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Re: [space-elevator] Re: Space-Based Solar Power Breakthrough to Be Announced

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  • Ian Woollard
    ... You don t necessarily need high power, modern silicon is now up to gigahertz speeds anyway, this bit is if anything getting easier. Some designs just stick
    Message 1 of 65 , Oct 1, 2008
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      On 30/09/2008, Andreas <awnd329@...> wrote:
      > --- In space-elevator@yahoogroups.com, "Ian Woollard"
      > <ian.woollard@...> wrote:
      >>
      >>
      >> No, no. These are carefully worked estimates.
      >>
      > Maybe carefully worked, but also very optimistic. None of the
      > component efficiencies are worse than 88%.
      >
      > Klystrons currently available have around 60%, but are not
      > phase-stable enough. TWT amplifiers are also very efficient, generally
      > 60%. There are rumours of devices reaching up to 80%, but I have not
      > found concrete examples.

      You don't necessarily need high power, modern silicon is now up to gigahertz speeds anyway, this bit is if anything getting easier. Some designs just stick the transmitter on the back of the solar panels and uses low power phased array techniques. I think the main challenges are in the spectral purity.

      I forget what the record link efficiency was. It was around 40-50%, and I don't think they were trying all that hard for maximum efficiency. It was only over a few miles, but the beam physics for longer distances is extremely well understood.

      > And that is only one of the components. I am particularly intrigued
      > about how they plan to capture 88% of the beam, what with side-lobes
      > caused by imperfect phase or geometry which will send part of the
      > power into empty space. A large part, if everything is not absolutely
      > perfect. And the 88% also includes RF capture by the rectenna, which
      > is equally hard. The rectenna must neither reflect nor transmit more
      > than 12% of the power that hits it, much less if not all power hits
      > it. That sounds hard to me.

      Nah, not particularly. The wavelength is order centimetres, getting the waves lined up to that kind of accuracy is not difficult. There's also a concept of a pilot wave system where it transmits a beacon and you adjust your phase to aim for that. You essentially can't miss with those kinds of systems.

      > Andreas

      > There is not a Klystron or other microwave source currently available
      > better than 50-60%, AFAIK.

      Dunno, it's not an area of electronics I've looked at too hard. You have to credit the US DOE authors with some degree of technical skill though.

      --
      -Ian Woollard

      We live in an imperfectly imperfect world. Life in a perfectly imperfect world would be much better.
    • Andreas
      ... Are you seriously saying that we don t need to build a functioning system because our computer models tell us it is trivial? Why, then, would Brown and
      Message 65 of 65 , Oct 3, 2008
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        --- In space-elevator@yahoogroups.com, "Ian Woollard"
        <ian.woollard@...> wrote:
        >
        > Why didn't they? Your argument that it was too hard is just bizarre.
        > They just didn't think it proved anything. They weren't trying to
        > prove that you can make arbitrarily fine beams, because diffraction
        > limited beam production is completely trivial!
        >
        ...
        >
        > Because it wouldn't have proven anything, and would have cost more?
        >

        Are you seriously saying that we don't need to build a functioning
        system because our computer models tell us it is trivial? Why, then,
        would Brown and others go to all this trouble if not to build
        something useful in the end?

        > I honestly can't believe we're having this discussion.

        Me, neither.

        Andreas
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