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Comment by dmd | Hacker News Reader

I know you're not being serious, but I like estimating stuff like this.

The biggest solar panel array in space right now, AFAIK, is the ISS at 2500 m^2.

There are currently ~6000 satellites in (any) orbit. Starlink has 12000 more planned. Let's go nuts and say there's gonna be 50000 total satellites.

Let's say ALL of them are as big as the ISS's, ridiculous as that is. And let's say they cast a 1:1 shadow, even though that's also patently ridiculous. I'm just making all of these number as big as possible so nobody can possibly say "no, it's bigger".

2500 m^2 * 50000 = 125 square kilometers.

So with many times the number of satellites planned, with each one being anywhere between 50 and 100 times as big as it really is, with each one casting a shadow as big as it is... we shade - out of the entire planet - an area about 1.5 the size of Manhattan.

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You don't need to cover the whole planet, just the parts under the sun. I'm not an orbital machinist, but maybe we could park just enough blockers in an orbit that's always between the sun and Earth to halt the warming. How much of the sun would need to be blocked to bend the curve down? Everything necessary on the ground to stop putting CO2 in the air is already underway. All we need is more time.

This is something that's been considered, particularly for doing things like terraforming Venus. There are these areas called Lagrange points[1] that provide a location where one can park a satellite where it'll remain stationary relative to the two-body system of interest. The point directly between the sun and earth is the L1 point and allows you to place a sunshade such that it'll always be directly between the sun and earth. It should be noted, however, that these points are generally not stable and so require some degree of station-keeping to remain viable long term.

[1] https://en.wikipedia.org/wiki/Lagrange_point

A solar shade would also be a solar sail -- it could maneuver by changing its shape to catch the solar wind differently. It would still need to station-keep (perhaps even more because of fluctuations in solar wind), but it wouldn't need to use propellant.

Can you tack in space?

The moon has the perfect size already. We just need to nudge it around a little bit to provide some local shade. Solar eclipse on demand, how hard can it be?

You know, you might be on to something. Set up a mine to blast rock out from the moon to create a ring at a higher orbit to block the light. The moon will eventually scoop it all back up as it continues its trip away from the planet.

There has been some research on this: https://en.wikipedia.org/wiki/Space_sunshade

It's interesting how cheap it can be done ($20B-$200B), which may be $1T in real life, but that's still cheap compared to the programs the governments are running.

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