hop/railroad/asteroidresources.html)

While milling about in the Trojan cluster it might be possible for two
asteroids from very different orgins to collide at low velocity and form
a "peanut". Then the asteroid drifts out to become a Near Earth Comet
and then a later earth approach alters its orbit, dropping its aphelion.
Even later, happy investors discover this peanut with metals in one lobe
and volatile ices in the other.


Then push it off toward Earth. Now let's look at
the shipment failure modes.

CLOSE, BUT NO CIGAR

There's a navigation error: it misses aerobraking, and you lose a
shipment. You've blown a lot of capital, but not much life/limb risk
here. (Except crew loss if manned; see below.)

TOO CLOSE

There's a navigation error: it flies past Earth at or somewhat below
its aerocapture threshold. Well, then, maybe it makes it all the way
down. BUT, if it has a very low mass/volume ration, maybe it just
falls to a certain altitude in the atmosphere and ... floats.

It depends on duration of transit through the atmosphere. If its passage
lasts long enough for heat to be conducted through the metal shell, the
volatiles will turn to gas and provide supporting pressure. But if the
volatiles don't vaporize fast enough, I'd expect the metal ball to
crumple. Is it possible to have a metal shell strong enough to keep its
shape while enclosing vacuum but light enough to float? I don't know.

Given your conditions above, the object has a low flight path angle so
it might have a long enough trip for heat to conduct through the shell.


Even
with all the volatiles inside, boiled off, it might enclose a lot of
relative vacuum compared to some point in the atmosphere. And a thin
IR-reflective coating on the exterior of the sphere might give it more
thermal load toleration during atmospheric entry, as the radiative
heat losses during the long transit would reduce the temperature of
the internal volatiles to some very low equilibrium point. If the
volatiles mix is mostly H2O, so much the better: H2O has a lot of heat
capacity.

DIRECT HIT

There's a navigation error: it enters the Earth's atmosphere at a high
angle. This is by far the most worrisome scenario, and I would only
hope that a large, thin-walled sphere would simply vaporize much more
easily, at much higher altitudes, than any chunk of rock of the same
mass.

Some things I like about this idea, if it could be made to work:

(1) Gradually scalable. Relatively small spheres might be returned to
Earth just for starters, with relatively high value payloads (e.g.,
those platinum-group metals some talk about.) You could get people
used to the idea that stuff can arrive ballistically from space
without serious hazard to people on Earth.

(2) Testable elsewhe one initial use for a Venus cycler might be to
perform small-scale experiments on the idea, prototyping it by
watching what happens in the TOO CLOSE and DIRECT HIT modes. Likewise
for a Mars cycler. The results might have some scientific value for
studying upper atmosphere composition on those planets -- assuming
much more work needs to be done in that area (I wouldn't know.)

(3) Putting terrestrial uses first: building a space economy might
depend on first exploiting space material resources for use on Earth.
And there might be a case for that. Digging up ore from the Earth's
crust, transporting it by ship, processing it into steel -- these are
all energy-intensive, with all the environmental issues that are
raised by generating the required energy on Earth. A big ball of
mostly-pure iron appearing in the atmosphere, ready to be aerially
towed to steel mills with an assist from prevailing winds, might offer
all kinds of financial and environmental economies, maybe enough to
offset the costs of making it possible.

(4) Water, water, water: if H2O proves to be the most valuable of
volatiles for improving the heat load tolerance of such spheres, you
might end up with a net surplus of water for use in space. As I've
conjectured elsewhere, how we do things in space might change a lot if
assume a relative abundance of water. Even payloads slated for
delivery to Earth might offer a way to deliver water to cislunar space
-- initial aerobraking passes might require the most water, and if so,
you might jettison the vapor into balloons at the perigee after each
pass, and use a little more vented vapor to propel the balloons to
highly elliptical orbits that don't graze the upper atmosphere, or
that aerobrake them more gently for delivery to LEO.

(5) Human return vehicle: while I lean toward unmanned, automated/
teleoperated asteroid mining operations to keep costs down, human
presence might turn out to be necessary for a while, and those people
will probably want to come back. A big metal sphere would have
obvious debris-strike protection value; one with lots of frozen
volatiles inside might provide the foundation for a reasonable cosmic-
ray-shield habitat as well. Well, it would be hellishly cold in
there, though, right? But perhaps the process of applying a uniform,
highly IR-reflective coating to the exterior could wait until late in
the return journey.

Do I know what I'm talking about? No. Is anybody else talking about
this? Not that I've heard. If nobody else is talking about it, maybe
it hasn't been shot down yet. My clay pigeon for the day, the product
of little more than an afternoon's idle thought.

I took a few pot shots, more with a .22 than a 12 gauge though. I agree
density should be considered when establishing payload ceilings. Hollow
payloads may well be more amenable to aerobraking.


Hop

Troy wrote:

On Oct 23, 2:36 am, Damien Valentine wrote:

On Oct 20, 11:08 am, Hop David wrote:


This is like saying if modest log cabins were good enough for the
pioneers then why should their descendants bother with high rise buildings.

Because building things in space (whatever those things may be)
doesn't automatically lead to either log cabins or high rises.
Someone mentioned oil rigs a few posts back; we may have 24-hour crews
on them, but the crews don't stay on the rig for their whole lives and
raise kids. There are no "oil rig cities", so far as I know.


But there are such things as mining towns. Oil rigs are extremely
dangerous and rather unpleasant places, plus they run out of resource
eventually. They also have to be towed out in one piece. Johannesburg
was once a mine, now it's South Africa's largest city.

As Dr. Schilling pointed out when he kindly took the time to rip my
argument to shreds, a bunch of small scattered habs is not going to
make a decent permanent settlement.

True, supplying habs scattered thoughout the solar system is more
difficult than supplying habs all in the same neighborhood.

This is one of the reasons I advocate placing asteroidal payloads in
orbits about Earth, Venus and Mars.

Habs orbiting on the slopes of gravity wells are also more accessible in
terms of delta vee (For example it takes less delta vee to land on
Phobos or Deimos than it does a Mars Trojan).


Mars does lend itself to permanent
settlement because of the availability of resources and infrastructure
concentration of a base of operations.

If you have a single large base of operations which processes towed-in
asteroids, support infrastructure will spring up around it, requiring
more and more human presence. Trips back Earthside may happen every 6
months or so, but if you close your resource loop, it's effectively a
permanent settlement. As the habitat becomes more... habitable, people
may stay longer.

On Oct 23, 10:46 am, Hop David wrote:
Damien Valentine wrote:
On Oct 20, 11:08 am, Hop David wrote:

This is like saying if modest log cabins were good enough for the
pioneers then why should their descendants bother with high rise buildings.

Because building things in space (whatever those things may be)
doesn't automatically lead to either log cabins or high rises.
Someone mentioned oil rigs a few posts back; we may have 24-hour crews
on them, but the crews don't stay on the rig for their whole lives and
raise kids. There are no "oil rig cities", so far as I know.

Many cities have sprung up around oil fields in formerly desolate, hard
to reach areas. Same with mining towns.

So far as I know, most long duration off shore drilling rigs aren't far
from land and it's not a major investment for a worker to make a trip to
a coastal settlement. But if it's very hard to access coastal
settlements, I believe service industries would grow around a long
duration rig. Eventually there'd be schools, churches, etc.

Sounds like what Halliburton sets up in Iraq for the war effort.


Hop

"Hop David" wrote in message
...

On the other hand, there's no superhighways, oceans or rivers that can be
used for transportation on Mars. Transportation will be a substantial
barrier to self sufficiency on Mars as well as among the NEOs.

There seems to be an assumption that overland travel on Mars has got to be
easier than moving between asteroids because the latter is space travel and
the former isn't, and as everybody knows, space travel is difficult,
dangerous, and hideously expensive. I think this notion overlooks two
points:

1. Overland travel on Mars, unlike same on Earth, will have pressurization
and other life-support requirements little different from space travel.

2. Our notions of space travel are influenced by our most common experience
of it, which is to say, travel from the surface of the Earth into orbit.
Such travel requires large amounts of thrust (greatly in excess of vehicle
weight in 1-G) quickly achieved, and an aerodynamic shape. None of these
will be requirements for systems traveling from one asteroid to another.

There's certainly some ore concentrating processes on Mars, but I don't
regard it as a given Mars would have all the same ores earth does.

And we cannot until we go there and obtain ground truth.

Making them useful requires more than just keeping them spinning, as you
ought to know by now.

Could you elaborate?

My point was that saying Mars provides us with free gravity may not be
saying a lot if there's no large additional cost associated with spinning.
John seems to be pretending he thinks my point is that having a space
settlement is as easy as making something spin.


--


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

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

If you have a single large base of operations which processes towed-in
asteroids, support infrastructure will spring up around it, requiring
more and more human presence.


And I think there will be a single large base of operations. This might be
where Hop parts company with me, but I really don't expect this process to
start out at distant asteroids. I expect it to start out in HEO, close to
the only servable market currently in existence, which is Earth. I expect
the initial major product to be solar power satellites. Entire asteroids
may or may not get towed into this orbital base of operations, but even if
not, I'm sure that loads of ore pulled from some NEO will be getting towed
in.

--


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

Mike Combs wrote:

On the other hand, one might note that with the SMF with the
spartan living conditions one sees quick turnover in skilled
workers. People sign-on for 2 year tours (or whatever), fill up
their bank accounts, and then come back to Earth to spend their
money, because what are they going to spend it on living in an
aluminum can in HEO? Then you might note that since you've got
mining facilities on the moon and/or a NEA, a means of
transporting ore to HEO, ore refineries and parts fabrication
facilities in that same orbit, most of what you need to build a
Bernal Sphere or Stanford Torus is already in place (and perhaps
already paid for by SPS profits). So it might be worth a bit of
investment for your workers to be able to live under natural
sunlight surrounded by greenery, and able to do ordinary things
like fish in a pond or walk in a park. Perhaps highly-trained
and skilled workers might be more apt to spend their entire
careers with you if they can look at their apartment or house in
Bernal Alpha as "home" rather than some place on Earth.
Families might be more apt to form in such a place than in a
place which more resembled an off-shore oil rig.

Mike, you're a good guy and everything, but the above is a textbook
example of thinking with your heart instead of your head. In any
other context except space (you yourself bring up oil rigs) you
would quickly recognize the absurdities. But since this is space
we're talking about...well, things are different in space, right?

Jim Davis