[ExI] Written for another list

[Keith Henson]

On Thu, Aug 2, 2012 at 4:51 AM,  Adrian Tymes <atymes at gmail.com> wrote:

> 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?

The power can be used to raise 500,000 tons per year to GEO.  At
$100/kg this is worth $50 B per year.  3.5 GW sold for power at 2 cent
per kWh brings in $0.56 B/year

> What other sources of
> energy could be used to bring up parts, that you are comparing
> its value to?

It's not the source of energy but the location in GEO that makes it
useful.  In space, sunlight is really cheap energy, which is the point
of the whole project.

>> 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.

Between 2 and 3.  You need a minimum induced voltage on the rectenna
diodes for them to forward conduct.  50 MW is 1/100 of 5000 MW.  So
the ground antenna would need to be one km across and the antenna in
space 10 km in diameter and would cost 100 times as much as a
transmitter for a 5 GW unit.  Microwave optics is a bitch.

>> 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.

Not at all.  To be useful for propulsion, they need to put about all
that power into 150 square meters at 20 MW/m^2.  That's a little over
12 meters across.  4 GW is exactly one ton of TNT per second by
definition.  Takes 26 meter optics at GEO to focus the beam that
tight.  Expensive.

> 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?

Then a cloud cuts off the power.  It's part of the reason we start the
laser propulsion above 10 km, to get over the clouds.

>>>>>> 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?

Off an on since 1989.

> 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.

Well, this is one specific proposal.  There is no certainty that I got
either the assumptions or the spreadsheet formulas right though.

>>>>>> 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.

OK.  The rough cost breakdown is in the paper.

>>> 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 communication satellites are already up there pouring down kWs of
power.  Why do I need to put up a mW cube sat when they are already
doing the same thing at orders of magnitude more power?

> 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.)

The hard part is not the power satellite design or getting the power
down.  That's been understood for decades, Boeing had a $10 M plus
contract to do so back in the late 70s plus they spent a *lot* of
their own money on it and still have enough interest to send people to
conferences.

The hard part is getting the cost of lifting hundreds of thousands of
tons of parts to GEO down to where power sats make economic sense.
Laser propulsion is the way to go.  That's only recently become
possible with large versions of the tiny laser diodes in CD player.

> 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.

No sane investor is going to put me in charge of spending the national
budget of a fair sized country for ten years.  And putting up a
CubeSat would not affect that fact one iota.  This is about a
*concept* for how to get the cost to GEO down.  I don't even have an
IP interest in it because (for various reasons) I have been doing this
work open source.  The idea, meme if you want, stands or falls without
me.

>> 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?

It's easy enough to calculate.

One mw is one mJ/s.  100% applied to one mg it would generate
acceleration at one meter/sec, which is about 10% of what you need
just to overcome gravity.

But a CubeSat would be hard pressed to put out a mW.  And that mW
could not be focused by something that small so the energy would go
more or less uniformly over the entire space.

Keith