I must be sounding schitzophrenic -first one thing, then another.
Playing devil's advocate, trying to bolster _and_ pick apart
proposals. All part of developing ideas.

However, NEAs are starting to look better all the time.

>-go to the Moon
>
>Yes, in that it is a nearby source of raw materials
>outside of the steepest part of the Earth's gravity well.

Nearby, yes, but NEAs are more accessible (distance doesn't matter
nearly as much as relative velocity), as well as richer sources.
Now we have some choices: If you pick a light CC (like Diemos),
you've got volatiles aplenty, but very little metals (probably about
like Lunar ores). An extinct short period comet core may be nothing
but crumbly ices, with a covering of dark dust. Halley's comet core
has a density of .2gm/cc (20% of water). Even though it's mostly
hollow, most of what's left is ices.
Go to an Iron asteroid, and you've got 80% iron/nickle/cobalt, with
attendant rich Pt & precious/strategic metals, but very little
process chemicals to work them with.
Get some of each? Certainly, in the long run, we'll do this.

The best bet is to find a little chunk of a stony-iron. As close to
1AU/1year orbit as possible.
Such a stony-iron would probably have about 30% metals, and the
remainder would be about 20% volatiles. Still, if we're catching a
300 meter asteroid, we're rich!
A stony-Iron NEA seems to be the best bet. Far better than Luna,
infinitely better than Mars surface. The retrieval mission would be
the second thing built; first, the LEO ET station. It receives the
first small samples from the NEA, and as the shipments build up, it
builds the shielded HEEO base, with rotating habitat section. The NEA
chunk is brought to HEEO, to pace near the HEEO station.

When somebody uses the O'Leary idea of a mass driver bringing an
asteroid chunk back, the idea of a Lunar mine may be in trouble.
This may also happen with a mass driver or high strength tether
facility at the NEA, and another (couple) in Earth orbit. (The rock
doesn't need to be _in_ HEEO, if it can get loads to there
frequently.)
I'm not sure how often a reasonable tether/mass driver can throw
payloads back to HEO, but the needed delta-V is tiny at the best
times. If you can throw (SWAG) 100kg loads with 3km/sec, then you can
probably have loads coming into HEO to be caught, through most of the
year. At the best times, less than 1km/sec.

It's also interesting in that this very exact type of NEA (stony
iron, 1AU/1year) is the greatest threat to Earth! It approaches
slowly, so when it hits the atmosphere, it doesn't build up a
ferocious pressure wave of superheated air, to crush it high above
the ground. It's more solid than a light CC, so it's crush strength
is higher. Even worse, since we rarely have it in our night skies
while it's near enough, we have trouble seeing it.

A question: Could rock dust be vaporised and used as propellant in
an arc jet of some kind? Solar thermal? Is this any better than a
mass driver rocket? It seems simpler, but the idea of electrically
propelling rock vapor is rather technically horrendous.

Moderate sized NEAs seemed to be covered with a layer of dust and gravel.
Should be reasonably easy to scoop up (this needs to be tested). If this is
true, a small facility on a convenient NEA could supply materials to other
small vehicles for return to earth. Perhaps use a shuttle between the NEA
and NEA low orbit so the return vehicles don't need to land.

I like small because it's relatively easy to do, you use lots of them so you
get economies of scale and have built-in redundancy. See
http://www.nas.nasa.gov/~globus/papers/AsterAnts/paper.html for my thinking
before I realized you could probably scoop up the dust.

John Frazer wrote:

> I must be sounding schitzophrenic -first one thing, then another.
> Playing devil's advocate, trying to bolster _and_ pick apart
> proposals. All part of developing ideas.
>
> However, NEAs are starting to look better all the time.
>
> >-go to the Moon
> >
> >Yes, in that it is a nearby source of raw materials
> >outside of the steepest part of the Earth's gravity well.
>
> Nearby, yes, but NEAs are more accessible (distance doesn't matter
> nearly as much as relative velocity), as well as richer sources.
> Now we have some choices: If you pick a light CC (like Diemos),
> you've got volatiles aplenty, but very little metals (probably about
> like Lunar ores). An extinct short period comet core may be nothing
> but crumbly ices, with a covering of dark dust. Halley's comet core
> has a density of .2gm/cc (20% of water). Even though it's mostly
> hollow, most of what's left is ices.
> Go to an Iron asteroid, and you've got 80% iron/nickle/cobalt, with
> attendant rich Pt & precious/strategic metals, but very little
> process chemicals to work them with.
> Get some of each? Certainly, in the long run, we'll do this.
>
> The best bet is to find a little chunk of a stony-iron. As close to
> 1AU/1year orbit as possible.
> Such a stony-iron would probably have about 30% metals, and the
> remainder would be about 20% volatiles. Still, if we're catching a
> 300 meter asteroid, we're rich!
> A stony-Iron NEA seems to be the best bet. Far better than Luna,
> infinitely better than Mars surface. The retrieval mission would be
> the second thing built; first, the LEO ET station. It receives the
> first small samples from the NEA, and as the shipments build up, it
> builds the shielded HEEO base, with rotating habitat section. The NEA
> chunk is brought to HEEO, to pace near the HEEO station.
>
> When somebody uses the O'Leary idea of a mass driver bringing an
> asteroid chunk back, the idea of a Lunar mine may be in trouble.
> This may also happen with a mass driver or high strength tether
> facility at the NEA, and another (couple) in Earth orbit. (The rock
> doesn't need to be _in_ HEEO, if it can get loads to there
> frequently.)
> I'm not sure how often a reasonable tether/mass driver can throw
> payloads back to HEO, but the needed delta-V is tiny at the best
> times. If you can throw (SWAG) 100kg loads with 3km/sec, then you can
> probably have loads coming into HEO to be caught, through most of the
> year. At the best times, less than 1km/sec.
>
> It's also interesting in that this very exact type of NEA (stony
> iron, 1AU/1year) is the greatest threat to Earth! It approaches
> slowly, so when it hits the atmosphere, it doesn't build up a
> ferocious pressure wave of superheated air, to crush it high above
> the ground. It's more solid than a light CC, so it's crush strength
> is higher. Even worse, since we rarely have it in our night skies
> while it's near enough, we have trouble seeing it.
>
> A question: Could rock dust be vaporised and used as propellant in
> an arc jet of some kind? Solar thermal? Is this any better than a
> mass driver rocket? It seems simpler, but the idea of electrically
> propelling rock vapor is rather technically horrendous.
>

Al Globus
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.

I think we should:

1. Devote half of NASA's budget ($7 billion) to reaching NASA's 2020 goal of
reducing launch costs to Low-Earth-Orbit to $220/kg with a 0.01% failure
rate.
This should enable space tourism. The resulting orbital hotels will need to
develop efficient orbital life support and other necessary technologies.

2. Build orbital space colonies. The materials in the largest asteroid are
sufficient for orbital colonies with a combined surface area about 500 times
greater than Earth's. Eros alone could make over ten thousand space colonies,

each with about about 10 square kilometers of 1g living area.

3. After a few generations of orbital living, people won't need their colony
to be near Sol. Then small groups of colonies with populations in the
tens-of-thousands can set out on multi-decade journeys to nearby stars.

Except the launch goals, none of this is even a little bit official.

--- In spacesettlers@y..., Al Globus wrote:
>
> Moderate sized NEAs seemed to be covered with a layer of dust
> and gravel. Should be reasonably easy to scoop up (this needs
> to be tested). If this is true, a small facility on a
> convenient NEA could supply materials to other small
> vehicles for return to earth. Perhaps use a shuttle
> between the NEA and NEA low orbit so the return vehicles
> don't need to land.

By moderate sized NEAs, I take it you mean sub-1km. Certainly there
should be enough of these out there, even if we only have a handle on
maybe 10% of them (at best) at the moment. The question (for the
purposes of selecting one to mine for resources) is how accessable it
is to Earth. This is a combination of relative velocities and
distance. As a rule, I think we can predict that no asteroid will
remain close to Earth at all times. At best, we could hope for one
that approaches Earth at regular intervals, and that personnel or
material transfers were executed at the times of closest approach.

JPL maintains a list of NEAs. A subset of that list is the
Potentially Hazardous Asteroid catalog. The PHA catalog lists bodies
with an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 AU
or less and an absolute magnitude (H) of 22.0 or less are considered
PHAs. In other words, asteroids that can't get any closer to the
Earth (i.e. MOID) than 0.05 AU (roughly 7,480,000 km or 4,650,000 mi)
or are smaller than about 150 m (500 ft) in diameter (i.e. H = 22.0
with assumed albedo of 13%) are not considered PHAs. Quite a few
PHA's have a relative velocity to Earth of under 6 km/s.

Another question that occurs to me to ask is: is it better to seek a
minimal closest approach, or a minimal velocity difference between
Earth and our target asteroid? Having both at a minimum would be
best, but from what I see in the PHA table, you're lucky to get one
or the other, and don't often see both. If we are talking sending
out a simple robotic collector, it might actually be cheaper to use a
slower orbit, and have the probe travel with the asteroid for most of
one orbit. Yes, the money for the venture is tied up longer, but
there's less of it.

If we did this, the orbit would need to be fairly short (from closest
approach to closest appraoch). A quick examination of the PHA
catalog suggests the asteroids 1991 JW (May 23, 2009/0.0812 AU/5.08
km/s & Nov 28, 2010/0.0952 AU/7.82 km/s) or 2000 EE104 (April 12
2001/0.0822 AU/7.43 km/s, April 12 2002/0.126 AU/6.32 km/s, April 4,
2003/0.1701 AU/5.82 km/s, etc...), for example. Unfortunately, the
PHA catalog offers no indication of object composition or size.

Last point: if we are able to find a short-period asteroid as I
described, it would make a lot more sense to first send out small
(read: inexpensive) robotic probes to a number of candidate
asteroids. The probes should be capable of sampling the material and
signaling the result back to us. Based on the results of these
probes, we would have a better idea of what equipment to send along
on the mining vehicle a year or two later. End result is a net
savings.

Michael E. Eckardt
mike@...
http://orbitalhabitat.com

John Frazer wrote:

> I must be sounding schitzophrenic -first one thing, then another.
> Playing devil's advocate, trying to bolster _and_ pick apart
> proposals. All part of developing ideas.
>
> However, NEAs are starting to look better all the time.

In some ways.

>
>> -go to the Moon
>>
>> Yes, in that it is a nearby source of raw materials
>> outside of the steepest part of the Earth's gravity well.
>
> Nearby, yes, but NEAs are more accessible (distance doesn't matter
> nearly as much as relative velocity), as well as richer sources.
> Now we have some choices: If you pick a light CC (like Diemos),
> you've got volatiles aplenty, but very little metals (probably about
> like Lunar ores).

That much? If so, that's plenty. But it's not clear to me that they do.
What makes you say so?

> An extinct short period comet core may be nothing
> but crumbly ices, with a covering of dark dust. Halley's comet core
> has a density of .2gm/cc (20% of water). Even though it's mostly
> hollow, most of what's left is ices.

Ice is heaven. Rocket fuel. Steam rocket. Or LH/LOX. Carbon may mean
plastics. Plastics make seals. But you need metals to make mirrors,
rockets, conductors etc.

> Go to an Iron asteroid, and you've got 80% iron/nickle/cobalt, with
> attendant rich Pt & precious/strategic metals, but very little
> process chemicals to work them with.

Yes. Not good initially. Long run different.

> Get some of each? Certainly, in the long run, we'll do this.
>
> The best bet is to find a little chunk of a stony-iron. As close to
> 1AU/1year orbit as possible.
> Such a stony-iron would probably have about 30% metals, and the
> remainder would be about 20% volatiles. Still, if we're catching a
> 300 meter asteroid, we're rich!
> A stony-Iron NEA seems to be the best bet. Far better than Luna,
> infinitely better than Mars surface. The retrieval mission would be
> the second thing built; first, the LEO ET station. It receives the
> first small samples from the NEA, and as the shipments build up, it
> builds the shielded HEEO base, with rotating habitat section. The NEA
> chunk is brought to HEEO, to pace near the HEEO station.

Yes, but as it says in an old cookery book I once read: 'First catch
your chicken.'

Also, NEA are problematical, they are hard to get to, telepresence
cannot be used. Still, its all pros and cons.

> When somebody uses the O'Leary idea of a mass driver bringing an
> asteroid chunk back, the idea of a Lunar mine may be in trouble.
> This may also happen with a mass driver or high strength tether
> facility at the NEA, and another (couple) in Earth orbit. (The rock
> doesn't need to be _in_ HEEO, if it can get loads to there
> frequently.)
> I'm not sure how often a reasonable tether/mass driver can throw
> payloads back to HEO, but the needed delta-V is tiny at the best
> times. If you can throw (SWAG) 100kg loads with 3km/sec, then you can
> probably have loads coming into HEO to be caught, through most of the
> year. At the best times, less than 1km/sec.

You can probably achieve that with a mass driver, which may be
atleast as useful to build in the long run.

> It's also interesting in that this very exact type of NEA (stony
> iron, 1AU/1year) is the greatest threat to Earth! It approaches
> slowly, so when it hits the atmosphere, it doesn't build up a
> ferocious pressure wave of superheated air, to crush it high above
> the ground. It's more solid than a light CC, so it's crush strength
> is higher. Even worse, since we rarely have it in our night skies
> while it's near enough, we have trouble seeing it.
>
> A question: Could rock dust be vaporised and used as propellant in
> an arc jet of some kind? Solar thermal? Is this any better than a
> mass driver rocket? It seems simpler, but the idea of electrically
> propelling rock vapor is rather technically horrendous.

Off hand, probably doable, but its likely to give bad performance
for a given temperature of exhaust. Low molecular weight is important
in deep space applications.

>

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding technological
civilization?"
- Gerard O'Neill

> John Frazer wrote:
>> (Luna is) Nearby, yes, but NEAs are more accessible (distance
doesn't matter nearly as much as relative velocity), as well as
richer sources.
>> Now we have some choices: If you pick a light CC (like Diemos),
you've got volatiles aplenty, but very little metals (probably
about like Lunar ores).

Ian Woollard wrote:
> That much? If so, that's plenty. But it's not clear to me that they
do.
> What makes you say so?

It's the understanding of planetary scientists that this is what
extinct comet cores (which seem synonymous to extremely light CCs,
which is what Diemos seems to be) are like. I believe Temple-Tuttle is
now an Earth Crosser. It was seen early in the 20th century as a faint
comet, and was lost. It was rediscovered as an Earth crosser, and
turned out to be the former comet. It orbits the Sun in a torus cloud
of escaped dusts (an annual meteor stream, when the Earth sweeps
through it)

Halley's comet core is over 80% covered with dark dust. A few holes
are poked through this (presumeably by impacts) and all the outgassing
we see comes from these few percent of the surface.
The dark surface dust is what's left over of the body's material
after ices evaporate. A layer of this regolith dust is what's left to
build up. (Regolith: fine powder-like dust layered relatively evenly
over a body by repeated impacts) It's reasonable to say that it's
comparable to Lunar regolith, because it's conservative; Lunar
regolith is relatively poor in useful resources.
I should have been more specific: aside from the ices, the dirt left
over is probably about like Lunar regolith. A tiny fraction of a CC
asteroid/extinct comet mass will be metals. Lewis says that a CC is
about the consistency of partially dried, frozen mud.

> Ice is heaven. Rocket fuel. Steam rocket. Or LH/LOX. Carbon may mean
plastics. Plastics make seals. But you need metals to make mirrors,
rockets, conductors etc.

Better than this, along with the H2O ice, there's most likely CO,
CO2, CH4, and NH3.

> Yes, but as it says in an old cookery book I once read: 'First catch
your chicken.'
>
> Also, NEA are problematical, they are hard to get to, telepresence
cannot be used. Still, its all pros and cons.

I understood that the debate was more than the next 3 years of
activity. Within the next 3 years, whoever has gotten the funding
together for this, decides which NEAs to send robots to. Better than
NEAR, we need soft landers, which can get around & drill & dig.
Decide which one is your preferred target, and after some better
robotic sampling (maybe a return) you get together the manned mission
(~10 years ahead?)

> A question: Could rock dust be vaporised and used as propellant in
> an arc jet of some kind? Solar thermal? Is this any better than a
> mass driver rocket? It seems simpler, but the idea of electrically
> propelling rock vapor is rather technically horrendous.

If you powderize the rock, to about 1 mm size, you can statically
charge it and accelerate it in a electric field. The velocities you
build can be enoromous 20 - 100 km/s. The method is used today as a
way of sorting minerals.

Bill

Mike Eckardt wrote:

> --- In spacesettlers@y..., Al Globus wrote:
> >
> > Moderate sized NEAs seemed to be covered with a layer of dust
> > and gravel. Should be reasonably easy to scoop up (this needs
> > to be tested). If this is true, a small facility on a
> > convenient NEA could supply materials to other small
> > vehicles for return to earth. Perhaps use a shuttle
> > between the NEA and NEA low orbit so the return vehicles
> > don't need to land.
>
> By moderate sized NEAs, I take it you mean sub-1km.

Actually, I think the current hypothesis is that larger asteroids have deeper
regolith covers, so the larger the better. However, the largest asteroids
appear to be in the main belt and in the near term, obviously,
near-earth-asteroids are much easier to get to. These tend to be smaller,
that's why I said moderate sized.

Al Globus
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.

I think we should:

1. Devote half of NASA's budget ($7 billion) to reaching NASA's 2020 goal of
reducing launch costs to Low-Earth-Orbit to $220/kg with a 0.01% failure
rate.
This should enable space tourism. The resulting orbital hotels will need to
develop efficient orbital life support and other necessary technologies.

2. Build orbital space colonies. The materials in the largest asteroid are
sufficient for orbital colonies with a combined surface area about 500 times
greater than Earth's. Eros alone could make over ten thousand space colonies,

each with about about 10 square kilometers of 1g living area.

3. After a few generations of orbital living, people won't need their colony
to be near Sol. Then small groups of colonies with populations in the
tens-of-thousands can set out on multi-decade journeys to nearby stars.

Except the launch goals, none of this is even a little bit official.

Would it be possible to test this on simulated Lunar material (the closest
approximation of asteroid regolith we have)? If it can be done on asteroid
regolith without additional materials, then we have a terrific source of
reaction mass for transportation.

Anyone know the size distribution of Lunar regolith?

Bill wrote:

> > A question: Could rock dust be vaporised and used as propellant in
> > an arc jet of some kind? Solar thermal? Is this any better than a
> > mass driver rocket? It seems simpler, but the idea of electrically
> > propelling rock vapor is rather technically horrendous.
>
> If you powderize the rock, to about 1 mm size, you can statically
> charge it and accelerate it in a electric field. The velocities you
> build can be enoromous 20 - 100 km/s. The method is used today as a
> way of sorting minerals.
>
> Bill
>

Al Globus
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.

I think we should:

1. Devote half of NASA's budget ($7 billion) to reaching NASA's 2020 goal of
reducing launch costs to Low-Earth-Orbit to $220/kg with a 0.01% failure
rate.
This should enable space tourism. The resulting orbital hotels will need to
develop efficient orbital life support and other necessary technologies.

2. Build orbital space colonies. The materials in the largest asteroid are
sufficient for orbital colonies with a combined surface area about 500 times
greater than Earth's. Eros alone could make over ten thousand space colonies,

each with about about 10 square kilometers of 1g living area.

3. After a few generations of orbital living, people won't need their colony
to be near Sol. Then small groups of colonies with populations in the
tens-of-thousands can set out on multi-decade journeys to nearby stars.

Except the launch goals, none of this is even a little bit official.