Interviews: L5 Society Cofounder Keith Henson Answers Your Questions 64
Last week you had the chance to ask electrical engineer and L5 society co-founder Keith Henson about space colonization, his solar power satellite project, and his run-ins with Scientology. Below you'll find his answers to your questions.
Microwaving power to Earth from space by Anonymous Coward
If the beam becomes misaligned and strikes Iowa, how do you stop the entire state from exploding into a massive popcorn volcano?
Henson: Sorry to disappoint about the popcorn, but it can’t happen. The transmission needs a guide beam to phase the wave front. Lose the beam and the power scatters into the entire half space in front of the antenna. Also, the power inside a microwave oven popping popcorn is around 10 kW/m^2. The beam from a power satellite is under 0.3 kW/m^2. Sunlight is around a kW/m^2.
Cost per KWh
by Rob Lister
What is the cost per KW for the build/deployment and resultant cost per KWh for the end user?
Henson: If you are going to do power satellites at all, they have to undercut coal or there is little point in doing them. If you go through the levelized cost of electric power for a no-fuel power source, the capital cost can’t exceed $2400/kW for 3 cent per kWh power. That undercuts coal, which costs around 4 cent per kWh. Because the cost of power to the end user includes a lot of fixed distribution cost, the retail cost to households probably will not change a lot, but it won’t go up either. Also it puts a cap on transport fuel because we can use cheap electricity to make cheap gasoline.
The investment to set up the parts pipeline to GEO is probably around $60 B (not counting Skylon). The financial model shows the whole capital investment paid off in less than ten years.
Minimum cost
by Winged Cat
By focusing only on $ per kW or $ per other unit, you seem to be ruling out consideration of $ per mission or $ per step, thus requiring $billions to be spent up front on technology that has only been proven in the laboratory. This is roughly as difficult as trying to kickstart a fusion reactor using nothing more than a matchbook.
Have you given any thought to demonstration missions, or realistic paths to funding that might eventually unlock enough money for the full system as you describe it? ("Government funding" not being a realistic path, given their demonstrated history with regard to projects that might actually give cheap power to the masses. This applies to any government large enough to fund this - such as US, EU, Russia, or China - though the exact means by which each one has demonstrated it wouldn't fund this, except to sabotage it and thereby waste the energy of those who might otherwise build this for real, varies by government.)
If not, why not? That's as much a part of the problem that needs solving here as the technology, and you've shown you can solve the technical side.
Henson: I have thought a lot about demonstration missions. Sorry to say, but they don’t make sense, at least not if you are trying to use expendable rockets. For less than the cost of one full sized demonstration power satellite, you can set up the low cost transport system and build half a dozen. That recently (last few days) might have changed. There may be a reason to build a 1/8th scale power satellite using a 25 GHz transmission beam. It’s to power the LEO to GEO leg of the transport system, but it would also demonstrate that power satellites work. It also looks like it will cost much less than the alternate, a $15-20 B, 8 GW transmitter on the ground at the equator.
As for why not, convincing governments or private investors to build any part of this is a different skill set. Be delighted to have you (or anyone) help. And thanks for the compliment.
What "wear and tear" factors are relevant
by ShieldW0lf
Could you give a general overview of what the wear factors are for your system, how long you would expect a satellite to last, and what the post failure plan would be?
Henson: PV type power satellites degrade because of radiation damage to the cells. That’s predictable but it might not be as bad as what we have seen on communication satellites. If you build many power satellites, and that’s the only program that makes sense, then the satellites capture the trapped particles in the Van Allen belt. When you start talking about hundreds to thousands of power satellites at 32,500 tons each and a total of 3 kg of protons trapped in the belts, you can see that the trapped particles are going to be soaked up rather fast. There is also a proposal to drain the belts.
If we build thermal power satellites, then there will be a lot of turbines, steam or possibly supercritical CO2. How the bearings will work in space is unknown, but the forces are so small that we could use noncontact bearings. Seals are harder. The levelized cost calculations included 10% per year maintenance based on the cost of the original parts. Thermal power satellites also require steady patching of micrometeorite holes in the radiators.
There is no reason I can think of why a power satellite would last less than several decades. For worn out power satellites, the assumption is that we reprocess the material into new ones. Mass in GEO is worth $200/kg, and it costs much less to reprocess mass than to haul up new materials. If the program comes about, there would be a substantial industrial and human presence in GEO, perhaps upwards of 10,000 people.
Why geosynchronous orbit?
by Anonymous Coward
Has anyone considered using a semi synchronous orbit with multiple receivers around the world to provide electricity to places at peak times (4pm to 8pm) when electricity is more expensive? I'm curious about the economics of it all.. e.g. how much down time would such a system have (as it's over the pacific say), what's the price of a receiving station, what's the comparative peak vs base load price of electricity? Would the sun still be visible to a satellite in semi synchronous orbit that can beam to a place on earth at 8pm (I imagine so) etc.
Henson: Addressing the economics, electricity is a commodity, especially base load power. Market goes to the lowest cost producers. Power satellites are cheaper than ground solar in close to the ratio of their utilization (i.e., fraction of the year they are selling power). Ground solar plants sell power about 20% of the time, vs space-based upwards of 90%. The problem with orbits other than GEO is the low utilization when the power satellites are in a bad location to deliver power. The last thing a utility wants is a big intermittent power plant.
If we build space-based solar power at all, it has to be 3 cents a kWh or less, otherwise the project just does not happen. Since the power uses no fuel and costs 3 cents a kWh, then run half the time it would cost 6 cents a kWh. That’s the same price as gas turbines used for intermediate and peaking loads. In a mature market, off peak power might be worth 2 cents a kWh to make hydrogen. The hydrogen plants are not efficiently used, but there is no reason they should be expensive, which is to say $200/kW or less. The effect of a 2-cent diversion market for power over the base load reduces the cost of intermediate power used half the time to 4 cents (6 +2)/2.
The long-range effect of power satellites will be to greatly reduce the value of peaking power, essentially to zero. What do we do with the hydrogen? Combine it with CO2 to make transport fuel. That solves the other half of the energy problem.
Space Elevator
by Btrot69
Most of us on slashdot will probably agree that "Economics, Energy, Carbon and Climate" are all one big problem that needs more investment. But the devil is in the details of how to do it.
I'm not an expert on this subject like Henson, but IMHO a space elevator seems just as close to being technically viable as space plane powered by a ground-based laser and microwave power beamed to earth.
Not only that -- a space elevator would be much cleaner and the cables might even be able to double as power transmission lines.And -- since all the good tethering points are in the third world (the equator) it would be a big solution to economic disparities too.
Why does Henson's article not consider the possibility of a space elevator?
Henson: The easy reason is that we don’t have the materials for the cable. I worked on the problem years ago, even figured out how to make a step-taper, moving-cable elevator. I can’t make one work for the Earth. I am not down on elevators; a Lunar elevator out through L1 makes sense with current strong materials such as Spectra. If someone finds material good enough for an Earth to GEO cable, we can then try to solve the other problems with satellites hitting and vaporizing the cable.
We've learned a lot
by Geoffrey.landis
We've learned a lot since the rather naive plans of the 1970s, when space colonization was first proposed by Gerard O'Neill and his students.How are things different now? What's the most important thing we've learned since then?
Henson: The main thing that is different now is the single-stage-to-orbit space plane—Skylon. Space has always been tightly constrained by the cost of launch, $20,000 to get a kg to GEO. The energy cost is under a dollar so there is lots of room to improve. At 10,000 flights per year Skylon should get the cost down to around $120/kg to LEO and with remotely powered electric rockets, the cost to GEO should not exceed $200/kg.
It’s hard to say what is the most important thing we have learned since O’Neill’s days. For me it might be that humans may not leave the Earth in significant numbers, but instead leave reality as we know it (by uploading).
I think O’Neill was aware of the problem, but if you read up on the space-station activities, the fraction of time they spend on maintenance is impressive. I think the solution might be to send up families, and put the kids to work.
If you want to keep up with the progress look here, It used to be low traffic, but activity is picking up. There are a few conferences on the topic and it gets coverage at the International Space Development Conference.
Transportation station
by Jack Dixon
With some of the income and infrastructure from this project, why not use it as a way station for Mars expeditions? Build a self sufficient habitat and inject it into the favorable orbit between L5 and Mars. Then every two years a group of colonists could ride it with very little fuel expenditure to Mars. They would need to park their descent vehicle nearby. Food, water, and radiation protection could be provided in the habitat, with artificial gravity and greenhouse food production managed by a team of robots during the long sector of the orbit.
Henson: I am not a big Mars fan. O’Neill convinced me long ago that planetary surfaces are not good places for a growing industrial society. Still, I have proposed that the charter for the construction company include a “hundredth one goes to Mars” clause. The Mars fans can have a power satellite to move to Mars and use there, or the mass (~30,000 tons) of one in GEO for a Mars mission. This could happen rapidly. Governments could decide that they just have to quit burning fossil fuels and that power satellites are the only way to do it without destroying the economy from high energy prices. If we started building power satellites at 5 per year in 2023, and doubled every year (mostly building more Skylons) then the Mars mission could leave before 2030.
Asteroid Mining
by meta-monkey
Leaving aside the not insignificant economic and safety concerns, I'm interested in the technical feasibility of extracting minerals from asteroids in useful quantities. On earth, we extract minerals concentrated by geological and biological processes that are unlikely to have occurred on an inert asteroid.
What do we know about the distribution of minerals within asteroids, what more do we need to know in order to design machines that can extract these minerals, and what can you speculate about how those machines might work?
Henson: You are correct, other than the Siderophile separation, same that sent most of the gold to the center of the Earth, it doesn’t look like the asteroids had mechanisms that concentrated minerals. There may be exceptions on asteroids as large as Vesta.
We know a lot about asteroid mineral concentrations from the tens of thousands of samples found as meteorites. Most of them would not be valuable if you found them in the millions of tons on Earth.
On the last question, you are in luck! I happen to be one of the few space fans who actually worked in mining. A few years ago I wrote up my thoughts on how to mine a huge asteroid (1986 DA). It is the metallic core of a differentiated asteroid.
So, whatever happened, anyway?
by Anonymous Coward
So, whatever happened to the scientology thing, anyway? I remember reading about what was going on, but I never really heard how it all came out.
Henson: It’s still in process. The cult has shrunk from around 100,000 when they tried to rmgroup alt.religion.scientology to (some say) 10,000. With all the data on the net, they have an awful time trying to recruit new members, and former members sue the cult in an orgy of litigation. After the recent “Going Clear” documentary on HBO, there are now many people saying the IRS should yank the cult’s tax-exempt status. The cult abused the IRS through the courts back in the early 1990s to get that status. The IRS still fears the cult so that’s not likely to happen soon, in spite of huge abuses such as hiring PIs that have no legitimate corporate function. That makes the money spent on them an illegal use of a non-profit funds (inurement). If any ordinary religion did this they would be facing jail time. Of course, the cult has more in common with organized crime than religion.
I got a couple of academic papers out of my involvement. I was trying to figure out why (some) people are so vulnerable to cult attention rewards that they act like drug addicts, for example abandoning their own children. Search for Sex, Drugs, and Cults or just go here. Other papers are here.
If it is 1/3 the power of the sun... (Score:2, Interesting)
"The beam from a power satellite is under 0.3 kW/m^2. Sunlight is around a kW/m^2."
then why would we use this instead of just using solar power? They must be using Republican math to try to justify this corporate welfare.
Re:If it is 1/3 the power of the sun... (Score:4, Insightful)
"The beam from a power satellite is under 0.3 kW/m^2. Sunlight is around a kW/m^2."
then why would we use this instead of just using solar power? They must be using Republican math to try to justify this corporate welfare.
Do you mean that math in the replies where Henson said:
Addressing the economics, electricity is a commodity, especially base load power. Market goes to the lowest cost producers. Power satellites are cheaper than ground solar in close to the ratio of their utilization (i.e., fraction of the year they are selling power). Ground solar plants sell power about 20% of the time, vs space-based upwards of 90%.
Now if you have an issue with his 20% and 90% numbers then feel free to present your own analysis that refutes those numbers.
Re: (Score:2)
I have in issue with his ignoring launch costs. When launch cost are not more than 4.5 (0.9 / 0.2, his numbers) times the cost of the actual solar equipment then power satellites will be cheaper. Ignoring transmission costs and assuming solar systems on orbit have the same life as on roof.
Re: (Score:1)
I am sorry you missed it, but launch cost are over half the capital cost even when you get the cost down to $200/kg.
Re: (Score:2)
Saying it's $200/kilo is the same as ignoring it. Everything that derives from that assumption is bullshit.
Re: (Score:1)
It's called design to cost. If you can't get the parts cost plus the kg/kW times the $/kg down to $2400 or less, then the project doesn't happen because you don't get the market for it to make any sense. You just can't sell power for less than it cost to make it.
Re: (Score:2)
Elon Musk ranted amusingly about space-solar power a few years ago in an interview [youtube.com] with Popular Mechanics, saying, "I wish I could stab that bloody thing through the heart." However, speaking off the cuff, he used a less favorable space/ground ratio than the L5 proposal. I'd be interested to hear what he thinks of this plan, especially as SpaceX is on the verge of proving its new reusable boosters, which would be a great enabler for the launch cost aspect.
Re: (Score:2)
Musk, i.e., SpaceX is correct to be down on power satellites. His stated reason, low efficiency from sunlight to electric power is bogus though. Efficiency isn't a concern, cost is. Think about it. What would be lower efficiency than sunlight to hydro power? But hydro power is the cheapest kind of electricity we have.
Using what amounts to V2, or Saturn V technology (at the most), I think SpaceX will get a full ten to one reduction on the cost of cargo to GEO. But as I put in another post, that's not c
Re: (Score:3)
Why focus on commercial baseload power? The cost to the military or other organizations to provide power in remote hostile locations is orders of magnitude higher than $0.03/Kwh. Isn't your best bet to fill that demand? Competing with coal seems a fool's errand when you can compete with diesel fuel humped over 3000km in tankers, forwarded to advanced basis in Afghanistan on Humvees, and burned in inefficient generators. The costs there are more like on the order of $30/Kwh. Building a reception grid for 10K
Re: (Score:1)
Lots of people have thought long and hard about military and other niche markets. The physics (and economics) is so against you that even the really smart guys have not figured out how to makehttp://interviews.slashdot.org/story/15/08/26/1644228/interviews-l5-society-cofounder-keith-henson-answers-your-questions# it work. If you can make a case for it, please do. You will be the first.
Re: (Score:2)
Well, I don't really expect you to tutor me in these numbers, but I've heard the case made pretty convincingly. What in the numbers doesn't work?
Re: (Score:1)
If you know of a case which is convincing, please point me to it.
In simple terms, microwaves that will get through the atmosphere can't be focused tight enough to deliver the small blocks of power needed for military and niche markets. Lasers will deliver small blocks of power, but are blocked by clouds. The scale/frequency problem is in one of the graphs here:
http://www.sspi.gatech.edu/aia... [gatech.edu]
$145,000/kW translates into $1.80 per kWh.
Re: (Score:2)
Well... That's not ENTIRELY true, you'd need a Rectenna of about 1000m in diameter, for reasonably high efficiency, but it could be considerably smaller in many cases and still be valuable, nor is that size necessarily prohibitive. This is all assuming only GEO, the divergence for lower orbits is MUCH less, so it becomes a balancing act between costs and limitations on the ground vs potentially needing more satellites and/or taking some time to reorient the ones you have.
Its not a perfect system by any mean
Re: (Score:2)
First thing I noticed.
Even if you get full power for more hours out of the day, I doubt 1 day of microwave beaming will outstrip 1 day of solar in a decent solar location.
It could make sense in places that suck for solar, I guess.
Re:If it is 1/3 the power of the sun... (Score:4, Interesting)
Sun to electric power conversion is ~15-25% efficient.
Microwave power transmission is up to 50% efficient.
Satellite power provides power 24/7 and does not need any form of energy storage, and would be a full replacement for traditional base-load power generation (like hydro, nuclear and coal).
Solar power is limited to roughly 8 hours a day, and needs either energy storage or other base-load generation. Power storage is either inefficient or costly.
The only relevant question is if it is possible to make it cheap enough, without the pie-in-the-sky Skylon.
What would it cost with Falcon-9 or Falcon-Heavy as launch vehicle for the satellites?
Re: (Score:1)
Parts including the rectenna are figured at $1100/kW
Eventually SpaceX will get the cost of parts to GEO down by a full factor of ten from the current of $20,000/kg At 6.5 kg/kW and $2000 per kg, the lift cost would be about $13,000, total $14,100 per installed kW.
The formula to go from capital equipment to $/kWh is to divide by 80,000 or 17.6 cent per kWh. Sorry, no market at that price.
The project does depend on Skylon or something else that will get the cost down to $200/kg to GEO. That's hard, I agree
Re: (Score:2)
I think he is comparing the energy in the beam to the total of all wavelengths in the sunlight, not just the microwaves. However the wording is certainly misleading and I read it the same way you did, too.
Re: (Score:1)
PV (solar power) is about 20% efficient, so you get about 200 watts out of a square meter. But you only get it about 1/5th of the time due to day/night and low sun angles so the average over a year even in good places is 40-50 watts per square meter. The rectenna is typically 85%, 24 hours a day, about 250 watts per square meter or about 5 times as much.
Plus the rectennas are mostly open space. They don't block sunlight much so you can get duel use out of the land by putting the rectenna over farmland or
Re: (Score:2)
Why? because in geostationary orbit the sun shines (mostly) at night, and always during the peak evening hours
Re: (Score:1)
Re: (Score:2)
Re: (Score:1)
Senior Life member IEEE.
Asteroid Mining (Score:2)
Henson linked this article above:
http://htyp.org/Mining_Asteroi... [htyp.org]
My question on that would be, why return the minerals to earth? They are way more valuable in space, just like he says about the decommissioned power satellites.
Re: (Score:2)
Did you read the link? He is talking about having a refinery launched to refine minerals out of an asteroid and ship them back to Earth.
Re: (Score:2)
Your question assumes a static economic situation, which is not what will happen. Launching whole factories to process the raw asteroid rock will cost too much at first. What you want to do instead is launch a starter kit of production machines. You use those machines to make parts for *more* machines out of some of the asteroid, plus some parts you bring from Earth. As your collection of machines in space grows, you can make a wider range of items, and need less from Earth.
In addition to growing the fa
Re: (Score:2)
Did you read the link? I was saying "why ship gold/platinum to Earth". He goes through the economics of it, and explains that common gold/platinum mining on Earth is working with 5 ppm of gold, so it makes more sense, but he also discusses in the solar power item here that things are worth $200/kg in GEO, so I can't see why you would ship them down, when gold and platinum are damn useful in orbit (as well as the iron that he plans to use for structural components in space).
Re: (Score:1)
Earth is where the market for gold is so you have to bring it back if you want to sell it. Mind you, I don't think anyone will be mining asteroids for gold until second generation power satellites have been made with space mined nickel and iron for some time. But I think it can be done, profitably, with enough bootstrapping in space.
Ah, *that* Kieth Henson (Score:3)
I'd almost forgotten about that nutcase and his obsession with Skylon.
Re: (Score:2)
TVA. (Score:3)
"Government funding" not being a realistic path, given their demonstrated history with regard to projects that might actually give cheap power to the masses.
The are vast regions in the US that have benefited enormously from governmental investment in electric power.
Even by Depression standards, the Tennessee Valley was economically dismal in 1933. Thirty percent of the population was affected by malaria, and the average income was only $639 per year, with some families surviving on as little as $100 per year. Much of the land had been farmed too hard for too long, eroding and depleting the soil. Crop yields had fallen along with farm incomes. The best timber had been cut, with another 10% of forests being burnt each year.
TVA was designed to modernize the region, using experts and electricity to combat human and economic problems. TVA developed fertilizers, taught farmers ways to improve crop yields and helped replant forests, control forest fires, and improve habitat for fish and wildlife. The most dramatic change in Valley life came from TVA-generated electricity. Electric lights and modern home appliances made life easier and farms more productive. Electricity also drew industries into the region, providing desperately needed jobs.
Tennessee Valley Authority [wikipedia.org]
Re: (Score:2)
Yeah, I immediately thought of TVA, too. I believe Hoover Dam was also socialistic make-work for the masses, too. Or a quest for resources to grow population and business in the southwest US. Or something.
from wiki...
"The Fall-Davis report cited use of the Colorado River as a federal concern, because the river's basin covered several states, and the river eventually entered Mexico."
Fwiw, I don't think a project like this would fly nowadays.
Re: (Score:1)
I don't think the US is likely to lead the power satellite project. To much cheap shale gas.
But if it was to be done, something like TVA would be the a good organizational model.
Re: (Score:2)
Never Say Never Again.
Skylon? Seriously? (Score:4, Interesting)
Sorry Keith, but while I'm a big supporter, AFAICT Skylon remains a pipe dream. It may be slightly closer to reality with a bit more research funding, but it still exists only in a computer simulation. I've been reading about Skylon for something like 15-20 years now, and I'm not holding my breath.
Skylon needs an 'Elon Musk' to put real money into it and build a working prototype vehicle (not just an engine). Then it might be a game changer, but definitely not now.
- Necron69
Re: (Score:2)
Re: (Score:2)
Skylon needs an 'Elon Musk' to put real money into it and build a working prototype vehicle (not just an engine). Then it might be a game changer, but definitely not now.
Skylon's problem is that the 'working prototype' would probably cost over $10,000,000,000. SpaceX could start with an expendable rocket and make money as they work up to reusability and low cost launches. Skylon can't. If it doesn't work, you've just blown $10,000,000,000 with nothing to show for it.
That's why I don't believe it will ever fly.
Re: (Score:1)
The precooler heat exchanger is the only unique part of Skylon engines, the rest is regular turbomachinery. It enable an engine cycle that produces thrust at far higher altitudes and velocity than anything we have known before and it does it on a remarkably small amount of light weight hydrogen.
The AFRL decided recently that the engine would work as advertized, Airbus wants to build the airframe.
http://www.reactionengines.co.... [reactionengines.co.uk]
Skylon, or something with similar performance is the only way economical power
Re: (Score:2)
Yes, and back in the 1970s, we all believed the space shuttle would fly 50 times a year and save tons of money with their reusable architecture. I simply can't believe these pipe dreams anymore, especially when they are backed by a government bureaucracy.
- Necron69
Re: (Score:1)
Reaction Engines has some government support, but isn't part of the UK government.
I don't think you appreciate the technical aspects of the project. They are remarkable.
Re: (Score:2)
Lets assume Skylon works, that doesn't solve your problems. At current sorts of launch scales a hypothetical SSTO launch vehicle might be cheaper to operate than say SpaceX's launchers, but that doesn't mean launch services will be that much cheaper. Their costs are related to supply and demand, and with the initial system probably limited to a fairly small throw weight and requiring a conventional upper stage for GEO chances are slim that an SPS will make economic sense (IE GEO costs will still be far abov
Re: (Score:1)
" requiring a conventional upper stage for GEO "
Indeed, a conventional upper stage increases the cost to GEO by a factor of at least 2.5 to one. That makes the power more expensive than coal and there goes the market.
The only reasonable thing I could figure out to hold down the amount of reaction mass is to use high exhaust velocity electric engines (20-25 km/s). Unfortunately you can't power them from sunlight or they take so long climbing through the space junk bands that the vehicle gets above 2000 km
Re: (Score:2)
Trump is amusing, at least for some values of amusing.
The question is, then, even if you had this microwave powered electric tug, will it really be affordable? I mean its going to cost what, $10 billion to get that going? At least that much, and that'll get you what, one? So, maybe you gotta go slower and accept the hits. Don't deploy your SPS until it gets to GEO. There are creative answers.
Re: (Score:1)
Depending on how you do it, the tug (small change) and a ground based power plant (big bucks) could run to $20 B or more. But that's not excessive considering it about doubles the fraction of cargo delivered to GEO by a $50 B fleet of Skylons. (100 or more at half a billion each.)
Almost all the dense space junk is below 2000 km, so you could deploy a power sat at that altitude and self power out to GEO. But if the power sat is not deployed, how do you power the arcjets from 300 km LEO out to 2000 km?
The
Re: (Score:2)
I only have one thing to say, Nuclear Thermal Rocket.
Re: (Score:1)
I have been a fan of Nuclear Thermal Rockets since before L5 Society. But good as they are, they don't give the exhaust velocity of electric rockets and you have to lug around the considerable mass of a reactor. For where you can reach with microwave power transmission beams, that seems to be a more cost effective solution. For way out where it's too dark for solar electric propulsion, they don't give as high an exhaust velocity as you really need for missions out there. After having done a lot of work
Re: (Score:2)
Simple, reliable, easy to build, but not really optimum at all for a first stage. Much better for high impulse orbital transfer. Yes, nuclear electric might be more efficient, but its unlikely you're going to build a really high thrust nuclear electric design, and for lower impulse designs why not make it solar? The real advantage here though is the ease of development and deployment, you get quite a lot of bang for few bucks. The basic design of a Nerva-class system is already in the bag, it could be flyin
$2400/kW for 3 cent per kWh (Score:2)