[ExI] Fwd: Help Us Reimagine Energy for the DoD!

Keith Henson hkeithhenson at gmail.com
Fri Sep 4 18:51:11 UTC 2020


Adrian Tymes <atymes at gmail.com> wrote:

On Thu, Sep 3, 2020 at 2:43 PM Keith Henson via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

> Adrian Tymes <atymes at gmail.com> wrote:
> > Keith: might you be interested in writing up your understanding of how to
> do solar power satellites for these guys?  The US Department of Defense
> drops billions on projects like nobody else.
>
>> Unfortunately, I don't have a solution.  For microwave optice reasons,
>> the size of a power satellite optimizes around 5 GW.  The demand of a
>> big forward base is around 5 MW, so we are talking about a scale
>> mismatch of around 1000 to one.

>So they want something that is technically inefficient.  It is possible to
>make something technically inefficient if that is what the customer will
>pay for, no?

>No protests about "but it is inefficient".  Is it possible, or is it not
>possible, to make a less-than-optimally-efficient 5 MW power satellite?

Of course it is technically possible.  A 5 watt power satellite would
be possible, but even the military is going to be upset at the cost
per kWh.  I have not worked out the numbers, but as a guess, the cost
of power would go up by something like 100 times as the scale shrinks
by 1000.

That would make the cost of power a few dollars a kWh.

I think the scale mismatch problem is so bad that it is not worth
looking into.  But if you are interested (and know how to do it) I am
willing to check your Excel model if you want to create one.  I think
Seth Potter's 2009 paper has the math you would need.

Such a power satellite would be very different from those considered
in the past.  To decrease the spot size on the ground by a factor of
ten requires enlarging the transmitter in GEO by the same factor.  So
a 1 km transmitting antenna becomes 10 km, 100 times the area.  The
much lower power density would prevent thermal problems.

However, ten km diameter is 78.539.816 square meters.  If you can get
the mass down to a kg/m^2, then this object would mass around 79
million tons.  At $100/kg, the lift cost alone would be about $7.9 T
or around 1.5 B/kW.  The cost of power by LCOE would run around $200
per kWh.  (Assuming it ran for 20 years without interruption).

>Because that is what they want, inefficiency and all.

If you think these numbers are acceptable to the military, and you
want to sell them on the idea, I can introduce you to Paul Jaffe.

Keith


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