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Comment by p1mrx | Hacker News Reader

When you can resolve territorial borders and labels, that's a pretty strong sign of intelligent life.

Jokes aside, if they have artificial lighting, it should be visible.

Holy smokes, when I saw the resolution I got excited. When I read this, I went wow!!

And the reason we as a society aren't doing this already is what? This thing should be consuming a percent of two of US GDP until it's done.

I think this mistakenly assumes that tax money is spent on the things that are a priority to the society that pays the taxes. This is not how tax money is allocated at all.

> And the reason we as a society aren't doing this already is what?

Because you have to park it 900AU away from the sun (Voyager 1 is at 147AU after 40 years and not in a solar orbit) and it has to have a special kind of coronagraph that flies as a separate spacecraft from the telescope (hasn't been invented yet) and your telescope is limited to looking at objects directly opposite the star from the orbit of the spacecraft. At 900AU it would take decades to slew such a telescope to view a new object in the sky.

At the current time this is basically a science fiction project that promises that if we put a very special spacecraft in a very specific place then it is within our technological capability to image an exoplanet. That doesn't mean it's even a remotely practical idea. It's interesting to talk about but useless to get all worked up about why it's not getting funded.

Indeed, there are a lot of engineering challenges related to the distance. Solar power is much, much dimmer at 900 AU -- that's like 20x Pluto distance -- so you'll need to bring something like an RTG. But your RTG will decay while the spacecraft travels (Voyager's RTG has already lost 30% of capacity). Once there you'll need a lot of power to transmit data the back with any sort of speed or reliability. All of this is on top of the usual telescope-reliability concerns; in many ways it would make the James Webb telescope mission look straightforward.

This is one of the reasons for papers such as this one: exploring what meaningful solutions to these problems, and meaningful mission profiles, would actually look like in practice.

> All of this is on top of the usual telescope-reliability concerns

I'd hope less of a risk of micrometeorites (though it would have to look on its own for incoming projectiles and take evasive action). Then again, 900 AU is in the middle of the Oort Cloud so perhaps there's a lot of small junk out there too.

> But your RTG will decay while the spacecraft travels (Voyager's RTG has already lost 30% of capacity).

So just bring 50% more? I don't think the weight of the Pu-238 is a key limiting factor on this mission.

I'd rather put the money into solving climate change so we're around long enough to meet the other society!

I've been told that some national borders make it clear about the difference attitudes toward the environment. That is, one side of the border is filled with trees and the other is denuded by a population that doesn't think in the long term and simply trashed the environment.

That kind of difference might be visible through one of these telescopes, especially if the border is long.

Yea that's a good point. The classic example is Haiti and the Dominican Republic, where the DR has trees on the border in contrast with often a bare landscape just on the other side.

Though I've heard this is actually overstated.

You can see it more clearly on the Israel-Egypt border

I think that's just different sources of imagery with different lighting. At some zoom levels it's more or less apparent, and it's mostly the same desert on both sides: https://www.google.com/maps/@31.03477,34.3411577,15440m/data...

You can see the national borders of DPRK from space at night.[0]

[0] https://www.npr.org/sections/thetwo-way/2014/02/26/282909885...

Night sky must be great in NK!

There's also the less prominent East/West Berlin border which is still visible due to the different light bulbs used in the different format street lights.

https://www.businessinsider.com/divide-between-west-east-ber...

West Berlin still has gas light, slowly transitioning to LED.

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