Proposal: LEO thin film dust cloud to modify direct solar insolation
LEO thin film dust cloud to modify direct solar insolation by jeremyc
Various ideas for directly modulating solar insolation have been proposed to reverse global warming effects. These include:
Atmospheric injection of sulphate aerosols
Mirrors placed in various orbits directly between the sun and earth
Dust rings in equatorial orbit or further out in space such as at the L1 Lagrange point.
Lenton and Vaughn in analysing geoengineering concepts for either CO2 drawdown or mitigation of warming state that "for 2050, only stratospheric aerosol injections or sunshades in space have the potential to cool the climate back toward its pre-industrial state" (2009).
This proposal simplifies the idea of an orbital dust cloud by placing it in a low polar orbit to decrease sunlight in the polar regions and cool them. Caldeira and Wood (2008) analyses the effect of shading northern polar latitudes (using aerosols) to increase the ice pack. A cloud could lead to a positive feedback as ice cover increases reflecting more sunlight.
A polar orbit dust cloud is a simplification because other space based dust cloud proposals require very large industrial efforts in deep space that may not be feasible before irreversible effects occur from warming at earth's poles. Inititial construction could be commenced using ground based Energia sized launches, but with the bulk of the material being delivered from asteroids mined post 2025 using recently announced space mining ventures.
Such a cloud could be intially placed at a height, on a smaller scale, where its orbit could decay within a year or two while its affects are analysed so reducing the risk of unanticipated side effects. Other advantages of a low orbit include:
Less energy needed by space craft intially delivering cloud material from earth's surface
Ability to alter the cloud's shape and coverage as required
Passive control simpler than active control such as needed for mirrors
Near term commencement e.g. from 2020.
Once concurrent efforts to reduce CO2 are successful the cloud(s) can be allowed to decay away.
Reduction and reversal of shrinkage in the Arctic ice cap leading to more sunlight being reflected back into space generating a positive feedback effect.
As the cloud(s) decays particles falling into earth's atmosphere could have a 'second' life by acting in the upper atmosphere in the way that has been proposed for spraying aerosols. This would depend on a number of factors including: how particles enter the atmosphere and their distribution upon entry and their reflectivity.
The most important key benefit is perhaps that a cloud(s) is not permanent and so the project can have a definite life time and or end date to aid in negotiations to bring it about and for financing. It is envisaged that once efforts and projects to bring CO2 levels back to safe levels are successful then this cloud project will no longer be required and it can be progressively reduced in size and finally allowed to decay away.
It is not known at this stage how much it would cost to tow into very high earth orbit or or more asteroids and then excavate and then deliver the resulting material in a steady stream to polar, low earth orbit.
Launching from the ground
List price of the man rated Space X Falcon Heavy lift is $83 million minimum to geosynchronus orbithttp://www.spacex.com/falcon_heavy.phpviewed June 2013) while Energia (also man rated) launch prices are more vague with one quote from 1995 of $120 millionhttp://chapters.marssociety.org/canada/winnipeg/files/lv.htmlviewed May 2013). Its not clear whether this is to LEO or beyond and as well variants of Energia are mentioned when searching using google of up to 200 tonnes in orbit (using 8 boosters).
Man-rating a rocket is said to have an impact on launch costs and in this case all we need is the 1980's concept of a big dumb booster to get dirt or dust up to an orbit of perhaps 300 miles max in the initial stages of constructing a space cloud.
The $120 million will be taken as a starting point for 2013 dollars due to Space X's (desingers of Falcon Heavy) demonstration of costs reductions happening across the launch industry.
$120 million by 100 launches is $12 billion and this would be spread across perhaps 2 to 4 years. On top of this would be administration and research costs and the costs for developing a space based production and delivery operation.
LEO thin film dust cloud to modify direct solar insolation
By: Jeremy Cavanagh