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Dollar a Gallon Gasoline

Keith Henson's picture
, L5 Society
  • Member since 2018
  • 43 items added with 8,076 views
  • Apr 2, 2014

Gail Tverberg recently posted an article here.  She makes a strong case that, if we are to avoid economic disaster, a sustainable source of energy must not only be abundant; it must be cheap.  I pinned her down at a conference late last year and she bracketed oil at $30-50 per bbl for a vibrant economy.

Some years ago, the first time gasoline went over $4 per gallon, I set a similar goal of synthetic gasoline (or other transport fuels) for a dollar a gallon, close enough to Gail’s numbers.  Electric power at 1-2 cents per kWh will make transport fuel out of CO2 from the air and hydrogen from water at that price.  At this energy cost, the synthetic fuel is about 1/3 capital investment and 2/3 energy.  There is about 40 kWh of energy in a gallon of gasoline, so this is reasonable.  (Physics and chemistry worked out here:

So how do you get 1-2 cent per kWh?  Nuclear will not do it; neither will wind nor ground solar.  Projections for the best of them are several times too much for making dollar a gallon gasoline.  Hydropower will get into this cost range, but there is not enough of it.

Space-based solar power (or powersats), are one possible exception.  (There may be others.)  Located in geosynchronous orbit (GEO) they are out of the Earth’s shadow 99% of the time.  The solar collectors (PV or thermal) get about 5 times the illumination of the driest deserts.  The percentage of time with illumination is over ten times that of cloudy Germany or Japan.  There is a 50% loss getting the energy down by microwaves.  That still gives a 2.5 times advantage over the best and 5 times or more for typical places where humans want energy.  Powersats don’t need storage.  In most cases, the power can come down to receiving antennas (rectennas) located near large loads.  That reduces the cost of earth-side transmission to well under 1 cent per kWh.  (The cost is ~1 cent per kWh per 1000 km.)

Over time, we will build far more powersats than needed for peak demand.  Excess energy above current load will go into making hydrogen.  Combined with carbon, the hydrogen makes synthetic transport fuels via Fisher/Tropsch synthesis.

The problem with this idea is the cost of lifting parts for powersats to geosynchronous orbit.  That’s been the problem ever since Dr. Peter Glaser patented them in 1968.  The transport cost is so high that one study arrived at a figure of $145,000 per kW.  Powersats are low maintenance and no-fuel-cost energy sources.  The method for converting capital cost in dollars to power cost in cents for such sources is to divide by 80,000.  Electricity from a powersat costing $145k/kW would break even at $1.81 per kWh.  That is about 100 times too expensive to solve the problems.

Design to Cost

Design to cost is a management strategy with supporting methodologies.  The point of design to cost is to achieve an affordable product.  It does so by treating target cost as a design parameter during the development of a product.  If you have not met the target price, then you keep working on the design until you do, or management gives up on the product. 

A design that does not meet the cost metric is worse than useless; it will bankrupt the company or country that tries it.  The Germans are to some extent in this situation with expensive renewable energy.

Two cents per kWh implies at most a capital expenditure of $1600/kW or $1.6 B/GW.  (For comparison, nuclear costs ~$5 B/GW even in China.)  Major cost items for power satellites are the rectenna, the power satellite parts (and labor) and the transport to GEO.

That is, rectenna plus power satellite parts and labor plus transport cost to GEO must be less than $1600/kW.

The rectennas should cost around $200/kW.  This assumes near zero cost for the land, perhaps trading air rights over farmland for electricity.  If $200/kW is close to the actual rectenna cost, it is 1/8th of the total target cost.  Thus, the total cost is not sensitive to even major variation in the rectenna cost.  At the scale needed, $900/kW is a reasonable figure for the parts and labor.  That’s the case even including the microwave generators and transmitting antenna.  It includes a factor of two for the loss in the microwave transmission link.

To stay inside the cost target requires no more than $500/kW for transport to GEO.  At a specific mass of 5 kg/kW, the transport cost has to come in at $100/kg or less.  This is a hundred-fold reduction from current prices for sending communication satellites to GEO.  That sounds like a lot of reduction, but based on the physics, it is well above the lower limit of around a dollar a kg.  It takes less than a dollar of energy to raise a kg to GEO.  The design-to-cost target for power satellites is to get the transport cost to GEO down to $100/kg.

That’s not the only design to cost solution.  Taking the rectenna and the power satellite parts and labor as fixed, the product of kg/kW and $/kg to GEO needs to come in at $500 or less.  Solaren has proposed as much as 85 times as much power from a kg of power satellite.  As an electrical engineer, I am skeptical that such low masses are possible.  The other end of the range is John Mankin’s recent design at 10 kg/kW.  That requires a difficult (but not impossible) transport cost of $50/kg.  The original work by Boeing in the 1970s proposed 10 kg/kW.  Phil Chapman (Solar High) has a thermal design at 8 kg/kW.

So what does it take to reduce the cost of lifting parts to space?

There are several reasons rockets are so expensive.  First, we build and fly rockets in small numbers.  That raises the cost just as you expect to pay a lot more for automobiles built in limited numbers.  For cars this is around a factor of ten, i.e., a hand built $250,000 car would cost about $25,000 if it came off a production line.  Just making and flying thousands or tens of thousands of identical rockets would reduce the cost per flight by a factor of 10-20.

Unfortunately, that’s not enough.  We need another reduction factor of at least five.  To explain how takes “rocket science” at the level taught in high school.  You also need a bit of understanding of the tradeoffs between reusability and payload.

The rocket equation sets the fuel fraction of a rocket.  If exponentials in equations scare you, perhaps they should.  They are the essence of compound interest and eat into the performance of rockets like a payday loan shark eats into income.  The formula for the propellant fraction of a rocket is:



The Space Shuttle Main Engine (SSME) is about the limit of performance practical for chemical fuels.  They have an exhaust velocity (Ve) above the atmosphere of about 4.5 km/s.  It takes somewhat over 9 km/s to get into orbit.  At a Ve of 4.5 km/s, the equation reduces to 1 – 1/e2 where  e is 2.71828183 . . . , squared is ~7.39, and 1/7.39 ~.135.  The fuel fraction of a single stage to orbit (SSTO) using the best engines is 86.5% and everything else 13.5%.

The engineering consensus is that a reusable vehicle will need about 15% of takeoff mass in structure.  If the fraction available is 13.5%, we get a negative payload.  It is no wonder that SSTO rockets, especially reusable ones, don’t exist.

The situation is much better if the average exhaust velocity is twice that high.  By the formula, 1/e is ~.368, making payload plus structure 36.8%.  Even with 16.8% rocket structure, the payload fraction is 20%.

It’s possible to get exhaust velocity in this range.  The NERVA engines (nuclear reactors heating hydrogen) did it in the 1960s.  Unfortunately, NERVA type rockets are not suitable for the hard step of getting into orbit.  Engineering might overcome the weight problem for nuclear reactors.  Overcoming political opposition to flying nuclear reactors would be much harder.

The Skylon rocket plane does better than the equivalent of an exhaust velocity of 9 km/s.  This counts only the hydrogen consumed, not the air.

Skylon, was developed over the last 20 years by a UK company, Reaction Engines, Ltd.  They now have serious funding from the UK government and other sources.  They worked on a small scale for many years and finally produced a precooler.  It is the hardest part of the Synergetic Air-Breathing Rocket Engine that powers the Skylon to orbit.


Figure 1 Slylon taking off

The precooler has 26 km of fine tubing in it, so fine it looks like fabric.  Ram air at high Mach numbers is too hot to compress.  The precooler drops the temperature from as high as 1000 deg C to -140 deg C in a fraction of a second.  The low temperature makes the air easy to compress.  The engines use the heat extracted from the incoming air and the cold from hydrogen flowing to the engines to power a helium turbine.  The output of the turbine runs a compressor for the cooled air.  This method gets more energy out of the liquid hydrogen than just burning it (50 kWh/kg).  The helium turbine recovers much of the 20 kWh it takes to liquefy hydrogen.

At ~26 km, and about 1/4 of the velocity to orbit, a Skylon runs out of air.  After that, on 150 tons of internal liquid oxygen it does no better than a SSME.  Still, the high exhaust velocity up to 26 km allows an estimated payload of 15 tons out of ~300 tons at takeoff (5%).  A  Skylon that used air until it ran out and then switched to laser heated hydrogen would have a payload of 20%.  This would be better by a factor of four than the already remarkable payload of a SSTO Skylon.

Lasers will heat hydrogen into the 7-8 km/s range (or higher).  It takes a high power level, a few GW, to heat the hydrogen reaction mass.  Spread over 500,000 tons per year and 5 years, the cost for the laser lift is under $20/kg of payload.


Figure 2 Laser variation of Skylon nearing LEO on hydrogen heated by lasers

Running it only half time would double the laser part of the lift cost.  If you are trying to launch vehicles using lasers, the only way that makes sense is to run the lasers as close to 24/7 as possible


Figure 3 Laser propulsion station, disk is a rectenna powering the lasers.  Large surface is 3 GW of waste heat radiators.


Figure 4 Detail of lasers, optics, radiator tubes, flash drums and steam recovery compressors.  Shapes between radiator tubes are reflectors.

The smallest production of power satellites that makes economic sense is about 100 GW/year.  At 5 kg/kW, that’s 500,000 tons per year or 57 tons per hour, 60 tph if run 95% of the time.  The longest launch time is around 20 minutes.  Any longer or slower acceleration and the vehicles do not go into orbit.

Thus, the problem is to get a few GW of lasers into GEO where they can energize launching three 30-ton payloads per hour.  Smaller lasers then push the payload out to GEO at a high enough exhaust velocity that 2/3rd of the vehicle mass gets to GEO.  Rather than return empty, we scrap the second stage at GEO for part of the material needed to build power satellites.  This way the entire dry mass of the second stage becomes payload.

If we already had a power satellite in GEO, we would hook lasers to it and use it to power the transport of parts for hundreds more powersats.

Unfortunately we don’t.  We need to bootstrap the Skylon into a full-scale laser transport system. 

The current scheme is to use 5-6 conventional Skylons to lift the parts needed for a 3 GW laser and a 3 GW radiator to LEO.  This will take around a thousand flights in a bit over a year.  At first, we power the propulsion laser from the ground since a 6 GW rectenna weighs a lot less than a power satellite of the same output. 

Using power from the ground and electric thrusters, we fly the laser propulsion station [LPS] from LEO to GEO.  This takes a month or two.  Then the LPS powers a half million ton per year stream of cargo.  After the installation of such industrial base as needed, a small power satellite replaces the rectenna on the LPS.  Then we turn off the ground station and rebuild it as a rectenna.

On one LPS (and 150 Skylons), power satellite production ramps up to 100 GW per year.  With the transport system in place, it is much less expensive to add more lasers.  When there are 20 laser propulsion stations, the production rate for power satellite would be about two TW per year of new, low-cost power.

It takes less than a decade at that rate to displace fossil fuels of all kinds with clean, low- cost, electric power from space and low-cost synthetic fuel.

It looks like there is a way to engineer our way out of the energy, carbon, climate and economic problems.  At least that’s what the work to date indicates. 

More details including the transfers orbits are here: or at

There is also a rapidly changing technical draft document on the design of the laser propulsion station shown in the illustrations.  It is available on request from 

Bill Hannahan's picture
Bill Hannahan on Apr 2, 2014

Keith said in the intro, “It will be interesting to see how much flack I get for this article.”

Actually Keith, I have no problem with your objective and your facts. It is a well written and detailed essay.

I am puzzled by your logic. You rule out nuclear because it requires a 3:1 cost reduction, then claim you can achieve a 100:1 cost reduction in space based power systems.

We have yet to design the Model T of nuclear power plants. They are hand built, outside in remote locations. You point out that going from hand built cars to mass production reduced cost by a factor of 10. There is huge cost reduction available in factory massed produced land based and floating nuclear plants.

The usual life cycle of new technology starts with very expensive low production runs followed by rapid drop in price and increase in quality and reliability. The irrational fear of the N word has resulted in a continuous ramping of regulations that drives cost up and strangles development of new technology. There are dozens of ways to split uranium and thorium atoms, a steroidal submarine reactor is not the best.

The use of inherently safe designs combined with a streamlined common sense regulatory process can simplify the technology providing additional cost reductions not available to space based systems.

A 3:1 cost reduction in nuclear cost can be achieved more quickly and easily than the technology leap that you are proposing.  Looking forward to  $1/gal non fossil gas.

Keith Henson's picture
Keith Henson on Apr 3, 2014

Nuclear is (in my opinion) the next best solution to power satellites for non-carbon, low cost energy. 

What bothers me is the scale, and to a lesser extent the thermal polution.

It would take around 15,000 one GW plants.  It’s not going to be easy to site them.  They would dump about 30 TW of waste heat, call it 200% of output.  Rectennas dump about 15% of rated output as heat.

And, with that many reactors, we would just have to put up with a Fukushima type event every few years.

Re the 100 to one reduction in transport cost to GEO, $100/kg to GEO is around 100 times the minimum energy cost, so we are not really pushing the physics.


Robert Bernal's picture
Robert Bernal on Apr 3, 2014

I don’t believe that Fukashima type events could ever happen with a molten salt reactor. These can also be used to power the gas turbine, thus slightly less thermal waste as coal (especially if CCS is enacted, large scale). But thermal heat “exerted upon the land” is really nothing compared to sunlight. Its “damage” is so trivial, also, compared to the great excess CO2 problem.

My concern is that we develop the easiest way to abandon hydrocarbons (which could have been some sort of nuclear). We need to bring back to flight this most abundant (already developed and proven) source. However, it is next to impossible when the majority of the weight is in politics. Thus we need an awareness, an energy source awareness, across the ever so polarized masses, if we are to save this planet from the next OAE.

Robert Hargraves's picture
Robert Hargraves on Apr 3, 2014

I applaud the focus on costs. It’s critical that costs be addressed at design time, not by subsequent cost-reduction efforts. Costs are a focus of the book, THORIUM: energy cheaper than coal.

You rule out dollar-a-gallon gasoline from nuclear power because achieving that price will require electricty costing 1-2 cents/kWh. However new designs for thorium molten salt reactors promise costs of 3-4 cents/kWh, so two-dollar-a-gallon gasoline might be achievable. These new reactors should cost ~$2/watt of capacity. Westinghouse AP1000 nuclear power plants today in China are being built at $2/watt, much better than the $5/watt stated.

Skylon looks cool.

Paul Ebert's picture
Paul Ebert on Apr 3, 2014

This is cool stuff, Keith.  Thank you for your detailed analysis.

Cost is a vital concern, but so is time.  We’ve got, at best, a few decades.  This approach seems like a lot of advanced technology to develop and deploy in that time frame.

Your thoughts?

I really wish the UN would form a group like the IPCC but with the charter of formulating a global, risk and science based plan for dealing with climate change.  This seems overdue to me.

Keith Henson's picture
Keith Henson on Apr 3, 2014

I really need to write a book.

The longest lead time time item is the Skylon.  Given the resources, Reaction Engines thinks they can deliver the frist one in 2021 and produce them at 1 per month thereafter.  It would take about a year from the first flight to lift enough material for the propulsion laser and a few weeks to fly the laser to GEO using electric thrusters.

One laser needs about 150 second generation Skylons.  Assuming production rate similar to Boeing’s peak 747 production, it takes only a year or two to reach 100 GW/year production rate.  That makes an awful lot of money, but it doesn’t solve the energy problem.  The production rate would have to grow by a factor of 20 to do that. 

Assuming the Skylon and second stage production can keep up, diverting ten percent of the lift capacity to more laser propulsion will double the production capacity every year.  The model I ran took 22 years from start to enough power satellites in place to completely displace fossil fuels. 

Given that Reaction Engines was funded for the engine development last summer and that the engines are the longest lead time item, it’s possible that the Earth could be entirely off fossil fuels by 2035.

Keith Henson's picture
Keith Henson on Apr 3, 2014

Robert, you are almost certainly right.  But when you are talking about 15,000 of the things (or more) then someone, somewhere is going to have a disaster.  I can’t tell you what kind of disaster, but the Black Swan will get you sooner or later.

Power satellites are not immune from this.  A nearby gamma ray burst would take them all out plus access to space unless steps are taken to recover from such an event.  And who knows what else?

Nathan Wilson's picture
Nathan Wilson on Apr 4, 2014

Spaceplanes are cool, but this claim that Skylon will be cheaper than verticle take-off rockets baffles me.  Reusability sound good, but SpaceX claims that their rockets will be reusable.  The reduction in take-off weight sound good, but it seems to me that the dry-weight is a better measure of the cost, since the primary component of take-off weight, liquid oxygen, is very inexpensive.

Comparing take-off weights, rockets seem pretty good.  SpaceX claims their newest Falcon 9 rockets can launch 2.5% of their launch weight into LEO, and the first stages have a ratio of 30:1 fueled versus dry.  Even allowing a penalty of adding reusability, this means the dry rockets can put around half their own weight into orbit.

Furthermore, the launch facility need for a verticle take-off and landing rocket are likely to cheaper than the runway that is required for a rocket plane.  Sharing an existing runway may not be acceptable, since most runways are near densly populated areas, and at least initially, Skylons may be considered more dangerous to people on the ground than normal aircraft.

Nathan Wilson's picture
Nathan Wilson on Apr 4, 2014

when you are talking about 15,000 of the things (or more) [nukes] then someone, somewhere is going to have a disaster.

Actually, there will be accidents, and no doubt we will be told that the accidents are “disasters”, but are they really?  It’s been decades since Chernobyl, and still there has been no cancer epidemic (except the thyroid cancers which have/will probably kill far fewer people than the rooftop solar industry).  There is no doubt that the reactors we are building today will demonstrate accident rates which are orders of magnitude lower than that of the RBMK reactors at Chernobyl.  And the Fukushima accident proved that LWRs accident severity is an order of magnitude less than that of the RBMK.

Another risk with space-based solar power is vulnerability to floating debris and sabotage.  It would be very easy to imagine a derelict satellite drifting around and destroying the entire constellation (but not quite as quickly as in the movie “Gravity”).  I would think this risk places it in the same category as Desertec (the European plan to import solar energy from the Middle East and North Africa): a great energy source as long as they are not too dependent on it and maintain 100% local backup.

Keith Henson's picture
Keith Henson on Apr 4, 2014

Nathan. at low flight rates, Skylon is more expensive than vertical rockets.  See figure 2 here:

It’s only when talking about thousands of flights per year that Skylon starts to shine.  You are right about runways, for two reasons.  The runway has to be specially hardened to take the very high loading of the landing gear.  A 300 ton Skylon would leave ruts in a regular runway.  The other reason is that the runway has to be within a couple of hundred km of the equator with a few thousand km of water to the east.  (In case something goes wrong and the propulsion laser misses.)

The first generation Skylons (of which there may be fewer than ten built) have a 15 ton payload out of 300 tons at takeoff.  That’s 5%.  They are too expensive to build power satellites, but they are cheap enough to haul up 15,000 tons of parts for a propulsion laser.  Takes 5-6 of them flying every other day for a year to get the job done.

The second generation (with the wing heaters) uses no oxygen at all.  It should mass around 165 tons and put a 30 ton payload in LEO with the aid of a 3 GW propulsion laser to heat the hydrogen.  The 30 ton payload is a second stage that gets to GEO with 20 tons of mass remaining.

There is a lot of difference between a vehicle designed from the start to be reuseable and one that is descended from rockets of the Apollo era.  It’s just got to be less expensive to service an aijrplane shaped object than it is to gether up widely scattered pieces and restack them.  But, of course, I wish only the best for SpaceX.


Bill Hannahan's picture
Bill Hannahan on Apr 4, 2014

“They would dump about 30 TW of waste heat”

The sun delivers about 20 megawatts per person, a 1% increase in solar retention would be 200,000 watts per person, 1,400 TW.

“we would just have to put up with a Fukushima type event every few years.”

Fission produces about 400 different fission products. Why is cesium the only serious problem? Cesium melts at 83°F and boils at 1,240°F

UO2 fuel pellets melt at 5,189 F. Melting a spent fuel pellet is like shaking up a champagne bottle and smashing it. The cesium is released as a gas. Most condenses on  cold surfaces, but if there is a path to the outside, some escapes.

In an MSR cesium ions latch onto a fluorine ion to become cesium fluoride, melting point, 1,259 F, boiling point 2,283 F.  MSR’s operate in the neighborhood of 1,200 F, so the CsF would tend to precipitate out in the colder parts of the system and not be available for release in an accident. Also there is no hydrogen production due to the lack of zirconium.

A Fukushima type event is not possible with an MSR. Can you think of any credible way to release a large mass of fission products over a large area from a well designed MSR ?

Keith Henson's picture
Keith Henson on Apr 4, 2014

Nathan, there have been communication sats in GEO for decades.  I have never heard of one of them being damaged by either natural space junk or human caused.  If this comes about, there will be thousands of people in GEO to recover anything that’s not where it belongs.

I would be really interested if you have any idea about sabotage.  There would be upwards of 3000 power satellites separated by several hundred km.  They could, of course, be destroyed by a large number of nuclear weapons, but sabotage seems no more likely than trying to destroy a ground based solar power plant that way.


Keith Henson's picture
Keith Henson on Apr 4, 2014

I am really not here to discuss the merits (or lack) of MSR.  Generally I think they are a pretty good idea compared to the other options.  Of course, I think power satellites might be a better option if, and only if, we can get the transport cost down.

But since you asked, what would happen if a MSR at full operating temperature were dunked in water?  I have no idea and have not seen this discussed before, but after Fukushima I presume someone has thought about it.

Keith Henson's picture
Keith Henson on Apr 4, 2014

Dennis, this is essentially Jerry O’Neill’s space colony scheme.  It failed to take root because it cost too much and took too long.  The current estimate for this project is ~$60 B and ten years to 500% ROI.  The only recent work I know of for a lunar industral base up to the task of building power satellites was estimated at $2 T and generated no revenue for 20 yeears.

I know this stuff fairly well.

Eventually, with nanotechnology, it will be possible to put an industrial seed in a coke can.  But that’s a ways off.


Keith Henson's picture
Keith Henson on Apr 4, 2014

NN, the transmission of microwaves from space to the earth is not just theory.  It’s the basis of the entire $100 billion communication satellite industry. 

Colisions in GEO don’t genearte fragments since the relative speeds are, at most, in the fender bender range.  As you say, there are a lot of them up there and there has yet to be a colision.  Lower satellies in inclinded orbits are different.

Higher temperatures would be better, but the current versions of nuclear power plants disipate about 2kW of waste heat for every kW they put on the lines.  Rectennas disipate around 150 W for each kW they put on the lines.  I.e., nuclear reactors put about 13 times as much heat into the earth’s ecosystem as power from space would.

I am not oppoised to nuclear reactors.  As you note, they have been around a long time.  They have problems, China, for example is finding it hard to place any more of them near sources of cooling water.

You might note that I am not a supporter of space based solar power unless it is substantially less expensive than anything except hydro.

Roger Arnold's picture
Roger Arnold on Apr 4, 2014

NN: there may be valid holes you could poke into Keith’s proposal, but the technical issues you raise aren’t among them.  

The space junk issue of cascading collisions and breakups applies to low earth orbit, where satellites in different orbital planes cross paths with high relative velocities.  All satellites in geosynchronous orbit share a single orbital plane and have the same orbital velocity.  The orbit is not physically crowded; it’s a ring 250,000 miles around, and the normal spacing between adjacent satellites is still hundreds of miles.  It’s “crowded” in terms of electromagnetic spectrum, in that the angular separation between satellites, as seen from earth, can be small enough that cheap dish antennas have trouble resolving their signals.

Nor is the technology for microwave power transmission a risk area for power satellites.  As Keith mentions, microwave transmissions from geosynchronous orbit are commonplace.  It’s what comm satellites do.  Obviously, they’re transmitting communication signals, not power, but a power beam is nothing more than the collective output of thousands to millions of tiny transmitters, all locked to the same frequency with controlled phasing.  There’s nothing speculative about that; it’s the basis for all modern radar systems.  The only difference is the scale of the phased arrays.

Microwave rectennas have been built and tested in the lab.  And yes, they can achieve 85% efficiency. No scaling issues.  Just millions of tiny dipole antenna wires, each connected to a tiny high speed diode.  They’ve never been mass produced and deployed at scale in the field, so cost estimates are open to challenge, but there’s no reason to believe that the estimates going back to the old Boeing study are grossly optimistic.  In fact, the technologies available for building such things are now much more advanced.

No, the real hurdles that face space solar power are economic and political, not technical.  Without really cheap space launch capability, SSP is an economic non-starter.  Keith has addressed that, but his solution depends on multi-gigawatt lasers in high orbit.  With the way laser technologies have been going, there’s little doubt that the required laser systems could be built.  What Keith doesn’t emphasize is that another name for such lasers is Ultimate Super-weapons.  Surgical precision that would make each a general’s wet-dream, and no pesky radioactive after-effects to inhibit using it against any target we might wish to destroy.  

Putin wouldn’t let us get away with fomenting a coup against the elected government of Ukraine, adding it to NATO, and cutting off Russia’s access to the Black Sea.  Does anyone seriously think he would allow us to deploy a system that could enforce “full spectrum dominance” over all nations of the world? “Resistance is futile!”  Now where have I heard that before?

Robert Bernal's picture
Robert Bernal on Apr 4, 2014

I agree that out can be done just as some best nuclear design. Therefore, who cares about what Russia thinks… It should be an international effort, anyways.

Paul O's picture
Paul O on Apr 5, 2014

The reason that skylons don’t exist today is technical, not merely funding. Even well funded systems like our Boeing 787’s, or or new F35 fighters continue to run technical issues that are being resolved.

Basically I am a hard nosed skeptic who really dislikes Pies in the Sky, show me a Skylon and you have my attention. But besides the launch craft problem, I do have a really difficult time with the practicality of the beam power down approach. Yeah for sure it is doable, THEORETICALLY. Here are issues I see as problematic.


1) How many Square feet of solar panels are needed

2) How feasible is it to AIM microwaves at the (relatively Tiny) recieving target on the ground, through the Moist/humid atmosphere, that loves to absorb microwaves.

3) How much power should the beamed microwaves have in order to be able to provide useful electricity without storage.

4) What is the danger of cooking people accidentally (and birds for sure)?

5) For this scheme to be worthwhile we will need Tons and Tons of Solar Panels, and How long do solar panels last?

6) We can always make more Hydrogen, but the Helium for the turbines, well….


I like this Write up as a fun scifi/ futuristic/ intriguing mental excercise, but Frankly I don’t think it will ever happen.

Roger Arnold's picture
Roger Arnold on Apr 5, 2014

Any big project runs into engineering issues that have to be worked through.  I tend to think of “technical issues” as at least semi-fundamental issues for which there is no obvious or immediate solution.  But that’s what the term means to me; it may have a different meaning to others.  There are no “technical issues” (as I  use the term) that I know of standing in the way of developing the Skylon.  At one time, I would have said that the performance required from the inlet heat exchanger was a technical issue, but that’s the first thing Reaction Engines was at pains to prototype.  They’ve demonstrated that it works. Without that, they would never have gotten the funding for the next phase.  There will certainly be “technical issues” (in the more general use of the term) that will come up as they work their way toward a a flight vehicle, but (AFAIK) there are as yet no identified show-stoppers.  The real question is whether the final solution will be economical.  It could go the way of the Space Shuttle, a costly white elephant.

To answer the six questions you raise:

1) How many square feet of solar panels are needed?  About one third as many as would be needed to deliver the same amount of energy via  solar panels on earth.  The cost per square foot, exclusive of launch cost, would be quite a bit lower as well. (The cells can be thinner, with no encapsulation, on really flimsy mounting film.  No weather to worry about.)

2) How is it possible to AIM microwaves at the .. receiving target?  You don’t aim them at all.  They effectively aim themselves by the manner in which they’re generated.  The power beam is formed by phase conjugation of a pilot beam transmitted from the center of the receiving antenna.  A more properly descriptive term for the power transmitter would be “an amplifying phase-conjugated retro-reflector” for the pilot beam.

3) How much power should the beamed microwaves have in order to be able to provide useful electricity without storage?  Not sure what you mean hear.  The beam delivers steady baseload power; it could certainly be cut back and operated at partial capacity, but why?  The unused capacity would go to waste.  Better to use it, as Keith proposes, to make hydrogen for synthetic fuels.

4) What is the danger of cooking people accidentally (and birds for sure)?  Zero.  The power density of the beam, even if one were standing at the center of the rectenna, would be only about 25% that of sunlight.  Prolonged exposure to that level of microwave power isn’t recommended, but it wouldn’t cook anything — at least not quickly enough that you couldn’t walk (or fly) away from the beam.

5) .. How long do solar panels last?  I can’t say precisely, but there are satellites in orbit whose panels have been working for 20 years or more.

6) We can always make more Hydrogen, but the Helium for the turbines,.?  Keep in mind that Brayton cycle, concentrated solar power generation (the approach that Keith tends to favor) does not involve large arrays of solar panels.  And vs. vs.  One or the other, not both.  As to the amount of helium needed if the Brayton cycle approach is taken, it would be something on the order of a kilogram per megawatt.  Or one tonne per gigawatt.  Recycled, not expended, so we’re talking about a small fraction of the world annual helium diverted for building power satellites.

So you see, the technical issues all have answers.  But like you, I don’t expect to see any of these satellites actually built.  I don’t see any viable way around the political issues.  I don’t see how we could get the necessary reduction in launch costs without launch lasers, and I don’t see how the weapons potential of launch lasers can be restrained.  

It’s far worse, IMO, than the bogus problem of nuclear proliferation that has been used to stop development of nuclear power.

Keith Henson's picture
Keith Henson on Apr 5, 2014

NN, I don’t mind criticism, but I would appreciate it if you get the numbers right.  For a search term, you might use “geosynchronous collision.”  I don’t think there have been any of them.  “. . . large number of devices in orbit,” actually it’s only perhaps 3000 of them.  They tend to be large, 5 GW each.  For the rest of your thoughts, you might want to talk to someone who is in the orbital mechanics business.  

My objection to nuclear energy cost is simply that it isn’t cheap enough to make transport fuels at a low enough price to meet Gail Tverberg’s criteria for a vibrant economy.  1-2 cents a kWh for TW of energy is a tough goal.  There are other problems, cooling water being a big one. 

As to dismissing this simply because it hasn’t been done already, there is a reason.  It’s only been a few years since lasers got big enough and cheap enough to consider using them to power rockets.

Your complaints about solar are well founded, though in some cases solar cost less than any other source of power.  The big problem with solar, of course, is the fact that the rated output happens at best only about 1/5th of the time.  Solar works a lot better in a place (geo) where the sun shines 99% of the time.  It works even better when you don’t have to support the collectors against gravity and wind.

Re the rest of your concerns, if you are in the US, you don’t need to worry about the cost of this project coming off your taxes.  Whatever merits and cost the project may have, it’s very unlikely the US will have anything to do with it until we are buying synthetic transport hydrocarbons from the Chinese.


Jim Warden's picture
Jim Warden on Apr 5, 2014

I am reading that in Canada some scientists are driving around on GreenNH3 for $2 a gallon Wouldnt that be a good start considering you and I are paying close to $4  ?

They are also saying that some group from mideast and russia can make low cost safe thorium reactors which fit in a small number of 20 ft shipping containers and produce electric for three cents a kw,hr.   The beauty of the GreenNH3 synthesizer is it can use up all the excess nuclear which is being made and stores it in tanks for use as fuel or fertilizer. See

They are looking for investors to build thousands of GreenNH3 synthesis machines.

Jim Warden's picture
Jim Warden on Apr 5, 2014

I am reading that in Canada some scientists are driving around on GreenNH3 for $2 a gallon Wouldnt that be a good start considering you and I are paying close to $4  ?

They are also saying that some group from mideast and russia can make low cost safe thorium reactors which fit in a small number of 20 ft shipping containers and produce electric for three cents a kw,hr.   The beauty of the GreenNH3 synthesizer is it can use up all the excess nuclear which is being made and stores it in tanks for use as fuel or fertilizer. See

They are looking for investors to build thousands of GreenNH3 synthesis machines.

Paul O's picture
Paul O on Apr 5, 2014

Thanks for your reply..more food for thought.

Gary Tulie's picture
Gary Tulie on Apr 5, 2014

Do we need such low cost energy to make a strong economy?

I would question the need for such low cost energy – end used fuel costs in Europe are of the order of $8 to $10 per US gallon which results in european people choosing much more fuel efficient cars than their US counterparts. Likewise with electricity, prices are far higher in Europe but average bills are not very different as europeans by necessity have made far greater efforts to use electricity efficiently and to avoid electricity guzzling appliances. 

I would therefore suggest that higher gasoline prices even at $8 per gallon will not be a problem if serious efforts are made in the direction of energy efficiency as it is technically possible to halve average consumption without adverse impacts on function so doubling the cost of fuel need not necessarily increase the cost of running a vehicle.

Is constant economic growth desirable or even possible?

If growth depends on ever higher levels of population and physical consumption, it is highly likely that growth will come at the cost of “natural capital” i.e. the ability of the planet’s natural ecosystems to clense water, remove pollution etc whilst maintaining diverse habitats and biodiversity.

To take an absurd example – if we all bought a new refrigerator every month which consumes 10 times as much electricity as current models it may look as though the economy is very strong as sales of “white goods” and electricity would go through the roof. Would we be better off? No – Why? because the expenditure would serve no useful function and would be horendously inefficient of resources.

Going to the other extreme, suppose we all bought very robust refrigerators which last 30 years, and use a quarter of the electricity of the average model on today’s market, sales of white goods and electricity would go through the floor. Would the buyer of such a refrigerator be worse off? No because their cost of refrigeration would be a fraction of business as usual, leaving money to be used elsewhere – for example downloading E-books or music with a minimal physical footprint.  

Higher energy costs can therefore in my view serve a useful purose in driving efficiency and innovation in efficient technology. 

Note also that energy costs by long term historic values are in some regards absurdly low – compare the running cost of Kerosine lamps used by millions of the world’s poor with the cost of running an LED light with equivalent light output – in cash terms, for a given light output that could otherwise come from an LED, kerosine lamps cost possibly $250 per kWh, and that in parts of the world where eare possibly 5 to 10% of Western levels. 

Robert Bernal's picture
Robert Bernal on Apr 5, 2014

After reading about the Kessler Syndrome I have reservations about the entire space based solar idea. I know that it’s far less probable at GEO than LEO, but the threat would still exist, especially if a rogue object intersected one of the large structures.

I know developing some best form of nuclear is much easier and proven on the tech level.

I also understand that the developed world has gone crazy concerning trivial (but still very much energy consuming) stuff… But what are your ideas about replacing the car? I live in California and it’s a real pain in the butt to not have one! I got my ideas, but they involve completely brand new 3d cities…

Nathan Wilson's picture
Nathan Wilson on Apr 5, 2014

A few points:

– solar PV cells do have to be encapsulated in space, to protect against the trapped radiation (the outer Van Allen belts reach past geo sync orbit).  It’s mostly electrons at that altitude, so not super penetrating, but it still wears out solar PV panels several times faster than on Earth. (I suspect that those 20 year old panels you mentioned put out a small fraction of their initial power by now).

– the satellites will provide pretty good baseload power, but they still require redundant grid connection and/or backup power sources, as they will occasionally go down for maintenance or pass through the Earth’s shadow (1.2 hours to pass through the shadow, not sure how often: shadow alignment events could happen twice per year, each event might be one or more nights in a row?).

– I don’t think it is possible for one receiver to be powered by two satellites at once (ie. no redundancy).  If the wavelength is the same, then interference patterns result (blind spots & hot spots).  For different wavelengths, the receiver will produce out-of-band radio noise (called “inter-modulation products”) – and these systems are already extremely bad radio-neighbors.

– here is an article about phased-array radars.  it explains how an array of microwave transmitters, each of which makes a fixed wide beam, can be combined to make an electronically steerable narrow beam. Cool technology, and commonly used in the military and for radio telescopes.

– speaking of microwave beams, the beaming problem causes an extremely severe “critical mass” problem.  Unlike nuclear plants, which can theoretically be built in any size (from a 10 MW submarine motor to a 6 GW electrical plant); solar power satellites with microwave beams can’t make efficient beams in sub-GW sizes (assuming fixed power density of 25% of solar intensity).  It is really the transmitting antenna and receiving rectifying antenna (rectenna) sizes that are the problem; small antennas just can’t make tight beams.  The product of the minimum antenna diameters is a constant (make one smaller and the other must be bigger) which is proportional to the wavelength (and the 4-12 GHz frequency bands that we use for TV/comm satellites are the only microwave bands which can penetrate weather).  Gerard K. O’neill proposed a 7 km diameter receiver and transmitter around 1km in diameter (e.g. at 200 Watts/m^2  the received power is 6200m*6200m*80%= 6.2 GWatts)

– Switching from microwaves to lasers shrinks the wavelength from millimeters to microns, therefore allowing smaller receivers for lower power.  The military would like to be able to send a MWatt to each of many different off-grid locations, all at once, so lasers are perfect.  As you said though, this power source would also be an effective weapon.  Also, it is not clear to me that there are any eye-safe wavelengths for near-solar intensity.

– I’m more optimistic about vertical take-off reusable rockets than I am about rocket planes (the trade-off of less oxygen to carry vs. the need for more thermal protection sounds dubious).  The laser planes strike me as particularly unlikely (expensive infrastructure).  

– However, it is the very high cost of on-orbit labor that I think is the show stopper.  No society that is afraid of radiation from nuclear waste (i.e. the only societies that would invest in any large scale solar power) would ever send a large workforce into space, because space is literally filled with radiation (not just wholesome electron and proton radiation from our benevolent sun which is trapped by Earth’s protective magnetic field, but a really nasty radiation form called “heavy primaries” which come from evil alien stars and are heavy nuclei which are energetic enough to penetrate any imaginable space suit; the Apollo astronauts reported seeing frequent flashes of light, each was interpreted as being a group of brain cells being killed by a single heavy primary). 

Nathan Wilson's picture
Nathan Wilson on Apr 5, 2014

On collision likelihood: note that you are proposing to increase the collision probability by a factor of a million!  (going from tens of KWatts per satellite to GWatts will increase the surface area proportionately, and from hundreds of satellites to thousands.)  And our first satellite collision has already happened, back in 2009 (see Iridium_satellite_destroyed).

Before I was a clean-energy enthusiast, I was a space enthusiast.  So I can tell you a little about orbital mechanics.  

It is true that with ion engines thrusting for months at minescule levels, space craft can arrive at geosync orbit at a low relative velocity.  But people cannot travel through the radiation belts at such a leisurely pace without extremely heavy radiation protection.  But even for cargo, the time-value of money is such that there is an incentive to get there faster than ion engines would allow.  All chemically powered rockets go to geosync orbit using a minimum energy (or Hohmann transfer) orbit called GTO (geosync transfer orbit).  [All elliptical orbits conform to this equations: v^2 = GM(2/r – 1/a), where v is the velocity, GM/r^2 is gravitational accel, a is half the width of the ellipse, and r is the distance from the center of the primary body to the vehicle.]

The GTO orbit takes 5.25 hours to go from low Earth orbit (LEO) to geosynchronous orbit.  It departs LEO at 23,000 mph, and arrives moving at 3,560 mph, which is a velocity which is 3,320 mph less  than the 6,880 mph required for a round orbit, hence the need for another rocket burn (or apogee kick) upon arrival.  A collision between the arriving vehicle and a satellite or an explosion of the apogee motor before the burn (the 3,320 mph difference is faster than the highest velocity anti-tank projectile) would make a debris field which would cross geosynchronous orbit and a range of lower orbits, and eventually hit all of the geosynchronous satellites.

The proposed solution to this debris problem is that robotic spacecraft would gather up the large debris, and yet another giant laser would use photon pressure (or laser ablation) to sweep the small debris away.  The laser must be very powerful, as photon pressure is feeble.

There is another space race going on: to see whether we’ll develop debris removal technology before the first space warfare actions create a debris field so dense that it ends human spaceflight for the next 10,000 years. And putting tempting targets in orbit will accelerate the race.

Nathan Wilson's picture
Nathan Wilson on Apr 5, 2014

I suspect that the $2/gallon cost requires starting from a really cheap energy source like stranded natural gas (gas that comes out of oil wells in a location with no pipelines for transport – oil and NH3 can be conventiently tank-stored and truck-transported, but methane cannot without expensive cryo-liquification).  But still it shows that NH3 (ammonia) is a cheap fuel to synthesize (and the cheapest which can be made from space solar, terestrial solar, wind, or nuclear power).

Expect to pay $8 retail per gallon of gasoline equivalent (gge) for NH3 from today’s wind or desert solar (each gallon has 34 kWh of energy, and there are conversion losses); Chinese or Indian nuclear can beat this by a factor of 3, and Gen IV nuclear w/ thermo-chemical H2 providing another 20-50% reduction.  

But as Gary says above, Europe does fine with fuel cost in the $8/gge range, and to NNadir’s point below, such a price would help us reduce unnecessary dependence on cars. Gail T’s warnings against expensive fuel are mostly aimed at deeply indebted governments and those which are funded largely with large fuel taxes (i.e. not the US or China).

Roger Arnold's picture
Roger Arnold on Apr 5, 2014

Those are all good points Nathan.  Thanks for posting them.  I’ll just comment briefly on a couple.  

It’s true that trying to supply power to one rectenna from two or more sattelites “at the same time” would create an interference pattern — alternating peaks and nulls — at the rectenna.  I don’t know whether or not that would actually be a problem, but in any case it can be avoided.  A functionally equivalent level of redundancy can be achieved via time slicing.

Because the beam is formed by phase conjugation of a pilot beam, it can be switched in nanoseconds from one rectenna to another.  It’s just a matter of turning off the pilot from one rectenna and turning it on for the other.  The time slice can be much shorter than the speed-of-light transit time from rectenna to power sat; the various rectennas must simply have synchronized clocks and a negotiated allocation of time slots.  The same sort of time slicing schema that underpins cellular phone systems.

Time slicing allows one large transmitting array to service dozens, or even hundreds, of smaller receiving rectennas.  Conversely, it allows one receiving rectenna to take power from dozens of transmitting arrays.  It allows the net power to any given array to be varied according to demand.  The periodic shutdown of individual transmitter arrays as they pass through the earth’s shadow around the spring and fall equinoxes becomes a non-issue.

Pulsed operation requires only modest capacitance distributed within the rectenna circuits to smooth the flow of power between time slices.  I personally consider the ability of space-based solar power to integrate responsive wireless power distribution to be its strongest advantage.  That doesn’t mean I think it will happen, but it’s a strong reason why maybe it should.  


Roger Arnold's picture
Roger Arnold on Apr 5, 2014

Debris from the explosion of an apogee kick motor doesn’t hang around at geosync.  It falls.  Pieces that hit the atmosphere burn up; those that miss the earth will return and potentially cause trouble.  But they’ll have a wide distribution of velocity increments imparted by the initial explosion; the apogees for their elipical orbits mostly will not intersect the ring where geosynchronous satellites orbit.

If a payload is directed for insertion just ahead of a geosynchronous satellite, then explosion of the arriving payload’s apogee kick motor likely would shred the satellite.  For that reason, the main insertion burn is performed behind and / or below the nearest satellite.  Commonly below, I believe.  That leaves the arriving payload in a not-quite geosynchronous orbit, moving slowly eastward relative to the satellites above it.  When it approaches its intended stationary location, it takes only a short burn from its station keeping engines to place it into true geosync.

Also worth noting is that a power satellite hit by debris doesn’t break up — much less explode.  It simply gets a hole punched in its solar panel array at the point of impact.  Since power output would be distributed via an interconnected mesh of wiring, the loss of a few cells would likely not even be noticed.

I really don’t think one can make a case against power satellites on the basis of risk from space junk. My bet remains on politics.

Jim Warden's picture
Jim Warden on Apr 5, 2014

I probably would not convert natural gas to NH3 , but rather use it as is for fuel, why convert ?

The GreenNH3 synthesis machine can run on stranded electric or electric from wind blowing at

times when it is not needed. I believe they value that at whatever they can get for it, so say

7 cents a kw would make the GreenNH3 for 7 kw hr x 7 cents / kw hr = 49 cents a liter.

compare that to what a northern comunity sometimes pays up to $3 a liter to have dirty diesel flown in

 and they could be making their own zero emissions GreenNH3 for 50 cents a liter.

Also some utilities like in Ontario Canada now pay millions some nights to have excess electric taken off their hands, when they could make it into GreenNH3 and use it later to power peaker units ect.

Some people consider GreenNH3 an (a ?) (the ?) holy grail in the energy grid structure.

Robert Bernal's picture
Robert Bernal on Apr 6, 2014

We should expend our precious billions on whatever best nuclear and then consider building a lunar equatorial “grid” connected to silicon panels made by machine and the lunar regolith. But I don’t know for sure if the rectennas would work from the surface.

Nathan Wilson's picture
Nathan Wilson on Apr 6, 2014

Yes, time-slice beam switching could be a good solution to allow a receiver to share multiple satellites, or vice versa.  But note that time-slicing is a form of modulation, and a modulated signal is much more likely to cause radio frequency interference with other users of the radio spectrum.  So now, in addition to keeping your beam power below 250 W/m^2 for animal safety, and your out-of-beam leakage power below something like 1 W/m^2 for human safety (same range as cell phones), you might get another out-of-beam leakage limit for compatibility with radios, satellite TV receivers, and wireless devices.

To make a single satellite power multiple receivers, you can alternatively use electronic beam forming to make an antenna pattern with multiple beams with constant (and selectable) power.  It might complicate the beam control electronics, but not by much (it only effect the low power electronics, the high power output stages are exactly the same).

Nathan Wilson's picture
Nathan Wilson on Apr 6, 2014

Since the Moon is about ten times farther away than geosynchronous orbit, it will take a transmitting array that is ten time bigger in diameter (and 10x higher precision) to make the same beam width at Earth.  This has been proposed as a solution for orbital debris risk.

But note that unlike a geosynchronous satellite, a given point on the Earth can only see the Moon for half of the day (and it is not synchronized to day/night cycles).  Also, only half of the Moon can see the Sun at a given time, so you need twice as many Lunar power stations.

Roger Arnold's picture
Roger Arnold on Apr 6, 2014

You’re right.

Robert Bernal's picture
Robert Bernal on Apr 6, 2014

Thanks for the reply. I used to be more interested in space, too. I didn’t really figure out the rocket equations other than that I knew it takes a lot of energy to make such changes in velocity (Delta vee, I read “Mining the Sky” by John S. Lewis and thought it was a wonderful book. In contrast, I also like Tom Murphy and his “do the math” about how hard it will be to continue supporting billions of people without fossil fuels. He thinks it next to impossible for mankind to access the energy requirements to become a full blown space based race).

I assume it would be “much easier” for robotics to “cast” the panels on the moon to make up for the low angle and night time losses. I guess there would have to be a global grid here on Earth with many recievers in order to avoid interuptions or the necessity of storage. Speaking of which, how much more efficiency loss would there be to convert the energy to NH3? I know, purely for the curious at mind… unless there was no hope for nuclear!

Keith Henson's picture
Keith Henson on Apr 6, 2014

“What portion of humanity is concerned with gasoline?”

I am using gasoline as a catchall term for liquid transportation fuels.  Everyone who eats is concerned with fuel for the tractors that plow the fields to the ships that transport grain across oceans.  Do you fly?  If you do and you are concerned about the cost of tickets, you are concerned with the cost of jet fuel.

If you ever need a ride to a hospital, you are concerned about the cost of gasoline.  If you buy anything made out of plastic, you are concerned with the price of oil even if you don’t know the details of the organic chemistry that makes plastics.

Gail Tverberg is deeply concerned with the pervasive effect of oil as goods and services move through the economy.  If you expect a pension, you are indirectly concerned with the cost of gasoline (oil).

Your concern for power satellites crashing into each other is misplaced.  They are worth more than communication satellites.  Keeping them in the right places would be a done at least as carefully with the added advantage that there would be plenty of people in GEO to deal with whatever problems came about.

I partly agree with you, “Right now there are no space craft that can do the job,” but I disagree with “decades will pass before there are.”  Reaction Engines will take orders for Skylons with delivery dates starting in 2021.  It will take 5-6 of them to haul the parts for the laser propulsion station to LEO.  That will take about a year, and then a couple of months to fly the station out to GEO where it can start hauling parts out for power satellites.

I find it amusing that people such as you object that Skylon has not flown.  As far as I know, there are no MSR around, and, as far as I know, no funds have been allocated to build one.  Let me know when there is progress and I will be cheering.  You might consider doing the same for Skylon.  It’s not like these project compete for skilled workers or even funding.

I use gasoline simply because more people are aware of what they pay at the pump than they are for most other forms of energy.  Would you be more in favor if I emphasized desalinating water and pumping it inland for irrigation?  Cheap energy lets you recycle just about everything that now winds up in landfills.  Would it help if the proposal included sending the hundredth power satellite to Mars where it could support tens of tons per hour to and from the surface and to and from the earth?

Nathan Wilson's picture
Nathan Wilson on Apr 6, 2014

On the Moon, it is dark for 14 days at a time.  Solar energy is a very inconvient resource there.

So it’s likely that only a society that embraces nuclear energy can colonize the Moon.

In O’neill’s book, the Moon is mined for iron-rich dirt, which is launched to a free-floating spacing space colony.  All complicated manufacturing is done at the colony, since he believed that labor and energy would both be much cheaper at the colony.  Certainly crops will grow better and solar energy works better without the 28 day light/dark cycle.  Also, the mass driver that launches 20 lb buckets of dirt is much simpler than one that launches 1 ton mechanical sub-assemblies.

The sci-fi vision of robots is also a giant leap from where we are today.  Robots today do simple repetitve tasks faster and more accurately than humans.  But they always require a very large amount of human support, for a variety of tasks.  Ultimately, humans are the brains of the world, the robots are just our strong-arms.

Keith Henson's picture
Keith Henson on Apr 6, 2014

Roger, if the US were to build power satellites including the propulsion lasers, what could the Russians do?

If the Chinese were to build propulsion lasers, what could the US do?  (Short of going to war.)  And if the EU did it, currently the most likely possibility, what could anyone do about it?

I am not saying you are wrong, just that I don’t see (for example) the US having an effective arguement against the Chinese or a Chinese/Indian joint project to responsibly solve their energy problems.


Nathan Wilson's picture
Nathan Wilson on Apr 6, 2014

Using off-the-shelf technology, we can convert electricity and water to hydrogen with about 70% efficiency.  I’m not sure about the hydrogen to ammonia efficiency, somewhere in the 60-90% range depending on plant size.  

But there have been lab demos of reverse ammonia fuel cells (using PCCs or proton-conducting ceramics) which convert electricity, water, and nitrogen directly to ammonia, with over 70% efficiency.  We should be putting more research dollars into this technology.

Ammonia synthesis is a great solution for transportation fuel and for seasonal energy storage (e.g. summer peaking and combined heat-and-power).  For daily energy storage (such as you’d need for terrestrial solar, or Lunar solar), I’d say pumped-hydro is the leading solution today.  Over the next twenty years, advanced batteries and thermal energy storage at Gen IV nuclear plants will likely play a role in mono-culture grids.  But diversified grids with even a small amount of dispatchable fuel synthesis likely won’t use much storage.

Roger Arnold's picture
Roger Arnold on Apr 6, 2014

Uh, how about a nuclear bomb, targetting the site where the launch laser was being assembled?  

It likely would never come to that, but that’s what the last resort would be, if threats and negotiations failed to kill the project short of that.  “But that would be an act of war!”  Yes, certainly.  But so would be deployment of a system that could strike instantly against any unhardened surface target, take out bridges, rail lines, and aircraft in seconds, and neutralize a target country’s capacity to defend itself.  

In the strategic thinking of any nation’s military leadership, allowing such a system to be deployed under control of another nation would be viewed as unconditional surrender to any demands the controlling nation might wish to impose on it.  

If you don’t think nations are prickly about such things, think back to the Cuban missile crisis, and how the US reacted to the threat of Soviet nuclear missiles 90 miles off its shore.  Kennedy was willing to risk all-out nuclear war to stop that from happening.  Kruschev ultimately backed down, and the loss of face he suffered in doing so led to his ouster and replacement by hard-liners Brezhev and Kosygen.  

Since I posted my initial comment, I’ve been thinking about what sort of protocol could be implemented to allow orbiting launch lasers to be built.  It might be possible.  It would have to allow all parties to feel secure that the lasers could not be diverted for military use.  Probably involve multiple tamper-proof self-destruct systems built into the satellite, each controlled by one of the competing powers.  Any one of them would have an assured ability to destroy the satellite, if it were used against them.  It would be a small-scale version of the policy of Mutually Assured Destruction that got us through the (first) cold war.

Bill Hannahan's picture
Bill Hannahan on Apr 6, 2014



How do you tell if a lifestyle is sustainable or not?  Imagine a world in which everybody lives the lifestyle in question, continue forward as many generations as necessary to see if it leads to catastrophe or not.

You will find that the only factor of significance is the number of children produced. Two people raising two kids in a nice house with two cars is sustainable. Two people living off the land in a tee-pee raising three children is not sustainable.

If you disagree, describe a lifestyle that produces 3 or more children that passes the above test.

I live a sustainable lifestyle, I like my vehicles and I like cheap energy including cheap gas.

Nathan Wilson's picture
Nathan Wilson on Apr 7, 2014

Ok, it makes sense to me that a power satellite would be made robust against small impacts, and that using a GTO and apogee kick which doesn’t quite reach the final orbit would do a lot to keep the orbit free of debris.

Of course old satellites have to be removed.  As you mentioned, geosynchronous satellites all start out with a tank of station keeping fuel.  Periodic station keeping adjustments are required since the Sun and Moon act to slowly perturb the orbit (they would eventually have new orbits which passed through the geosynchronous orbit daily at a speed on the order of a thousand miles per hour).  For this reason there will be a decomissioning cost for these satellites, to move them out of the high-value geosynchronous orbit slots, and a cost to keep the orbit free of large debris.

But I agree that the technical issues are probably solvable; the economics however will be challenging.  Politically, I would expect the low-intensity microwave version to be acceptable in some locations, but again low-intensity makes the whole system less versatile and the receiver facility large and less attractive compared to alternatives.

Nathan Wilson's picture
Nathan Wilson on Apr 7, 2014

It seems to me that construction of a launch laser would make it really likely that several world powers would develop and deploy anti-satellite weapons.  

The US has already tested such a weapon under Pres. Reagan, I believe.  The weapon was tested on a relatively low altitude (a couple hundred miles) weather satellite, so the debris may all be gone by now.

A launch laser would need to be higher to keep the launch vehicle in view longer, which could result in an anti-satellite weapons test at higher altitude.  This would result in a debris field that would last thousands of years!  Effectively, it would prevent humanity from developing space elevators and space tethers, which would be a real trajedy.

Keith Henson's picture
Keith Henson on Apr 7, 2014

Roger, part of the problem is how seriously do we take the buildup of CO2 in the atmosphere? 

Is that more or less important than military surpemacy?

There is also the point that the need to defend mid east oil supplies will go down if synthetic oil is seen on the horizon.

Another factor is that a propulsion laser can only see about 1/3 of the earth at a time.  For example, if the Chinese and Indians built one, the optimal place for the propulsion laser is over about longitude 130.  From there, in GEO, you can’t see any of the continental US, and even Hawaii is an extreme slant.

I like your ideas re multiple people being able to cut them off.  Perhaps using a signal that is required for them to opperate at all.  To avoid accidental shutdown, perhaps the loss of two out of 7 signals would turn it off.

Bill Hannahan's picture
Bill Hannahan on Apr 7, 2014

“Why go to the trouble of reducing electricity costs only to throw 2/3 or more of it away?”

To stop burning fossil fuel.

Robert Bernal's picture
Robert Bernal on Apr 9, 2014

I believe sun synchronous is about a million miles away, such as where SOHO is.

Keith Henson's picture
Keith Henson on Apr 9, 2014

Royce, that’s not much of an argument.  Earth’s shadow eclipses GEO power satellites less than one percent of the time.  And it happens spring and fall when the power demands are so small that the grid can shift power an hour east or west to cover the outages.

Cost is the determing factor.  With the lift cost reduced to $100/kg, I make a case for power satellites cheap enough to displace coal, 2 cents per kWh, and I can go through all the steps to justify that cost.  What cost do you get for the Sun-synchronous orbit?

I can’t make a case for existing launch vehicles even if the tranmission was free.

Keith Henson's picture
Keith Henson on Apr 9, 2014

Robert, try here

It’s an orbit that uses the earth’s equitorial bulge to precess as fast as the earth goes around the sun.

Robert Bernal's picture
Robert Bernal on Apr 9, 2014

Hi Keith,

I was in a rush, now at lunch and wanted to edit my mistake. Thanks for verifying that. Now, will check out that orbit…


Keith Henson's picture
Thank Keith for the Post!
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