Re: Solar powered lasers in space

On Sep 19, 6:42 am, Ian Parker <ianpark...@xxxxxxxxx> wrote:
On 18 Sep, 19:05, Willie.Moo...@xxxxxxxxx wrote:

On Sep 18, 11:56 am, Ian Parker <ianpark...@xxxxxxxxx> wrote:

One further point on phase mirrors. They will not work in deep space.
In the case of an asteroid one wouold have to have a pilot spacecraft
where the Asteroid will be a double journey into the future.

- Ian Parker

On my google groups tree this is response 41 when sorted by reply, and
for the life of me I cannot bring up response 40 - so I don't know
what to say there.

I'm sorry. I had that rather as an afterthought. The pure phase mirror
will work only for stationary targets. For targets aroung the Earth
you have about 1/3 sec. For the asteroid it might be up to 1hr.



Beaming a tiny spot to an asteroid is a matter of figuring out the
wavelength and the Rayleigh criterion. The assertion you make here -
and the conclusion - doesn't make any sense - so you've missed
something friend.

If we are to seriously consider asteroid capture, or its twin,
asteroid deflection, using sunlight, then we need lots and lots of
power. That means we'll have to dip in close to the sun - this is
several powersat generations away - and it won't be the first thing we
build. But we WILL use micro-nuclear triggered fusion pulse - to get
rid of nuclear materials relatively cleanly - in a variety of ways in
space - one of which is to develop techniques of moving asteroidal
materials swiftly around the solar system.

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,

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

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

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...

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.

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.

Consider though in the far future, a thin film automated system of
cells, that use a combination of solar wind and light pressure to
navigate to a region inside the orbit of Mercury. These cells -
manufactured and sent into space - operate at a relatively high temp,
and so can withstand being a few million km from the surface of the
sun. They are stationary held above the sun by a combination light
pressure and solar wind. The cells join together to form a mat - by
self-assembly - and they coordinate with each other by all seeing the
same reference laser from the target - beamed from anywhere in the
solar system. In this way laser emitters several hundred kilometers
across - operating at 1 MW per sq meter or more - can be contemplated.

Forward contemplated using fresnel lenses to collimate large solar
pumped lasers - in the TW range - to project light efficiently to
laser light sail spacecraft.

Here, we are using advanced laser beaming technology at the emitter
itself, combined with very large structures, located close to the sun,
to produce similar beams.

sin theta-r = 1.22 * lambda / diam

where lambda = 1 micron (1e-9 m)
diam = 20 km (2e4 m)

so, sin theta-r = 6.1e-14

Now, a spot 20 cm in diameter can be formed 1.2 billion km away.from a
20 km diameter emitter using 1 micron wavelength radiation. Emitting
1 MW per sq m - a 20 km diam disk emits a total of 314 TW. This
heat source operating a thermal rocket having an ejection speed of 10
km/sec - can produce a steady thrust of;

F = P/(2V) = 3.14e14 / (2*10,000) = 15.7 GN = 1.6 million metric
tons force

So, a spherical mass of 1 km with a density of 2 g/cc - has a mass of
8 billion metric tons. - and can be accelerated continuously at 7 m/s
per hour. (1/5000th gee)

To impart a delta vee of 7 km/sec (which is typical of moving an
object from the asteroid belt) requires 1000 hours of illumination by
this source. 8 objects per year can be handled by this single source
- harvesting 64 billion metric tons of material into MEO each year -
10 tons for every man woman and child on the planet.

Since the asteroid itself is ejected as the rocket exhaust - we can
estimate how much of the asteroid will be used up;

u = 1 - 1/exp(7/10) = 0.5034 = 50.34%

About half.. part at the outset, part when braking into Earth orbit.

So, 5 tons for every man woman and child on the planet.

First, there would be a survey of all the small bodies inthe solar
system, and then they would be rated for their value. The highest
value objects would then be harvested.

While the survey is going on the sun-centerd solar powered laser
system is built.

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 solar powered laser then beams energy to a manned spacecraft that
travels to the asteroid, and erects a solar powered thermal rocket
describes - it also uses laser energy to process the asteroid into
portions to keep and portions to eject in the rocket.

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.

A small safety team stays on the asteroid, riding it back to Earth on
a minimum energy orbit - and making sure all system operate as planned
- and the main spacecraft, goes to the next target.

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.

Five years - R&D - Five years construction - Five years - mission.

A five year mission - haha- would collect 40 asteroids totalling some
160 billion metric tons of highly useful materials into MEO.

Those asteroids would then be processed by orbiting factories - solar
powered of course - via telerobotics (light delay negligible) - which
then deorbit products directly to users on Earth - or deliver them
anywhere in the cislunar system they're needed.

This will form the basis of the first space farm, and space home
developments. And support the large scale movement of people off
Earth into space - aboard their own space colonies.

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.

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. 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'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.

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.

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.

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- Hide quoted text -

- Show quoted text -


.

Relevant Pages

  • Re: We can meet all our needs through space development
    ... But rather than parroting sources - do you understand why solar cells ... specific band-gap energy. ... of the sunniest places on Earth and it will be a fantastic solar panel ... For example, you could get a dense metallic asteroid orbiting nearby, ...
    (sci.space.policy)
  • Re: Great Untapped Financial Resources for Space Projects
    ... Laser Pulse Rockets (Solar pumped laser) ... a space faring economy. ... unleashed the idea that the Earth was a single place at the level ...
    (sci.space.policy)
  • Re: Solar powered lasers in space
    ... A laser film with active optical film layered together - responding to ... Earth and its people to use commercially. ... all the objects in the solar system will ... beaming energy to asteroids that will one day strike the Earth - from ...
    (sci.space.policy)
  • Re: Solar powered lasers in space
    ... In the case of an asteroid one wouold have to have a pilot spacecraft ... materials swiftly around the solar system. ... In this way laser emitters several hundred kilometers ... - harvesting 64 billion metric tons of material into MEO each year - ...
    (sci.space.policy)
  • Re: We can meet all our needs through space development
    ... in the solar system can be completed in a reasonable time, ... is sent back to Earth orbit will have to be engineered and processed ... day from the asteroid belt 57,000 metric tons per day must start out ...
    (sci.space.policy)