Re: We can meet all our needs through space development

On Jan 29, 10:52 pm, Einar <eina...@xxxxxxxxx> wrote:

It´s all interesting and all that to observe your pye in the sky
figures.

You are making highly prejudicial statements before even presenting
one whit of evidence.

The problem with them your assumptions are so far beyond what
one hears ellsewhere,

What one hears and what one knows to be fact explains a lot. In
addition to reading popularizations of science I am also member of
several engineering societies and I get their publications and read
those. I also support research among qualified vendors and I am aware
of what not only is possible today, but what is very likely possible
in the next five to ten years.

which explains my deep scepticism...

Well, I see you are doing a little self-analysis here. So, I feel it
only right to respond in kind.

The disconnect you mentioned between what you perceive and what I say
here is merely a rationalization not an explanation. It is far more
likely that your skepticism comes from the conclusion that we don't
have shortages as a species. From my implied statement that we need
not fight over limited resources. From the implication that we should
rather spend our remaining resources and effort here to work together
to develop the resources nature provides us.

This conclusion, rather than the basis for it, offends your
sensibilities. It flies in the face of beliefs you are committed to -
and so, you seek to rationalize your opposition in response

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 rather than parroting sources - do you understand why solar cells
have the efficiency they do? It has to do with the response
photovoltaic cells have to various colors. Silicon for example has a
specific band-gap energy. All PV materials do.

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

Silicon's is 1.11 electron volts. The energy of a photon is given by

E = plancks constant * speed of light / lambda

where lambda is the wavelength.

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

So, 1.11 electron volts corresponds to 1,108 nm wavelength.

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_body
http://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...

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% ...

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

I am mass producing CPV systems that routinely achieve 18%

so federal funded development effort is
assumed to bring the efficiencies up to 13%...

I operate outside Federally funded programs.

which they assume to be
the necessary minimum to make theyr program work.

You seem to be quoting literature that was current as of 1970s 80s
time frame. I am looking at programs I am funding for commercial
system I am building today in 2008...

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 page
http://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.

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.htm
http://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%


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.

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?

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.

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_mirror
http://en.wikipedia.org/wiki/Uhdtv
.
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.

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

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.

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.


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.

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.

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.

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.

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.html

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.

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.

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.
.

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.

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_vector
http://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..


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.

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.

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

That's right.

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 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.

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.

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.

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.

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

The surface gravity of Ceres is 28,000 microgees.

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.

.

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