Dust down those orbital power plans

The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

On Jul 12, 4:17 am, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

Please let me know more, especially who to talk to. I am hkhenson on
Skype or hkeithhenson at gmail dot com

Keith

On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)
\
Julian

Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and lighter
to launch.


-- Peter Fairbrother

On 19/07/2011 10:48 PM, Peter Fairbrother wrote:
Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and lighter
to launch.

Will it run maintenance free for a couple of decades?

Sylvia.

Sylvia Else wrote:
On 19/07/2011 10:48 PM, Peter Fairbrother wrote:
Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw
$Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power
satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and lighter
to launch.

Will it run maintenance free for a couple of decades?

The compressor and turbine, I don't see why not. It's only one moving
part, gas bearings are well-developed technology and there are no
critical rotating seals.

It's much simpler than a Stirling engine, and they reckon they can make
those work for long periods in space.

The generator? Yes, I'd think so too.

The heat exchangers might need some work though, probably multiple
redundant circuits. leak sealing and gas refills or something. Likewise
the mirrors and mirror pointing stuff.


But would it need to last 20 years without maintenance? If you are going
to build it in the first place, you'd need a good launch capability anyway.

And if it's providing a goodly proportion of your energy, you'd want to
be able to fix it if it breaks. no matter what the built-in reliability
claimed was.


-- Peter Fairbrother



Sylvia.

On 20/07/2011 3:35 AM, Peter Fairbrother wrote:
Sylvia Else wrote:
On 19/07/2011 10:48 PM, Peter Fairbrother wrote:
Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw
$Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power
satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and lighter
to launch.

Will it run maintenance free for a couple of decades?

The compressor and turbine, I don't see why not. It's only one moving
part, gas bearings are well-developed technology and there are no
critical rotating seals.

It's much simpler than a Stirling engine, and they reckon they can make
those work for long periods in space.

The generator? Yes, I'd think so too.

The heat exchangers might need some work though, probably multiple
redundant circuits. leak sealing and gas refills or something. Likewise
the mirrors and mirror pointing stuff.


But would it need to last 20 years without maintenance? If you are going
to build it in the first place, you'd need a good launch capability anyway.

And if it's providing a goodly proportion of your energy, you'd want to
be able to fix it if it breaks. no matter what the built-in reliability
claimed was.

I would assume that there would be enough examples in orbit to provide
redundancy in the case of failure. After all, even if you can perform
in-orbit maintenance, it's unlikely you can do so at the kind of short
notice required for power supply failures that cause blackouts.

If it lasts 20 years on average without intervention, then you can
probably afford to deorbit it when it breaks, and send up a new one. If
you're talking about in-orbit repairs you're almost certainly talking
about manned missions, with all that that entails. One thing the shuttle
missions have shown us is that getting up there is just the start.
Fixing things in zero-g while wearing a space suit is not such an easy task.

Sylvia.

Sylvia Else wrote:
On 20/07/2011 3:35 AM, Peter Fairbrother wrote:
Sylvia Else wrote:
On 19/07/2011 10:48 PM, Peter Fairbrother wrote:
[..]

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and
lighter
to launch.

Will it run maintenance free for a couple of decades?

The compressor and turbine, I don't see why not. It's only one moving
part, gas bearings are well-developed technology and there are no
critical rotating seals.

It's much simpler than a Stirling engine, and they reckon they can make
those work for long periods in space.

The generator? Yes, I'd think so too.

The heat exchangers might need some work though, probably multiple
redundant circuits. leak sealing and gas refills or something. Likewise
the mirrors and mirror pointing stuff.


But would it need to last 20 years without maintenance? If you are going
to build it in the first place, you'd need a good launch capability
anyway.

And if it's providing a goodly proportion of your energy, you'd want to
be able to fix it if it breaks. no matter what the built-in reliability
claimed was.

I would assume that there would be enough examples in orbit to provide
redundancy in the case of failure. After all, even if you can perform
in-orbit maintenance, it's unlikely you can do so at the kind of short
notice required for power supply failures that cause blackouts.

If it lasts 20 years on average without intervention, then you can
probably afford to deorbit it when it breaks, and send up a new one. If
you're talking about in-orbit repairs you're almost certainly talking
about manned missions, with all that that entails. One thing the shuttle
missions have shown us is that getting up there is just the start.
Fixing things in zero-g while wearing a space suit is not such an easy
task.

Hmmm - suppose a 1 million square meter (just over 1.1 km across) mirror
shining on a 1000 square meter (35 meters across) collector/Brayton
engine/radiator. It collects a little over a gigawatt of solar energy,
and produces maybe 500MW of electricity. It short-range-beams that to
the downlink satellite, which beams it on to Earth, and that provides
300MW on Earth.


The downlink satellite services a flight of - what, 100 of these
powersats? - giving 30 GW electrical on Earth, equivalent to 20 large
nuclear power stations. Say you have three downlink stations which can
be fed by any of the powersats as required, and 300 powersats, that's
maybe 80 GWe on Earth, or GWeE.

The 300 powersats can be deorbited (or perhaps brought to LEO for
refurbishment in a shirt-sleeve atmosphere?) if they fail, so an average
life of twenty years is acceptable. I don't think that would be too hard
to achieve, though they might need a scheduled resupply of maneuvering
fuel. However as they have ample power, ion drives using very little
fuel might be okay.


I've been considering what to make the powersats from, the hard part is
the high temperature solar collector. First, operating fluid. Initial
options are hydrogen, helium, methane, water, neon and argon. Strike
helium for leakyness and neon for lack of availability. Methane, water
and hydrogen are liable to have reactivity problems over 20 years, and
we are left with argon. A little heavy, but in the amounts needed the
extra weight is lost in the noise.

Apart from that, argon is all good. First it's cheap and readily
available. It is monatomic, which is thermodynamically useful, as it
gives better efficiency. And it is almost completely inert chemically,
which means we can use it a high temperatures (with concomitant high
efficiency) without worrying too much about chemical corrosion of the parts.


On to the collector. It has an area of 1,000 square meters, and receives
1 MW/m^2 of energy. That's a blackbody temperature of 2050 K. We could
make it really thin, say 0.1 kg/m^2 - like a thin sheet of paper - so it
would only weigh 100 kg, but a very thin collector would be leaky, and
it would require many tiny channels. We could make it from
carbon-carbon-carbon-carbon or something, but that would be leaky and
fragile.

I suggest zirconium (or a zircalloy) at 0.8 mm thick, which would mass
about 5 tons. That won't melt even if the gas supply fails. The
collector is made from 2 large sheets of 0.4mm zircalloy, one
corrugated, which are roller-welded in strips, so as to leave channels
for the gas between welds. This provides a very low-leak solution.


The waste heat radiator could be made from something less heat resistant
and lighter, possibly titanium. It would need an area of about 6,000
square meters, but unlike the collector it could be double sided,
meaning 3,000 square meters overall. Mass, about 10 tons.



The engine could be about 10 tons - compared to a jet engine which
weighs 4 tons in aircraft form and produces 60 MWe in marinised form,
that's 15 MW/ton, the spools are simpler and do less work and there are
no combustion chambers, so 30 MW/ton should be quite possible using
available technology.

A bit of handwavium now, I'm out of time:

Add 20 tons for the alternator, 5 tons for the beam transmitter, 10 tons
for fuel, 5 for pipework etc, and 5 for the mirror, and we have a mass
of 70 tons. If the mirror support structure can come in under 30 tons,
that's 100 tons for the powersats.

300 of them is 30,000 tons in GEO. Plus you need the downlinks, say
10,000 tons each, or 60,000 tons in total. For 80GWe.


-- Peter Fairbrother

On Jul 19, 5:48 am, Peter Fairbrother wrote:
Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au
10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites.
At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

And it would be hard to scale up to the number needed for 100 GW/year
of new construction.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and lighter
to launch.

The turbines themselves are around 1/10th of a kg/kW. The
concentrating reflectors, radiators and heat absorbers seem to make up
the bulk of the satellite.

I have offered a spreadsheet before to anyone interested.

It's partly a refutation of an influential paper published
in 1962 and never revisited as far as I can tell.

What I did was very simple. In the radiation spread sheet, the first
column is absolute temperature, column B is deg C. Col C is
radiation per square meter at 0.95, D is at 0.1. E is how many square
meters per kW based on C (both sides radiate). D isn't further used.
Column E is the area to radiate on kW. F is the Carnot efficiency
from 1400 K down to the radiation temperature, G is the 75% of F based
on the typical real turbines. H is the square meters required to
collect one kW out at 100% of Carnot efficiency based on
1.366kW/meter^2. I is how much area it would take to collect sunlight
based on .75 of Carnot efficiency. I is the area it would take to
radiate heat from ideal Carnot, K is the area for real (.75) of
Carnot. L sums the areas for ideal Carnot cycle, M sums the radiator
area plus collector area at the temperature required to get rid of the
heat rejected by a real (75%) Carnot cycle.

This doesn't take into account the reflector (concentrator) loss or
the re-radiation loss from the working fluid heater, but I have
reasons to think both will be small.

Of course I could have expressed area as a function of the sum of the
two areas computed from radiation and Carnot efficiency as a function
of T and solved it analytically by setting the derivative to zero. I
find spreadsheets give me more insight though.

Assuming the radiator and collector mass per square meter is about the
same, then you can see from the graph that the minimum occurs a bit
above 100 deg C, which is far below the 370-650 deg C quoted in an old
paper he

http://contrails.iit.edu/DigitalColl...2article42.pdf

I can't say for sure what the mass per unit area of radiation or
collection are. I need to analyze a canvas tube (like an air
mattress) radiator filled with low pressure gas and air float
charcoal, Buckey balls or BeO. Assuming they are both around a
kg/m^2, a kW should come in around 3.2 kg. Turbines and generators
are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have
been analyzed at less than a kg/kW. So giving room for such parts as
power conductors and the joint to the transmitter, it *might* come in
at 5kg/kW.

If anyone has some spare web space to hang a small xls file, I can
send it to you.

Keith

-- Peter Fairbrother

Keith Henson wrote:
[...]

Assuming the radiator and collector mass per square meter is about the
same, then you can see from the graph that the minimum occurs a bit
above 100 deg C, which is far below the 370-650 deg C quoted in an old
paper he

http://contrails.iit.edu/DigitalColl...2article42.pdf


I'd use something like 1,000 K as T_l. High efficiency and high rate
heat radiation in space is problematic unless the temp is high.

Incident radiation on the collector is 1.1 MW/m^2, the mirror (which
weighs 0.005 kg/m^2 excluding support) concentrates sunlight from 1.33
kW/m^2 to 1.1 MW/m^2, approximately 820 times at 80% efficiency.


T_h is 1800 K, Carnot efficiency is 44%, overall efficiency to local
electricity is 29%.


I can't say for sure what the mass per unit area of radiation or
collection are. I need to analyze a canvas tube (like an air
mattress) radiator filled with low pressure gas and air float
charcoal, Bucky balls or BeO. Assuming they are both around a
kg/m2, a kW should come in around 3.2 kg.


I do not understand that. Ignoring the mirror, which I think - actually,
I don't know what you are doing at all - I assumed that that figure is
for heat collectors and radiators??


In my example design, which I have just posted to sci.space.tech but
which is on sci.space.policy (moderation delay?), the single sided
collector has a mass of 5 kg/m^2, and the double sided radiator has a
mass of 1 kg/m^2.

Those figures are for the radiation transfer areas. The gas contact
areas are 15-20 times the collecting or radiating areas. This can be
done in manufacture by strip-bonding two high-surface-area sheets, or by
forming an open-cell foam between the two outer sheets after bonding (my
reference structure), or by other means.

The coefficients of convective heat transfer are 800 and 80 W/m^2 K. The
the gas in the high temperature collector is at twelve times the
pressure of the low temperature radiator - the collector is at 5 MPa,
the radiator is at 0.4 MPa. The fluid is argon gas.

The collector surface is at 1900 K, the radiator surface is at 900 K,
collector gas-out is at 1,800 K and the radiator gas-out is at 1,000 K.

The high temperature collector is at 1900 K, with an incident radiative
energy of 1.1 MW and a blackbody temperature of 2200 K, which means that
it has to be shrouded to prevent losses - but the shroud can be very
light, a few tens of grams per square meter, and the shroud mass is
negligible.

Radiative heat dispersal is about 80 kW/m^2 for the low temp radiator,
at 900 K.

One m^2 of collector produces 400 kWe local, and needs 8 or 10 square
meters of radiator, so 15 kg of collectors and radiators are needed to
produce 400 kWe, or 0.0375 kg/kW.

My numbers might be a little hard to achieve, though they are meant to
be only medium-tech at best, so let's be generous and say 100 grams per kW.

That's still 30 times less than your estimate. I don't know why that is,
I'm designing this on-the-fly - have I made a mistake, or a ridiculous
assumption? I'm no Henry Spencer, and I'm not infallible.


Turbines and generators
are around 0.1 kg/kW based on Boeing 777 engines.

Okay, though I may have more to say on this later.

Transmitters have been analyzed at less than a kg/kW.

I have a 1kW FM transmitter which weighs about 100g (and which would be
totally illegal to use

So giving room for such parts as
power conductors and the joint to the transmitter, it *might* come in
at 5kg/kW.

I think it might come in at less than 1 kg/kW overall, for a very large
system.



If anyone has some spare web space to hang a small xls file, I can
send it to you.


Yes please. Will put it up too. Can put the other one up if you like
too. Link/URL will be ok for few years, but not forever.

-- Peter Fairbrother



Keith

-- Peter Fairbrother