[ExI] Written for another list

[Keith Henson]

On Sat, Aug 4, 2012 at 2:10 AM,  Eugen Leitl <eugen at leitl.org> wrote:

> On Fri, Aug 03, 2012 at 12:00:47PM -0400, John Clark wrote:

snip

>> By the way I don't think conserving energy is enough, the government should
>
> I never said a single thing about conserving energy. We need 50-100 TW
> by 2050, and if we can't fill that envelope the population will react
> adaptively.

Model I have worked out should be up to cranking out two TW/year by
2025 so 50 TW should be OK.  100 TW would not be much harder.  Even
ten years ago this would have been unthinkable because we had no idea
of how to build the propulsion lasers.

>> pass a law making us conserve angular momentum too. I'm thinking of
>> starting a advocacy group.

Heh.  If we had the material to build space elevators, they can be
more than 100% energy efficient at raising cargo to GEO.  If the up
traffic is greater than the down traffic, then the elevator leans back
in the sky against the direction of the rotation of the Earth and
extracts payload velocity to GEO from the rotation of the Earth.
Slowing the Earth lengthens the day by an exceedingly small amount,
but it is enough to generate a protest slogan "Conserve Angular
Momentum."

 Adrian Tymes <atymes at gmail.com> wrote

> On Thu, Aug 2, 2012 at 8:29 AM, Keith Henson <hkeithhenson at gmail.com> wrote:
>> 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
>
> False comparison: you're leaving out all the non-energy
> costs of launching stuff - and the vast bulk of modern
> launch costs is non-energy.  Instead, it is the
> bureaucratese and project management that comes
> with a series of one-off prototypes, one after another.
>
> So, no, you would not be getting $100/kg out of it.
> (Even if you were, you're "paying" yourself: always a
> red flag that you're getting an incorrect value, and not
> an income stream you can use to fund the rest of the
> project with in any case.)

You asked how I calculated what the first power sat was worth powering
propulsion lasers vs selling the power.

>>>> 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.
>
> Your proof does not convince of that.
>
>> You need a minimum induced voltage on the rectenna
>> diodes for them to forward conduct.
>
> Watts are not a measure of voltage.  Volts are voltage.
> The minimum voltage can be induced for a power less
> than MW, possibly sub-W.

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.

> For example, the common household microwave oven
> can induce voltage in rectennas places within them.
> They use much less than a MW to do so, and the
> rectennas are less than a meter across.  (The results
> tend to destroy the oven, so casually experimenting
> with this is not advised, but there is ample evidence
> that power transfer on this small magnitude works.)

The power level in a microwave oven is around 20 kW/m^2.

> Granted, the distances are far, far less than orbital,
> but we're just talking about the minimum power
> received to drive the rectenna.
>
>> 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.
>
> How does the fact that you're transmitting less power
> translate into requiring a larger antenna?  Unless
> you're basing off the minimum - in which case, you
> need to show why the minimum is so gigantic.

Microwave optics.  It's what drives power sats to such large sizes.

>>>> 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.
>
> That's "strategic" in modern military parlance.  You're
> hitting an entire building, not a person or vehicle.
> This is trivially defeated by colocating the target with
> civilian infrastructure, which infrastructure is an
> unacceptable target (to most modern Western
> militaries, anyway).
>
> Besides, they already have ample and sufficient
> weapons to take out targets of that size - and more
> controllable, too.  A missile can be pulled off if it is
> realized after the shot that the target is incorrect.

For the kind of missiles using on drones, I don't think that is the
case.  But I am not sure.

> A laser - once you pull the trigger, that's it.
>
>>> 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'm talking about for prototypes and bootstrapping,
> where intermittent interruption by clouds is acceptable.
> You're not going to have need or even much use for
> launch power 24/7 until way down the line, when you
> have enough capital that you're manufacturing sats
> like crazy.  (Remember, the satellites themselves
> cost a lot of money, beyond their launch costs.

In this model, about twice the lift cost.

> Unless you have them manufactured on the Moon -
> and let's assume fully automated manufacture so we
> can handwave ongoing labor costs - but then, the
> tough part becomes getting the infrastructure up there
> first.)
>
>>>>>>>> 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.
>
> You must have been off every time the case was made,
> then.

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.

>>> 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.
>
> Yes, but you said you wanted to make the case that
> there is at least one way.  That case has already been
> made in general.  What you're actually talking about
> is your specific proposal, so you need to be clearer
> about your intent.
>
> 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.

>>> 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.
>
> That's the one you haven't sent?

I don't recall your asking for it.  Taking this as a request, will
send the current draft.

> Or did you mean the
> Boeing one, which I reject as an unreliable data source
> since they have a history of invalid (and often
> cost-inflated) data for this sort of thing.

Boeing is well aware, and has been since the 70s, that for them to get
any income from such a project they have to make an economic case.  I
would expect underestimation rather than cost-inflated from them.

>>>> 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?
>
> Because there are concerns other than
> just "can it be done in theory" that you must demonstrate.
> The biggest one: can *YOU* do it?

No.

> 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?

Personally?  Not a chance.

>  (All the analysis in the world might miss some
> physics objections; actually doing it will automatically do
> it.)
>
> Put another way: why do you believe that the fact that
> other people have put up comsats pouring down KW
> of power for communication, will convince anyone that
> you, personally, have the know-how and ability (if funded)
> to put up satellites that would pour down any amount of
> power for a different use (power itself)?

The existence of communication satellites shows that a lot of the
physics questions have been answered.

>> 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.
>
> Perhaps it wouldn't be hard for Boeing.  But we're not
> talking about Boeing.  We're talking about you.
>
>> 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.
>
> Right.  So, how are you going to show people that you
> can do this?

Me personally? No way.

>> 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.
>
> By itself, perhaps not.  But putting up a CubeSat would
> justify putting you in charge of something larger.  And
> if that works, larger still.
>
> And that's *how* people eventually wind up in charge
> of budgets like that: they worked their way up.

Ah, even if I wanted to be in charge of this, how many years would it take?

>> 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.
>
> Then your work is in vain.  If there's no chance that
> anyone will ever bend metal to your design, be inspired
> by it, or any other concrete result, you may as well have
> done nothing.

Other than try to hang the ideas together into a mutually supporting
business framework, this is not work I originated.  Power satellites
were invented by Peter Glaser, Skylon by Alan Bond, Richard Varvill
and the rest of the people at Reaction Engines.  The beamed energy
propulsion work was done by Jordin Kare and Kevin Parkins.

> I speak from experience.  I have multiple patents for
> various systems, and I now and then try to get others
> to build them - see what it would take.

I too have a list of patents.  One of them made other people a lot of money.

>  If I just made
> the design and left it there, not seeking to get it to
> those who could make it real, it would have been a
> wasted effort.  (As it happens, I have yet to get some
> of the designs to said people, so those efforts have
> yet to bear fruit.  Others have born fruit, and it was
> excellent.  But that never would have happened had I
> paid no attention to the intermediate phases of how
> to make the ideas real.)
>
>>> 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.
>
> So you could launch a 1 mg vehicle with about 50 mW, then,
> assuming 20% efficiency?

No.  Scaling problems.

>> But a CubeSat would be hard pressed to put out a mW.
>
> CubeSats - if dedicated mostly to solar panels and
> transmitter - can pull in and put out a few Ws.  For
> example:
> http://www.clyde-space.com/cubesat_shop/solar_panels/1u_solar_panels/50_1u-cubesat-side-solar-panel
>
>> And that mW
>> could not be focused by something that small so the energy would go
>> more or less uniformly over the entire space.
>
> Orbit-to-ground laser communicators are being
> investigated for CubeSats.  Last I heard, 1 W of
> power at the source results in some number of
> mW power of signal received.  One could simply
> not bother to encode a signal, and instead use it
> for power directly.  I forget whether they're using
> visual, microwave, or another frequency, but the
> receivers are less than a meter across.

I don't have an idea of why you want me to work on CubeSats, but the
scaling is akin to launching a multi ton comm sat with Estes rockets.

snip

From: John Clark <johnkclark at gmail.com>

> Thanks for the news flash. I could be wrong but I'm guessing that Fast
> breeders are faster than slow breeders. Am I correct?

Fast breeders use unmoderated, i.e., use fast neutrons.  Permits
fission of U238 in some cases.  That's how a fission-fusion-fission
bomb works.

Keith