Low Mass Space Mirrors for Global Warming

The idea of reflecting sunlight using mirrors at the Earth-Sun L1
Lagrange point is well established. It appears to be based on
manufacturing mirrors on the Moon from refined regolith and launching
them for assembly at L1: this is to reduce the launch costs of a
massive mirror needed to deal with global warming.

But has consideration been given to launching very low mass mirrors
directly from Earth? Large mirrors (say 100m diameter) made from thin
reflective sheet (like space blanket) could be launched directly from
Earth. The problems arise when you try to wallpaper a vacuum with
them and then maintain their shape, orientation and position. A
rotating space-station, similar to that in the film 2001 could be used
for this purpose. The reflective sheet would be unfurled across the
sunward face of the space station and the rotational forces would
stretch and maintain the mirrors shape, keeping it rigid. Once the
mirror was stable the space station would detach and move on to the
next piece of vacuum to be wallpapered, leaving hundreds of spinning
mirrors in its wake.

Two types of mirror might be considered. A “passive mirror” would
float away to be recovered and reused once out of position. To
maintain its orientation it could be convex shaped against the solar
wind and it might initially be launched against the solar wind using
puffs of thruster gas from the space station to extend its life. A
better option would involve an “active mirror” having a number of
solar-powered miniature ion-thrusters installed around its outer
edge. These would maintain the mirrors rotation, orientation and
position in space. This would avoid (or at least reduce) the
hazardous activity of recovering out-of-position mirrors.

Active mirrors would be flexible and might be useful in Earth orbit to
reduce warming, manipulate the weather and even replace street
lighting in urban areas. At Lagrange points L4 and L5 they could
reflect sunlight towards Earth in the event of cooling brought on by
natural disaster (volcanic eruption or asteroid impact). A spinning
Earth orbit space station built for scientific purposes could include
facilities to unfurl mirrors at relatively little extra cost. An
entire fleet of low mass mirrors sent to this station might require
less launch capacity than is needed just to build a Moon base and
could be a flexible and relatively low cost means to control global
warming.

John Hampson

John Hampson wrote:

But has consideration been given to launching very low mass mirrors
directly from Earth?


One idea, which is hard to beat for simplicity, is to launch millions
upon millions of helium or hydrogen-filled chromed super-pressure
balloons into the upper reaches of the atmosphere, where they would
hover for years on end reflecting sunlight back into space.
Unlike conventional balloons, super-pressure balloons maintain the same
gas volume during there whole flight to altitude, and therefore end up
flying at a fixed maximum height once they reach it.
Small super-pressure balloons have already flown flights of over 700
days duration.
All-in-all, this sounds a lot easier and cheaper to do than building
giant mirrors in space, either from Earth-launched or Lunar-mined materials.

Pat