Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 



Forgot your password?
typodupeerror
Power Space Technology

Interviews: Ask Engineer and L5 Society Cofounder Keith Henson a Question 111

Keith Henson is an electrical engineer and writer on space engineering, space law, cryonics, and evolutionary psychology. He co-founded the L5 society in 1975, which sought to promote space colonization. In addition to being an outspoken critic and target of the Church of Scientology, Keith has recently been working on the design of an orbiting power satellite (video here). The proposed satellite would collect solar energy, send it to Earth via microwaves, and Henson has a plan on how to launch it cheaply. Keith has agreed to give us some of his time and answer any questions you might have. As usual, ask as many as you'd like, but please, one question per post.
This discussion has been archived. No new comments can be posted.

Interviews: Ask Engineer and L5 Society Cofounder Keith Henson a Question

Comments Filter:
  • 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?
    • Disable Disasters in the Disasters menu.
    • by Grishnakh ( 216268 ) on Monday August 17, 2015 @12:36PM (#50332929)

      I'm not Keith, but from what I've read about such systems, this isn't a concern: when they hit the Earth's surface, the microwave beam is very large so it wouldn't have a fatal effect on anyone or anything that happened to cross through it, though it might warm you up a bit. Also, the frequency is pretty important; microwave ovens work because they're tuned to the resonant frequency of water, which most of our food is largely composed of, so it excites the water molecules and makes them heat up. If the beam is tuned to something else, it might have very little effect on lifeforms crossing through it (which is probably the intention, since tuning it for water would make it attenuate too much on cloudy days).

      • by Muad'Dave ( 255648 ) on Monday August 17, 2015 @12:56PM (#50333157) Homepage

        ... microwave ovens work because they're tuned to the resonant frequency of water ...

        Bzzt. Microwave ovens use 2.4GHz because there's an ISM band [wikipedia.org] there. There is no resonance at 2.4 GHz for water [flitetest.com]. If there was your food would explode in the oven.

      • Yes, very low energy per given area can ensure safety. But that means absolutely huge receivers are required to get a useful power level.
        • Yes, very low energy per given area can ensure safety. But that means absolutely huge receivers are required to get a useful power level.

          To receive the kind of power levels we're talking about efficiently, you're going to need pretty damned big receivers. Luckily, they don't have to be large single physical structures - you'll have a rectenna array rather than one big one.

          • A bunch of little ones all together, a smaller number of bigger ones, what does it matter? It still must cover a tremendous area.
            • A bunch of little ones all together, a smaller number of bigger ones, what does it matter? It still must cover a tremendous area.

              It does take up a lot of space, but you can put it someplace crappy that nobody goes anyway and it doesn't look like much of anything.

            • So do solar panels. The difference is a rectenna array generates 300 W/m^2 for 24 hours a day, while solar panels generate about 200 W/m^2 from 4-6 hours a day in most decent locations. In crappy locations for solar (Seattle, Germany), the energy per land area is *way* higher for space beamed power.

              • ' a rectenna array generates 300 W/m^2 for 24 hours a day

                That is possible on the high end, but the topic of this thread was doing so with safe energy levels, and to be safe you need to be a lot closer to the 20 W/M^2 range. You can have a setup with higher levels in the center and lower at the edges of the beam, but when beaming from such a great distance it is difficult to manage such an intensity distribution.

                For even 80 W/M^2 average, it would take a receiver surface area of about 3 square miles to produce 600 MW ( the size of a medium fossil plant, just fo

                • Why do you need 20W/m^2 for safety? The sun beams 200W/m^2 on sunny days and the worst damage it does is sunburn and deterioration of plastics.

                  • UV radiation is the component of sunlight that burns, it is only a slice of the spectrum. That part of the spectrum is not 200 W/m2.

                    Microwaves interact differently with the human body than UV radiation, so the comparison would not necessarily be telling. My quick searches showed safe levels need to be in the range I specified, I'll admit I don't know the science behind them.
                    • Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.

                      300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.

                    • Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.

                      300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.

                      That is not the configuration that most articles describe, where the antenna covers the full range down to safe levels. And it makes no sense because if you don't you are wasting a lot of energy falling on what is now a unusable zone outside the receiver, not to mention still taking up all that area which was part of the original point.

                      These space to earth systems are still a paper exercise. To state that "300W/m^2 is the average intensity on the receiving antenna elements." is not based on anything prov

                    • ' a rectenna array generates 300 W/m^2 for 24 hours a day

                      That is possible on the high end, but

                      Not even possible on the high end. The diffraction-limited beam spread means that you can't focus the beam to a tight spot, without making the space transmitter correspondingly larger. The Glaser sizing of a kilometer-scale transmitter in space beaming to a ten-kilometer scale spot on the ground wasn't picked at random; those are the sizes you need. And the keep-out zone around the ground receiver is much larger; due to the diffraction wings.

                      Shorter wavelengths make things better... but if you go too sho

    • As I understand this (Score:4, Informative)

      by Ungrounded Lightning ( 62228 ) on Monday August 17, 2015 @01:36PM (#50333577) Journal

      Keith can give you the accurate and current story on it.

      But as I recall it (from the proposals in the early days of the L5 society and some experience with microwave and synthetic aperture techniques):

      The powersat has many transmitters. Each single transmitter, even with a very directional antenna, puts out a very wide beam. (It might cover the whole face of the planet (and beyond)). One transmitter would look more like a radar transmitter at least (26,199 - 3,959) = 22,240 miles away - about 9 times the distance from New York to Los Angeles.

      The transmitter/antenna devices distributed across the platform are phase-synchronized by a pilot signal transmitted from the ground rectenna site. They compute the complex conjugate of the (equivelnt at their frequency) signal they receive and transmit that. This orchestrates them so they form a beam that retraces the path through space, correcting for flexing of the powersat structure, the turbulence of the atmosphere, clouds, aircraft - metal, wood, or feathered - rainstorms, ionospheric distortions, etc. and focuses on the pilot transmitting antenna(s), like a hologram.

      A number of factors defocus the beam somewhat, so you get a spot that covers the rectenna efficiently rather than tightly focussed on the pilot transmitting antenna(s), or leaking all over the surrounding county. The main one is the diffraction limit at the frequency involved, given the size of the transmitting array and distance from it: The bigger the transmitting array, the more tightly focussed the spot on the rectenna site can be. You don't want it TOO tight, to keep the power density reasonable (like a few times sunlight's power density). But the battle is to get it tight enough so your rectenna farm isn't city-sized, not to keep it from being too tight.

      If pilot lock is lost by a single transmitter, it no longer stays locked to the rest of them - its signal spreads out like that of any lone transmitter. It stops contributing to the power in the rectenna and "shines" on the whole face of the planet - becoming microwave background noise. If pilot lock fails completely, all the transmitters VERY quickly go out of sync with each other (and can be deliberately given individual drift rates to insure this happens quickly). They ALL shine, incoherently, all over the world. All the power spreads out over the whole face of the planet and beyond. That part of the sky gets loud in microwaves, so you don't want to park a commsat there. But it's not going to toast Tokyo, or cause malfunctions in old-style pacemakers in Cleveland.

      Of course you can design the transmitters so any that doesn't have pilot lock just shut down, if the solar array can accept the loss of the load. You can also modulate the pilot with a cryptographic identifier, to keep people from stealing power - or warming Central Park slightly - by setting up a second pilot transmitter at another site and making the "hologram" deliver a second spot.

      Meanwhile you're not going to have roast birds falling out of the sky (like you do with the point-focus solar power systems). Microwave ovens cook because they use a frequency that is strongly absorbed by water. Milimeter-wave power systems use a frequency that is chosen to NOT be strongly absorbed by water. This lets it go THROUGH clouds, and birds, rather than being absorbed and heating them. They're not PERFECTLY transparent to it. But at the frequencies and power levels involved at the best focus you can get it's more like having an incandescent lamp in the room than like being in a microwave oven.

      Meanwhile the rectenna is spidery enough that most of the sunlight passes through it, and efficient enough that most of the power does not. You can put it up on poles and graze cattle under it, without cooking the cows or the grass.

  • He co-founded the L5 society in 1975, which sought to promote space colonization.

    I was born three years earlier than this project and that's the first time I ever hear about it.

    • Re:L5? (Score:4, Informative)

      by ShanghaiBill ( 739463 ) on Monday August 17, 2015 @01:28PM (#50333473)

      I was born three years earlier than this project and that's the first time I ever hear about it.

      The L5 Society [wikipedia.org] is well known among space colonization kooks (SCKs). As a SCK, I first learned about the L5 Society in the 1980s. They do good work, advocating practical projects. Putting O'Neill Cylinders [wikipedia.org] at the Lagrangian points is a much more sensible goal than trying to put a human colony on Mars.

      • Why not L1 or L2? They both have a lower delta-v budget than L5. Is there some particular advantage to L5 that makes it a better choice?

        • Re:L5? (Score:4, Informative)

          by ShanghaiBill ( 739463 ) on Monday August 17, 2015 @03:39PM (#50334563)

          Why not L1 or L2?

          L1 and L2 are not stable. A slight perturbation can push you out of orbit, and energy must be continuously expended to stay in position. L4 and L5 are stable. After a slight perturbation, a space station would settle back into the original orbit.

          They both have a lower delta-v budget than L5.

          Sure, but a bit extra delta-v is no big deal once you are "in space". The hard part is getting out of the atmosphere and into orbit. You need expensive chemical rockets for that. But once in orbit, you can take your time, and use cheap ion thrusters to move to your final position.

  • Asteroid Mining (Score:5, Interesting)

    by meta-monkey ( 321000 ) on Monday August 17, 2015 @12:42PM (#50333009) Journal

    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 [wikipedia.org] 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?

    Thank you!

    • From what I read, we recently just missed an asteroid that was estimated to have a quadrillion dollars' worth of platinum in it.

      • Sure, but when you're talking about quantities like that, it crashes the market. Who can buy a quadrillion dollars' worth of anything?

        That's not a reason not to do it, of course. But as far as capitalism goes it's kind of a catch-22. It's expensive because it's rare, but spend $100 billion getting an asteroid full of it and it's now so common as to be worthless. So in my question I wanted to avoid those kinds of questions. I'm just curious about the machines.

        • Sure, but when you're talking about quantities like that, it crashes the market. Who can buy a quadrillion dollars' worth of anything?

          Shhh ... don't say that ... or the copyright cartels will have to explain how they've lost more to piracy than the next 100 years of the economic output of planet Earth. Stock valuations will have to be reconsidered. Executive bonuses recalculated.

          There are business models which rely heavily on made up projections of value.

          Business models!! Don't go messing with business m

          • Thanks for having my back. Almost got myself in trouble in there.

            The Emperor's clothes are beautiful, the Emperor's clothes are beautiful, the Emperor's clothes...

        • Well yes, obviously if some company captured that asteroid and dumped that much platinum on the world market at dirt-cheap prices, the price would crash (to whatever price they sold it at). But they'd probably limit the supply of the material (since they have so much of it relative to anyone else) to keep the price from crashing too much, plus they'd still make tons of money selling it. And don't forget, their acquisition costs would be huge (no one's captured an asteroid before), so they're not going to

    • Re:Asteroid Mining (Score:4, Informative)

      by DanielRavenNest ( 107550 ) on Monday August 17, 2015 @06:14PM (#50335535)

      I've been working on a textbook about Space Systems Engineering: http://en.wikibooks.org/wiki/S... [wikibooks.org]

      In section 4.9 I do the numbers for orbital mining: https://en.wikibooks.org/wiki/... [wikibooks.org]

      The first product of asteroid mining is likely to be rocket fuel. Some asteroids (the carbonaceous type) contain up to 20% water and carbon compounds. This can be processed to Oxygen + Hydrocarbons, which is a common high-thrust rocket fuel. The lifetime mass return ratio of an asteroid tug is ~350:1, and if 20% is usable fuel, then you gain 70:1 just on that one product. Extracting water and carbon compounds only requires kitchen oven level heat, which is easy to do by concentrating sunlight.

      There are lots of other products we can potentially extract from asteroids, but that's the easiest and most useful, since most anything you do in space needs some fuel to get where you want to go.

      Asteroids did have geological processes, just different ones. The "metallic" type come from protoplanets which melted internally from radioactive decay early in their history. The iron and iron-loving elements sank to the core because they are the densest. Later collisions broke up the protoplanets, exposing their cores. The metallics are a high percentage of iron, nickel, cobalt, and a few other elements. The "stony-irons" come from regions that didn't fully separate the core and rocky layers. They range from low to high percentage iron, with the remainder being rock.

      The other process that happened is thermal. Depending how far from the Sun a given asteroid first formed, and later orbit history, certain compounds condensed or not, and then could be baked. Probably the most significant difference is due to the "frost line", the distance at which water ice can remain solid in a vacuum. It happens to be right in the middle of the Asteroid Belt, where Ceres is. Objects beyond that distance tend to have a lot of water. Anything closer tends to have little water, though it can contain "hydrated minerals", where the water is chemically bound.

      We actually know quite a bit about the composition of asteroids. Nature delivers samples to Earth in the form of meteorites. We can compare the spectra of meteorites to those from asteroids we get through telescopes, and infer what they are made of. We have flown past or orbited several asteroids, most notably the Dawn mission to Vesta and now Ceres, two of the largest asteroids. Spacecraft carry a larger variety of instruments and can do a better job of telling what the asteroids are made of.

      As far as materials processing, we can design machines based on meteorite samples, or simulated samples, since meteorites are rare and valuable. If the Asteroid Redirect Mission that NASA wants to do happens, we would have a sizable boulder to experiment with. After taking science samples, they could try various processing methods on an actual piece of asteroid rock, in zero-g. I don't think we can design serious production units without a a few rounds of trying it on a small scale. For that, we would need at least a small asteroid tug that fetches back chunks from different asteroid types, so we have enough raw materials to experiment on. Most known asteroids are too big to move whole. A 30 meter one is anywhere from 18,000 to 90,000 tons. So for early space mining, we are talking about scraping loose stuff off their surfaces, or grabbing boulders.

      my email is the same as my user name here, but lowercase, and add (at)gmail. Feel free to contact me if you want more information. I can point you at sources I have, or send you stuff directly.

  • What is the cost per KW for the build/deployment and resultant cost per KWh for the end user?
    • What is the cost per KW for the build/deployment and resultant cost per KWh for the end user?

      Ha hah ha! Cost he says.. Hah! What a funny guy! The answer is of course, "cheaply". After all, its the future.

    • Maybe he's one of those wacky future looking people who is interested in getting scarce resources less scarce, and less in the hands of corporations worried about the cost per KWh for the consumer?

      In which case it's not so much of a business plan, as a future direction for humans to solve our energy problems because the sun makes more than we could ever need.

      And then the MBAs and CEOs will come in and fuck it up and try to figure out how maximize return on investment and shareholder value.

    • Competitive with ground power, or it would never be built in the first place.

      In space you get ~7 times as much sunlight as the average place on Earth. That's due to absorption, night, and weather that happens down here, but not in space. The logic is then you can spend up to 7 times as much building your space solar power system and be competitive with Earth solar power. If it costs you more than that, just build ground solar.

      • Hopefully his answer will be a little more specific than simply 'competitive'. I'm not looking for an exact number but, given the technology at hand, a somewhat narrow range would be nice.
      • Competitive with ground power, or it would never be built in the first place. n space you get ~7 times as much sunlight as the average place on Earth.

        Well, but of course you don't put solar arrays on the average places on Earth, you put them in the best places. With a tracking array, that number gets to be much closer to a factor to two than a factor of 7. So the take-away lesson is that you don't build space power systems for terrestrial use until after the market for power from the best solar sites has already been saturated. This means that the market for space solar power substitutes for storage and power transmission technologies.

        That's due to absorption, night, and weather that happens down here, but not in space. The logic is then you can spend up to 7 times as much building your space solar power system and be competitive with Earth solar power.

        Only if the tran

  • 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 transmissi

    • I recently did a class on space elevator design:

      - Class notes: https://en.wikibooks.org/wiki/... [wikibooks.org]

      - Slides: http://imgur.com/a/cCTY5 [imgur.com]

      The "classical" space elevator (ground to GEO) can't be built, even with carbon nanotube cable. There are more modern versions that can be built. Realistic engineering designs have to consider a lot of factors that artist's illustrations you most likely have seen don't.

  • Did NASA get through the firmament? Why can't anyone go to Antarctica? The edges seem to have been closed off around the same time (late 1950s).
  • You seem to get to a similar place as O'Neill did in "The High Frontier" -- only without the inspirational Bernal Sphere to Stanford Torus to O'Neill Cylinder progression. I hope you still see those as real opportunities.
  • If nothing else, this post was awesome for directing me to "Home, home on Lagrange"

    Oh, give me a locus where the gravitons focus Where the three-body problem is solved, Where the microwaves play down at three degrees K, And the cold virus never evolved. (chorus)

    We eat algae pie, our vacuum is high, Our ball bearings are perfectly round. Our horizon is curved, our warheads are MIRVed, And a kilogram weighs half a pound. (chorus)

    If we run out of space for our burgeoning race No more Lebensraum left for the Mensch When we're ready to start, we can take Mars apart, If we just find a big enough wrench. (chorus)

    I'm sick of this place, it's just McDonald's in space, And living up here is a bore. Tell the shiggies, "Don't cry," they can kiss me goodbye 'Cause I'm moving next week to L4! (chorus)

    CHORUS: Home, home on LaGrange, Where the space debris always collects, We possess, so it seems, two of Man's greatest dreams: Solar power and zero-gee sex.

    It's like the entire 70's were just ahead of their time.

  • 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.

  • 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?

    • Hi Geoff. Dani Eder here. I would say the most important thing we have learned is "there are a whole lot of Near Earth Asteroids". In 1980 there were 52 known NEA's ( http://neo.jpl.nasa.gov/stats/ [nasa.gov] ). Today we are rapidly approaching 13,000 at a rate of about 1,500 new ones a year. This has completely changed the accessibility of raw materials. Given that we now have well developed electric propulsion, 90% of NEA's take less fuel to reach than the surface of the Moon.

      Even if you want to go to the Moon

      • True enough.

        I think you have O'Neill's reasoning backwards, though. He didn't say "we need to build solar power satellites, therefore we need a colony of 10,000 people"-- he said "we've shown that there are no showstoppers to building a colony of 10,000 people; what will they do? Here's an idea; they will build solar power satellites."

        So, the question now is, if you don't need very many people-- and possibly don't need any people--in space to build solar power satellites, what is the economic base for of

  • by Anonymous Coward

    What's new in the way of freezing dead people? We heard a lot about this several decades back, but the idea doesn't make the news any more. Still a viable concept?

  • 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?

  • 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
  • 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

The human mind ordinarily operates at only ten percent of its capacity -- the rest is overhead for the operating system.

Working...