Its a boondoggle if it doesn't work an isn't needed and overpriced.

It will work,
It is probably needed, but should consist of venetian blinds to vary
the amount of sunlight admitted.

Is it worth the cost? Well, if its cheaper than getting off oil, if
we can do it quicker than getting off oil - maybe.


Lets do some engineering calculations...

In the Aug 2008 press release they say a 2% reduction in sunlight is
needed. I'd like to see the heat balance calculation for that, but
let's go with that for now, realizing that if we build a venetian
blind system we can vary the amount of sunlight as sunspots change and
so forth.

First where will be put it? At the point between the sun and Earth
where gravity is equal. Where is that? L! - lagrange point 1 -
between Earth and Sun.

distance to L1 from Earth is calculated by

r= AU*(Mearth/Msol)^(1/3) = 1,500,000 kilometers.

Now the angle subtended by the sun is

arcsin(Dsol/AU) = arcsin(1,392,500/150,000,000) = 0.53 deg

Now, to reduce the solar output by 2% requires that 2% of the solar
disk be obsurced by a reflective film. This means that the disk must
subtend 14.142% of the entire sun. That's 0.0752 degrees.

That means a disk stationed along the line connecting the sun's center
to the Earth's center located at L1, using sunlight and solar wind
along with solar energy to maintain its position and operate it, must
be

Dmirror = RL1 * sin(0.0752) = 1,969.3 km

in diameter That's 3.045 million sq km.

GBO film - is 99.999% reflective and operates even when 5 microns
thick.

GBO reference
http://www.scienceonline.org/cgi/con.../287/5462/2451

Alright, the plastic that the GBO film is made from masses about 1.4
metric tons per cubic meter. 5 microns is 5/1,000,000th of a meter
thick, so, 200,000 sq meters - or 0.2 sq km - masses 1.4 metric tons.
An inflatable structure using very low pressure gas - has been used to
stabilize structures in space

http://www.astronautix.com/craft/echo.htm

So, the film is the dominant mass. So, 3,045,948 sq km mass
21,321,637 metric tons - around 22 million tons of film.

This is 3x the annual production of ALL plastics. Oil is used
primarily for plastics production. About 0.2% of the world's oil
production is used to make plastics. We could easily increase the
output of the plastics industry by 10% to build this area in 30
years. Assuming a longevity of 30 to 50 years - this would be a
permanent fixture - and would provide revenue to the oil industry, as
we lowered use of oil in other ways. That is, as far as oil is
concerned, we would be diverting from adding it to the atmosphere and
putting into the sunshade.

All we have to do is put the sunshade element in low earth orbit,
inflate it, and use solar sailing techniques to navigate it to L1 and
keep it there. It would be a cool thing to do for a Space Shuttle
flight.

I had mentioned a reusable Heavy Lift Launcher built around Shuttle
hardware that consists of 7 reusable ET tanks with advanced TPS. Put
together in parallel, each ET with 6 RS68 pumpsets 42 in all - feeding
an aerospike engine under each - 7 annular aerospikes in all with fold
away wings and cross-feed.

Looking down from the cluster of ET tanks we number them as follows

(1)(2)
(3)(4)(5)
(6)(7)

1 and 6 feed 3
3 feeds 4

2 and 7 feed 5
5 feeds 4

All fire at lift off, 1,6,2,7 drain - that's the first stage.

When empty, 1,2,6,7 drop away, re-enter downrange, slow to subsonic
speeds, an deploy their wings. There, using GPS they each rendezvous
with recovery planes downrange and are snagged with a towline mid-
flight. Each are then air-towed back to the launch center and
released for landing.

Meanwhile

(3)(4)(5)

continue onward toward space.

3 and 5 feed 4

3 and 5 are drained while all fire.

This is the second stage.

When empty 3 and 5 fall away and are recovered like the first four.

4 continues on to orbit until empty.

It attains orbit, and ejects the inflatable reflector.

Then 4 deorbits and is recovered as the other six are.

The entire system is 100% reusable - and improved checkout and
automation at the launch center reduces the standing army needed for
the Shuttle - to a bare minimum. Launch costs are les than $5 million
per flight - the amount lofted to orbit is 550 metric tons!! This is
110 sq km of solar reflector per launch! At $2,000 per ton, that's a
million per satellite. Lets budget another $$ million per satellite
for other costs associated with it. A total of $10 million per
launch.

So, 27,690 launches are needed for the entire system - and a cost of
$276.9 billion. Over 30 years that's $9.23 billion per year. A
launch every 9.5 hours.

With seven elements per launch vehicle, and 14 day cycle time, 35
vehicles - or 245 launch elements are needed, add 5 spares that's 250
- each capable of 1,000 launches - each costing about $100 million -
that's $25 billion for the launchers - and a $15 billion non-recurring
engineering charge - a total of $40 billion to get started

So, a 5 year program that peaks at $9.23 billion per year - would get
us started, and continue at $9.23 billion per year forever - as the
sheets wore out over 30 to 40 years - slight variation in the
production rate would grow the array as needed until we got things
under control.

We could take older reflectors and use them as solar sails to send
paylods throughout the solar system - at the end of their ueful lives.

50 ton Payloads would be carried with new reflectors to L1, an then
old reflectors replaced, while the payloads transferred to them.

Or old reflectors would sail back to LEO to hook up with payloads left
there as the new reflector pass through.

So, this is a quite doable program - well within our capacity to
achieve.

The world burns about 28 billion barrels of oil each year. A $0.50
per barrel reflector tax would generate $14 billion per year - and pay
$4.4 billion in overhead and administration, and $9.6 billion in
program costs. $2 billion might go to space research to build
research payloads and other applications of the boosters - for mars
missions and so forth.

This adds to the value of the program in my view.