Re: [geo] SRM offset standards?

[Russell Seitz]

As  the limit of polymer manufacturability have often exceeded those of 
otheer materials, it is encuraging to note that metals ranf=ging from 
 aluminum to  gold have long been manufactured  in submicron thickness- low 
tech   aluminum,copper and gold  leaf  can be bought in the 0.1 to 0.3 
 micron  thickness range , and sails might  be  metallized ( and 
re-metallized after long wear) after deployment by vaccum evaporation 




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Re: [geo] SRM offset standards?

[Tim Sippel]

The GoeShade focus is to start with existing technology.  We are currently 
targeting vacuum aluminized clear polymer film (CP1) from Nexolve.  Based 
on my discussions with them, 2.5um thick is the best they have to offer, 
and maybe a practical limit for manufacturability.  CP1 will be used for 
the NEA Scout sail (2021 launch).  It's better than the 4.5um mylar film on 
Lightsail 2.  Yes, I have ideas for, and will pursue improvements in the 
sail film for future launches.  I expect ripstop to always be a part of the 
plan.

There are several advantages for using a reflective film.  The primary one 
is for the ability to sail from LEO, greatly reducing launch costs (factor 
of 5 or 10X).  It also helps protect the polymer from UV damage, and 
generally helps with thermal managment by reflecting the solar heat away 
rather than dealing with partial absorption when passing through the 
polymer.  One disadvantage is that the equilibrium location ends up farther 
sunward than Lagrange 1, reducing the fraction of sunlight that gets 
blocked (up to a factor of 2.5).

Yes, "little sail" by Planetary Society:  about 32 m2.  NEA Scout will be 
86 m2.  GeoShade 1km radius will have 2.5M m2 of sail area.  The GeoShade 
design has a different set of design challenges.  Its much larger size will 
have a much higher total cost, with most likely a dedicated launch.  It 
will have about 20X the solar acceleration.

On Thursday, May 7, 2020 at 11:53:35 AM UTC-7, Russell Seitz wrote:
>
> You're quite right.  I couldn't find an envelope back to write on, and 
> dropped an order of magnitude running the numbers in my head. 
>
> But I  wonder if  we could get the density down below a gram per square 
> meter: ,  since solar sails need not be specular, the film need not be 100% 
>  dense when there's a whole technology devoted to making polymer films 
> porous-- breathable gortex is the oldest.
>
> As the  little sail  orbited by the Planetary Society features ripstop 
> filament reinforcement,  a significant reduction in big sail weight might 
> be achieved with a vacuum aluminized  poromer film -- every order of 
> magnitude helps.
>
> On Thursday, May 7, 2020 at 2:18:04 AM UTC-4, Tim Sippel wrote:
>>
>> Russell,
>>
>> Your analysis seems to assume we want to counteract about 2.5B tonnes of 
>> CO2.  I didn't know that number to use as a starting point.  Instead, I 
>> started from annual RF increases, assuming 40G tonnes CO2 equivalent 
>> emmissions per year.  This is more direct for incremental offsets, and 
>> allows the calculation to be linear instead of logrithmic. 
>>
>> Your dimensional analysis was correct.  Except maybe for confusion about 
>> the density, for which you didn't specify the units.  1.5 g/cm3 is a good 
>> estimate for the polymer.  That works out to 1.5 g/m2 of 1um film.  Not 150 
>> milligrams/m2.
>>
>> The actual film being targeted is 2.5um thick, and has a density of 1.54 
>> g/cm3.  Hence, 3.9 g/m^2.   I need to add about 6% to account for the thin 
>> Al coating (increasing the launch cost, and adding about 3% to total cost).
>>
>> I am very focused on the cost of the design.  Douglas MacMartin has 
>> highlighted a significant error with how I converted from RF.  I believe 
>> the factors are (i) 4X, (ii) 1/0.7, and (iv) ERF/RF=0.92. So overall 6.2X, 
>> raising the cost estimate from $10 to $62/tonne CO2 equivalent.  There are 
>> ways to bring this cost down over time.  Maybe half?  Probably not as low 
>> as $10/tonne CO2 equivalent.
>>
>> Tim
>>
>>
>> On Wednesday, May 6, 2020 at 2:21:12 PM UTC-7, Russell Seitz wrote:
>>>
>>> Thanks for the sailing directions, Tim- I had no idea of the radius from 
>>> L1 that corresponds to an  increase in solar gravity equivalent to the sail 
>>> thrust.
>>>
>>> I am however, still concerned by the sail mass parameters.The  3.9 g/m2 
>>>  you cite is about a factor of 25 greater than  the 150 miliigrams  I 
>>> assumed in the dimensional analysis in my earlier remarks, 
>>>
>>> While it dampens the acceleration issues,it increases the cost to 
>>> orbit  proportionately, and raising the cost per equivalent tonne of C02 
>>> 25-fold would by your reckoning  move solar shades  from ~10$ to ~$250 / 
>>> tonne-- posing much the same economic quandry as  open air Carbon Capture 
>>> and Sequestration 
>>>
>>>

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Re: [geo] SRM offset standards?

[Russell Seitz]

You're quite right.  I couldn't find an envelope back to write on, and 
dropped an order of magnitude running the numbers in my head. 

But I  wonder if  we could get the density down below a gram per square 
meter: ,  since solar sails need not be specular, the film need not be 100% 
 dense when there's a whole technology devoted to making polymer films 
porous-- breathable gortex is the oldest.

As the  little sail  orbited by the Planetary Society features ripstop 
filament reinforcement,  a significant reduction in big sail weight might 
be achieved with a vacuum aluminized  poromer film -- every order of 
magnitude helps.

On Thursday, May 7, 2020 at 2:18:04 AM UTC-4, Tim Sippel wrote:
>
> Russell,
>
> Your analysis seems to assume we want to counteract about 2.5B tonnes of 
> CO2.  I didn't know that number to use as a starting point.  Instead, I 
> started from annual RF increases, assuming 40G tonnes CO2 equivalent 
> emmissions per year.  This is more direct for incremental offsets, and 
> allows the calculation to be linear instead of logrithmic. 
>
> Your dimensional analysis was correct.  Except maybe for confusion about 
> the density, for which you didn't specify the units.  1.5 g/cm3 is a good 
> estimate for the polymer.  That works out to 1.5 g/m2 of 1um film.  Not 150 
> milligrams/m2.
>
> The actual film being targeted is 2.5um thick, and has a density of 1.54 
> g/cm3.  Hence, 3.9 g/m^2.   I need to add about 6% to account for the thin 
> Al coating (increasing the launch cost, and adding about 3% to total cost).
>
> I am very focused on the cost of the design.  Douglas MacMartin has 
> highlighted a significant error with how I converted from RF.  I believe 
> the factors are (i) 4X, (ii) 1/0.7, and (iv) ERF/RF=0.92. So overall 6.2X, 
> raising the cost estimate from $10 to $62/tonne CO2 equivalent.  There are 
> ways to bring this cost down over time.  Maybe half?  Probably not as low 
> as $10/tonne CO2 equivalent.
>
> Tim
>
>
> On Wednesday, May 6, 2020 at 2:21:12 PM UTC-7, Russell Seitz wrote:
>>
>> Thanks for the sailing directions, Tim- I had no idea of the radius from 
>> L1 that corresponds to an  increase in solar gravity equivalent to the sail 
>> thrust.
>>
>> I am however, still concerned by the sail mass parameters.The  3.9 g/m2 
>>  you cite is about a factor of 25 greater than  the 150 miliigrams  I 
>> assumed in the dimensional analysis in my earlier remarks, 
>>
>> While it dampens the acceleration issues,it increases the cost to 
>> orbit  proportionately, and raising the cost per equivalent tonne of C02 
>> 25-fold would by your reckoning  move solar shades  from ~10$ to ~$250 / 
>> tonne-- posing much the same economic quandry as  open air Carbon Capture 
>> and Sequestration 
>>
>>

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Re: [geo] SRM offset standards?

[Tim Sippel]

Russell,

Your analysis seems to assume we want to counteract about 2.5B tonnes of 
CO2.  I didn't know that number to use as a starting point.  Instead, I 
started from annual RF increases, assuming 40G tonnes CO2 equivalent 
emmissions per year.  This is more direct for incremental offsets, and 
allows the calculation to be linear instead of logrithmic. 

Your dimensional analysis was correct.  Except maybe for confusion about 
the density, for which you didn't specify the units.  1.5 g/cm3 is a good 
estimate for the polymer.  That works out to 1.5 g/m2 of 1um film.  Not 150 
milligrams/m2.

The actual film being targeted is 2.5um thick, and has a density of 1.54 
g/cm3.  Hence, 3.9 g/m^2.   I need to add about 6% to account for the thin 
Al coating (increasing the launch cost, and adding about 3% to total cost).

I am very focused on the cost of the design.  Douglas MacMartin has 
highlighted a significant error with how I converted from RF.  I believe 
the factors are (i) 4X, (ii) 1/0.7, and (iv) ERF/RF=0.92. So overall 6.2X, 
raising the cost estimate from $10 to $62/tonne CO2 equivalent.  There are 
ways to bring this cost down over time.  Maybe half?  Probably not as low 
as $10/tonne CO2 equivalent.

Tim


On Wednesday, May 6, 2020 at 2:21:12 PM UTC-7, Russell Seitz wrote:
>
> Thanks for the sailing directions, Tim- I had no idea of the radius from 
> L1 that corresponds to an  increase in solar gravity equivalent to the sail 
> thrust.
>
> I am however, still concerned by the sail mass parameters.The  3.9 g/m2 
>  you cite is about a factor of 25 greater than  the 150 miliigrams  I 
> assumed in the dimensional analysis in my earlier remarks, 
>
> While it dampens the acceleration issues,it increases the cost to 
> orbit  proportionately, and raising the cost per equivalent tonne of C02 
> 25-fold would by your reckoning  move solar shades  from ~10$ to ~$250 / 
> tonne-- posing much the same economic quandry as  open air Carbon Capture 
> and Sequestration 
>
>

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Re: [geo] SRM offset standards?

[Russell Seitz]

Thanks for the sailing directions, Tim- I had no idea of the radius from L1 
that corresponds to an  increase in solar gravity equivalent to the sail 
thrust.

I am however, still concerned by the sail mass parameters.The  3.9 g/m2 
 you cite is about a factor of 25 greater than  the 150 miliigrams  I 
assumed in the dimensional analysis in my earlier remarks, 

While it dampens the acceleration issues,it increases the cost to orbit 
 proportionately, and raising the cost per equivalent tonne of C02 25-fold 
would by your reckoning  move solar shades  from ~10$ to ~$250 / tonne-- 
posing much the same economic quandry as  open air Carbon Capture and 
Sequestration 

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Re: [geo] SRM offset standards?

[Tim Sippel]

Douglas,

Ok, I'll definitely do more homework to improve my understanding in this 
area.   Thanks for the extra explanation and link.

Fortunately, my calculations are not off by 4 orders of magnitude, since 
the 1km mirror was intending to cancel the RF of 10M tons of CO2, not the 
full annual amount of 40G tons. But it looks possible that my cost estimate 
may end up being off by 1 order of magnitude (each mirror cancel 1M tons 
equivalent instead of 10M tons).

Regards,
Tim

On Tuesday, May 5, 2020 at 7:02:46 AM UTC-7, Douglas MacMartin wrote:
>
> Hi Tim,
>
>  
>
> -  The 0.2% in the link you sent is completely irrelevant; that’s 
> not a measure of the extra forcing from GHG, it’s an estimate of the 
> current imbalance (that is, GHG warm the planet, and therefore the planet 
> radiates more to space, so in equilibrium there is zero net energy flow)
>
> -  If you want to start from a radiative forcing perspective you 
> don’t get to ignore albedo.  2xCO2 is 3.7W/m2, the energy we get from the 
> sun is ~240 W/m2 (i.e., 1367/4*0.7).  So if the efficacy was one, then 
> you’d need to reflect about 3.7/240 = 1.55% of the sunlight
>
> -  But you also don’t get to ignore the efficacy, which is 
> uncertain, but the reason that models typically require more like 2% of 
> sunlight to be reflected to balance the 2xCO2.  And sorry, typed in the 
> year wrong on Hansen’s paper: 
> https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2005JD005776.  Simone 
> also posted the table of what models needed for 4xCO2 a week or two ago, so 
> you can just take those numbers and divide by two.  (And that gives an idea 
> of the uncertainty too.)
>
>  
>
> Sure, you can compute an incremental area needed to compensate an 
> incremental increase in CO2.  If you want to compensate 37mW/m2 instead of 
> 3.7, then you’d need to block 0.02% of sunlight instead of 2%.  That is, 
> you need a radius at L1 of 1.4% of Earth’s radius, or 95km, not 1km.  
> That’ll make your cost estimates off by roughly 4 orders of magnitude from 
> what you had if I did my 30-seconds of math right (no guarantee of that!)
>
>  
>
> Most recent cost estimate for SAI is here: 
> https://iopscience.iop.org/article/10.1088/1748-9326/aae98d/meta
>
> (from which you could compute the cost per W/m2, but it isn’t quoted that 
> way in the paper, so I’ll let you do the work of converting it).
>
>  
>
>  
>
> *From:* geoengi...@googlegroups.com  <
> geoengi...@googlegroups.com > *On Behalf Of *Tim Sippel
> *Sent:* Tuesday, May 5, 2020 2:26 AM
> *To:* geoengineering >
> *Subject:* Re: [geo] SRM offset standards?
>
>  
>
> Douglas,
>
>  
>
> Thanks for the comments.  I stuggled with this discrepancy a while ago.  
> Now I'm struggling again with it.  It's a very important parameter for my 
> calculations.
>
>  
>
> I don't actually rely on the 2% (or 0.22%) number.  Rather, I start from 
> the annual increment in RF, and use that to compute what percentage of the 
> sunlight needs to be blocked to cancel out the effect of those annual 
> emissions.  It is looking like 0.22% comes from measurements, and 2% comes 
> from a simulation model.  For example this breakdown from NASA shows 0.2% 
> RF: 
> https://science-edu.larc.nasa.gov/energy_budget/pdf/ERB_Litho_Edits_Percent_2016_v7.pdf
>  
> .
>
>  
>
> Addressing your factors:
>
>  
>
> (i)  Yes, the sun shines on the earth's cross-sectional area, while the 
> earth's heat radiates out over the it's surface area, which is 4X larger.  
> If I calculate that 37 mW/m^2 needs to be blocked to cancel out the effects 
> of 40G tons of CO2 equivalent emissions, I need to compute this relative 
> incoming sunlight of 1367/4 W/m^2 rather than the full 1367 W/m^2.  Looks 
> like a factor of 4 error on my part.  Ouch!
>
>  
>
> (ii) I don't see a need for factoring in albido.  If I block 0.2% of the 
> incoming sunlight, that will reduce both the 30% reflected light by 0.2% 
> and the absorbed 70% of light by 0.2%.
>
>  
>
> (iii) So the 2% estimate is based on simulations of 2XCO2. I still don't 
> understand why NASA's measurements are so much lower, but hopefully this 
> doesn't impact my calculation.
>
>  
>
> (iv) I found a paper by Hansen et. al. titled "Ice melt, sea level rise 
> and superstorms:...".  It goes into a lot of detail about the simulation 
> model.  I don't understand this area enough to make sense out of it. So I 
> wasn't able to understand the basis for the final factor of 2.  I'm hoping 
> it dosn't matter if I focus on just canceling out incremental increases in 
> RF.
>
>  
>
>  
>
> I found an IPCC reference (
>

Re: [geo] SRM offset standards?

[Tim Sippel]

Douglas,

Thanks for the comments.  I stuggled with this discrepancy a while ago.  
Now I'm struggling again with it.  It's a very important parameter for my 
calculations.

I don't actually rely on the 2% (or 0.22%) number.  Rather, I start from 
the annual increment in RF, and use that to compute what percentage of the 
sunlight needs to be blocked to cancel out the effect of those annual 
emissions.  It is looking like 0.22% comes from measurements, and 2% comes 
from a simulation model.  For example this breakdown from NASA shows 0.2% 
RF: 
https://science-edu.larc.nasa.gov/energy_budget/pdf/ERB_Litho_Edits_Percent_2016_v7.pdf
 
.

Addressing your factors:

(i)  Yes, the sun shines on the earth's cross-sectional area, while the 
earth's heat radiates out over the it's surface area, which is 4X larger.  
If I calculate that 37 mW/m^2 needs to be blocked to cancel out the effects 
of 40G tons of CO2 equivalent emissions, I need to compute this relative 
incoming sunlight of 1367/4 W/m^2 rather than the full 1367 W/m^2.  Looks 
like a factor of 4 error on my part.  Ouch!

(ii) I don't see a need for factoring in albido.  If I block 0.2% of the 
incoming sunlight, that will reduce both the 30% reflected light by 0.2% 
and the absorbed 70% of light by 0.2%.

(iii) So the 2% estimate is based on simulations of 2XCO2. I still don't 
understand why NASA's measurements are so much lower, but hopefully this 
doesn't impact my calculation.

(iv) I found a paper by Hansen et. al. titled "Ice melt, sea level rise and 
superstorms:...".  It goes into a lot of detail about the simulation 
model.  I don't understand this area enough to make sense out of it. So I 
wasn't able to understand the basis for the final factor of 2.  I'm hoping 
it dosn't matter if I focus on just canceling out incremental increases in 
RF.


I found an IPCC reference 
(https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter08_FINAL.pdf 
p. 661) saying
"Over the last decade RF of CO2 has an average growth rate of 0.27 
(0.24 to 0.30) W m–2 per decade."

So 27 mW/m-2 per year.  My calculations were based on 37 mw/m-2 coming from 
40G ton equivalent annual CO2 emissions.  If I re-calculate with this 
value, my error reduces from a factor of 4 to a factor of 3.

Regards,
Tim


On Monday, May 4, 2020 at 4:07:30 PM UTC-7, Douglas MacMartin wrote:
>
> Tim – the difference between the 0.22% and 2% is (i) factor of 4 from 
> ratio of projected area to surface area of a sphere, (ii) factor of 1/0.7 
> to account for the existing albedo of the Earth, (iii) factor of 3/3.7 
> since 2% is a rough estimate for 2xCO2, and (iv) efficacy of response to 
> solar vs CO2 is not one (that is, the same radiative forcing doesn’t give 
> the same warming for different mechanisms, see Hansen et al 2015).
>
>  
>
> *From:* geoengi...@googlegroups.com  <
> geoengi...@googlegroups.com > *On Behalf Of *Tim Sippel
> *Sent:* Monday, May 4, 2020 4:08 AM
> *To:* geoengineering >
> *Subject:* Re: [geo] SRM offset standards?
>
>  
>
> Thanks for the feedback.  It was great to learn about a planned December 
> 2020 publication of ISO 14082, which is being drafted as a standard for 
> radiative forcing accounting.  Now I am also aware of Andrew's 2016 
> 'License to chill' paper (1).
>
>  
>
> Methane reductions qualify for carbon offsets, despite the fact that the 
> methane breaks down in the atmosphere over about a decade.  So if the 
> lifetime of a solar sail can be 20 years (not uncommon for many 
> satellites), maybe it will be reasonable to qualify for some form of SRM 
> offset standard.  It should be easier to make funding decisions once the 
> benefits are quantified in a standard.
>
>  
>
> GeoShade is focused on a 1km radius design that deploys to sub-L1. A key 
> metric is g/m^2, which determines the craft's solar acceleration.  L1 is 
> 1.5M km from earth.  A new location farther sunward from L1 (maybe 2.4M km) 
> will be an equilibrium position that accounts for the sail's solar 
> acceleration.  Using its sail, active stationkeeping is possible without 
> any fuel-based thrust.  The GeoShade design doesn't rely on any exotic 
> technologies.  It uses existing materials that are manufactured 
> terrestrially.  It doesn't rely on capturing an asteroid for building 
> materials. The goal is to be able to manufacture and deploy in a relatively 
> short amount of time.  So it is very different from a 2006 proposal by 
> Roger Angel (2).
>
>  
>
> A 1km radius disk at sub-L1 can cancel the radiative forcing of about 10M 
> tons of CO2 emissions (based on calculations I mentioned previously).  I 
> can't imagine trying to cancel out ALL anthropogenic RF with mirrors.  To 
> cancel today's 3W of RF requires 3/1367 W/m^2 = 0.2% of earth's sunlight 
> (although else

RE: [geo] SRM offset standards?

[Douglas MacMartin]

Tim – the difference between the 0.22% and 2% is (i) factor of 4 from ratio of 
projected area to surface area of a sphere, (ii) factor of 1/0.7 to account for 
the existing albedo of the Earth, (iii) factor of 3/3.7 since 2% is a rough 
estimate for 2xCO2, and (iv) efficacy of response to solar vs CO2 is not one 
(that is, the same radiative forcing doesn’t give the same warming for 
different mechanisms, see Hansen et al 2015).

From: geoengineering@googlegroups.com  On 
Behalf Of Tim Sippel
Sent: Monday, May 4, 2020 4:08 AM
To: geoengineering 
Subject: Re: [geo] SRM offset standards?

Thanks for the feedback.  It was great to learn about a planned December 2020 
publication of ISO 14082, which is being drafted as a standard for radiative 
forcing accounting.  Now I am also aware of Andrew's 2016 'License to chill' 
paper (1).

Methane reductions qualify for carbon offsets, despite the fact that the 
methane breaks down in the atmosphere over about a decade.  So if the lifetime 
of a solar sail can be 20 years (not uncommon for many satellites), maybe it 
will be reasonable to qualify for some form of SRM offset standard.  It should 
be easier to make funding decisions once the benefits are quantified in a 
standard.

GeoShade is focused on a 1km radius design that deploys to sub-L1. A key metric 
is g/m^2, which determines the craft's solar acceleration.  L1 is 1.5M km from 
earth.  A new location farther sunward from L1 (maybe 2.4M km) will be an 
equilibrium position that accounts for the sail's solar acceleration.  Using 
its sail, active stationkeeping is possible without any fuel-based thrust.  The 
GeoShade design doesn't rely on any exotic technologies.  It uses existing 
materials that are manufactured terrestrially.  It doesn't rely on capturing an 
asteroid for building materials. The goal is to be able to manufacture and 
deploy in a relatively short amount of time.  So it is very different from a 
2006 proposal by Roger Angel (2).

A 1km radius disk at sub-L1 can cancel the radiative forcing of about 10M tons 
of CO2 emissions (based on calculations I mentioned previously).  I can't 
imagine trying to cancel out ALL anthropogenic RF with mirrors.  To cancel 
today's 3W of RF requires 3/1367 W/m^2 = 0.2% of earth's sunlight (although 
elsewhere I see a value of 2.0% being used).  The intent would be to supplement 
the primary ongoing efforts to replace fossil fuel energy with renewable energy 
sources.  These sun shades are to help buy time since we are not progressing as 
quickly as needed to achieve the IPCC 1.5C target.

The cost for the GeoShade design is estimated to be about $10/ton equivalent.  
(Based on IPCC 2018 2.8.4, it seems sufficient to assume a linear relationship 
rather than logrithmic.)  My impression is that $10/ton is 10X to 100X the cost 
of other SRM options.  (Pointers to better estimates would be appreciated.)  
Hopefully the cost remains low enough to be affordable as a temporary offset.

Could a space-based solution be used to lead the way in achieving approval for 
SRM offsets?  Once in position, sun shades look like a small sunspot.  
Hopefully something people can easily wrap their heads around.  The RF benefits 
may be easier to quantify, track, and control compared to other SRM methods.  
The solar reduction is guaranteed to be small and uniform amount across the 
globe.  It can be quickly stoped by turning the sails sideways.  As long as RF 
reductions are a small fraction of RF increases due to greenhouse gas 
emissions, concerns about unintendended consequences should be minimal.

For those interested in more details, the GeoShade design is based on a 
reflective film with a 3.9 g/m^2 density plus a 1X mass overhead for the 
structure and controls.  A 1km radius disk produces a thrust of about 20N, 
resulting in a solar acceleration of about 1mm/s^2.  Attitude control at sub-L1 
involves very slow adjustments of the center of mass vs. the center of 
pressure.  This is accomplished by adjusting the position of a mass, or by 
tilting a subset of sail panels.  The more difficult problem to solve was more 
dramatic attitude changes that are required to support orbit raising from its 
start at a high LEO (enabling a significant reduction in cost).  It will take 
about 1 year to sail to sub-L1.

(1) Licence to chill: Building a legitimate authorisation process for 
commercial SRM operations, 2016, Andrew Lockley.  
https://journals.sagepub.com/doi/10.1177/1461452916630082
(2) Feasibility of cooling the Earth with a cloud of small spacecraft near the 
inner Lagrange point (L1), 2006, Roger Angel, Univ of Arizona.  
http://www.pnas.org/content/pnas/103/46/17184.full.pdf

Reference Textbooks:
  Space Sailing, 1992, Wright
  Solar Sailing, 2004, McInnes
  Solar Sails, 2008, Vulpetti, Johnson, Matloff
  Advances in Solar Sailing, 2014, Editor: Macdonald

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Re: [geo] SRM offset standards?

[Tim Sippel]

Thanks for the feedback.  It was great to learn about a planned December 
2020 publication of ISO 14082, which is being drafted as a standard for 
radiative forcing accounting.  Now I am also aware of Andrew's 2016 
'License to chill' paper (1).

Methane reductions qualify for carbon offsets, despite the fact that the 
methane breaks down in the atmosphere over about a decade.  So if the 
lifetime of a solar sail can be 20 years (not uncommon for many 
satellites), maybe it will be reasonable to qualify for some form of SRM 
offset standard.  It should be easier to make funding decisions once the 
benefits are quantified in a standard.

GeoShade is focused on a 1km radius design that deploys to sub-L1. A key 
metric is g/m^2, which determines the craft's solar acceleration.  L1 is 
1.5M km from earth.  A new location farther sunward from L1 (maybe 2.4M km) 
will be an equilibrium position that accounts for the sail's solar 
acceleration.  Using its sail, active stationkeeping is possible without 
any fuel-based thrust.  The GeoShade design doesn't rely on any exotic 
technologies.  It uses existing materials that are manufactured 
terrestrially.  It doesn't rely on capturing an asteroid for building 
materials. The goal is to be able to manufacture and deploy in a relatively 
short amount of time.  So it is very different from a 2006 proposal by 
Roger Angel (2).

A 1km radius disk at sub-L1 can cancel the radiative forcing of about 10M 
tons of CO2 emissions (based on calculations I mentioned previously).  I 
can't imagine trying to cancel out ALL anthropogenic RF with mirrors.  To 
cancel today's 3W of RF requires 3/1367 W/m^2 = 0.2% of earth's sunlight 
(although elsewhere I see a value of 2.0% being used).  The intent would be 
to supplement the primary ongoing efforts to replace fossil fuel energy 
with renewable energy sources.  These sun shades are to help buy time since 
we are not progressing as quickly as needed to achieve the IPCC 1.5C target.

The cost for the GeoShade design is estimated to be about $10/ton 
equivalent.  (Based on IPCC 2018 2.8.4, it seems sufficient to assume a 
linear relationship rather than logrithmic.)  My impression is that $10/ton 
is 10X to 100X the cost of other SRM options.  (Pointers to better 
estimates would be appreciated.)  Hopefully the cost remains low enough to 
be affordable as a temporary offset.

Could a space-based solution be used to lead the way in achieving approval 
for SRM offsets?  Once in position, sun shades look like a small sunspot.  
Hopefully something people can easily wrap their heads around.  The RF 
benefits may be easier to quantify, track, and control compared to other 
SRM methods.  The solar reduction is guaranteed to be small and uniform 
amount across the globe.  It can be quickly stoped by turning the sails 
sideways.  As long as RF reductions are a small fraction of RF increases 
due to greenhouse gas emissions, concerns about unintendended consequences 
should be minimal.

For those interested in more details, the GeoShade design is based on a 
reflective film with a 3.9 g/m^2 density plus a 1X mass overhead for the 
structure and controls.  A 1km radius disk produces a thrust of about 20N, 
resulting in a solar acceleration of about 1mm/s^2.  Attitude control at 
sub-L1 involves very slow adjustments of the center of mass vs. the center 
of pressure.  This is accomplished by adjusting the position of a mass, or 
by tilting a subset of sail panels.  The more difficult problem to solve 
was more dramatic attitude changes that are required to support orbit 
raising from its start at a high LEO (enabling a significant reduction in 
cost).  It will take about 1 year to sail to sub-L1.

(1) Licence to chill: Building a legitimate authorisation process for 
commercial SRM operations, 2016, Andrew Lockley.  
https://journals.sagepub.com/doi/10.1177/1461452916630082
(2) Feasibility of cooling the Earth with a cloud of small spacecraft near 
the inner Lagrange point (L1), 2006, Roger Angel, Univ of Arizona.  
http://www.pnas.org/content/pnas/103/46/17184.full.pdf

Reference Textbooks:
  Space Sailing, 1992, Wright
  Solar Sailing, 2004, McInnes
  Solar Sails, 2008, Vulpetti, Johnson, Matloff
  Advances in Solar Sailing, 2014, Editor: Macdonald

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Re: [geo] SRM offset standards?

[Andrew Lockley]

Harvard recently held a workshop on this, so the idea is far from obsolete.

A

On Fri, 1 May 2020, 10:49 Haywood, Jim, 
wrote:

> All,
>
> Before anyone gets too carried away with this idea, one has to realise
> that anything placed at the L1 point is not likely to stay there owing to
> radiation pressure etc. This implies that it’s not a one shot and your done
> problem. There would have to be replenishment.
>
> For your information, the best discussion on this that I have found on
> this appears in the link below. We’re deep in the realms of astrophysics
> here, but I can’t see anything wrong with the calculations.
>
>
> https://pure.strath.ac.uk/ws/portalfiles/portal/547235/strathprints027439.pdf
>
> You’ll see that it’s from 10 years ago, when this idea might have had some
> initial credibility.
>
> Hope this helps.
>
> Best Regards
>
> Jim
>
>
>
> --
> *From:* geoengineering@googlegroups.com 
> on behalf of Janos Pasztor 
> *Sent:* Friday, May 1, 2020 10:25:35 AM
> *To:* andrew.lock...@gmail.com ;
> t...@geo-shade.com ; geoengineering <
> geoengineering@googlegroups.com>
> *Subject:* Re: [geo] SRM offset standards?
>
>
> Tim,
>
>
>
> Without passing any judgement on this [rather controversial activity], you
> may find that ISO’s work in this area
> <https://www.iso.org/search.html?q=radiative%20forcing> could be relevant
> to answering part of your question.
>
>
>
> Janos
>
> ===
> Janos Pasztor 
> Executive Director
> *Carnegie Climate Governance Initiative (C2G)*
> Geneva, Switzerland
>
> Email: jpasz...@c2g2.net | Mobile: +41-79-7395503 | Twitter: @jpasztor |
> Skype: jpasztor
>
> [image: signature_540100778] <https://www.c2g2.net/>
>
> www.c2g2.net
>
> Follow C2G on
> [image: signature_756483353] <https://twitter.com/c2g2net> [image:
> signature_1141076971] <https://www.facebook.com/C2G2net> [image:
> signature_291258080]
> <https://www.linkedin.com/company/carnegie-climate-governance-initiative>
>
>
>
>
>
>
>
> *From: * on behalf of Andrew Lockley <
> andrew.lock...@gmail.com>
> *Reply to: *"andrew.lock...@gmail.com" 
> *Date: *Friday, 1 May 2020 at 11:06
> *To: *"t...@geo-shade.com" 
> *Cc: *geoengineering 
> *Subject: *Re: [geo] SRM offset standards?
>
>
>
> You're correct in that there is an equivalence between radiative forcing
> (RF) and CO2 concentrations. There are caveats
>
> 1) the relationship is non linear
>
> 2) even space based methods are short lived, compared to the lifetime of
> CO2
>
> 3) there is no established economic market for RF based credits. Any
> economic incentives would, in the short term, have to be based on the
> carbon credits
>
>
>
> Andrew
>
>
>
> On Fri, 1 May 2020, 09:15 Tim Sippel,  wrote:
>
> The transition from fossil fuel to renewable energy sources is not
> happening quickly enough, so it seems likely that we will need to
> supplement with SRM to buy time.
>
>
>
> Is work being done towards standards to validate and quantify SRM offsets,
> similar to carbon offset standards (VCS, Gold Standard, etc.)?  This could
> reduce the dependency on strained government budgets to support approved
> SRM efforts.
>
>
>
> I am also interested in feedback on the following rough calculations.
> Sunlight energy reaching earth is 1367 W/m^2.  By eyeballing the slope on a
> graph here (https://www.esrl.noaa.gov/gmd/aggi/aggi.html), I have
> estimated that worldwide annual CO2 emissions (~40G tons) is increasing
> radiative forcing by about 37 mW/m^2.  From this, I estimate that the
> incremental radiative forcing of 1 ton of CO2 emissions can be canceled out
> with about 1/4 m^2 of sun shade near the Sun-Earth Lagrange 1 equilibrium
> point.  Using an estimate for the cost of deploying a space-based sunshade,
> I am able to compare the cost/ton equivalent of an SRM offset vs cost/ton
> of a carbon offset.  Does this approach seem valid?
>
>
>
> Regards,
>
> Tim Sippel
>
> --
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>
> -

Re: [geo] SRM offset standards?

[Andrew Lockley]

You're correct in that there is an equivalence between radiative forcing
(RF) and CO2 concentrations. There are caveats
1) the relationship is non linear
2) even space based methods are short lived, compared to the lifetime of
CO2
3) there is no established economic market for RF based credits. Any
economic incentives would, in the short term, have to be based on the
carbon credits

Andrew

On Fri, 1 May 2020, 09:15 Tim Sippel,  wrote:

> The transition from fossil fuel to renewable energy sources is not
> happening quickly enough, so it seems likely that we will need to
> supplement with SRM to buy time.
>
> Is work being done towards standards to validate and quantify SRM offsets,
> similar to carbon offset standards (VCS, Gold Standard, etc.)?  This could
> reduce the dependency on strained government budgets to support approved
> SRM efforts.
>
> I am also interested in feedback on the following rough calculations.
> Sunlight energy reaching earth is 1367 W/m^2.  By eyeballing the slope on a
> graph here (https://www.esrl.noaa.gov/gmd/aggi/aggi.html), I have
> estimated that worldwide annual CO2 emissions (~40G tons) is increasing
> radiative forcing by about 37 mW/m^2.  From this, I estimate that the
> incremental radiative forcing of 1 ton of CO2 emissions can be canceled out
> with about 1/4 m^2 of sun shade near the Sun-Earth Lagrange 1 equilibrium
> point.  Using an estimate for the cost of deploying a space-based sunshade,
> I am able to compare the cost/ton equivalent of an SRM offset vs cost/ton
> of a carbon offset.  Does this approach seem valid?
>
> Regards,
> Tim Sippel
>
> --
> You received this message because you are subscribed to the Google Groups
> "geoengineering" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to geoengineering+unsubscr...@googlegroups.com.
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> 
> .
>

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[geo] SRM offset standards?

[Tim Sippel]

The transition from fossil fuel to renewable energy sources is not 
happening quickly enough, so it seems likely that we will need to 
supplement with SRM to buy time.

Is work being done towards standards to validate and quantify SRM offsets, 
similar to carbon offset standards (VCS, Gold Standard, etc.)?  This could 
reduce the dependency on strained government budgets to support approved 
SRM efforts.

I am also interested in feedback on the following rough calculations.  
Sunlight energy reaching earth is 1367 W/m^2.  By eyeballing the slope on a 
graph here (https://www.esrl.noaa.gov/gmd/aggi/aggi.html), I have estimated 
that worldwide annual CO2 emissions (~40G tons) is increasing radiative 
forcing by about 37 mW/m^2.  From this, I estimate that the incremental 
radiative forcing of 1 ton of CO2 emissions can be canceled out with about 
1/4 m^2 of sun shade near the Sun-Earth Lagrange 1 equilibrium point.  
Using an estimate for the cost of deploying a space-based sunshade, I am 
able to compare the cost/ton equivalent of an SRM offset vs cost/ton of a 
carbon offset.  Does this approach seem valid?

Regards,
Tim Sippel

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