SPS = Solar Power Satellite

Nice idea, but not ever likely to become economically viable.

That part about the rectenna being 100 yards square sounds a bit iffy. I thought they had to be MUCH bigger than that.

The idea of thermal solar has also largely been dropped because photovoltaic has improved so much and has a much longer and cheaper lifespan.

In the end, if you wanted to do this you'd be better off just building them on planet. Putting one each in the sahara, arizona, gobi, and australian desserts would likely still cost less than putting one in orbit and would be a whole lot easier to maintain.

In the extreme long term, it could be a good idea for "recharging" long range spacecraft or small colonies.

Hi Adrien: I also understood 100 meters square was impractical from 24,000 miles except by going to 100 gigahertz and square miles of transmitting antenna.
The engine is probably a rankine cycle that uses 80% ammonia and 20% water. The web site said a proto type had been built, but did not state the output power, project the cost, nor how many humans would need to attend a scaled up model. They believed it was cost effective to extract energy from the hot exhaust of a gas turbine, so likely it is also suitable for Thermal Solar.
Another source claimed 30% efficiency photovoltaic panels were available, but did not mention price per square kilometer or per square meter. On Earth's surface the array needs to be steerable to catch both morning and afternoon sun, especially at high latitudes in late June when the sun rises in the North-east and sets in the North-west. Neil

I like the idea, but the first thing that popped into my head was the maintenance. Was the mylar sail not a very fragile construction? If something ruptured it, you would need to send a shuttle up to repair it.

Naj.

Actually, maintenance of such a satellite in space might be less than a "similar" system on earth. The mirror, once deployed, should be maintenance free unless struck by a sizable bit of debris. Virtually the only moving parts would be in the generators. In zero-G there should be much less friction, so heat and wear in bearing surfaces should be minimal. The liquid/gas exchange might be accomplished solely by the differences in pressure. Other components for controlling the system and transmitting the beam to the ground, should last almost indefinitely. The power to run the system would require only a small bleed-off from the total electrical power produces.

In effect, this is not too different from the systems used to power submarines. The differences are, it seems to me, all positive. No reactor with its poisonous wastes, the nuclear power is supplied by the sun, 24/7/365. No need for cooling systems because the cold of space will draw off the heat and return the gas to liquid. The benefit of Zero-G has already been alluded to.

The greatest cost is in boosting the satellite into orbit. Weight to output is important, so the highest GigW. per pound is needed.

Microwave transmissions can be on very tight beams, but that might be hazardous to anything flying through the beam carrying many Gigs of power. By increasing the width of the beam to a larger receiving antenna, would reduce the likelihood of cooked goose.

The prototype power satellite would be simple, small and only capable of delivering a portion of the power that might later be attained by linking the heat source to a series of generators.

The cost of photo-electric cells is still far too high to supply even a portion of the power possible in an atomic reactor, or in the proposed power satellite.

Now, for the most difficult problem I see. Can a microwave transmitter/receiver system carry Gig-watts of power over the distance required? I think so, and a physicist friend assures me this is so. Is it?

Scaling the transmitter/receiver system certainly would be possible ... but practical and feasible might be another matter. That apart, a somewhat simpler and less costly power generation mecanism than photo-voltaic/electromechanical is available. A conductor in motion within a magnetic field produces current, the stronger the magnetic field and the greater the length and relative velocity of the conductor, the greater the current produced. A simple wire or cable of sufficient length (which would be many, many miles, but in space, who cares?) positioned and configured to maintain an orbit in such manner as to perpendicularly intersect the planet's magnetic field, or even that of the sun itself, would be capable of producing enormous power density with no moving parts whatsoever beyond those required by the steering and orbit maintenance systems ... which themselves easily and logically might be powered directly by tapping a negligible fraction of the generated electricity.

On the other hand, I figure it likely that for all its elusiveness, economic power generation via hydrogen fusion will reveal its secrets well before any sort of space-based system for the generation of terrestrial power becomes practicable.

Timber,

The thing is that a Power Satellite is well within existing technology. The primary cost is the boost, thereafter we might expect low-cost, non-polluting electrical energy almost indefinitely. We could at least theoretically implement either the Thermal idea, or your alternative, in about the same amount of time necessary to launch vehicles to the outer planets ... and get some relief from our ever burgeoning power needs.

I agree that the base technology is there for the most part, whichever generating system is used. Apart from boost cost, however, considerable R&D, with attendant and significant additional cost would be required in order to implement any such scheme. I could be wrong - I recall once having assumed I had been in misapprehension, only to discover on further reflection such had not been the case :wink: :wink: - but I really think fusion and superconductor technologies more likely to prove out and be applied well before space-based power generation becomes technologically and economically practicable.

Agreed that fusion and superconducting are both very good options. However, neither are anywhere near term operational. The space based system may required a little tinkering, but nothing compared with the containment problems in fusion, or the temperature problems with superconducting.

Re: SPS = Solar Power Satellite


This part could be a problem, too. The initial temperature gradient should be enormous, but in the absence of either conduction or convection to maintain the coolth, it doesn't seem that radiation alone would be sufficient to pass off the heat quickly enough. A lot would depend on the size and efficiency of the radiator.

~Here are answers I pasted from www.abuzz.com~
I looked at the Spectrolab website. Their 28% efficiency solar panels
are the size of small store coupons and 6 or 7 need to be
connected in series to charge a 12 volt battery. They produce
about 300 milliamps at 0.6 watts so you would need about 1,666,666
of them to get one megawatt in bright sun light. They are
manufacture rejects. So the cheapest ones would be about
1,800,000 of them per megawatt and have to be mini spot welded
because the terminals are only about 2 mm long, but they cost
less per watt than small quantities available elsewhere. The ones
with 1/4 inch terminals are about average price per watt in small
quantities. They are all built to very high standards for
satellites, so they are worth a small premium for five or ten
watt projects, but useless for supplying the national power grid
in my opinion.

The arithmetic looks bad. But not quite as bad as you
supposed. Typically GEO satellites shade Earth undetectably
twice per year for a total of perhaps 200 hours per year.
Thousand square mile mirrors would dim the sun noticeably =
partial solar eclipse and cool Earth perhaps 1/2 degree c = .9
degrees f during these hours. Since the over all efficiency may
be as low as 5% this would produce a net heat loss (during
the eclipse) for planet Earth even though nearly all the energy
in the microwave beam would become low grade heat typically
in less than one second.

We gain because the sun shines 24/7 in GEO orbits
except for a rather rare and brief eclipse by the Earth or moon.
We gain because Earth's atmosphere absorbs more sun light energy
than absorption and scattering of the micro wave beam, assuming
we chose a good microwave frequency.

Your one megawatt in the beam is about right if hot spots in the
the illuminated spot are limited to one kilowatt per square
meter. For average it is ten megawatts in the beam (100E2 times
one kilowatt) I really think we must think about one square
kilometer for the rectenna, unless most of the energy missing the
rectenna is acceptable. A typical one kilowatt microwave oven
sprays most of the energy onto about 1/10 square meter, so a beam
1/10 th that strong is only slightly dangerous and likely panning
rapidly if it is not aimed at the rectenna. A tin foil hat would
protect your brain and the rest of you would feel slightly
feverish if you were in the beam for one minute. Most any type of
metal or material would weaken the beam considerably.
A billion watt beam = one gigawatt evenly distributed over one
square kilometer would produce a field strength of one kilowatt
per square meter.
The SPS energy from space does heat Earth a few parts per
trillion, but so do forest fires and burning fossil fuel. I don't
think it is significant till we reach ten billion humans
consuming energy at about the rate Americans do now. Neil

Hi naj: The mylar needs to be very thin, perhaps 1/100 millimeter = 0.00001 meters. That would be ten cubic meters of mylar per square kilometer which weighs about 25 tons. The prototype can have less than one square kilometer, but more is needed to put 100 megawatts on the grid at 9% efficiency, which is likely optimistic since there are about a dozen places in the system where there is considerable power loss. 1 the mylar will absorb several percent of the solar energy 2 several percent of the reflected energy will miss the boilers because the mirror is not a perfect parabola 2 the boilers will reflect instead of absorb several percent of the energy. The hot outer surface of the boilers will radiate at least one percent of the boiler energy into space. 3 as little as 20% of the energy in the boilers will become electricity. Klystrons convert about 50% of the electricity to microwave. A better solid state microwave generator may be available by launch time. We don't want to use magnetrons as they can not be modulated with broadband data. The data from the SPS will be receivable over about 1/2 of Earth and about 1/2 of the solar system. This side benefit may justify much of the cost.
Millions of microscopic holes will be punched the first day, perhaps a bus size hole annually. With good design the sunlight delivered to the boilers will only decrease a few percent per decade. Last I heard, all 4 of the echo satellites = 300 foot mylar balloons at an altitude of 400 miles are still reflecting radio signals more than 40 years after launch, so mylar looks encouraging. Neil

Hi Asherman: All excellent analysis. My guess, no insurmountable problems before scale up of the mirror to several square miles. Then rare hot spots from the aging mirror might damage the boilers or other parts of the system.
The launch cost of a large system may remain prohibitive long term, or we may have Dr. Edward's Space Elevator in one decade. Neil

Hi Timber: Cheap, space rated suprconductors at nitrogen temperatures, should make the tether generators practical. If the failure due to excessive energy is typical, perhaps a megawatt per mile? Does any one have any guestimates for GEO orbit, which will likely be less than LEO = low Earth Orbit?
Perhaps an unshielded nuclear power plant without containment building can be put in GEO orbit. I presume keeping it secret from the public is delaying development.
Even if something beter is available in a decade or two, we need to practice with pilot models as soon as possible. Neil

Hi roger: I think you are correct the outer surface of the satellite will have insufficient surface area to radiate waste heat into space fast enough. Additional thermal radiators will likely be needed for systems larger than the proto type.
The diodes used in the 12 volt coolers are reversable and convert up to perhaps 100 degrees c to low voltage dc. provided a lower temperature is available= Same principle as a thermocouple, but more efficient. This can help cool critical components.

On the cliimber design for the space elevator it is now thought that, large radiators will be needed to dispose of the waste heat the traction motors produce, and the heat absorbed from the laser energy that is absorbed by parts that don't need the heat. There is even some concern that the tether will overheat due to various trancients = vibrations and unintended laser energy. Neil

~CB typed on www.abuzz.com ~ You talk about stationing a satellite over Nevada. It
sounds like you envision a geostationary satellite. These only
can be located over the equator you know. Otherwise the thing
will be orbiting like the space station. What you envision is a heat pipe but there are other more useful effects. Try a Seebeck generator like we are using for Cassini. The same type of generators could be used as the
RTGs on Cassini. Actually, you could mount the hot side on the
back of a solar cell and take any waste heat rejected from the
back side and generate a little electricity with it. The
Cassini RTGs are rather primitive ones as they just copied the
designs from earlier space craft and did not make use of more
sophisticated materials or manufacturing techniques. I happen to
know about that topic. Anyway, there are unanswered questions
and better solutions. For instance, putting a unit at the L5
point gets it farther away from low orbit space junk and better
light. From there you can direct power to an earth station or
another satellite. Stuff has been done in studying these
proposals.

Well, bein' an oldfart and all, I prolly ain't gonna be around to see it, but my money is on earth-based energy production from fusion, superconductor, and renewable biomass technologies as opposed to any space-based scheme. Then again, back in the '70s, I was sure Quadraphonic was the next big thing in sound, and in the '80's, I went for BetaMax, Laser Disc, and Big Dish Satellite TV, so what do I know :wink:
(to my credit, though, I never took 8-Track or Disco seriously)

Hi timber: A few people think cold fusion will hit the market soon. If a billion homes, business etc each had a one kilowatt (average) cold fusion electric source on the grid continuously, some neighborhoods would have a frequent surplus of electricity, but we would still need about 3/4 of the present world capacity during the daily peak demand period in each time zone. This would be costly for the 100,000 1/3 gigawatt steam turbines as it is impractical to stop them from turning 22 hours per day; then restart them. Other alternative energy methods produce similar ecconomic problems for these huge rotating machines. The present solution is a million gas turbine units of about 1/10 gigawatt each that only run about two hours per day on the average. These could run on hydrogen gas that was produced a few hours earlier when the grid had a glut of electricity. The draw back is (twice?) as much electricity is used to make the hydrogen as is put on the grid by the hydrogen powered gas turbines. Most other energy storage methods have even worse problems.
Nitrogen temperature super conductors might make sending electricity thousands of miles cost effective. At present up to 99% of the energy heats the power lines. Failing that, electricity could be stored in the magnetic field produced by a one ? turn super conducting coil. The current dilemma is nitrogen temperature super conductors can't tolerate strong magnetic fields. Will we find a solution soon? Perhaps. Please embellish, correct etc if you have more correct numbers. Neil

We can use liquid helium (or hydrogen= 20 degrees K) temperature superconductors, now for both applications, but a gigawatt per month of new super conductors will run the price of helium sky high due to commodity speculators and eventually a real shortage will occur as there are few low cost options for increasing the world production of helium. Both gases have bad leakage problems and the fire and explosion hazard is significant for hydrogen making for PR problems. The cost/energy of collecting and re-licquifing both gases makes the economics marginal in most applications. We could perhaps vent the hydrogen at lower cost, but enviormentalists would go ballistic if that projected to doubling the free hydrogen content of the Earth's atmosphere to (0.4?) parts per million. Neil

Im not leafin' through texts and studies as I follow along here, niel, just goin' from the top of my head so to speak, so stand by for errors :wink:

I question for one thing your nominal 1KW cold fusion generator; I think that a wildly unrealistic low-end "average". I live in a rural area, afflicted with frequent shortcomings of the electrical grid. Consequently, I have a propane-fired generator which, in the event of grid power disruption, or, during peak demand times, by remote command from the electric utility, automatically switches my house and outbuildings (its a real farm) to self-generated power. That generator's rated constant-duty output capacity is 15KW with surge capacity of up to 22.5KW for up to 10 minutes continuous. Typically, the output/consumption runs in the 6-to-9 KV range, with furnace fan motors and water circulation pumps, well and sump pumps, elaborate, big-screen, high-power surround sound home entertainment system, a refrigerator and two freezers, a constant-duty pond pump/filtersystem, comprehensive security system, several computers, and assorted lights, and other appliances and/or other equipment running in the house and outbuildings. If the water heater kicks in while everything else is goin', the output/consumption spikes to around 12 to 14KW during its heating cycle, but drops right back. All that said, my self-generated power winds up costing me quite a bit more than grid-delivered power.

A 1KW generator wouldn't even run my microwave oven, let alone much else, to say nothing of being adequate to meet the likely even heavier power demand to be brought about by the future "Wiring" of our civilization and its appurtenances. I doubt individual, low capacity, even 10-to-20KW on-site generation facillities would be practical as primary power sources; the economy of scale just makes one very big generator and an appropriate delivery grid far more efficient and practical than many smaller ones. I understand and agree there is no practical way to run very big generators only a few hours a day; the energy required to spin up a massive turbine is enormous ... far more than the energy required to keep the associated generator operating at nominal output for some considerable period of time once the turbine is at-speed.

A bit earlier, I mentioned renewable biomass. I consider that a very promising source for power-generation fuel as opposed to our current dependence on fossil fuels; biomass processing can even now yield relatively economic, clean-burning, high-BTU hydrocarbons. With further R&D, there is every reason to expect even greater efficiencies. Apart from crop and livestock byproducts and waste, biomass fuel source material can be specifically cultivated. I also see the present ultra-low-temperature barrier restricting the practicality of superconductors a mere technological hurdle to be overcome, and indeed contemporary research into new ceramet compounds shows great promise in the quest for sturdy, durable, economically producible and emplaceable ambient temperature superconductors.

In short, I think that the economics involved with R&D and emplacement, and the thrust of techonological development, ensure a long future for earth-based power generation, with that power being distributed over what will amount to the direct evolutionary descendant of our existing power grid.