Re: Solar powered lasers in space

On Sep 19, 11:26 am, Ian Parker <ianpark...@xxxxxxxxx> wrote:
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,

That wasn't clear from your jumbled numbers above.. It looked sort of
right, but it was hard to tell what you were doing.

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.

Really If i rewrite the formula above to solve for diameter I still
divide by the angle - rewriting the formula above to solve for diam
you get;

diam = 1.22 * lambda / sin(theta-r)

so, you still haven't explained yourself adequately sorry. What are
you mulitplying to get apeture? (don't say secant either! haha)

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.

AND planetary defense - yes.

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.

Laser powered ion I presume you are saying.. I agree.

Also here a
reminder of the Forward interstellar proposal may not be out of place
here.

Not at all. Pwerful light sails may also be appropriate for probes in
interplanetary space.

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.

Correct. Forward's ideas also scale - you start with small probes and
graduate to larger payloads - eventually piloted missions involving
Bernal stations and whatnot.

Doing as Dyson suggests, and converting the entire output of the sun
to industrial use - but in this case, using stationary laser cells
held in place by solar wind - that coordinate their action by creating
a phased array of the elements - using an external reference beam - at
20% efficiency - would be far far less massive than a typical Dyson
sphere, and be able to establish substantial interstellar commerce.

For example, a 1 mm thick laser film made of some sort of ceramic -
engulfing the sun at a radius of 5 million km - would mass only 754
trillion tons - a sold sphere only 120 km in diameter - So, a handful
of well chosen asteroids converted to cells that form the type of film
we're talking about would be able to produce as laser energy 85e24
watts!!! Converted to kinetic energy at 30% efficiency using laser
light sails permits 5.1 million metric tons per second to be
dispatched to the stars at 1/3 light speed. That's 10 or so space
colony sized payloads each second.

Reducing payload speeds to 3% light speed - increases mass-flow rate
100x. 3% light speed is the delta vee of a spacecraft at constant 1
gee boost travelling from Earth to Pluto.

Engulfing the sun in this way - taking care to not adversely impact
the natural sunlight illuminating the solar system - permits humanity
to treat the solar system as an integrated nation-state, and the
nearby stars as frontiers which anyone who owns a (space) home could
decide to emmigrate to.

Here is where the von-neuman self replication can have benefits.
Sending a Forward 2-stage star-sail to nearby stars, carrying a
replicator probe that made laser cells from any appropriate asteroidal
materials found locally - then a 1 stage laser light sail could
navigate between the stars at high speed. When the star was fully
engulfted - and the planetary system fully surveyed - and the results
radioed back to the parent star. Then 2 unexplored nearby stars would
be chosen to send daughter probes to - and the system will have joined
human space...

600 million space colonies per year arriving from Earth - would flow
thorugh this network - but, if they contained a family each - say 5
people - with a retinue of robots, and replicators - along with their
portable biosphere - and radio telescope - a world of 12 billion
humans would only be able to supply a 5 year pulse before denuding the
solar system of people.

This may be the answer to Fermi's whree are they question. High rates
of reproduction only occur at certain places and time for any
species. Once they become space faring - their reproductive rates
fall, and technology spreads them throughout the galaxy - and the
average density of ANY species - is small - far from their point of
origin..

A ball of stars 100 light ywars across centered on Earth there is
something like 15,000 star systems. 2.4 billion space colonies spread
across this volume of space mean only 160,000 colonies per star system
- 1000 light years and there are 15 million stars - at 3/8% growth
rate per year - exponential growth - human numbers - increase 42 times
- to 100 billion space colonies - but the stars available to humanity
increase 1,000x to 15 million - and the number of five person space
colonies per star drop to less than 7,000 !!! 35,000 people.




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.

Correct. That's what I was getting at.

Spephen Hawking says we should go
into space to safeguard the Earth.

That's nice.

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.

Correct. Humanity needs to be space faring. I think Tsiolkovski said
it best. Earth is mankind's cradle, bt a man cannot live in the
cradle forever. The first step is to make use of offworld resources
for our economic well being. We are doing that with comsats, navsats,
infosats. We will extend it with terrestrial solar, and powersats.
Extend it again by capturing asteroids and putting up factory sats.
And from there there will be a diaspora. We will engulf the sun, and
the age of easy interstellar travel will be born. We will over the
next 10,000 years expand at a large fraction of light speec across the
cosmos - undoing the limitations of modern hive culture of
civilization as we become ever more nomadic and self sufficient -
ending in nomadic tribes sparsely spread throughout the cosmos.

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.

This has been an issue because missiles were first developed as part
of strategic bombing doctrine and containment of that ability has been
the number one job of the post world war 2 era. That doctrine has
protected us and maintained an uneasy world peace. But that is
crumbling in the face of modern terror threats. Those terror threats
arise because control of ability is no longer effective. We must
graduate (as experts have long warned us to do) to the next phase of
maintaining peace - control of willingness.. Success on this front
will permit the means for space travel to finally be made more broadly
available to approved commercial and scientific users.


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

I agree. But selling the government on a space sheild is far harder
than selling a group of investors on a supply for titanium or
osmium... or even for energy and food.

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.

The people are not the problem. The governments and societies they
have structured for themselves are the problem. Ken Arrow a Nobel
Prize winning economist has outlined precisely why governments and
markets cannot achieve what we expect of them. Alice Miller explains
why we are fascinated as a species with power and death. Sigmund
Frued explains why we have adopted a father in the sky figure as our
expression of absolute power. Joseph Campbell has explained how
religions have tapped into our impulse for life and subverted it.
Brownowski has explained how technology and science has been subverte
by culture.

We know the answers - scientists and rational folk have just been shy
about asserting what they know to be true - sensing that reality
doesn't matter to the bulk of humanity. Everyone else is being lied
to and their emotions managed for selfish ends.

The greatest threat humanity faces isn't from space. Its from
outselves. People sense that, and so talk of space shields and space
travel even, makes no sense to them.

Providing a clear practical vision of the next step for our culture
clears a lot of the bull*** away. This is so wanted by people that
folks who falsely claim such knowledge become hugely powerful. As
Campbell said, this is the hero task of the modern age. In the end we
will either become space faring nomads ranging across the stars, or
post-technological nomads ranging across a burned out dying world. We
are choosing now the future of all our generations. We have not
chosen wisely for the past 50 years - we have chosen out of fear
rather than hope.


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

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