Re: Solar powered lasers in space

On 19 Sep, 15:30, Willie.Moo...@xxxxxxxxx wrote:
I don't think I have missed anything. At 200m km you have 2*10^11
wavelenths. This means that 1.22d1.d2= 2*10^11 wavelengths or
2.44*10^5m^2. If we focus a 10m beam on asteroid this gives us a
diameter of 2.44*10^4m. 24km. Is that possible.

Please point to what you're talking about. I see the 1.22 factor in
there, so it looks like Rayleigh limit,

The 10m spot on the asteroid is at the first minimum of a circular
aperture. It is Rayleigh,

But I divide, not multiply to get the Rayleigh limit

sin(theta-r) = 1.22 lambda / diam
= 1.22 * 1e-6 / 24e6
= 5.083e-14

You multiply to get the apeture.

And the radius around the center line of the Airy disk at a range of
200 million km from a 24 km diameter emitter you have;

R = 5.083e-14 * 2e11 = 1 cm

24km 1.22lambda/d radians or 1.22/24*10^9 or 5*10^-11 radians = at
200million km or 200*10^9m or 2*10^11m 2*10^11 * 5*10^-11 = 10m
at 20 billion km

R = 5.083e-14 * 2e14 = 1 m

I think we're talking past each other. I should have said, I missed
what you were saying...

I think you are right. I think too we were talking about different
things. NASA was talking about planetary defense. You are talking
about using asteroids.

A laser film with active optical film layered together - responding to
a 'seed' to use your terminology AT the target - emitting 1 MW or more
of laser energy per square meter is what I'm talking about. Several
of these films operating together to form an array of phase controlled
elements 20 km wide or more is what I'm talking about.

Now, what's the commercial value of this infrastructure? The answer
obviously is to gather the riches of the solar system to bring back to
Earth and its people to use commercially. And payback with some
return the folks who put the money into building it in the first
place. As a side benefit, all the objects in the solar system will
have been surveyed, and all the objects that will collide with the
Earth will be deflected - a new epoch will have arrived for the people
of Earth.

This is true.

One point which is
often missed when discussing this is the fact of phase coherence
across an array.

Right. That's the point of the pilot beam from the target. You can
set it up so that a 'seed' beam as you called it, could be used as a
reference. Basic holography really - and that reference could direct
the energy to another point. But to my way of thinking a pilot beam
FROM the target is a simple solution. The ability to direct the beam
elsewhere -other than where the pilot or seed beam comes from- and
change its phase across the surface- can be used for a wide range of
applications though - and I do have a notion how this can be used to
provide some interesting safety and reliability features going
forward. Even to charge customers for their power use! lol.

This is really the point I am trying to get across.

This is an important point. It lets you use flexible films and yet
coordinate their actions as a single device. It also lets multiple
emitters act as a single device as well. I think I wasn't clear that
the pilot beam concept I spoke of decades ago is precisely this.

If you have a single laster with a 10cm mirror that will extend to
500m at 42,000km. If you have a phased array however you can focus
onto points < 1m in size.

What are you saying here?

1.22 lambda / diam = 1.22 1.0e-6 / 1.0e-1 = 1.22e-5 = sin theta-r

R = sin theta-r * 42e6 m = 1.22e-5 * 42e6 = 512.4 m

This is the Rayleigh limit for a 10 cm diameter system. 1 m is far
smaller than this. So, you are saying that an array of points with
phase control can exceed the Rayleigh criterion!

So I must ask. Do you have any references for that? Pointers to peer
reviewed papers and such?

I'm really not tracking what you're saying because in this instance
you're saying you can do better than Rayleigh tells us, and above
you're saying we do considerably worse.

So, a pointer to your source material would be great. I'll study it
and get back with you.


Of course we do everything in parallel. We are looking at orbits as of
now. As I said in my first contribution to the thread on the NASA
report, a laser system would determine the orbit more precisely, give
greater warning and add up to a far lower delta v.

Correct. You are doing something much more limited than I am
suggesting. You are looking for small bodies from Earth and then
beaming energy to asteroids that will one day strike the Earth - from
Earth based lasers - as they approach.


The idea of a nuclear bomb is that it vaporizes the surface thereby
proving a small delta v. A laser would essentially do the same thing
but act over a longer time period.

Correct. A shaped nuclear charge that vaporizes a well defined
region. The energy in both cases are comparable however.

You don't send it back to Earth, you simply deflect it so that it goes
close to the Earth but does not collide. That is the basic idea.

That's YOUR idea. And it has ZERO immediate economic utility. It
avoids disaster sure, so it does have some utility and is worth doing
- like paying your insurance premium. Actually better than paying
your insurance premium, it avoids disaster. But MY idea is to take it
up a notch. Build an infrastructure than can RETURN RICH ASTEROIDS TO
EARTH ORBIT - they don't hit the Earth either. They enter a
controlled well defined polar orbit. Once there, they are visited by
private developers who have paid for the right to build solar powered
factories that extract the material process it in space using sunlight
as an energy source and return the processed material to customers
anywhere they are found in the solar system. But principally to
Earth. The same technology that brought us JDAMs can also bring us
low cost entry carriers that deliver products made in space precisely
to customers anywhere in cislunar space.

This could be done in an unpiloted mode - but that would be after
extensive testing and a few successful piloted missions.

This is the basic gravitational well concept. Asteroids do not have a
well.

If you do this there is one thing for sure. Ion drive will be able to
reach anywhere in the solar system fast and cheaply. Also here a
reminder of the Forward interstellar proposal may not be out of place
here.

Of course the interesting fact is that a Forward probe (interstellar)
is going to be the end result. However there are a lot of intermediate
goodies in what you propose, so the chance of it getting off the
ground is increased.

This sort of scenario provides a way of gradually building up. In any
project you need to have intermediate stages or it wil never be built.

You have to have the prospect of immediate returns or you will be left
hat in hand begging the government to give you the money. Large
resources are routinely developed by humanity. Look at large undersea
oil and gas reserves. Tens of billions of dollars are spent by major
companies over decades to develop the technology and bring the
resource to market. Provided they have a clear ownership right, and a
clear idea of what sort of value they're creating.

Telling folks that you will avoid a catastrophe that might happen in
the next 65 million years - doesn't get anyone off the dime either.
Saying something bad could happen in the next 100 years - doesn't do
much either.

65 million years ago it was really big. There have been a lot of
impacts since, not quite so big. Spephen Hawking says we should go
into space to safeguard the Earth. Risks fall into two categories.
There are the natural risks 65 million BP and all that. Also
Yellowstone and other surpervolcanoes have erupted fairly regularly.
In fact if you had mirrors which could direct sunlight directly onto
the Earth you will recover far more quickly from a Yellowstone event.

There are the political and military risks. To me going into space
because of "political" risks is not a sound policy - if nothing ellse
for the simple reason that space will not solve the problems and could
easily make them worse.

In fact dangerous events occur far more often than once every 65
million years.

But if you can prove to folks that - lookee here - here is a list of
strategic materials that is important to the industrial development of
Earth. Here is the rate at which we use these materials today. If a
world of 10 billion people had a per capita use rate equal to that of
every American - here is what would be needed. There is a huge
difference. Lets remove the military infrastructure to revise some of
them downward.

And some of the existential risks. The question of military
expenditures, and the fact that the peoples on Earth are unable to
live together, is something profoundly worrying. Space alone will not
solve it.

There's still a huge shortage. Where to get it? Now
show them some spectra of asteroids that indicate its out there. Show
them some photos of asteroids. Show them pictures showing the orbits
of 30,000 known small bodies. Show them estimates of the actual
numbers. Then show them you can retrieve all the strategic material
industry will need for the next 100 years - within 15 years - by
funding a program today - and with 50% ownership - they'll make 30%
per year return compounded... and they'll be able to diversify their
risk and earn profits on their investments in as little as 5 years
when the whole thing is at a stage it is bankable and listable.

As all of you are probably aware my "hobbyhorse" is AI and robatics
and there seems little doubt that a solar complex would rapidly
develop into a Von Neumann complex in the way that you suggest. I
thought at one point that a VN machine would be needed to build
lasers.

Yes. That's a whole 'nother kettle of fish and tying the two
technologies together merely delays the day it arrives. Sort of like
AND gating all our technologies haha.. When EVERYTHING is done, we'll
be in heaven! lol. Well, lets see what we can do now?.

I do not think so. In fact I think that such a program will
"sleepwalk" into VN. Non Neumann himself postulated a robot with a
fuse which would put fuses into all the other robots. This is
replication at its simplest! I feel that a flatpack assembler will
make a VN machine inevitable.

I've spoken to some folks who have built high-velocity guns and rail
guns and they believe we can do a lot with off-the-shelf technology.
Gerald Bull and others have felt since the 1960s that we could shoot
stuff into orbit. We could build laser elements TODAY and shoot them
into space very cheaply with cannons at 5,000 gees. We could do it
with Earth based lasers as well - 5 gees to 50 gees - depending on the
size of the system and what you're sending into space. But whether
you settle on rail guns, super-cannons, or laser propulsion - you can
send lots of 100 kg payloads off world very cheaply - and feed the
launchers with a factory that churns out your basic laser element.
This can be done today.

I think the best way to get lasers into space fairly short term is to
use them as your "cheap" launch system. What in fact would be needed
is experiments on liquid hydrogen and carbon.

Then, once you have your laser element navigating above the solar
surface - beaming TW of energy under your radio command.. then you
can launch a survey ship that uses that energy to zip around the solar
system to check out candidates that you have already identified. Then
you process the asteroid using the laser into stuff you want to keep,
and stuff you want to eject. And ferry the stuff back to Earth
orbit.

If you have a carbon slurry in liquid hydrogen and low launch
costs this may not be the case.

Well this is an interesting technology - but super-cannons have
already been built, though none have yet attained orbit, they are
certainly capable of it. Rail guns too are capable of it. Laser
propulsion - more speculative - should be capable of it, and since
we're postulating super lasers, it makes sense to put that in the game
plan.

Any engineering on asteroids has to be
thought of in a Von Neumann context.

Why? You just said that if we had low launch costs that would
change.

I think you will sleepwalk into it. If you build more lasers out of
asteroid material you are probably pretty close. If you want a large
array you still need space manufacturing. You will find yourself
creating everything except perhaps for the really sophisticated chips.

In fact, you could create small 10 kg to 100 kg robots launched by the
same cannon as the solar pumped laser. These solar powered robots use
solar sails to fly to the asteroids - and call in laser blasts from
the solar laser when they're done sorting through the asteroidal
material. We build them by the millions in factories right here on
Earth and launch them by the millions with rail guns or laser
launchers.. and they spread throughout the solar system - processing
the richest asteroidal materials - readying them to be brought back to
Earth orbit.

These are automated - sure - but they're not self-reproducing. So,
they can be built today.

A $50 million study - resulting in a couple of factories costing a
few billion dollars each, and a launcher infrastructure costing the
same, and an operating budget of a few billion a year to build the
solar laser elements and the asteroidal crawlers - and in 10 years the
first material will be arriving in polar orbit above Earth. Then,
development rights are sold, along with transfer to the orbiting
bodies.. remotely controlled factories provide employment for
everyone on Earth, and everyone on Earth receives products delivered
directly from space factories that fly overhead twice a day.

Providing employment in an increasingly autmated age is going to be a
major problem. Perhaps at some point coal will have to be painted
white.

During the solar system wide survey that supports this effort there
are noted orbits of objects that will one day collide with Earth.
These are deflected to safer orbits - as a public service.

- Ian Parker

.

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