Can't quibble with the analysis or the sentiment of this article. Yet, even though running out of control on costs, the SLS isn't going away anytime soon because the owners of the aging Shuttle/SLS technology and contract infrastructure are very powerful players in Washington. At best, we can only hope that the Shuttle/SLS standing army -- that will be paid one way or another -- spends their time doing something productive during the gaps between 2-year martian launch-window opportunities.

I am only "down" on space power production for use on Earth because we let physics and economics guide our systems engineering analysis. Space power production for use on Earth simply does not work and never will work because, no matter what you build in space, I can produce the same output on Earth at a cost that is hundreds of times less per watt. Look at roof tops on Google Earth -- that is where we are heading. And even if some unobtainable launch system drives the cost to GEO down to $100/kg -- the cost to build a space-rated power station in orbit would still continue to make this an unattractive option to investors.

I understand the allure of making power in space for use on Earth, but the ability to gather photons in space and beam them to Earth is only 4-6 times more efficiently per square meter in space compared to my roof on Earth. The Earth is in space, too -- it's just a bit less efficient to collect power here -- but we make up for that by our abilty to install as many cheap non-space-rated solar panels on cheap aluminum frames as we want and plug them straight into the grid with no need to launch hundreds of thousands of rockets, assemble city-sized spacecraft, deal with microwave losses, and worry about the maintenance of hardware at GEO.

If you add the cost and complexity to design and maintain what you are proposing compared to the same production on Earth (even including battery storage) -- you will see what I am talking about. I hope that you will do this so that we can move onto space topics that are genuinely workable.

When we teach space systems engineering at my institution of higher learning, we let the students ruminate on possible space projects that they might propose for a class project -- including an initial cost estimate. One team briefly considered the idea of growing tomatoes in orbit as a novelty item until it became obvious that the tomatoes would cost at least $1,000 each to produce aboard the ISS -- not including the return trip to Earth. Most of the reasons that make those tomatoes so absurdly expensive apply to the idea of lofting solar power stations into orbit.

Personally, it makes a lot more sense to build roof-top solar arrays and use the power right where it produced -- even adding batteries for overnight if someone wants to go 100% off-grid. A rooftop system does not clutter the Earth or precious GEO slots, or produce huge satellites that will die someday to create even more space debris hazards than we have already produced.

Photons reach the Earth with less efficiency than at GEO. However, the solar energy advantage of a space-based system is only ~4X greater than on Earth. That means that you can only spend $4-8 / watt on a space-based system before I can build a more efficient system on my roof. I keep hearing about the inordinate figure of $186 per kg for Skylon -- yet meanwhile I would be paying UPS ground just $1-2 per kg, and I won't need a space-qualified deployable system that needs to survive launch and survive the space radiation environment, and I won't need a microwave antenna to beam power thousands of miles across space to my house to use it.

Producing power for use in space (like aboard the ISS) makes 100% sense. Making power in space for use on the Earth at a cost that is realistically 500-1,000 times greater per watt in space than on the Earth makes no sense at all. Even if Leprechauns deliver the power plant satellites to orbit, it will still cost far more than a comparable collection of simple roof-top systems -- and nobody will ever pay for an expensive system in space when a far less expensive system on Earth is available.

A lot of people do not want to believe this, so if making power in space for use on Earth is too much of a sacred cow, I suggest that you cost out the production of tomatoes aboard the ISS for sale on Earth. The numbers are clear if you are willing to look at them.

In response to those who say that orbiting power stations have the advantage of 24/7 --- unless you are planning to build a 120 terawatt/hour-per-day orbiting system (typical total USA electrical consumption), solar power in AZ for peak usage without batteries would be a practical solution because we don't use as much power at night. But more to the point, I could buy plenty of batteries for the cost of a space-based system...

By any reasonable calculation -- including batteries -- building a system to produce 10% of the USA electrical power on Earth would cost about $200 billion. To produce the same amount of power from orbit, the cost is about $10 trillion, mainly because it requires 209,000 Falcon 9 launches at $50 million each. (In fact, 209,000 launches of anything is a problem).

If you want to believe that Skylon or some other futuristic space launch service can deliver your system to GEO for the same cost as a FedEx ground truck to the AZ desert -- and still make money -- you still have a host of other problems such as the need to build spacecraft rather than simple aluminum frames bolted to the ground ... and also the availability of GEO slots, microwave downlink land usage, and a 15-year on-orbit lifetime with no easy access for repair and replacement (and many other problems).

Ultimately, if access to space is as cheap as the enthusiasts hope -- building power stations in orbit will still need to compete with every other newly-enabled mission -- and, frankly making power in orbit for use on Earth at no special cost savings (and more likely costing at least 50X more) is not going to be on anyone's investing list.

Hi Paul -- 24/7 is where most of the 4X space advantage originates. If it were purely a matter of 24/7 -- it would be more like a 6X advantage in space -- but there is at least a 30% loss converting space solar power to microwaves, beaming this through the atmosphere, and then re-converting the microwaves to supply the national grid. Thanks for the reply, Ken

Robert Zubrin -- who is anything but a Moon person -- suggests that the Moon is a great place to explore between 2-year Mars launch opportunities, since (as he says) the SLS will come with a "standing army" -- and to stay sharp and reduce the cost per flight, we should explore both the Moon and Mars at the same time. There are, in fact, plenty of engineering goals that could also be achieve faster this way because, at worst, there is only a monthly launch window to the Moon and we could iterate a lot of Mars-oriented systems faster that way.

I realize that if you are a space-based-power enthusiast -- you may not want to read the following. But I assure you that if you look at the real numbers, it will be obvious that there is a good reason why space-based power for use on Earth has never happened and never will in any genuine sense of commercial reality.

In a nutshell, producing solar power and sending this back to Earth will never work financially -- ever -- even if you could launch for free, since I can always design a MUCH cheaper per watt off-the-shelf facility that is installed on the Earth -- complete with batteries and user manual -- all without any special space-rated parts, launch vehicle costs, or robotically-deployed spacecraft configurations.

The basic reason is simple: Even if not quite as effectively as in space, sunlight reaches the Earth, too. And it turns out that building ordinary commodity-item assemblies on Earth is SO much cheaper than building and launching spacecraft that the slight gain in space-based efficiency is absolutely minuscule compared to the added cost of building and launching spacecraft.

Here are some details...

Once all factors are considered, one square meter of solar power production from space has about the same production efficiency as 4 square meters on Earth. That's the TOTAL advantage of a space based system, and everything else is a downside. On Earth, the cost of solar power is about $250 per square meter installed (and dropping weekly). This means that if you want to build a solar collector in space and beam that power back to Earth -- you can can spend a total system cost of no more than $1,000 per square meter -- and still break even.

For your $1,000 per square meter -- you will need to engineer a deployable spacecraft that can be stuffed into a launch vehicle. On Earth, I don't need to engineer anything new other than the basic grid pattern and the proper sizing of the parts that I order online. In fact, I don't even need to see any parts until they arrive at the assembly site in Arizona.

Some people are hoping that Skylon or some other unproven system will cut launch costs to $185/kg. Yet even still -- by contrast -- on Earth, my solar array parts will arrive via UPS or FedEx Ground at a shipping cost of ~$1-2 / kg.

Beyond this, microwave energy needs to be beamed from orbit and will use up more land than we would ever need for a ground-based system -- so there is no real estate savings to using space, and when its time to replace solar panels in 15-20 years, I'll order new panels that show up by delivery van, whereas the space based people will need to build and launch a host of brand new spacecraft.

The reality is simple ... it will always cost FAR more to make solar power in space and send it back to Earth than to produce the same amount of solar power here on Earth -- including batteries and all the other worries that are typically raised by the space enthusiasts. For this reason, if I am a buyer of solar power I will NEVER invest in a space-based system. Ever. Furthermore, there is nothing to substantially drive down space-based costs since launching a spacecraft will always be a special process compared to the economies of scale of solar panel factories and FedEx Ground delivery.

Although the idea of space-based power for use on Earth has been around for more than 50 years -- I will always be able to build the same solar power generating capacity on Earth at a cost that is at least two orders of magnitude less per produced watt than anything that will ever be built in space. And frankly, if Skylon (or anyone else) ever does figure out how to turn a profit at $185/kg to LEO -- the total cost will still be much higher due to space-rated parts and how Skylon can't compete with FedEx Ground.

In view of how solar photons conveniently reach the Earth without any need to intercept these photons on the way -- and in view of how the Earth is, at worst, 25% as efficient per square meter as a spacecraft at adding this power to the national power grid -- it is time for smart people to pay attention to the reality that space-based power looks great until you look at the total system cost.

No matter what someone may quote for a space-based system -- even if based on a measure of phantasy -- I promise that I could produce a realistic Earth-based solar power quote that makes my case by contrast. So if you disagree, please list the cost breakout of your plan, and any solar power installer will be glad to validate my hypothesis.

My own reaction to the announcement of the death of Neil Armstrong came in unexpected waves. At first it was simply a news item until the first wave hit – shock, then another wave – grief, then another – a dizzying tightness in my throat, and then surprisingly – a wave of pure wonder as long buried memories poured out into view. Four and half minutes prior to the scheduled landing of the lunar module and nearly five and a half minutes before Armstrong actually set the lander down onto the dark Mare Tranquillitatis beyond a debris field of loose impact ejecta, Walter Cronkite matter-of-factly announced to the world that we had only “…four and half minutes left in this era…”

Today the pronouncement sounds preposterous to my 21st Century ear, yet I remember my Norwegian-born grandparents sitting in our living room that summer day in 1969 -- dumbstruck children of the late-19th Century bewildered and mesmerized in utter disbelief by the televised progress of the lunar landing. They had once known horses and wagons as modern-day conveniences, and here I sat on the floor recording the CBS News audio feed onto a reel-to-reel tape machine, an optimistic child of the mid-20th Century looking up at my elders trying to explain what it meant to land a four-legged wagon on another planet. The Earth simply stood still and there were no adequate words. Cronkite’s declaration drifted by unchallenged. Perhaps my grandparents really were watching the end of the world as they had ever known it. The bewilderment I saw in their eyes was far more akin to terror, yet fear of the future was something I could not fathom and I did not recognize until many years later.

Armstrong gave other people much of the credit for what he and Buzz accomplished that Sunday afternoon and evening. Perhaps it was a way of avoiding a moment in time that would unavoidably tie him to the Moon for the rest of his life, or maybe it was just the decent and proper thing to say in view of the Apollo program as a whole. Yet despite Armstrong's expressed humility and desire to quietly shift the limelight onto the hundreds of thousands of scientists, engineers and drafters who designed and built the machines and the methods for using them, no one among the entire supporting host ever confronted such a pure trial of character and capability. No one ever to walk the Earth has to this day so far from home stared into an abyss that on first inspection seemed to have no end and taken control of a spacecraft in a desperate bid to locate a smooth landing site on another planet with fuel running low and the point of no return largely passed. Later pilots landed on the moon with Armstrong’s knowledge in their hip pockets and made it look comparatively routine, yet somebody had to be first, somebody had to dig down deep and tap into a reservoir of skill and determination that few other people have ever possessed. Somebody had to do something entirely new that had never been done before with the whole world watching and waiting and praying and fearing that things might go horribly wrong.

Still a starry-eyed 14-year-old when I'd finally wrung every ounce of excitement from the day, I went off to bed that night slipping into dreams of wonderment. My grandparents had long since disappeared before the sun was down and they did not see the moonwalk and the next day avoided fast-selling newsprint coated in headlines that could be read from a mile away. I suspect for them that a live TV broadcast from the Moon and the detailed descriptions to follow would have been comparable to a functioning stargate in our own time, and from what I could see, they were content to live out their days in the world they had always known.

Years later, with the benefit of hindsight and the guidance of my own internal reactions to the passing of Neil Armstrong, I realize now that Walter Cronkite had been right. This was the beginning of a new era, and I do not clearly recognize this fact anymore because of how I have so completely forgotten what that older world felt like before humans first landed and walked on another world. And yet my Norwegian ancestors were also right — that we are clearly reminded of our common ultimate fate when the first man to walk on the Moon finally returns the Earth.

Hubert et al.

Part 2

Now let's look at the requirements of your solar array. To collect one megawatt in space would require a steerable array about 1/2 the size of a football field. My little home town west of Boston runs on an average of 10 megawatts -- which would require an acre of solar arrays. Boston runs on roughly a gigawatt -- requiring a square mile. Yet Boston isn't even close to 1% of national electrical consumption. To provide just 5% of our national electrical usage from space would require 21 gigawatts -- or 21 square miles of collection area.

This is where the wanna-bees run off the rails, because 21 square miles doesn't sound like a lot. Yet it isn't just the area that causes problems (from assembly and steering complexities, solar photon pressure and tidal forces). At 5 watts per pound you would need to launch 2 million metric tons of panels up to geosynchronous altitudes. Even if you're right and my original estimate was off by a factor of 20 -- that's still 200,000 metric tons. An Atlas V is typically rated for ~ 15 metric tons to GEO -- so you're looking at 12,000 launches based on your numbers, and more like 10 times that based on reality. Even if your pounds per dollar to orbit and your mass estimates are correct, you're still looking at launch costs of $1,000 x 200,000,000 kg, or roughly 100 trillion dollars -- just to launch enough panels to make just 5% of our electricity for the next 20 years (yes, solar cells, especially in space, do wear out). If MY estimates are right, the cost is more like 10 quadrillion dollars.

This is where the wanna-bees wax poetic about reusable launch vehicles and other nearly free methods for access to space. Yet we tried that -- it was called the Space Shuttle -- and it was very far from free and just barely reusable.

Okay so let's ignore all of those realities. Even still, you're not out of the woods yet. You still need to design and build huge clean-room facilities to fabricate the panels -- and as part of this, buy the exotic rare-earth elements to grow the solar cells (or make a bunch of Chinese companies rich by outsources all of this). But before anyone gets rich or saves any portion of the planet you still need to find some way to pay for this long before any power is beamed from space. And the money isn't just for technology. You'll also need to lease the land for your microwave collectors -- who pays the rent? If you somehow launch the system -- who fixes it when it breaks? Sorry, spacecraft at geostationary-altitudes are inaccessible unless you're planning on a human flight component to the plan. And before you go any further, those geo slots are auctioned to the highest bidder. Have you looked into those costs? -- typically they're auctioned at tens of millions per slot. Are there even any slots left for sale? The last I heard most over the USA are locked up.

Okay, so let's just skip the geo orbits -- yet any other orbit would require continuous steering of the microwave downlink antenna -- aiming this continuously at a fixed point on the planet -- with mayhem the price of missing the mark by any sort of wide margin. The problems of attitude control of spacecraft grow exponentially with size. If you lose your downlink lock, several megawatts of microwave energy could drift across a schoolyard playground, and suddenly your goal of saving the Earth heads exactly in the opposite direction. Satellites go rouge and become zombies at times. And you'd better hire the best security team on the planet -- because this would be the most awesomne terorist weapon ever conceived.

Beyond this, we haven't even scratched the earth-based operational and business side of the story. Who buys your electricity? If you can't sell it in bulk for way less than ~ 10 cents per kw hr, you'll never bring in a single dime of revenue. And even if you managed to charge $1,000/kw/hr -- the system would still never pay for itself.

Solar power from space for mass consumption on the earth does not need anyone to "damn" the idea since, as far as I can tell, those with potential funding dollars already understand how far removed this notion is from practicality -- now and for as many years into the future the futurists dare to predict.

Hubert et al.

Part 1

As Gerry points out -- there are terrific working alternatives to generate usable power at reasonable costs now and immediately ahead that do not require fantasy or magic. I wish to be kind about this however, since my goal in life is to illuminate, not to condemn. Sometimes this goes over the top when I see just how far astray from plausible reality a vaporous notion is carrying decent and well-meaning people.

Here's just a snapshot of things to consider....

"The best hope the world has for a prosperous future" begins with a sober assessment of physical and economic reality. Your "20X is too high" works out to 50 pounds for a 4KW system. That is inconceivable for a space-rated assembly. Okay, maybe I'm a bit high in my estimate -- yet I like my spacecraft to survive 10 g's and 165 db of sound pressure during launch. Typical commercial panels are 5 watts per pound. For just the panels we're looking at 800 pounds for a 4KW system. With framework, deployment motors and power conversion, we're easily over 1,000 pounds. You can try to work around this with expensive and exotic mass-saving designs, but it won't come close to solving any problems on the scales you're talking about.

Considering launch mass per dollar -- the economics are rooted in physics. If someone could have cracked this nut, it would have been cracked 50 years ago. Due to limits on energy from chemical fuels, only 1% of total launch mass can make it into orbit as a working payload. You can throw money at this to kick that percentage up a tiny bit -- but you won't save any money by doing that. On a cost-basis, that takes you in the wrong direction. Instead, everybody talks about cheaper launch costs. Yet every single estimate and promise underestimates or outright ignores the real costs. SpaceX (or any other launch vehicle company) can quote whatever they want -- but it doesn't reflect the $billions invested up front.