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Space Transportation Science

Fusion Thrusters For Space Travel 192

Posted by Soulskill from the trimming-parsecs-off-the-kessel-run dept.
kgeiger writes "John J. Chapman, a physicist and electronics engineer at NASA's Langley Research Center, envisions a laser-pumped fusion drive. Chapman estimates the drive can produce thrust 40 times more efficiently than existing ion engines such as those on the Dawn mission now exploring the asteroid belt."
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Fusion Thrusters For Space Travel More

Fusion Thrusters For Space Travel

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  • research! (Score:5, Insightful)

    by k6mfw ( 1182893 ) on Tuesday June 28, 2011 @07:02PM (#36605384)
    Alrighty so I haven't RTFA but this is the kind of stuff NASA should be doing more. Hire ambitious smart people with grand ideas, give them resources and turn 'em loose! Probably much of what they do will amount to nothing but you just never know (a great concept may become reality).

    • In the first golden age of space, that's what happened. Maybe we're about to see the second golden age of space?

      One can only hope.

      • Re: (Score:2, Interesting)

        by Nethemas the Great ( 909900 )
        That's easily answered. No. Not from government at any rate. If private enterprise can get a better hold on things sure but we need laws that promote the commercialization of space before even they will care. In the mean time we'll happily spend more than NASA's present budget to bring air conditioning to uninsulated tents out in the desserts of the middle east in support of our troops blowing holes in the sand.

        • Re:research! (Score:4, Interesting)

          by WindBourne ( 631190 ) on Tuesday June 28, 2011 @08:23PM (#36606070) Journal
          Really? Please show me what advanced R&D do you see coming from private enterprise on their own?
          1) SpaceX's rockets? The engines were developed by NASA in the 90's, but squelced by 1996 CONgress.
          2) Perhaps SpaceX's tank's? Again development by NASA, but squelced by 2001 W/CONgress destruction of X-33.
          3) Inflatable space stations? Transhab that was crush by 1996 CONgress, but allowed into private enterprise by Clinton
          4) Laser Drilling? Crushed by 1996 CONgress, but allowed to go to Colorado Mines by Clinton.
          5) VASIMR? Crushed by 1996 CONgress, but allowed to go private by Clinton.

          The list goes on and on and on. NASA does a LOT of R&D, but it is CONgress and typically short-sighted pres (nixon and W being the worst 2) that destroy it. You will be hard pressed to find any ORIGINAL SPACE R&D by private enterprise that is NOT an off branch of something that NASA came up with and funded.

          • Re: (Score:3, Informative)

            by Anonymous Coward

            1. Spacex's rockets were based on a concept engine called Fastrac, killed in 2001. Spacex have scaled up the thrust by a factor of four and the ISP from 260 seconds to 300.

            2. Spacex's aluminium-lithium friction stir welded tanks were developed by LockMart for the SLWT first flown by the space shuttle in 1998. X-33 used experimental composite tanks and ignored the lighter FSW technology because it wasn't "Space Age" enough. This is why X-33 failed.

            3. Transhab was not killed by the 1996 congress. Transhab did

          • That's neat and all, not sure you have all those correct, but it doesn't argue against what I just said. If anything it provides evidence demonstrating it. NASA will not be the one that brings it from conception through to delivery. Like it or not (in your case quite obviously the later) NASA is unable to see any of their advanced research through to a finished deliverable. However, you will note that business when it picks up a university/government research project or in some rarer cases original work
            • Commercialization IS the answer due to our piss poor CONgress and presidents that we have had for multiple times. However, private space has a near zero record of doing the R, and even most of the D. NASA's only real issue is politics.

              BTW, that is why I am opposed to SLS and support a COTS-SHLV for TWO SHLV. Better to fund 2 of these for say 5 billion each and offer to pay .5 billion / launch, then to do another constellation which is assuredly coming.
        • Yes, I think we should follow the lead of the 1960s space race, and leave everything up to private enterprise to organise, as we all know the 1969 moon landings were pretty much the apotheosis of the free market ideal.
          You muppet.

      • Re: (Score:3)

        by fyngyrz ( 762201 )

        Reading TFA, it strikes me that this might make an awesome power reactor -- there's provision for electrical capture already, and the thrust might be converted into mechanical energy. Plus, it's damn near a beryllium sphere... ok, a boron sphere, but hey. :^)

    • Re:research! (Score:4, Insightful)

      by youn ( 1516637 ) on Tuesday June 28, 2011 @07:14PM (#36605484) Homepage

      I think if Nasa was only allowed to carry projects from start to finish... and not successive radical change in direction mid projects... lots more cool stuff could come out. The problem, every time a new administration comes out big buzz words are introduced to completely change the direction, forcing many times redevelopment of the wheel.

      • That conventional wisdom (which I have my own issues with, but I digress) only applies to projects that consume a large fraction of NASA's budget and are thus highly visible.

        Plenty of small-ish projects get along just find without fear of national politics ending them. A small project just needs to stay on-time, on-budget, and not piss off the more immediate managers.

        • Re: (Score:2)

          by youn ( 1516637 )

          I totally agree with you, lots of great projects Nasa have brought (and are still bringing) awesome science, notably robotic missions... like the mars missions still bringing in useful data or the now extra solar probes. Though I still believe >more cool stuff would come out (I understand you disagree ;) if projects were allowed to go through until the end and budgets decisions were more results focused. It is sad to see so many promising yet abandoned projects... including lunar exploration. Today, to g

    • Re: (Score:2, Insightful)

      by Anonymous Coward

      If only they had a more reasonable budget.

      I mean look at this. [wikipedia.org]

      1963-1968 gave them a pretty darned reasonable budget. Then, until 1987 they had CRAP. Starting from 1987 they started to get a halfhearted budget that fluctuated up and down.

      Also it's pretty depressing their underwhelming budget represents 35% of the budget for academic scientific research in the US.

    • That is exactly what ppl like Obama and Bolden are pushing. NASA was actually built to be an R&D for Aerospace. Now, it has been turned into a jobs bill by the likes of Shelby, Wolf, Hutchinson, Hatch, Coffman, etc. We need to allow private space to do these launches and then have NASA focus on doing R&D like this.

    • I totally read your comment in the the voice of Cave Johnson, CEO of Aperture Science.

    • Re: (Score:2)

      by zrbyte ( 1666979 )
      Fusion drive, ion drive, chemical, blending down hamsters and spewing them out the exhaust, I don't really care! Whatever we use, let's just get out there and colonize some damn rock!
      (sorry for the wildly irrational rant, but this is how this issue makes me feel)

  • Let those words run by your ears... (Score:2, Insightful)

    by Anonymous Coward

    *LASER*-pumped *FUSION* drive... Say that out loud...

    Are we living in the future yet?

    • Would you like to check my assembly for the monitor unit of the inverse klystron tube transmitter?

      • Re: (Score:2)

        by hey! ( 33014 )

        He said *Laser*-pumped, not *Maser*-pumped.

        Do try to keep up, dear chap. It's not like we're knapping flint here, old boy.

        • TFA mentions use of a traveling wave tube, basically an inverse klystron tube, to reclaim some of the energy from the emitted alpha particles and convert it into electricity to power other vehicle systems. It does this using condensers out of your accelerator circuits, solenoids from your gyro stabilizers, and the Lavallois technique.
    • No, didn't you RTFA? It's 10 years away. 10 years not the typical 20 because we're going to use boron instead of helium-3.
  • I RTFA. The guy has an interesting idea to be sure. However, as he acknowledges, that level of technology is at least a decade away from a flying prototype (I'd wager more like two decades). Furthermore, the whole article was a bit scant on other details. Specifically, I would like to know the power requirements for a piece of equipment like this. If its reaction can sustain the apparatus's own power draw, that would be a huge point in its favor. However, something tells me this particular thruster would re

    • Specifically, I would like to know the power requirements for a piece of equipment like this. If its reaction can sustain the apparatus's own power draw, that would be a huge point in its favor.

      Well, I doubt that it could do that, because if it could, then we should have a working fusion power station on earth based on the same principles years before someone manages to build a rocket engine with it.

    • Re: (Score:2)

      by c0lo ( 1497653 )

      Specifically, I would like to know the power requirements for a piece of equipment like this.

      Computations on the back of a napkin:
      TFA: A beam with energy on the order of 2 x 10^18 watts per square centimeter, pulse frequencies up to 75 megahertz, and wavelengths between 1 and 10 micrometers is aimed at a two-layer, 20-centimeter-diameter target.

      Assumption: the entire target is hit.
      – Area of the target: 314 sq cm. => Total power required/pulse: 0.6e+21 W.
      – Considering a femptosecond pulses [wikipedia.org] => Total energy/pulse: 0.6e+6 J
      – Taking into consideration the frequency of pulse

      • Based off the operational design of existing ION thrusters, your power source is irrelevant. Assume you have a huge solar array, and power is unlimited. The only thing that matters is how fast you can accelerate your consumable fuel source. Traditional rockets dump exhaust at thousands of meters per second. ION drives do so at tens of thousands of meters per second. Using the several billion kelven reaction temperature, and a magnetic nozzle, you're looking at exhaust velocities in the millions of mete

        • Re: (Score:2)

          by c0lo ( 1497653 )

          Based off the operational design of existing ION thrusters, your power source is irrelevant.

          Huh? Efficiency is irrelevant? You mean you can accept a transformation of 450 kW source in 3.5 W in trust?

          Assume you have a huge solar array, ...

          450 kW of solar array, at 20% efficiency... Hmm... pricewise... why not solar sails?

          Higher exhaust velocity means higher total delta V, assuming you don't kill yourself in engine mass.

          deltaV comes from the impulse that you can "eject"... the small ejection mass is the problem of ion thrusters.

          • deltaV comes from the impulse that you can "eject"... the small ejection mass is the problem of ion thrusters

            The point of thrusters is to increase the kinetic energy of what they are attached to. The formula for kinetic energy is .5mv^2

            Note the exponent attached to the v term. Who cares what the ejection mass is if v is large enough?

            • Re: (Score:2)

              by c0lo ( 1497653 )

              The point of thrusters is to increase the kinetic energy of what they are attached to. The formula for kinetic energy is .5mv^2

              Note the exponent attached to the v term. Who cares what the ejection mass is if v is large enough?

              My apologies for being blunt, but you need to go back to school. The delta V comes from momentum conservation [wikipedia.org] - which is a linear dependency with both the term and variation of velocity.

  • I've always thought that we'd have viable fusion rockets long before we have practical fusion power generation. The reasoning being, power could come from another source (fission reactor) to trigger the fusion, the resulting high-velocity particles would be a source of thrust alone. This seems to be exactly what TFA describes. Proton-boron fusion spits out high-energy alpha particles that are easily deflected into thrust... clever.

    With todays tech something like electrostatic inertial confinement fusion

    • "The specific power of the proton-triggered boron fuel would be so great that a mere mole of it (11 grams) would yield roughly 300 megawatts of power. " (!) the efficiency sounds awesome.

      Come on IEEE, I expected better of you. Power output is irrelevent. We care about energy output. 11 grams of boron fuel will get you 300 megawatts for what duration?

      • Re: (Score:2)

        by steveha ( 103154 )

        Come on IEEE, I expected better of you. Power output is irrelevent. We care about energy output. 11 grams of boron fuel will get you 300 megawatts for what duration?

        I am not a physicist, but I think the info you want is in the article.

        pulse frequencies up to 75 megahertz

        Each pulse of the laser should generate roughly 100 000 particles

        a mere mole of it (11 grams) would yield roughly 300 megawatts of power.

        So a mole is 6.0221415e23, right?

        Now, please correct me if I'm wrong, and I may be wrong, but:

        6.02e23 /

        • I am not a physicist

          We can tell, because W/s is not a unit of energy. It's not a commonly used unit at all, really. You want to MULTIPLY watts by seconds to get joules.

          I'm pretty certain some number has been quoted incorrectly. 300 megawatts * 8e11 seconds is the equivalent of about 3000 kg of mass energy. The answer is nonsense.

          • Re: (Score:3)

            by mbone ( 558574 )

            The article is simply wrong.

            "The specific power of the proton-triggered boron fuel would be so great that a mere mole of it (11 grams) would yield roughly 300 megawatts of power."

            A Watt is a joule / second, i.e., energy / second. A given amount of material to fuse (such as a mole) can only provide a given amount of energy. So, a mole of something cannot just yield watts. It can yield watts for some period of time, or a mole per second (or per some other period of time) can yield watts, but, as written, the

        • Now, please correct me if I'm wrong, and I may be wrong, but:

          6.02e23 / 100 000 == 6.02e18 pulses to process one mole of boron

          6.02e18 / 75e6 == 8.02e11 seconds to process one mole of boron

          300e6 W / 8.02e11 seconds == 3.7e-3 W/sec

          I can't tell you how that compares with an ion drive.

          steveha

          Sorry, but I think you are wrong. wwagerrp wanted to know the energy the machine would get from 1 mol of boron fuel, the article gives us something in watts, and you gave something in watts/second when in fact what is needed will be in watt-seconds (or joules as most people say).

          This might be better: 75e6 * 1e5 gives 75e11 particles released per second. But, the article doesn't say how many of those go on to fuse, etc so this is all academic. Assuming it wasn't, though, 300e6 (Joule/second) / 750e11 (1/seco

    • Re: (Score:2)

      by LWATCDR ( 28044 )

      Well maybe if we used a Polywell reactor to power it. :)
      I wish I was 20 years younger :)

  • Tanks (Score:4, Funny)

    by avandesande ( 143899 ) on Tuesday June 28, 2011 @07:23PM (#36605546) Journal

    How will the shark tanks work in space with zero Gs?

  • We haven't gotten fusion to be a net energy gain here on Earth yet (outside tritium-boosted or thermonuclear atomic bombs). While I'm sure it will eventually happen, what makes it so that it's easier to make fusion work in space, compared to Earth?

    • This isn't about net energy gain. It's about specific impulse.

    • Yes, probably. (Score:2, Informative)

      by Anonymous Coward

      On Earth, we want to use fusion to power homes, ground vehicles, etc. However, the amount of work and energy we put into fusion gives us much less gain when compared to the amount of energy we can extract with fission, wind, solar, waves, geothermal, oil and coal. We attempt this with deuterium and tritium to produce neutrons. As the article puts it; [To make use of neutrons, "you need an absorbing wall that converts the kinetic energy of the particles to thermal energy," he says. "In effect, all you’

    • The output is three alpha particles; not exactly the same as three helium atoms...

      • I'd say close enough for gov't work, or for my tiny little brain :)
        Alpha particles [wikipedia.org]:

        Alpha particles (named after and denoted by the first letter in the Greek alphabet, ) consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, ...
        The nomenclature is not well defined, and thus not all high-velocity helium nuclei are considered by all authors as alpha particles. As with beta and gamma rays/particles, the name used for the particle carries some mild connotations about its production process and energy, but these are not rigorously applied.

    • We haven't gotten fusion to be a net energy gain here on Earth yet (outside tritium-boosted or thermonuclear atomic bombs). While I'm sure it will eventually happen, what makes it so that it's easier to make fusion work in space, compared to Earth?

      Who said they were trying for net gain?

  • It seems more fission than fusion (Score:5, Informative)

    by Michael Woodhams ( 112247 ) on Tuesday June 28, 2011 @07:29PM (#36605594) Journal

    The reaction is
    1H + 11B -> 12C -> 4He + 8Be -> 4He + 4He + 4He
    so there are more output nuclei than input.

    However, I suppose it is true that all of the energy is coming from fusion, as 12C -> 4He + 4He + 4He is exothermic. (The reverse reaction is an energy source for stars under some circumstances.)

    12C is normally stable, so for this reaction to go as stated the nucleus must be created in some suitable excited state.

    • The reaction is 1H + 11B -> 12C -> 4He + 8Be -> 4He + 4He + 4He so there are more output nuclei than input.

      However, I suppose it is true that all of the energy is coming from fusion, as 12C -> 4He + 4He + 4He is exothermic. (The reverse reaction is an energy source for stars under some circumstances.)

      12C is normally stable, so for this reaction to go as stated the nucleus must be created in some suitable excited state.

      Is there some physics version of the Web Bullshit Generator [dack.com]?

      • Make a substantive criticism, and I'll consider it, as I have for my other responder. Otherwise you're just a source of noise.

        • Make a substantive criticism, and I'll consider it, as I have for my other responder. Otherwise you're just a source of noise.

          I'm sorry if the humor didn't come across. It was not meant as any kind of substantive criticism, it was meant to make light of the fact that you are talking over the heads of probably 98% of the people who read what you wrote. I have no way of knowing if what you said was accurate or not, and that wasn't even part of what I was trying to communicate. If anything, I was teasing you for using such dense language with such little context. Really, though, what happened is that I read what you wrote, though

          • OK, thanks for the explanation, sorry to misunderstand you.

            I suspect I'm only over the heads of 75-90% of the readers - many have science background or self education. (As demonstrated by the fact I've had two people correct me already...)

          • 98%? There wasn't really anything in his discussion that would be out of place in an honors high school science class.

    • Re: (Score:2)

      by Co0Ps ( 1539395 )
      I don't think you can just count the number of input and output nuclei and come to that conclusion. Both fission and fusion reactions can involve decay into smaller particles while fusion reactions always has at least one element merging with another, in this case a free proton (hydrogen) and boron. E.g. the 1H + 11B -> 12C part (a neutron is not an "element" hence fission != fusion).

      • Well, I was actually saying it was both. (My thoughts moved on a bit as I was composing, and perhaps I should have gone back and edited my heading.)

        The Cambridge dictionary defines (nuclear) fission as "the splitting of the nucleus of an atom, which results in the release of a large amount of energy". Similarly, Websters says "the splitting of an atomic nucleus resulting in the release of large amounts of energy." I would not have made energy release part of the definition, but it seems the dictionaries dis

        • Re:It seems more fission than fusion (Score:4, Interesting)

          by newcastlejon ( 1483695 ) on Tuesday June 28, 2011 @09:44PM (#36606616)

          When the proton hits the boron-11 nucleus they fuse giving an excited (that bit's important) carbon-12, which in very short order (sorry, the exact time escapes me) splits into a helium nucleus and a beryllium-8 nucleus, which in turn splits into another two helium nuclei. So what you have in effect is a fusion-fission reaction but the fission part isn't usually mentioned - something to do with OMG nuke! types, perhaps?

          However, I suppose it is true that all of the energy is coming from fusion, as 12C -> 4He + 4He + 4He is exothermic. (The reverse reaction is an energy source for stars under some circumstances.)

          Actually, the triple-alpha process, which produces carbon in some stars is closer to this:

          He + He -> Be

          Be + He -> C

          I expect that the probability of a 3-body collision between 3 helium nuclei is so vanishingly small as to be insignificant, but hopefully someone who knows this subject well can fill in that particular blank.

          As for why the carbon that gets produced doesn't immediately decay like the one made in a p+B11 fusion reactor, I couldn't say as IANANP (just an interested layman) but I imagine it's something to do with that business of being in an excited state I touched upon earlier.

          P.S. A dictionary isn't a good place to start learning about nuclear physics; try an encyclopaedia instead. In fact, here [focusfusion.org] is a good article, which was the second result Google gave when I searched for p+B11. To address your issue with particles: yes, more atoms come out than go in, but the number of nucleons remains the same.

          • Re: (Score:2)

            by sFurbo ( 1361249 )
            You are right, the three-body collision is far to unlikely (and thus slow) for energy production in stars (and we are talking about furnaces whose first step is the mind-bogglingly slow H-1+H-1->H-2). Be-8 is extremely unstable (halflife 7*10^-17 s), but it exists just long enough to make the pseudo-three-body collision slightly probable.

            The carbon produced from He-4+Be-8->C-12 must have to low energy to decay, as it was just made from 3*He-4. And, even if most of it did decay, it would just revert t

            • There's an energy level in C-12 at just the right 'place' for the cross section of the He-4+Be-8->C-12 reaction to be greatly enhanced. Nobody's ever told me *how much* enhanced it is though. The triple alpha reaction has a rate which goes as density squared * temperature ^ 30, so doubling the temperature raises the rate by about a million. This means that relatively modest temperature increases can compensate for quite a lot of lack-of-resonance. However, Fred Hoyle predicted the resonance before it was

    • Re: (Score:3)

      by chgros ( 690878 )

      12C -> 4He + 4He + 4He is exothermic. (The reverse reaction is an energy source for stars under some circumstances.)
      You meant endothermic then.

    • However, I suppose it is true that all of the energy is coming from fusion, as 12C -> 4He + 4He + 4He is exothermic. (The reverse reaction is an energy source for stars under some circumstances.)

      IANANS, but if the reverse reaction is used as an energy source how can it be exothermic?
      That sounds like a perpetual motion machine:
      12C -> 4He + 4He + 4He + energy.
      Use energy
      4He + 4He + 4He -> 12C + energy
      Use energy.
      Rinse, repeat.

  • ...between power and energy.

  • It makes me sad (Score:5, Insightful)

    by hamburgler007 ( 1420537 ) on Tuesday June 28, 2011 @07:54PM (#36605834)
    When I think about how much more the US could do if we didn't squander our money on bullshit

    • Re: (Score:2)

      by asylumx ( 881307 )
      I'm confused. Are you saying this technology is bullshit and we shouldn't spend money on it, or are you saying we should be spending our money on this instead of all the other bullshit?

      • Re:It makes me sad (Score:4, Insightful)

        by catchblue22 ( 1004569 ) on Tuesday June 28, 2011 @11:59PM (#36607418) Homepage

        When I think about how much more the US could do if we didn't squander our money on bullshit

        The obsession with lowering taxes will imply that a larger percentage of national resources are funnelled into consumption. When a nation spends more on consumer goods, it will, in my opinion lead to a reduction in projects that are national in scale and for the public good. I think we have already seen this in the reductions both in NASA's budget, and in the general research budget. Most research is now carried out by private corporations, with the main aim of short term profit. The ironic thing is that the reduction in general research will probably harm the broad economy, reducing the potential profits of these same corporations.

  • So if the other engines had an efficiency of 2%, this could get 80%? And if they operated at more than 2.5% efficiency, it would be fusion with a net energy gain - a real reactor? It might easily not take diversion of much of the thrust to produce the energy necessary to sustain the reaction.

    So what if getting a sustainable fusion reaction requires a thruster design - that's easy to engineer around.

  • old news? (Score:3)

    by recharged95 ( 782975 ) on Tuesday June 28, 2011 @09:57PM (#36606734) Journal

    Sanger proposed this way back in the early 1950's.

    And Spencer wrote about it later:
    Spencer, Dwain F. "Fusion Propulsion for Interstellar Missions". Annals NY Academy of Sciences 140, 407-418 (1966).
    .
    Robert Forward documented all the above in a book I have on my shelf, but for the life of me can't remember the title. Heck, I was doing solar sail research/simulations on an x86 back in the 80's and we were proposing fusion drives as a power source for sails when the vehicle was in interstellar space.

    It's great for today's visionaries to talk about their theories, but we all need to remember our ideas are based on the shoulders of those before us, whether they are giants or not.

  • Fusion thrusters means we will be ready when we meet the Kzinti for the first time

  • Point It at the Earth (Score:4, Interesting)

    by Doc Ruby ( 173196 ) on Tuesday June 28, 2011 @11:37PM (#36607296) Homepage Journal

    We should have these power collectors/transmitters in orbit around the Sun, pointed down at the Earth to collectors floating on the seas. Where they could electrolyze water, or any of a number of other ways to get the energy back to the land where it can be consumed. Emissions free, vastly more power than we can use for the foreseeable future.

    The beams would have to be only a few times the intensity of sunlight, but shine all day/night (courtesy of geosync relay satellites) over a few dozen square kilometers on each station. No danger from a beam missing the target, though extra protection added by laser interlocks back from the surface to space that drop both up and down beams when the down beam goes off the target.

    That system would require several $billion, perhaps several hundred $billion, investment. But at $0.01:KWh, and $100B is only 1KW:m^2 * 3intensity * 36Km^2 * 6stations * $0.01:KWh = 22.5 months payback time. That's better than 50% ROI, on hundreds of $billions. Plus the value of eliminating emissions, terrestrial fuel production and distribution, energy wars and corruption. And regaining the envy of the world.

    • pointed down at the Earth

      What could possibly go wrong?

    • Re: (Score:2)

      by bazorg ( 911295 )

      I don't know about the envy of the rest of the world, but a project like that would certainly deserve my admiration.

    • I don't get it. What exactly are you collecting? Alpha particles? Can you really keep them in a "beam" from orbit to surface like that?

    • Re: (Score:2)

      by AmiMoJo ( 196126 )

      JAXA (Japanese space agency) is working on something like this. Something you said doesn't sound right though:

      The beams would have to be only a few times the intensity of sunlight, but shine all day/night

      If the beam is say 5x the intensity of sunlight and a ground based solar reflector plant will only get a 1/3 day/night ratio (conservative numbers here) then it seems like you could just build 15x as many collectors on earth and get the same effect. Energy is stored as heat to continue generation all night.

      The EU is trying to get such a project going with plants in north Africa. It would give those

      • But why build 15x as many collectors? And if you store energy as heat, you cut drastically the efficiency of recovering electricity from it.

        Besides, the space infrastructure would be useful for powering activities in space. And indeed it would be cool.

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