[ExI] Written for another list

Keith Henson hkeithhenson at gmail.com
Sun Aug 5 16:26:24 UTC 2012


On Sun, Aug 5, 2012 at 5:00 AM,  Adrian Tymes <atymes at gmail.com> wrote:

> On Sat, Aug 4, 2012 at 10:30 AM, Keith Henson <hkeithhenson at gmail.com> wrote:
>> You asked how I calculated what the first power sat was worth powering
>> propulsion lasers vs selling the power.
>
> Yes.  And as noted, I see that you calculated this
> using false assumptions.

OK.  Compared to selling the power on earth, what is the same power
used for propulsion lasers worth?  You now have the paper and if you
need the economic spreadsheet, ask for it.

snip

>> Schottky diodes have a forward voltage drop between approximately
>> 0.15?0.45 volts.  For voltage levels below where they start to
>> conduct, you don't get output at all from a rectenna.  Normal
>> operation of a rectenna is around 1/4 kW/m^2  At 25 diodes per m^2,
>> 250 W/25 is ten W/diode.  Assuming an antenna equivalent of 50 ohms,
>> the induced voltage across a diode would be V^2 =10*50.  Or 22.4
>> volts, plenty to put the diode in forward conduction.  Keep the
>> geometry the same and drop the power to 0.5 MW.  Now we are down to 1
>> mW/diode and V^2 = 0.01*50, or 0.22 volts.  No output.
>
> Use less diodes per m^2,

That might be possible, using an expensive horn antenna with one diode
down deep in the horn.  It's been close to 50 years since I had a
microwave antenna theory class so I am not sure.

> or assume more ohms.

Now, that you can't do.  The impedance of an antenna is fixed by physics.

> Or just use
> less m^2: at 1 m^2, that's 1/4 kW, which is less than MW.
> Even 1,000 m^2 is only 250 kW.  But less diodes per m^2 is
> probably the easiest solution, if you're designing for low power.

That means focusing the microwave beam into a tighter spot.  Which
means a larger transmitting antenna in space.

snip

>> Microwave optics.  It's what drives power sats to such large sizes.
>
> So again: use visible wavelengths.  Or perhaps masers,
> to reduce divergence.

Visible gets interrupted by clouds so it has the same storage problem
as solar PV.  How does a maser reduce divergence over a phased array?

snip

>> Other than this as yet unvetted proposal, I don't recall any such case
>> to solve energy problems being made.  And you have yet to point to a
>> specific past discussion.
>
> Would you call your proposal vetted?

No.

> I do not have the complete archive of this chat on hand.
> Rather, it is the nature of this chat that such discussions
> happen.  If you want a specific one, would some list
> member who is more familiar with the archives care to
> point out other energy discussions that have happened
> on this list?
>
>>> You need to be clearer to yourself, first and foremost,
>>> as to why you're doing this.  That will help you make
>>> your case better.
>>
>> I thought I stated it clearly.
>
> Are you just trying to make a theoretical case, or is this
> something you want to actually make happen?  There is
> a big difference between the two.

True.  Let's be generous and say I have put in $150,000 of time on
this over the past 7 years (with a year off for jail and related court
stuff).  If the project takes 150 B, that's a factor of a million
higher.

snip

>> The existence of communication satellites shows that a lot of the
>> physics questions have been answered.
>
> Ah.  Then you are just making the theoretical case,
> and to hell with the economics of how you would
> actually get it working.
>
> Okay, case made.  Now what?

The point, in case you missed it is that I don't need to put up a
cubesat to make the case that microwaves can be generated in space and
sent to the earth.

As for economics, showing how to get the cost down is the main point
of the work I have done.

You really don't need to be nasty.

>> Ah, even if I wanted to be in charge of this, how many years would it take?
>
> Something like this is going to take decades

I am 70.  Unless you are counting on serious life extension, I am not
the right person on that fact alone.

> to
> put into operation no matter who is in charge of it.
> The question is, how many?
>
> To answer that, you need to actually get into the
> economics of how to bootstrap it, and the step by
> step details of how the project could be realized.
> You can't just assume $B of funding from the
> get-go, because no funding agency - not even the
> US government - works that way.

I am not expecting the US to be involved.

> You start with
> small scale technical demonstrators, then work
> your way up.

There will be such done on the way to power sats, but they just don't
scale so to make money on the project you have to finish a very large
minimum set of infrastructure.

> If you really think the US government would just
> pony up lots of money for this tomorrow, I advise
> you to read up on Technology Readiness Levels
> and how technologies go from low TRLs to high
> TRLs.  All this stuff I've been saying about
> bootstrapping and demonstrating?  That is in
> fact a necessary prerequisite to getting the
> money to build and launch the first multi-GW
> powersat.  Just because these details are not
> physical or technical does not make them any
> less real, nor does it mean they can be
> dismissed if you truly wish to make the case
> that this can be done - because if there is, in
> fact, no path to the destination, then the
> destination can not be reached, whether or not
> the destination exists.

You are more likely to be correct about this than I am.  It is, after
all, easier not to do something than to do it.

However, the consequences of not doing something to solve energy and
carbon problems are dire.

If you have a better idea, please share it.

Keith



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