Re: [geo] Re: SRM offset standards?

[Russell Seitz]

Many thanks for the link .However, while the paper is convincing in term of 
 theoretical orbital mechanics,  I can't find any treatment of using solar 
sail  attitude alone  to manage torque and acceleration issues, for as the 
authors state, it 
"does not address practicality issues such as the design and deployment of 
the sunshades"

The closest the seem to come to my quetioni :
" in section I in Results and Discussion, the outcome of the geoengineering 
optimizations is an out-of-plane motion of the type z(t) = a sin(t + c) + b. 
Thus, we then know that the sail acceleration in the out-of-plane direction 
must be such that:

(19)

We may also require that the sunshade does not move away from the Sun-Earth 
line, i.e. y = 0, so that the shade is always cast symmetrically over the 
morning and afternoon side of the Earth. Thus,(20)

Precisely because of the two previous constraints, the control history of 
the clock angle δ must then satisfy:(21)

On the other hand, the control history of the cone angle α must also 
satisfy the following expression:(22)

If Eqs 21 

 and 22 

 are 
satisfied, the shape of the motion in the z and y coordinates will be as 
prescribed, and only x(t) remains to be solved."

Which is fine by way of celestial mechanics, but not much use  in terms of 
how to evolve sail to keep a 100 kilometer square rigger on tation in all 
kinds of space weather




On Sunday, May 3, 2020 at 7:11:26 PM UTC-4, Douglas MacMartin wrote:
>
> See 
> https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0136648
>
>  
>
> This is straightforward to calculate, and wouldn’t be any more difficult 
> to find than L1.  (That is, solar pressure is well known, so is gravity.)
>
>  
>
>
>

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RE: [geo] Re: SRM offset standards?

[Douglas MacMartin]

See https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0136648

This is straightforward to calculate, and wouldn’t be any more difficult to 
find than L1.  (That is, solar pressure is well known, so is gravity.)

From: geoengineering@googlegroups.com  On 
Behalf Of Russell Seitz
Sent: Sunday, May 3, 2020 3:06 PM
To: geoengineering 
Subject: Re: [geo] Re: SRM offset standards?

" you just need to displace yourself sunward until the forces balance…"

How far  sunward do you calculate that to be, and howfar from Lagrange 1  :

It'cold out there , and there's no valet parking.

On Sunday, May 3, 2020 at 10:36:24 AM UTC-4, Douglas MacMartin wrote:
You don’t need a countervailing force, you just need to displace yourself 
sunward until the forces balance… (though how far depends on areal mass 
density, and displacing too far sunward will require greater area to shade the 
Earth if I recall right).

But even if the propellant requirement is zero, still neither cheap nor 
near-term.

From: geoengi...@googlegroups.com 
> On Behalf Of Russell Seitz
Sent: Saturday, May 2, 2020 10:49 PM
To: geoengineering >
Subject: [geo] Re: SRM offset standards?

If 0.25 m2  per tonne CO2 is correct as presumed  , ~  10 billion m2, or 10,000 
km2 of  relector area would be  required

At 1 micron thickness that translates into 1 cubic meter per  km2. assuming  
for example' sake a  film with a  density  of   1, 5 , like  graphene 
strengthened aluminized one micron mylar, that would mean delivering 15,000 
tonnes to L 1, not counting frame, deployment systems , thrusters and fuel.

As the solar sail force would be on the order of 8 newtons / km2,  a  
countervailing thrust of 80kN, or ~8,000 kg would  be required for station 
keeping.
Even with solar powered ion thrusters, that would entail a  considerable 
propellent mass

As   the ~ 500 kg Deep Space probe consumed oved 100kg of xenon in the course 
of three years of generating  at most 86 millinewtons of thrust a linear 
extrapolation would be on the order of a million times more for so large a 
solar shade--in  which case station keeping at the L1 would requiresending 
up the whole sail system's weight in propellant every few years.

It's hard to see how its proponents  could underbid  earth-based SRM

On Friday, May 1, 2020 at 4:15:00 AM UTC-4, 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] Re: SRM offset standards?

[Russell Seitz]

" you just need to displace yourself sunward until the forces balance…"

How far  sunward do you calculate that to be, and howfar from Lagrange 1  :

It'cold out there , and there's no valet parking.

On Sunday, May 3, 2020 at 10:36:24 AM UTC-4, Douglas MacMartin wrote:
>
> You don’t need a countervailing force, you just need to displace yourself 
> sunward until the forces balance… (though how far depends on areal mass 
> density, and displacing too far sunward will require greater area to shade 
> the Earth if I recall right).
>
>  
>
> But even if the propellant requirement is zero, still neither cheap nor 
> near-term.
>
>  
>
> *From:* geoengi...@googlegroups.com  <
> geoengi...@googlegroups.com > *On Behalf Of *Russell Seitz
> *Sent:* Saturday, May 2, 2020 10:49 PM
> *To:* geoengineering >
> *Subject:* [geo] Re: SRM offset standards?
>
>  
>
> If 0.25 m2  per tonne CO2 is correct as presumed  , ~  10 billion m2, or 
> 10,000 km2 of  relector area would be  required
>
>  
>
> At 1 micron thickness that translates into 1 cubic meter per  km2. 
> assuming  for example' sake a  film with a  density  of   1, 5 , like 
>  graphene strengthened aluminized one micron mylar, that would mean 
> delivering 15,000 tonnes to L 1, not counting frame, deployment systems , 
> thrusters and fuel.
>
>  
>
> As the solar sail force would be on the order of 8 newtons / km2,  a 
>  countervailing thrust of 80kN, or ~8,000 kg would  be required for station 
> keeping. 
>
> Even with solar powered ion thrusters, that would entail a  considerable 
> propellent mass
>
>  
>
> As   the ~ 500 kg Deep Space probe consumed oved 100kg of xenon in the 
> course of three years of generating  at most 86 millinewtons of thrust a 
> linear extrapolation would be on the order of a million times more for so 
> large a solar shade--in  which case station keeping at the L1 would 
> requiresending up the whole sail system's weight in propellant every few 
> years.
>
>  
>
> It's hard to see how its proponents  could underbid  earth-based SRM 
>
> On Friday, May 1, 2020 at 4:15:00 AM UTC-4, 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 geoengi...@googlegroups.com .
> To view this discussion on the web visit 
> https://groups.google.com/d/msgid/geoengineering/2d993063-8375-45c4-a32e-10b2348ff94a%40googlegroups.com
>  
> 
> .
>

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RE: [geo] Re: SRM offset standards?

[Douglas MacMartin]

You don’t need a countervailing force, you just need to displace yourself 
sunward until the forces balance… (though how far depends on areal mass 
density, and displacing too far sunward will require greater area to shade the 
Earth if I recall right).

But even if the propellant requirement is zero, still neither cheap nor 
near-term.

From: geoengineering@googlegroups.com  On 
Behalf Of Russell Seitz
Sent: Saturday, May 2, 2020 10:49 PM
To: geoengineering 
Subject: [geo] Re: SRM offset standards?

If 0.25 m2  per tonne CO2 is correct as presumed  , ~  10 billion m2, or 10,000 
km2 of  relector area would be  required

At 1 micron thickness that translates into 1 cubic meter per  km2. assuming  
for example' sake a  film with a  density  of   1, 5 , like  graphene 
strengthened aluminized one micron mylar, that would mean delivering 15,000 
tonnes to L 1, not counting frame, deployment systems , thrusters and fuel.

As the solar sail force would be on the order of 8 newtons / km2,  a  
countervailing thrust of 80kN, or ~8,000 kg would  be required for station 
keeping.
Even with solar powered ion thrusters, that would entail a  considerable 
propellent mass

As   the ~ 500 kg Deep Space probe consumed oved 100kg of xenon in the course 
of three years of generating  at most 86 millinewtons of thrust a linear 
extrapolation would be on the order of a million times more for so large a 
solar shade--in  which case station keeping at the L1 would requiresending 
up the whole sail system's weight in propellant every few years.

It's hard to see how its proponents  could underbid  earth-based SRM

On Friday, May 1, 2020 at 4:15:00 AM UTC-4, 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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