Re: Solar powered lasers in space

On 20 Sep, 08:47, Willie.Moo...@xxxxxxxxx wrote:

> 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.

I doubt that. If you are going to travel at 0.03c you want an ion
drive that accelerates to 0.05c (say)

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.

You will need something with which to construct them.

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..

I think you will find that people want to live in settlements. They
try to strike a compromise between a city with its congestion and a
homestead. Somewhere there is a compromise that suits the majority of
people. If the lifespan of people radically increased, if people
started having "second families" you might have more of a case. The
case, as I see it at the moment, is for a solar powered Earth with a
population of 9 billion. Space based solar power may quite possibly be
the answer.

One of the facts about human habitation is that 90% of the worlds
population lives on 10% of the surface. If you do have abundant solar
power, one of the things that could be done is to desalinate and make
the desert fertiile. People who are not space enthusiasts will ask the
following questions.

1) Lots of people live in the so called Sahel region of scrubland
which is on the southern fringe of the Sahara. Can this area be made
reliably fertile?

2) Could cities be constructed in air conditioned domes, again in the
Sahara?

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.


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.

NASA has already been sold on the idea. It has produced the report. It
is putting quite a bit of effort in.

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.

I profoundly disagree. We have indeed been lied to about Iraq, but let
us remember this. It is the Iraqis and not the Americans that have
produced 4 million odd refugees. 2 million within Iraq and 2 million
is surrounding countries. I shall be going on a tour of Syria late on
the October. There are 1m Iraqis there.

I hold no brief for Bush, it is all his handiwork, getting rid of
Saddam Hussein opened up Pandora's box. However it does rather rubbish
the Rousseau theory. In fact I would put things the other way round.
Governments in fact reflect the prejudices of their populations. There
was anti semitism in Germany after WW1. Hitler did not create it. He
expoited it in an extremely cynical way, but it was there all the
time.

I was absolutely aghast when Einar, I think i was, suggested that
religious groups should set up colonies in space. She should go with
me to Syria and continue to the Iraqi border.

How can this be cured. Cetrtainly not by taking a wishy wasy Rousseau
position as you seem to. Governments have a responsibility to
eliminate prejudice as far as they can. They have a duty also to
protect their countries (obviously) but not to push the arms race
forward and always be prepared to sit down to discuss disarmament.

Man is not Rousseau, Man is the Lord of the Flies.

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.

This is true. People want answers to the above questions. recently
there was a Poker contest between Man and Machine. I posed in
sci.maths that Von Neumann was right (about Poker at least). The
minimax strategy works.

Howver the world is not a Poker game. The world is a stag hunt. Every
side will gain from cooperation. The problem is convincing people of
this. The irony is that I am not asking for people to be unselfish. In
fact in some ways I am asking them to be more selfish. The 9/11
hijackers were unselfish when all is said and done. They were in fact
the Lords of Flies and were NOT promted by any government.

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.

The next step for culture is the promation of rationality. OK we do
need resources as well. We basically need the resources of space on
Earth. I don't think we need to live in space, not at least in the
short or medium term.

There's still a huge shortage. Where to get it? Now



- Ian Parker

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