Re: We can meet all our needs through space development

On Jan 30, 2:44 pm, Willie.Moo...@xxxxxxxxx wrote:
On Jan 29, 10:52 pm, Einar <eina...@xxxxxxxxx> wrote:

like
expectations of 13% efficiency not 40% as you appear to assume with
solar energy. A large difference.

While 13% was the norm in the 1980s for silicon wafers and one can
actually point to them, they are not the norm for multi-specral
wafers.

http://en.wikipedia.org/wiki/Spectrolab

NREL has already demonstrated that multi-spectral cells exceed 40%
efficiency.

But they´re far more expensive and moreover the 40% efficiency you
were using existe only in laboratory, like I think I pointed out to
you earlier.

You should work with what is commonly available.

I have posted this to you before, but these people have an idea of
replasing much of the fossil fule use in USA.

"A Solar Grand Plan
By 2050 solar power could end U.S. dependence on foreign oil and slash
greenhouse gas emissions"
http://www.sciam.com/article.cfm?id=a-solar-grand-plan

They intend to only use cheap 13% efficiency wafers, and have made a
plan which sounds very doable within theyr stated timeframe, i.e. to
2050.

However, the what I keep repeating to you is that, while I think your
ideas are potentially workable, the timeframe you have thrown at us is
clearly unrealistic.

2100 sounds like a workable timeframe for such extensice ideas. Anyow,
by 2050 we will probably be ready to expand solar energy production
into space.

I´ll expect that before then there will be a time of experimentation,
i.e. small scale experiments with small solar powerstations,
experiments with beemed power, etc.

That´s what is allways lacking in your suggestions,,,the inevitable
experimental phase. By 2050 the experimental phase might be over and
we may be ready to begin your project of building them on a
significant scale - the way you suggest.


Now, when silicon is exposed to light, what happens is determined by
the colors of the light striking it. In the case of the sun, this is
given by the planck curve of a black body radiator operating at 5800K
- through an atmosphere that absorbs some of the energy - principally
hydrogen...

http://en.wikipedia.org/wiki/Black_bodyhttp://en.wikipedia.org/wiki/Solar_radiation

So photons that are longer or redder than 1,108 nm - don't operate the
silicon cell. They merely heat it.

And, photons that are shorter or bluer than 1,108 nm - contribute only
the bandgap energy to the circuit. (if its properly balanced with a
load)

What happens to the extra energy? Well, it shows up as ballistic
energy in the photons in the conduction band - yep - heating the
photocell again.

Then there's the recombination of electrons that get formed but not
picked up - this depends on temperature.

And that's not the only source of loss - there are junction losses -
resistances in the cell itself that cause current squared times
resistance (i-squared r) losses - which also causes heating.

The I-squared r losses can be reduced by reducing junction resistance
- in cells like those designed by Bob Swanson at Sunpower - or by
reducing current for a given power by increasing number of junctions
in series - in cells like those designed by Bernie Sater at Photovolt
- or by combining the two together like I do with my cells at Mok
Industries.

Keeping the silicon cool is how to reduce dark current losses.

This leaves you with ineffective photons. The long-wave photons that
don't contribute to the cells operation - and the short wave photons
that contribute onlty the bandgap energy.

Since the planck curve graphs in the references I gave are energy per
wavelength versus wavelength - the area under the curve.

For each wavelength, take a ratio of the wavelength and the bandgap
wavelength in the case of silicon 1,108 nm - and multiply the solar
output by that ratio. So, for example, the energy in a photon with a
wavelength of 554 nm (green) contributes only half its energy to the
operation of the circuit. 277 nm (Violet) contributes only one-
quarter its energy to the operation of the circuit. Do this across the
entire planck curve (its called convolving the silicon response curve
and the solar black body curve) - and you get what each color
contributes to the operation of the silicon cell. Now integrate the
convolved curves to get the area. Then, finally, divide the smaller
area of the convolved curve with the larger area of the planck aka
blackbody curve - and you get a number - around 23% - with small
junction losses and temperature losses.

Now what Spectrolab did - is they combined photocells of different
wavelengths and arranged to have bandgap matched light fall on each
type - and use the output of all of them. NREL has shown that they
operate at 40.7% efficiency with 3 bandgaps. We are discussing
building 6 bandgap system (GaAs can be doped to change its bandgap
energy) - that is expected to have efficiencies exceeding 60% - the
practical limit seems to be 20 bandgaps - with 80% efficiencies

So, 40% has been achieved

60% is a reasonable near term research target (and the focus of
current research, visit my web site, fill out a contact form,and I
will send you a white paper)

80% is a plausible long term achievement

I quoted 40% overall...

That sounds truly like an excellent technology, but how expensive
would such cells be when compaired to those that already are in mass
production? How quickly can the price be reduced through economies of
scale? Do they contain very expensive materials that will result in
them staying expensive no matter what?

These are worthy considerations. Remember you intend to use these on a
very large scale, presumably first in groundstations. The people with
the abow mentioned plan intend to make do with less sophisticated
technology, and still think that it will be possible to significantly
reduce the use of imported oil over the period to 2050.

The program I find believable assumed that it will take some years to
achieve that 13% efficiency,

40% has already been achieved, I'm funding research to see if we can
achieve 60% by doubling the number of junctions, and qualified
researchers feel that by increasing the number of junctions further
using MEMs technology - it may be possible to get to 80% ...

MEMs are a most important innovation. Clever use of manufacturing
techniques originally used in manufacture of chips, is how most of
them are made. The airbag of my car probably is activated by such a
MEM.

The question will the bee weather the trick of the chip makers can be
repeated, i.e. to make enough of them to shrink the prices down to
reasonable levels.

But if expensive materials are used, or materials which supply could
cause a bottleneck, then they might stay expensive anyhow. Moreover,
many of the chips have become so incredibly complex, so expensive to
develope that even though they are mass produced in great numbers, they
´re not especially cheap to purchase.

That is importan, the price. If you are to persuate people to use
them. Today, older tech solar cells have become cheap enough that
average people can affor to use them on a reasonable scale. Solar
cells f.e. on the roof of a house can really shrink the electricity
bill.

as current mass produced solar cells do
not achieve more than 10%,

I am mass producing CPV systems that routinely achieve 18%

At what cost when compaired with cheaper cells?


I can only assume that you are expecting what is now only possible in
controlled laboratory settings will become practical mass production,
which by the way is not an obvious assumption.

Lets do more than quote numbers shall we. Lets look behind the
numbers and then we can come to some logical conclusions.

The number you give is an average based on systems that use amorphous
or polycrystalling construction. Junction losses are extraordinarily
high in these systems. This is deemed acceptable because they can get
their silicon at very low cost compared to pure float silicon that is
a pure crystal.

What you term - experimental or laboratory - systems have far higher
efficiency.because they use float silicon - that costs about $1 per
square inch. This is about 3x higher in price than polysilicon
systems - but the output is less than double (14% versus 23%) -

I use float silicon - but fabricated in a way and cut into dies that
allow me to operate it at 1,000x solar intensity. (see my web pagehttp://www.usoal.com) - this cuts the PV costs per watt way down, and
lets me operate at higher efficiencies.

Ditto with the UTJ cells from spectrolab. They have a germanium
subtrate - and CVD epitaxially grown - GaAs and InPh layers - whose
thickness allows efficient capture of specific colors of light. These
are $12 per sq inch in quantity.

So, here's the deal; lets compare the older design, with my current
design (Patent #7,081,584 - Mook), and whats in the labs today that
I'm expecting to use on orbit tomorrow;

sunlight - 645 milliwatts per square inch terrestrial clear day
881 milliwatts per square inch space earth orbit

mass produced conventional solar panels
14% efficient
1x concentration
645 milliwatts per square inch solar
90.3 milliwatts electrical per square inch
$0.30 per square inch cost
$3.32 per peak watt (PV cost)

Mok terrestrial PV
18% efficient (filtered)
1000x concentration
645 watts per square inch solar
116 watts electrical per square inch
$1.00 per square inch cost
$0.01 per peak watt (PV Cost)

Spetrolab 6J PV (research)
55% efficient
5,000x concentration
4,405 watts per square inch solar
2,422 watts per square inch electrical
$12.00 per square inch cost
$0.005 per peak watt (PV Cost)

I simply must disbelieve your figures until you can give some idea how
you are arriving at them.

I have not only given you pointers to research results from one of my
vendors independently verified by government laboratories, I have
given you an insight into my current research efforts.

Thank you for that. But as your figures clearly demonstrate the newer
technologies are more expensive per square inc over to far more
expensive per square inc.

That matters a lot, when you intend to use them on a large scale.
However, there is naturally the issue in what setting the planned use
is for. I wouldn´t be surpriced, once perfected and shown to be
reliable, the high energy per square inch types will dominate
installations where cost per square inch is not so great an issue but
energy produced per square inch is.

Since you didn't bring it up, I haven't yet addressed the other big
issue - the laser efficiency, and then the efficiency of the
conversion on the ground. Free electron lasers have achieved 30%
efficiencies 20 years ago, diode lasers routinely exceed 10%
efficiency - yet are less tunable.

http://www.frascati.enea.it/fis/lac/fel/fel2.htmhttp://www.alfalight.com/press-detail.asp?articleid=24

The military has focused on lightweight compact applications for
years. But both teams believe for sound and valid reasons that 80% to
85% efficiencies are achievable with a dedicated effort over the next
five years.

So, I have used those figures for my estimates here.

sunglight ---> DC electricity 55% 55%
DC electricity ---> laser energy 85% 47%
laser energy ---> DC electricity 85% 40%

That´s a bit of an assumption.


By the way, the asteroid project you appear to be assuming sounds
really seriously expensive.

Cost is only one aspect, value created is the other. So, it is
important to create more value than you spend in order to achieve your
goals.

Now, this asteroid operation is clearly an operation in which the will
inevitably have to be a testing period. This will necessiate a large
trained cadre of astronauts. This will moreover also necessiate quite
bit of EVA training of those astronauts. This will in addition
necessiate the development of deepspace vessels, I´d say preferably
nuclear powered. Now, I know you have suggested beemed power over the
distance from the Sun. But that´s another development project with a
testing period all of its own, and expenses, potential bottlenecks,
etc, etc.

Beemed power will require years of testing, first small scale then
large scale all of its own. Now, today we may not foresee any great
difficulties. But there allmost allways are difficulties, especially
when working in an environment humans stichtly speaking still have got
very litle experience in working within.

But, if we accept nuclear power for at the very least the first
generation of deep space wessels, then at least that operation´s
initial successes will not depend on the rate of development of the
other program you apparently intend to run at the same time. So
different development scedules, unforseen bottlenecks need not harm
that operation as well.
You need allways to be able to take such in stride.

Now again about the asteroids, a test will have to be made with
capture and moving an asteroid. Now, an easy in the relative test
operation might be to attempt to move one of the asteroid that orbit
close to the Earth/Moon system around the Sun. Now, such tests are
very important, as you need to know weather you assumption are really
reasonable, i.e. that shining a laser can tell you enough about the
rock to be hauled in to be a practical method for future use, which
was one of the methods you mentioned. You need also to test the
capture operation itself, if for no other reason that your personnel
will need such training. But also in order to develope that operation
itself.

Most likely several such tests at the very least will be necessary in
order to hone the methods used. In addition as they will be necessary
for training purposes of the personnel, and therefore will need
probably to continue.

Naturally, there are several different problems. It would require
quite a different operation to attempt to capture an asteroid which is
only a looselly bound rubble, than an one which is solid through. Each
type will need testing and training of its own.

I expect this beginning phase to take from 15 - 20 years, a
concervative expectation. All through that time these personnel would
have to be maintained, the scientists paid theyr salaries,
etc...something you are familiar with. The ships themselves would also
be expensive.

It would be cheaper to send small ion
powered probes to check on the asteroids.

Cheaper than what? Please explain how you analysed the program and
come to this conclusion. Recall, that we precede dispatching the
probes with a terrestrial program of observation, and follow it up by
dispatching crews to the selected asteroids for processing.

What powers the ion engines in your suggested approach? I use beamed
laser energy.

What makes you think an ion engine is superior to a laser engine of
the same specific impulse but higher thrust to weight?

I am building an infrastructure to carry out a program. Does the use
of ion engine technology assist in that? If so how? Why is it
superior to laser propulsion systems that have equal specific impulse
and higher thrust to weight?

The ion engines using solar cell power, are a tried and tested system.
That´s what they have going for them. Thus they will clearly be
relativelly cheap, especially if massproduced. So many could be made.
That means theyr use will not depend on the development scedules of
all the other systems you intend to be developing. Remember, you are
planning to do this all in the incredibly short period till 2050. So,
I presume that all developmens scedules more or less have to run at
the same time.

So, to safe time ion engined probes can be put into production right
now,,,for all what it´s worth.

In addition, you idea for Earth observation necessiated apparently the
construction of number of sites. Those are not cheap. Depending though
on the size of the observatories you have in mind. But, as you intend
them to give the best idea possible from over here, they sound like
expensive large mirrors to achieve the necessary resolution of such
tiny at that distance objects. Now, such observatories can cost
several billion apiece.

So, ion engined probes while slow can be a cheap in the relative
option. They, I emphasize, may be means to grant your project the
necessary capability of surviving unatticipated development
bottlenecks...that when designing completelly new space based systems
are considered allmost inevitable by reasonably zynical space people.

Remember, laser propulsion is a separate developmen program. Most
certainly, it would be one of the necessary tests of such a system
during its development phase to test it on something, so some of the
probes might be launched away from Earth by a laser in Earth orbit.

After all they´d need to be
observed close up, as you appear to realize.

Of course - but you don't need to observe all of them close up. Then
you need to process those you finally select.

But a swarm of small probes can speed things up, and increase your
chances of actually getting things done in time.

The problem with Earth
observatories is that at the distance we are talking about, the pixels
have become pretty large.

I have some options on land in Chile in the atacama region - its one
of the sunniest places on Earth and it will be a fantastic solar panel
site to feed HVDC electricty to a wire running the entire length of
Chile. Chile is sort of like 4 Californias stacked end to end..
right on the Pacific. A perfect place for the baby boomers to retire
- provided there is enough power and infrastructure to support them.
A beachside house for everyone.

Atacama desert also has an astronomical observatory.

http://www.news.cornell.edu/stories/May06/Atacama.Giovanelli.html

An advanced terrestrial telescope system is easily placed there -
built around large numbers of commercially available telescopes -
operated with AI/automatically - using a variety of optical techniques
to create an optical vlbi as well as adaptive optics - a new approach
I've developed to remove the atmosphere effects -

http://en.wikipedia.org/wiki/Tip-tilt_mirrorhttp://en.wikipedia.org/wiki/Uhdtv

http://en.wikipedia.org/wiki/Adaptive_optics

Those methods of cancelling out athmosphere effects, like you rightly
point out are new. The observatories that are using them indeed are
all new or much renovated. Many of them can even be controlled through
the internet by someone with access. I have spent years chatting with
astronomers,,,so this isn´t an entirelly unfamiliar territory.

These methods remember have limitations. They work best if you look
through the athmosphere the shortest distance out of it and it´s
better to have less of it abow your observatory than more but that´s
true of all observatories. Still, the more of the athmosphere you are
looking through the less effective the adaptive obtics are in
cancelling out the disturbance. That has created the contraint that
the observatories have been limited the angles of view.

So even the best of them will only give a
very rough idea what to expect.

You are talking out of your gut - not out of a sound knowledge base.
Are you familiar with the Rayleigh limit in optics? It tells you what
sort of resolving power you get for a given apeture at a given
distance.

http://en.wikipedia.org/wiki/Optical_telescope#Angular_resolution

Ar = 1.22 lambda / D

Optical telescopes can be joined by optical fibers, synchronized by
laser pulses and using holographic techniques,to create synthetic
apetures that are very large, even while the elements are mass
produced. So a modest array of telescopes in the Atacama desert can
do quite a lot to observe asteroids.

But those will not have adabtive optics. Mind you it doesn´t matter
how many scopes you gather together in that fashion. There is still a
limitation in how much resolution you can get. What a large group of
scope can enable you is to gather a lot of light, which mean you can
observe either of the to; very faint objects or very distant ones.

But the asteroid are so small at the distance, there is no way even
with huge constellations of observatories, to observe theyr surfaces
in except the most rough manner. Like I said, the pixels are to large
in the relation to the size of the objects being observed.

What you need to do is to bring the mirrors in closer like can be done
with spaceprobes. Then you don´t need a very large mirror, only a very
well made one. A superhighgrade camera.

Microwaves have far longer wavelengths, but operated at far larger
distances - vlbi - very long baseline interferometry - can achieve
remarkable results in the microwave region

http://www.news.cornell.edu/releases/Aug99/AsteroidPix.bpf.html

LOL, and Arecibo is well large. You were proposing constructing a
number of observatories. The asteroid in question was only at the
distance of 5,3 million miles. It was therefore very much closer to
the Earth than the asteroids in the asteroid belt.

"The astronomical unit (AU or au or a.u. or sometimes ua) is a unit of
length approximately equal to the distance from the Earth to the Sun.
The currently accepted value of the AU is 149,597,870,691 ± 30 metres
(nearly 150 million kilometres or 93 million miles)."

Near Earth asteroids are those that orbit within the distance of a
single astronomical unit from Earth. Naturally those in groups can be
imaged from surface based observatories. But that´s quite another
thing when we are talking about those the orbit witin the asteroid
belt propers,,,the pixels are to small or to large, whichever way you
prefer to think it.

A $30 million per year terrestrial program can achieve the goals I
have for it in 3 years according to the universities that I have
spoken with - continued funding of the equipment at a far lower level
- will allow it to continue finding new asteroids and mapping them to
the same degree.

Universities naturally want your money. But mapping them, will
probably mean mapping theyr orbits, in theyr speak, not theyr
surfaces...as tha´s clearly not possible at the distance involved
except in very, very roughest outlines and then only with the very
largest.

Of course sending sensible energy to an asteroid and observing the
effect on the ground - is a far larger program. Yet, assuming power
satellites on orbit feeding energy to terrestrial systems on Earth -
it is easy to see what sort of optical upgrades are required to make
spots on asteroidal surfaces that can produce jets.

Oh, so you were actually thinking about blasting them with lasers from
over here. Yeah, indeed that would call for some incredible focusing
of the laser in order so that the beem will not become far, far to
wide at that distance.

Wow...really. That will be gigantically expensive. You are talking
about a huge focusing system. Ultra precision well beyond anything
possible today. Orbital mind you. Will have to be shielded against
micrometeroids, one hit could ruin the whole thing. Think in terms of
hundreds of billion.

Admittedly the alternative is also super expensive, i.e. a trained
cadre of astronauts. Deep space vessels. But those you will have to
use aniway.

The problem with rubble piles is that they can´t be shifted, lest they
come apart.

Why not? Explain your reasoning. Consider that you're in zero
gravity. So, shifting a loose load under those conditions -
especially one that is gravitationally bound already - is not the same
as doing the same thing on Earth under one gravity. So, lets start
right there.

Eeer...we are talking about a very small levels of gravity. Meaning
that if say you happened to be standing on the surface,
hypothetically, then simply jumping would launch you into orbit.

The gravity is to small to compact them together. So they are very
loselly bound. That astronomers know as a fact, as many of them even
the metallic ones have smaller density than water...which can only be
explained if there are large empty space within due to them being so
looselly bound together that theyr material isn´t actually compaced at
all.

Yeah really, they would come apart. You can trust that.

For example, you could get a dense metallic asteroid orbiting nearby,
attach a thruster to it, and use the metallic asteroid as propellant
and a gravity 'tug' - to pull both back to Earth - at reasonable gees
in reasonable times.

Even the metallic asteroids will not be used to acceleration. I´m
talking about those that are solid through. They will have been stable
in theyr environment for billions of years. You absolutelly don´t want
to begin to shift them with high acceleration. In such a case even
they might come apart.

Remember these are rocks that are in space. Never have seen any
athmosphere. Theyr qualities are not identical to rocks you can
observe here on Earth.

Then, consider that taking the asteroids apart is a step in the
process using them to build stuff. Since the rubble piles are
already broken apart, it seems that part of the work is already done.

Will be very tricky to shift them any. But, a factory ship might be
able to use an one if the ship would first travel to each of them.
Then either of the two tugs could move the product gradually over to
Earth or solar sail could be attached to each cargo item independently
and then that could cruise ever so gradually over to Earth. Solar
sails as is known can either of the two cruise on solar energy alone
or they can be speeded up with lasers.

An alternative type of operation, but quite possible.

You´d need some sort of a factory ship on the spot, is my
expectation.

I said you'd need to dispatch crews to the asteroids you selected to
process them for return. Since it takes about 7 years on a hohmann
transfer orbit to bring back an asteroid, and a year or a year and a
half at each end to accelerate them - you'll have time to do quite a
bit of work en-route.

But an alternative is for the refined ore to cruise on a solar sail of
its own towars Earth. A very economic operation it would appear.
Hohmanns transfer can be made with low thrust.

You appear not to consider solar sails as propulsion method,

I considered it and rejected it because the thrusts are too low to
meet my requirement that it take less than 18 months to impart the
required delta vee to the targets.

http://www.nasa.gov/centers/glenn/testfacilities/Sailing_on_Sunbeams....

But, you really want to accelerate asteroids gently. So solar sails
really would be ideal. Anyhow, we have time enough. The asteroids aren
´t going anywhere.

Low power equals low thrust equals long mission times. This may be
acceptable for missions like planetary defense where you locate an
asteroid that will collide with Earth in 206 years and then dispatch a
solar sail to take 100 years to modify its orbit - and its orbit is
earth crossing so its spends time closer to the sun than Earth.

They can be speeded up with your beemed power, in which case theyr
thrust will depend on the power of your laser. In addition, as the
target will be far larger than your intended one, i.e. the backend of
whatever unit you intend to do the accelerating, the problem of
focusing the beem will be more managable presumably.

It is unacceptable for something you want to get done to feed all the
people of Earth before 2040 operating at distances where light levels
are only a small fraction of what they are at Earth. It als is
unacceptable if you want to earn a profit in your lifetime.

There is no reason to decide to feed all the people of Earth by that
time in that fashion. We have lived over here quite comfortably for a
long time.

I reckon that if food produced in space in the fashion you suggest
becomes economic, then it will be imported to Earth. That way, large
tracts of land currently used for food production could be given back
to nature,,,yet the population would essentially stay put.

Ceres is a good representative asteroid. Its the biggest and the
first one discovered. It has a semimajor axis of 2.76AU - that means
that the sunlight on Ceres is only 13.1% of that on Earth. So, you'll
need 7.6 times the sail area at Ceres as you need on Earth to get the
same level of thrust - or get 1/8th the thrust as you do on earth -
and what takes a day to do on Earth with a solar sail - will take a
week on Ceres. since power level equates to thrust - thrust is very
low.

Thrust and specific impulse and power are related. Solar sails use
photons, the specific impulse is infinite since no propellant is used
- but the power needed to produce a Newton of thrust is tremendous.
Using laser energy generated in Earth orbit from sunlight, and beaming
that reliably to a thruster in the asteroid belt, to move material
around - can operate at a wide range of specific impulses. Either as
a laser light sail - with infinite specific impulse or energizing a
portion of the asteroidal mass. What specific impulse do we need?
The answer is, the one that has the least cost and time associated
with it. And that is, the one where the specific impulse has the
exhaust speed equal delta vee. For a hohmann transfer orbit from
Ceres this is around 800 sec Isp.

I would like to keep Ceres undisturbed. The fact is that moving it
would disturb the rest of the asteroid belt in a hard to predict
fashion. After all Ceres is a large percentage of the overall mass of
the asteroid belt. Believe me, you really dont whish to move Ceres or
the other five largest asteroids. Gravity is a bitch sometimes.

Anyhow, Ceres might sometime become rather useful for a whole other
purpose, i.e. moving the Earth itself. But if a large enough object
moves in an orbital resonance between the Earth and Jubiter, the orbit
of Earth can be gradually widened.

An option humanity might really like to keep open for the later
future.


but they
have the merit of not needing fuel

Thats true but they need a tremendous amount of energy. Given that
energy -particularly solar energy- is in short supply while billions
of metric tons of materials are freely available to use as propellant
- one clearly would like to reduce energy use to a minimum. Since
there are other constraints of a for profit system - such as getting
things done in less than a decade - thrust levels needed cannot be
achieved by any practical solar sail system. The mass of the sail
gets unweildy when trying to move things quickly at that distance.

But with Solar sail in comination with beemed energy, you´d not need
to waste any mass.

and would also benefit from your
lasers you assume will be plased in the viscinity of the Sun.

Compute the power level needed to bring the 21,000 metric tons of
material from the asteroid belt each day using an optimized laser
rocket blasting 36,000 metric tons of propellant - which was less than
20 GW. and compute the power needed to do the same thing - with laser
light sails.

http://en.wikipedia.org/wiki/Poynting_vectorhttp://science.howstuffworks.com/solarsail.htm/printable

Force = 2* Power / speed of light

Now 21,000 metric tons per day is 243 kg per second. The delta vee
total at both ends of the journey is 8,000 m/sec - I have limited the
acceleration time to 36 months overall - 94.67 million seconds.

Velocity = acceleration x time

so, acceleration = velocity / time
= 8,000 m/s / 94,672,800 s
= 8.45e-5 m/s2

Force = mass x acceleration

Now the acceleration period is 3 years - and in 3 years at a 21,000
metric tons per day rate a total of

mass = 243 kg/sec x 94,672,800 sec = 23,005,490,400 kg

Force = 23.00e+9 kg * 8.45e-5 m/s2 = 1,943,964 Newtons

Force = 2 x Power / speed of light

Rewriting this to solve for power level needed

Power = Force * speed of light / 2
= 1.944e+6 * 3e+8 / 2 = 2.916e+14 = 291.6 TRILLION
watts

This reduces the mass flow needed to be supplied by the asteroid belt
to zero. However, it increases the power level of the system by a
factor of about 15,000 !!!! Using solar power at the asteroid belt
means collector area is increased by a factor of 115,000x from what I
proposed originally. Since the station masses 500 metric tons and
covers 75.5 sq km. Converting to solar sails means we need 7.5
million metric tons of sails if powered from earth and 57.5 million
metric tons of sails/collectors if powered from the asteroid belt.

The sails can be reprocessed into useful stuff when they arrive, but
the cost of making the sails is wasted - then there's the logistical
problem of having sails the areas needed. No, the lower cost system
is the one I have proposed with very few technical risks..

Now, the thing is you only need these asteroids at this scale levels
if it´s there is a reason to move all foodproduction into space. If
the reason is only to supply rawmaterials for industry, then the most
economic method possible would be used. Solar sails, they can be
accelerated with a laser, but they also can move without such a boost.
In addition, it might be more sence to operate factory ships that
would cruise about the asteroid belt. In that case the sails would
only be moving the refined ore packages.

I don´t think it´s necessary to move all foodproduction into space. At
the present time the Earth is making sufficient amount of food for
all, even though it´s somewhat unequally distributed meaning food is
scarce for some. It would make sence to produce food in space for
those who come to live there.

Earth would continue to supply its own food.

The thing with asteroids, would be gentle movements. Sounds very
doubtful that even the solid ones would be able to handle rapit rates
of movement, so gentle acceleration perhaps like 0,001g or even
0,0001g which would make solar sails ideal.

You haven't done the calculations. I can accept no less than 84.5
micro gees. This can be done with quite reasonable thrusts
(approximately 200,000 kgf) - rubble piles can easily be moved at
these levels using gravity tugs. So attaching to an appropriately
sized dense metallic asteroid and navigating appropriately around a
rubble pile, brings both back. Building a pipe from the rubble pile
and pumping volatiles into the rocket engine - energized by laser
light from a powersat in Earth orbit - provides adequate propellant to
maintain the thrust for the needed period.

Using laser sails at the same power setting reduces the mass flow rate
to a trickle.

At the present time it´s not known wether asteroids can be safely
moved at that rate. That´s a rather big undertainty don´t you think. I
assume that the rate of movement will have to be gentle.

That´s a reasonable assumption I think.

In addition, as you think
rubble piles can be strapped together in some fashion.

I didn't say that.

..a delicate
operation for certain, I think you´d prefer towing to pulling. In fact
towing may be preferable to pulling.

If done gravitationally yes.

Yeah right, then you will have to be moving a quite massive oject for
them to cling to. Problem there are none available that can be safely
moved. At the very least none massive enough.

Gravity is a bitch sometimes.

In addition it´s necessary to consider the effects on the other
asteroids.

That's right.

Which means you have to leave the more massive asteroid alone. That
means you´ll lack the eer massive object you intend to let that rubble
cling to.

The path chosen has to be very carefully worked out, as
after all you really don´t whish to make other asteroids careen out of
theyr orbits.

Correct

That will go out of the window if you attempt to shift any of the 5
largest asteroids. They will have to be a big no. They can though
probably be safely mined by a mining ship which would move to them.

That means it´s very unlikely that some sort of a direct
trajectory towards the Earth will prove practical.

You are talking about terminal maneuvers during the 18 month period
the asteroid is undergoing powered thrust. The 7 years it spends in
transit this will unlikely be a problem. There are issues related to
the stream of asteroids produced however, and that can actually assist
things.

That time probably will at the very least be 14 years, probably longer
than that.

More probably it
will be necessary to take several orbits around the Sun, before an
asteroid can be finally moved out of the belt proper.

Please show me your analysis on this? Certainly, if you have vastly
lower gee forces than I am contemplating you will take centuries to
move things. So, yes you will go round and round and round the sun as
you spiral end. Assuming nothing breaks in all that time.

Ceres orbital period is 4.599 years. My limit on acceleration says we
have to complete the delta vee at the asteroid belt in less than a
year - the delta vee at the asteroid belt is the smaller one - so,
that means you're clear of the belt in less than 1/5th a turn. You
have about two years to slow into Earth orbit. Here you're chasing
the Earth a couple of times around the sun before sliding into your
spot in polar orbit above Earth.

Now, Ceres will clearly be a big 'NO,' unless you whish to observe the
orbits of a significant percentage of the other asteroids change as
you move it. Undoubtedly interesting to watch, but you might not be
popular with the rest of humanity afterwards.

It will depend on which asteroid, naturally, but with more than
million of them about, I expect that it will take several Solar orbits
to nudge the average small average size asteroid free if the intend is
to cause the minimum disturbance to other asteroids.

Think about it, even though the volume of the Solar system is vast,
and the volume of the asteroid belt huge, most are orbiting more or
less along the plane of the rest of the Solar System. You will
inevitably be crossing a real lot of orbits of the other asteroids.
You will have to move it, nudge it, each time, when there is a good
distance so gravity effects will be minimal. Sounds reasonable it will
tale several orbits, even when assuming that you will be using the
technologies you are assuming and moreover assuming that they really
will work the way you assume they´ll work.

So my expectation is that you will be making a series of nudges till
you are free of the other orbits. So moving clear will take unknown
number of years, depending on the number of orbits necessary to cross.

I think it would be reasonable to reckon with 5 - 10 years of gentle
moving and nudging untill Earth orbit.

You haven't done any analysis of the critical factors and are wrongly
assuming I haven't analyzed the noncritical factors you cite. That's
why you are making so many mistakes.

A hohmann transfer orbit from Ceres to Earth is about 7 years. I have
put a 10 year limit on the transfer - this gets us the 84.5 micro gee
limit. You have proposed using solar sails, any practical solar sail
operated at the asteroid belt will take centuries not decades to
complete a transfer.

Assuming there are no other orbits in between that must not be
disturbed. However, that´s not the reality. Remember over million
asteroids.

And we can´t move the largest asteroids.

It may even be that 15 - 20
years would even be necessary for the more fragile or distant ones.

You are talking out of your hat. You haven't done the numbers so you
are just waving your hands.

True, but it´s clear you are talking about a time consuming affair if
you really intend not to send asteroids careening this and that way.

The surface gravity of even a small rubble pile is greater than 84.5
microgees.

The surface gravity of Ceres is 28,000 microgees.

Ceres must not be moved.

The force exerted by an 800 sec Isp laser powered thruster operated at
a GW scale is 200,000 kgf -
The force exerted by an infinite Isp laser light sail operated at the
same power level is 4 kgf -

Now, your ideas sound very nice,

Yours do not - they are dead wrong.

but your figures sound to good to be
true.

Where? The figures you cite are either out of date or wrong.



Einar

I would suggest you spend a little more thought on your responses in
the future.

Now, I haven´t said that your ideas are impossible. Only that the
timeframe you suggest is.

Einar
.

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