[ExI] Written for another list

Adrian Tymes atymes at gmail.com
Thu Aug 2 00:46:39 UTC 2012


On Tue, Jul 31, 2012 at 9:52 PM, Keith Henson <hkeithhenson at gmail.com> wrote:
> In the bootstrap plan I have outlined, the power from the first
> expensive (built with conventional rockets) power sat is used to power
> propulsion lasers.  That lets you build more power sats at a much
> lower cost than the first one.  The energy the first one generates is
> worth around 100 times as much bringing up parts for more power
> satellites as it would be to sell it to ground markets.

How do you calculate this 100 times?  What other sources of
energy could be used to bring up parts, that you are comparing
its value to?

> There has been a lot of looking at selling power from space to the
> military.  Never reached the big study phase because there are just
> too many problems.  The military wants power in MW or sub MW chunks.
> Microwave power sats at 2.45 GHz don't scale below 5 GW

So what happens if you put a 50 MW sat up?  Is it:

1) More expensive per MW?
2) More expensive overall - not per MW, but the total project cost -
than 5 GW?
3) Impossible?

If it's just #1 - so long as the total cost is lower, that's fine.

#2 or #3 would need serious justification.

> But if we were to build laser power sats for the military, they would
> probable use them as weapons rather than power.

Lasers like that are strategic weapons.  They hit areas, not
individual targets.

Most NATO militaries talk big about strategic weapons, but
in practice, they tend to make sure nobody uses them.
Collateral damage runs counter to just about every mission
they've been on for the past few decades, and this is unlikely
to change.  (Not that there hasn't been collateral damage,
just that they try to avoid wantonly inflicting it when they
have more precise options available.)

> For a given frequency at one of the atmospheric windows such as 2.45
> GHz, the minimum size to focus the microwave power beam is 1 km on the
> power sat and 10 km on the ground, or the other way around.  This is
> what leads to the huge size of these things, the microwave optics.
> This has been understood for over 200 years, look up Airy disk.
> http://en.wikipedia.org/wiki/Airy_disk

What about using shorter wavelengths, such as visible light?

>>>>> I am mainly interested in making a case that there *is* a way out of
>>>>> the energy/carbon problems without an 80% die off.
>>>>
>>>> The theoretical case has long been made.  The challenge now
>>>> is the litmus test: actually doing it.
>>>
>>> That's news to me.  Where?
>>
>> The theoretical case having been made?  Here, for one.
>> This very list.
>
> I don't remember such discussion.

And how long have you been on this list?

Ways to save the world without a massive dieoff are
discussed not infrequently.  Maybe not any specific
proposal or case, but the general discussion has
long since chased away any presumption that we
must necessarily fail and that humanity is doomed.

>>>>> The cost of power at current $10,000/kg is dominated by the lift cost
>>>>> of ~50,000/kW.  Cost of power at that transport rate is ~$2/kWh.
>>>>>
>>>>> For zero lift cost, the cost would be around 1.4 cents per kWh.  The
>>>>> derivation of this is in the paper.
>>>>
>>>> It sounds like you have bigger concerns than the lift cost, if
>>>> that is not a majority of the cost.
>>>
>>> It's around a third of the total cost.  I really don't understand your
>>> objection to the other costs.  Do you know of a less expensive way to
>>> make and transmit power to the Earth?
>>
>> Strawman.  My objections regarding the other costs have
>> to do with the other costs themselves, not the benefits.
>> To wit: what *are* the other costs, and how big of a factor
>> are they?
>
> You mean you don't understand the cost of generation equipment?

I meant that I didn't understand *that* the rest of the cost was
generation equipment.

>> A demonstration - pure demonstrator - satellite can be built
>> and launched for tens of thousands - not millions - of dollars.
>> It's called a CubeSat.
>
> You could pack a few mW of microwave transmitter into a CubSat.
>
> Why bother when there are communication satellites pouring down as
> much as ten kW of microwaves?

Because you don't have the money to put up a big enough
satellite to pour down 10 kW, but you might have enough for
a CubeSat.  And because there are concerns other than
just "can it be done in theory" that you must demonstrate.

The biggest one: can *YOU* do it?  Can you, personally, get
all the pieces together, make it fly, get some - any - amount
of power, and thus show that you have indeed solved all the
challenges?  (All the analysis in the world might miss some
physics objections; actually doing it will automatically do
it.)

A lot of people like us are incapable of understanding this
problem, but it is a huge one for investors.

No, no, seriously, this is a big problem.

This is the difference between theory and practice.  Once
you've shown that you can actually do it, even at
extraordinarily inefficient rates, then you become far more
able to get investment to do the full-size project, because
you have proven that you, personally, can get power sats
up and running if given the funding.

> You have the right idea, but the scaling laws won't let you do it that
> small.  There is a size, 5-10 tons depending on the technology, below
> which you can't get *any* payload to orbit.  It has to do with the
> amount of atmosphere you have to punch through, and the square/cube
> scaling of the vehicles.  I assure you that if I could start with 1 kW
> I would.

Uh huh.  I've told you about CubeCab, right?  I happen to
be looking at the minimum cost - and with it, rocket size
and mass, payload capacity, et cetera - to get something
into orbit.  A lot of people have said it is impossible to put
a single, 1U CubeSat into orbit by itself - that rockets just
don't scale that small.  I've been finding it is possible - you
have to accept horribly bad mass fractions, but you can
still greatly lower the minimum amount of rocket by doing
so.

If a single CubeSat can get a few mW down to the ground,
what kind of thrust could you get on a 1-mg launch vehicle?



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