Settle the moon first using tethers

After a suborbital rocket gets things started, all the
energy/momentum for lifting people/cargo the rest of the way
to the moon and then lowering them down onto the moon can
come from moon rocks going the other way. This fantastic
situation is due to using rotating space tethers for momentum
exchange. You can do this with 2 or 3 tethers. You need
one in LEO and one around the moon, and might want one at
GEO as a step along the way. So you only need a rocket to
get halfway to LEO and then the tethers take you the rest of
the way to the moon. The lowering of moon-rocks into the
Earth's gravity-well is where the energy comes from to lift
people/cargo up.

I think this ease of getting to the moon will make
the moon the first destination for space settlement.

Note that the space tethers I am talking about can be built
with existing Spectra-2000 (used for fishing line) and do not
need any new materials.

Space tethers also mean that small X-prize type reusable suborbital
vehicles are probably closer to what we eventually need than the
big orbital rockets we have now. So they may be the important
evolutionary path for rockets. Some people have tried to claim
that X-prize type vehicles are not an evolutionary step toward
getting to orbit, but with space tethers they really are. You
need more delta-V, but should be able to grow to the needed speed.

-- Vince

PS I have mentioned this before, but I think it is so important
it is worth repeating.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~
Vincent Cate Space Tether Enthusiast
http://spacetethers.com/
Anguilla, East Caribbean http://offshore.ai/vince
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~

You have to take life as it happens, but you should try to make it
happen the way you want to take it. - German Proverb

In Mike Combs sig file it says:
We should ask, critically and with appeal to the numbers, whether the
best site for a growing advancing industrial society is Earth, the
Moon, Mars, some other planet, or somewhere else entirely.
Surprisingly, the answer will be inescapable - the best site is
"somewhere else entirely."

Gerard O'Neill - "The High Frontier"

I think if O'Neill understood how easy rotating tethers
can really make Earth/Lunar traffic, he would not have said that.
But the first paper on rotating tethers (Moravec's below)
seems to have come out in 1977, the year after "The High
Frontier". So I can't fault O'Neill. But today we should
all understand this...

From Moravec's '77 paper:
Energy losses could be replaced by catching high velocity loads
launched from some convenient place (such as the moon),

http://www.frc.ri.cmu.edu/~hpm/proje...ers/scable.pox
H.P. Moravec, A Non-Synchronous Orbital Skyhook, 23rd AIAA
Meeting, The Industrialization of Space, San Francisco, Ca.,
October
18-20, 1977, also Journal of the Astronautical Sciences 25,
October-December, 1977.

The first paper I know of on the combination of a rotating tether and
a rocket was in 1983:

http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/1982.articles/carley.mss
F. Burke Carley and Hans P. Moravec, 1983,
"The Rocket/Skyhook Combination",
L-5 NEWS March pp. 4-6.

By splitting the work between a rotating tether and a rocket neither
has too much delta-V to do. Since both tethers and rockets get
exponentially larger for higher delta-Vs, this splitting the work
is a really good thing.

And in 1991 a paper explained using a combination of tethers to
get to the moon and back:

http://www.tethers.com/papers/LEO2Lunar'92.pdf
"Tether Transport from LEO to the Lunar Surface", R.L. Forward, AIAA
Paper
91-2322, 27th Joint Propulsion Conference, 1991.


The big advantage of being in orbit is that you can easily
get sun for solar power all the time. But it seems you
can get this on the moon by locating your solar on a mountain
peak at either the North or South pole.

The big advantage of being on the moon is that shielding is
really easy to do. In orbit you need to lift all the shielding
from Earth or the Moon. For a settlement, where people are staying
for many years, you need lots of heavy shielding.

Gravity is also free on the Moon and something you have to
make for a settlement in orbit.

So what seemed like the best place for a settlement in 1976
does not seem (at least to me) like the best location
today, given the new tech of rotating tethers. The cost
to make a lunar settlement for a given number of people
would be much less than for the same number in orbit.

-- Vince


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~
Vincent Cate Space Tether Enthusiast
http://spacetethers.com/
Anguilla, East Caribbean http://offshore.ai/vince
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~

You have to take life as it happens, but you should try to make it
happen the way you want to take it. - German Proverb

"Vincent Cate" wrote in message
om...

I think if O'Neill understood how easy rotating tethers
can really make Earth/Lunar traffic, he would not have said that.

The fact that the moon lies at the bottom of a gravity well is only one of
several disadvantages which O'Neill would cite. The others would be:

Solar energy only available half the time (though you mention this later)

Gravity which is the wrong amount, but which cannot be turned off when
inconvenient

Not a long-term solution to population growth

That said, your rotating tethers might make the installation of the first
moon base, mine, and mass-driver much less expensive, thus bringing High
Frontier about even more easily than anticipated. But O'Neill was
discussing not just a certain amount of industrialization, but mass
settlement on the scale of Europe's settlement of the New World. Improving
the logistics or economics of travel to and from the lunar surface might
well speed up space development, but I don't think they by themselves make
the moon the ideal second home for humanity.

Probably the most critical issue is availability of sunlight, which impacts
agriculture as well as the ability to create a pleasant climate. Life on
the moon will probably involve living under artificial illumination for the
forseeable future.

The big advantage of being in orbit is that you can easily
get sun for solar power all the time. But it seems you
can get this on the moon by locating your solar on a mountain
peak at either the North or South pole.

OK, so there are exactly two locations on the moon that might suffer less
from one of several disadvantages of planetary surfaces. That still doesn't
make the moon as a whole competitive with all of orbital space.

To see what I mean, can we discuss construction of a habitat at either the
North or South pole of the moon which is 4 miles in diameter, houses 10
million people, and continuously tracks the sun?

And even if we could, there's room in orbital space for billions of habitats
like this, not just 2.

The big advantage of being on the moon is that shielding is
really easy to do. In orbit you need to lift all the shielding
from Earth or the Moon. For a settlement, where people are staying
for many years, you need lots of heavy shielding.

Granted, though we'd certainly lift it from the moon rather than the Earth.
But another possibility is lifting shielding mass (as well as raw materials
for construction) from an asteroid.

Now to be honest, unless an asteroid happens along on a nearly-ideal
trajectory at the right time, I anticipate the first habitat will be built
in HEO from resources lifted from the moon. But talking long-term
(remember, O'Neill was talking about "the best site for a growing advancing
industrial society", not just where we could get the earliest modest start),
let's talk about a habitat built next door to a NEO. I don't see that
shielding mass would be any less convenient to obtain in that situation than
on the lunar surface.

Gravity is also free on the Moon and something you have to
make for a settlement in orbit.

But you say that as though providing gravity via rotation were some
significant expense. Is it?

O'Neill calculated the requirements to spin-up the largest of his habitat
designs, Island Three, on a time-scale of months rather than years. He
concluded that the electic motor needed to do so would be no larger than the
engine in most cars, and could be powered by no more solar energy than what
would fall on the end-cap of the habitat. One only need overcome inertia.
The same motor would also make up frictional losses. But with
sensibly-designed bearings, this would be trivial amounts of power.

So what seemed like the best place for a settlement in 1976
does not seem (at least to me) like the best location
today, given the new tech of rotating tethers.

I disagree. I haven't seen anything presented since that looks like a more
viable plan, in my opinion.

The cost
to make a lunar settlement for a given number of people
would be much less than for the same number in orbit.

Are you sure? At low numbers, you're probably right, provided that the
orbital habitat, no matter how small the population, is still required to
provide spin-gravity and radiation shielding. But can you be sure that a 10
million person lunar habitat would cost less than Island Three? Remember
that the cost of energy at the construction site would be a significant
factor. And in any case, the lunar habitat could not provide one-G of
gravity, and would never be able to continuously provide a normal day/night
cycle using natural illumination.

--


Regards,
Mike Combs
----------------------------------------------------------------------
We should ask, critically and with appeal to the numbers, whether the
best site for a growing advancing industrial society is Earth, the
Moon, Mars, some other planet, or somewhere else entirely.
Surprisingly, the answer will be inescapable - the best site is
"somewhere else entirely."

Gerard O'Neill - "The High Frontier"

In article ,
"Mike Combs" wrote:

But can you be sure that a 10
million person lunar habitat would cost less than Island Three? Remember
that the cost of energy at the construction site would be a significant
factor. And in any case, the lunar habitat could not provide one-G of
gravity, and would never be able to continuously provide a normal day/night
cycle using natural illumination.

Mike, I'm nearly as big a fan of orbital colonies as you are --
long-term, it seems obvious that that is where the bulk of humanity will
be living.

But, to be fair, if we had the resources to build Island Three, we could
also build ring-shaped lunar colonies which rotate to provide gravity.

And I disagree that natural illumination is either important nor
particularly desirable in an orbital colony. The requirement for piping
natural light into the habitat, while keeping harmful radiation out,
places rather large constraints on the entire design. In fact I'd go so
far as to say that some of the designs have gone through contortions to
satisfy this requirement, and for no good reason. Photons is photons;
artificial lighting these days can reproduce any desired spectrum
(within the visible and near-visible range anyway) at high efficiency.

I understand that the mental image of lying on a beach in a space
colony, tanning under the natural sun, is good marketing. But it's not
great engineering.

Best,
- Joe

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| http://www.macwebdir.com |
`------------------------------------------------------------------'

Vincent Cate wrote:

In Mike Combs sig file it says:
We should ask, critically and with appeal to the numbers, whether the
best site for a growing advancing industrial society is Earth, the
Moon, Mars, some other planet, or somewhere else entirely.
Surprisingly, the answer will be inescapable - the best site is
"somewhere else entirely."

Gerard O'Neill - "The High Frontier"

I think if O'Neill understood how easy rotating tethers
can really make Earth/Lunar traffic, he would not have said that.
But the first paper on rotating tethers (Moravec's below)
seems to have come out in 1977, the year after "The High
Frontier". So I can't fault O'Neill. But today we should
all understand this...

I don't think that the availability of tethers changes much about the
optimal placements of the first orbital settlements. Tethers make both
approaches (Moon and HEO) much easier. And a HEO settlement would still
have the advantages of continuous sunlight, controlled gravity and the lack
of a gravity well.

That said, I really think tethers should be the main topic of space
propulsion research. They offer more or less propellantless propulsion
throughout the inner solar system, and they do not even require
controversial technologies like nuclear reactors. They could also be built
today if the money were available. No nanotubes required, spectra or zylon
will work just fine.

Maybe if there was some way to calculate an Isp for tethers people would get
interested :-)

[snip]
By splitting the work between a rotating tether and a rocket neither
has too much delta-V to do. Since both tethers and rockets get
exponentially larger for higher delta-Vs, this splitting the work
is a really good thing.

Yes. For large payloads the best thing would be a ballistic reusable space
transport starting and landing on barges in the pacific ocean like sea
launch. The distance from the start barge to the landing barge would be
less than 1000km, so you could do one launch each two days with the same
vehicle.

And in 1991 a paper explained using a combination of tethers to
get to the moon and back:

http://www.tethers.com/papers/LEO2Lunar'92.pdf
"Tether Transport from LEO to the Lunar Surface", R.L. Forward, AIAA
Paper
91-2322, 27th Joint Propulsion Conference, 1991.


The big advantage of being in orbit is that you can easily
get sun for solar power all the time. But it seems you
can get this on the moon by locating your solar on a mountain
peak at either the North or South pole.

That seriously limits the choices for your base, and building a large solar
collector in lunar gravity is much harder than in free space.

The big advantage of being on the moon is that shielding is
really easy to do. In orbit you need to lift all the shielding
from Earth or the Moon. For a settlement, where people are staying
for many years, you need lots of heavy shielding.

I agree. But tethers make bringing mass from luna or earth to HEO much
easier.

Gravity is also free on the Moon and something you have to
make for a settlement in orbit.

Gravity on the moon is probably not enough to prevent bone damage, and
(using tethers) it is really easy to create artificial gravity even for
small free floating settlements. Creating earth gravity on the moon would
be a serious PITA.


What about a combined apprach: You have a small manned or unmanned base on
the moon that just packs bags of lunar soil and rock of a defined mass with
a handle. You use a lunar tether to pick up these bags and throw them into
a highly elliptical earth orbit.

In low earth orbit there is a second tether that picks up these bags and
decelerates them to suborbital velocity and drops them into the pacific.
The energy can be used by this tether to lift payloads from a suborbital
trajectory from the above mentioned ballistic suborbital space transport to
a settlement in HEO.

One advantage is that the tether does not need to be an electrodynamic
tether. Its straight momentum exchange. And while an electrodynamic tether
would take weeks or months to correct its orbit after lobbing a payload, a
momentum exchange tether could work much more often if enough bags of lunar
mass are available.

Your main lunar export in this scheme would be just mass on top of a gravity
well. No processing required except stuffing rocks in a bag. Each kg of
mass you get from the moon into the pacific lets you get a kg of mass from
a suborbital trajectory to HEO, where it can be incorporated in the
settlement.

Did I just invent that, or is there some prior art :-)

best regards,

Rüdiger

Joe Strout wrote:

[snip]
I understand that the mental image of lying on a beach in a space
colony, tanning under the natural sun, is good marketing. But it's not
great engineering.

Conversion of sunlight to electricity and back to something resembling
sunlight will not have an efficiency of more than 25% for the forseeable
future.

So just using a large concentrating mirror to focus the sunlight, a filter
to filter out the harmful parts, and a light pipe to get the sunlight into
the colony would be much more efficient.

I agree that the pictures of colonies with square kilometers of windows are
ridiculous though.

Joe Strout writes:

In article ,
"Mike Combs" wrote:

But can you be sure that a 10
million person lunar habitat would cost less than Island Three? Remember
that the cost of energy at the construction site would be a significant
factor. And in any case, the lunar habitat could not provide one-G of
gravity, and would never be able to continuously provide a normal day/night
cycle using natural illumination.

Mike, I'm nearly as big a fan of orbital colonies as you are --
long-term, it seems obvious that that is where the bulk of humanity will
be living.

But, to be fair, if we had the resources to build Island Three, we could
also build ring-shaped lunar colonies which rotate to provide gravity.


Yes, but the people who live in those one-gee rings could not readily
commute to *zero*-gee industrial parks. That, not arbitrary chunks of
living space, was the purpose of the O'Neill habitats.

The Moon is for mining. Manufacturing, other than for local consumption,
is probably best done in orbit.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-718-0955 or 661-275-6795 * -58th Rule of Acquisition *

In article ,
Ruediger Klaehn wrote:

Joe Strout wrote:

[snip]
I understand that the mental image of lying on a beach in a space
colony, tanning under the natural sun, is good marketing. But it's not
great engineering.

Conversion of sunlight to electricity and back to something resembling
sunlight will not have an efficiency of more than 25% for the forseeable
future.

True but not necessarily relevant. Also a bit misleading; this is often
construed to mean you'd need solar panels 4 times bigger than your crop
area, for example, which isn't true. Quick calculation: if we assume
20% efficiency for light-electricity, and 55% efficiency for
electricity-light (which is the current best rate, in sulfer discharge
lamps), the product is 11% efficiency. Multiply by 7, for amount of
sunlight available in GEO vs. the ground, and you have 77% as much light
available in this way as compared to using the light directly.

But this does not take into account that the artificial light generated
might be more efficiently used for photosynthesis. Chlorophyll
optimally absorbs certain wavelengths; artificial lights could be tuned
to emit exactly those wavelengths, which might mean that you need less
area for your solar panels than you need for the crops themselves.

So just using a large concentrating mirror to focus the sunlight, a filter
to filter out the harmful parts, and a light pipe to get the sunlight into
the colony would be much more efficient.

True, if efficiency is the primary concern. But it might not be. For
example, you may need some pretty exotic and expensive materials for
that light pipe to make it handle the energy densities involved. Or,
you might find it more economical to run your colony on a nuclear
reactor than to have square km^2 of solar panels and mirrors.

I agree though that if you're going to use natural light, that's the way
to do it -- no need to try to provide a view of the sky.

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| http://www.macwebdir.com |
`------------------------------------------------------------------'

Joe Strout wrote:

[snip]
So just using a large concentrating mirror to focus the sunlight, a
filter to filter out the harmful parts, and a light pipe to get the
sunlight into the colony would be much more efficient.

True, if efficiency is the primary concern. But it might not be. For
example, you may need some pretty exotic and expensive materials for
that light pipe to make it handle the energy densities involved.

If you have a concentration of 100 and a reflectivity of 99% (which is
really easy for mirrors in a vacuum), you get a heat load of 1kw/m^3, which
is not a big problem. And since a light pipe consists of a metal pipe with
mirrored walls you do not need any materials more exotic than aluminium or
glass.

Or,
you might find it more economical to run your colony on a nuclear
reactor than to have square km^2 of solar panels and mirrors.

That is highly unlikely since it is extremely easy to build a large mirror
in space. Even if you are in the main asteroid belt, it will probably be
cheaper to build mirrors than to mine uranium.

I agree though that if you're going to use natural light, that's the way
to do it -- no need to try to provide a view of the sky.

The rotating sky would make people sick anyway...

Ruediger Klaehn wrote in message ...
I don't think that the availability of tethers changes much about the
optimal placements of the first orbital settlements. Tethers make both
approaches (Moon and HEO) much easier.

Two-way traffic is really extra easy with tethers. Traffic to the
moon can always become two-way traffic because you can send moon
rocks the other way. You could not do this for traffic from Earth
to HEO (unless you first got an asteroid there). Granted you could
have rocks go one-way off the Moon to HEO and then do two-way
traffic from their to Earth, but this will not be as easy. Strange
as it may seem, it really takes less energy with tethers to send
stuff to the moon than LEO or HEO. This is why the moon is special
and why I think the first settlements will be there.

Gravity on the moon is probably not enough to prevent bone damage,
[...]

If I move to a settlement on the moon I would never expect to move
back to Earth. I moved to a tropical island and gave up my US
citizenship (I am now an Anguillian citizen) as I don't expect
I would ever want to move back. I could imagine moving from the
moon to an asteroid someday, but then I would need even less
bone strength. So for me, would there be any reason I should
care if my bones adjust to 1/6 G?

-- Vince