
China wants to put a solar farm in space by 2025 - bcOpus
https://www.engadget.com/2019/02/18/china-solar-farm-power-station-space-2025/
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DennisP
A year ago I read the book _The Case for Space Solar Power_ , which goes into
the engineering in detail.

The old SPS designs from the '70s were monolithic beasts that would have been
ridiculously expensive. Current designs would use a large number of identical
parts, of about eight types, which would self-assemble in space. That way they
can be mass produced in factories.

The basic design was PV with microwave transmission, which has already been
tested over distances of ten kilometers or so. (Iirc it was between a couple
Hawaiian islands.) The receiving station sends a sort of homing signal for a
phased array transmitter, which makes it difficult to redirect to somewhere
without the homing signal and keep a reasonably focused beam, though you could
switch between multiple receiving stations (which are fairly cheap). The
station would be in GEO.

The book did some detailed cost analysis and found that with pre-SpaceX launch
costs, the SPS could provide power at 15 cents/kWh retail.

Elon Musk has said that at scale the BFR could ultimately get to a $50/lb
launch cost, so for grins I plugged that number into the book's calculation
and got 4 cents/kWh.

Since this type of solar would work through the night, with little or no need
for storage, it could be pretty competitive.

book: [https://www.amazon.com/Case-Space-Solar-Power-
ebook/dp/B00HN...](https://www.amazon.com/Case-Space-Solar-Power-
ebook/dp/B00HNZ0Z96)

~~~
AstralStorm
It would be competitive, if there were no nuclear power or maintenance costs
or manufacturing costs. These are not counted in launch costs.

You have to launch replacement panels pretty often due to trash collisions or
put them in a less than convenient orbit.

The space solar module with a good enough battery and emitter would cost about
as much as half a radiotelescope... Because it is one.

And consider we have problems covering sizable area with wires and cheap
panels which are easy to maintain.

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DennisP
The costs I quoted include everything, including manufacturing and
maintenance. The book breaks down all these costs. In the 4 cents/kWh
scenario, launch isn't the dominant cost anymore, and dropping that further
wouldn't make much difference.

You don't put a battery on a solar power satellite. To whatever extent you
need battery, you put it on the ground, but you don't need much because a
satellite in geosynchronous is in full sunlight almost all the time.

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AstralStorm
You want to put it in synchronous? How do you keep it lit up all the time?

You do understand you need many more panel fields as opposed to receiving
stations that way and half of them is wasted anyway?

I thought the idea is to put them in solar Lagrange or solar synchronous orbit
and bend or reflect the maser to stations. 24 hour lit, though a bit trashy if
Lsun is used.

The math is suspicious anyway. Wouldn't it mean that the panels would cost 25%
of this on ground?

~~~
DennisP
Due to axial tilt, for most of the year geosynchronous satellites are in full
sunlight 24/7\. Twice a year, around each equinox, there's a period of 44 days
during which the satellite goes into shadow briefly each day, for a time
ranging from 2 minutes, to 72 minutes at the maximum.

[https://corpblog.viasat.com/how-satellites-are-affected-
by-t...](https://corpblog.viasat.com/how-satellites-are-affected-by-the-
spring-and-autumn-equinoxes/)

This compares pretty favorably to capacity factors of other power sources.

Illumination per square meter averages quite a bit higher than ground solar,
and except for the brief times in shadow is 30% higher than ground solar at
noon.

The book evaluated other locations including Lagrange points. Everything had
pros and cons; the main disadvantage of Lagrange points was the greater
distance, requiring bigger antennas. I think more delta-v in deployment was a
factor too, though I forget by how much.

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dexen
_A doomsday weapon in space._

As the article mentions, the station will beam the collected energy down to
Earth. Whether in visible light, microwave or any other spectral band, it will
need two things for everyday operations:

\- ability to point the beam at an arbitrary point on Earth, to track the
collector ground installation, and

\- ability to focus the beam to proper size

The second capability is crucial; if it's fixed focus - and one with
sufficiently large footprint at that - and fixed orbit, it would be safe.

However having either adjustable focus, or adjustable orbit[1] makes this a
proper weapon, due to the possibility of pointing multi-megawatt beam of
energy at any point on the ground, with little to no countermeasures
available. Whether "rogue hackers", or actual owners of the station, somebody
would have the capability to destroy, without warning, large swaths of
infrastructure on the ground.

I sure hope I'm very wrong about this - that somebody have figured out a way
of inherently neutralizing the danger. But for now I treat the project as a
doomsday weapon in space.

\--

[1] the later is a given to an extent, due to the need for orbital
stationkeeping, and only possible to limit via provision of weak engines
and/or limited fuel loadout

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adrianN
It's a pretty shitty weapon because many countries have the capability to
launch a bomb to the satellites and the satellites are way more expensive than
the bomb.

~~~
dexen
It takes a good while to detect preparations for an attack with this kind of
weapon & take the decision ("Mr President, the station has slightly shifted
around, should we nuke it now?"), and it takes long time for any physical
weapon to reach it.

A decent weapon would be space-burst version of ICBM. For intercontinental
ground attack, the flight time is typically 20 minutes, but the most
reasonable spot for the station is a geostationary orbit - some 36'000 km
above equator. With a sensible speed on the order of 8km/s, it would take our
missile around 1h25m to reach geostationary orbit assuming a naive straight-up
trajectory; with any realistic trajectory it would take way longer. The space
weapon would be able to rain terrible destruction in the meantime with
impunity.

An alternative would be using ground- or space-based lasers, which give near
instantaneous hit, but you'd need to precisely hit a proper part to guarantee
fast disabling of the weapon. Merely hitting a random spot on the dish would
probably not destroy it outright. You still have to account for the time to
make the observations & take the decision. And the current breed of [high
power] lasers is single-use only due to the destructive nature of generation
of the large energy needed.

~~~
adrianN
That's all true, but a 2h window for destruction of single targets is not very
useful against a modern military. There are enough ICBM silos that you can't
destroy all of them before someone kills you DEATH STAR and then you still
have to win the war that follows.

~~~
AstralStorm
Indeed, it is not a useful weapon in an all out war. I'd expect it to be used
as surgical strike capability instead. Special operations. You can blame its
use on inclement weather due to amount of electric charge this will paint on
anything in path and resulting lightning storm.

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neals
They intend to beam the energy to earth through a laser. I wonder if building
a space-mirror and focussing a beam of sunlight would be a much easier and
scalable solution.

Though I guess you would need multiple base stations to beam it somewhere
where there's no clouds?

~~~
En_gr_Student
Using a wavelength transformation to send this through the non-absorption
windows means more energy hits the ground and you aren't hacking terrestrial
albedo in a bad way. That global warming is about absorption of sunlight, so
putting a lot more sunlight on the same absorption percent means more heat
retained. It doesn't do any good to cut gwp materials in the air, then
increase sunlight hitting the atmosphere in a way that makes heat retention
higher.

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GistNoesis
I did a quick search on the Energy Returned on Energy Invested calculations.
The following site [https://dothemath.ucsd.edu/2012/03/space-based-solar-
power/](https://dothemath.ucsd.edu/2012/03/space-based-solar-power/) gave an
ERoEI of 10:1 for solar panels on earth vs ERoEI of 4.2:1 for solar panels in
space. Which would indicate that we would still be better laying solar panel
on the ground as long as we got the appropriate empty space.

What did I missed? Have we realized enough progress since 2012 energy-wise,
that the threshold has been crossed, or does it only make sense economically
due to lower launch prices.

~~~
adrianN
Solar panels in space also work during the night and while it's cloudy. Did
your calculation include the energy costs of storage?

~~~
AstralStorm
You do know that one can build the panels on the other hemisphere, right? It
is all a small matter of building a long enough high voltage DC line. Mostly a
political problem. Or you can use microwaves on ground if it is easier to
build a bunch of antennas.

Ultimately also reflect off space mirrors (meshes) for much cheaper.

The main problem is theoretically weather. Space has the other kind of weather
called space junk.

~~~
adrianN
HVDC lines are really neat tech and I fully support solar farms in the Sahara
to supply Europe, but I wouldn't be surprised if it's cheaper to launch
satellites than to build a global power grid that can provide solar power over
night.

I think debris is not a terrible problem right now. We manage to have a large
number of satellites in high orbits.

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fredley
With regards to climate change and global warming, what about putting this in
between the sun and the earth to block some of the energy reaching the planet
to allow it to cool?

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fouronnes3
aka geoengineering. The latest IPCC report is quite critical of it.

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0xcde4c3db
I wonder whether this meant to imply military capability, in the same way that
the space race was basically a way to advertise ICBM capabilities.

~~~
dalbasal
In the sense that fancy hats imply virility.

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En_gr_Student
I was pushing this a decade ago.

If you have "fusion in a bottle" and don't want to share, this is a decent way
to make it harder to steal/damage/use-for-terrorism.

Also, giant beam transmission facilities and giant beam weapons aren't so
different from each other. There are going to be detectable critical
differences, but with some modifications one can be made into the other.

Radiation damage is going to be a challenge but satellites do with solar for a
long time. Onboard robots?

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kdmedev
Finally, somebody decided to make solar collectors in space. Been waiting for
it since it was discussed in Isaac Arthur.

I bet spaceX might do something similar in the future. When they are not as
encumbered with star link and the BFR.

~~~
AstralStorm
1) It is not much more efficient due to transmission losses. (Compared to high
voltage DC.)

2) The costs, on top of super expensive solar panels, make this totally
pointless economically. Solar panels are hard enough to maintain on Earth.

3) It's a multi gigawatt level microwave gun in space. Want to blast some
lightning onto someone? Sure, now you can. Or fry it.

~~~
Shivetya
The costs just to put the materials up there makes me wonder the long term
viability of just trying to source it from the moon. By the time you are
willing to spend the billions required it cannot be much more of step and
provides other uses.

still I have to agree, how do you even maintain something like this. it would
probably lead to a full time presence in space unless robotics become just
that good. I just don't see the ROI except may be for national pride.

~~~
adrianN
I'd guess you maintain it by replacing the satellites. We're pretty good at
maintaining satellites by replacement.

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44Aman
How do they plan to beam energy back to Earth?

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cf141q5325
Its in the article

>China's proposal, meanwhile, appears to suggest converting solar energy into
electric energy in space, before beaming back to Earth using a microwave or
laser and feeding into the grid via a ground receiving system.

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AstralStorm
Short version: they can fry a target in any country in about a day.

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FerretFred
If the country is small enough they can fry that too. I can think of a likely
candidate already.

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izzydata
If there is a beam of energy being transferred from space to the surface will
it be visible?

Edit: Apparently this is a stupid question, but I still don't know the answer.

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thecopy
How would they prevent overheating?

~~~
electricityUser
How do satellites prevent overheating? Radiators!

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clojurestan
I would use this to mine cryptocoins in space, it's way easier to send
information back to earth than power

