Comment by cletus | Hacker News Reader

Comment by cletus | Hacker News Reader

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So there a few comments scattered around about this so I'll address those concerns here. Quite a few people are scoffing at the idea of colonizing Venus ("you'll get crushed, dude!") but the idea has had a lot of people put thought into it and it's not as impractical as you may think. Consider:

1. Venus is easier to reach than Mars. The Delta-V is 0.4km/s and 0.7km/s respectively [1];

2. Mars has practically no atmosphere and really low gravity. It's really not that much better than colonizing the Moon but a whole lot further away [2].

3. You wouldn't live on surface of Venus, at least not initially. You'd live in the atmosphere [3].

4. Energy will be plentiful on Venus, far more than on Mars or even the Earth, just from solar energy. [4]

5. Venus has nearly Earthlike gravity.

So it's actually not as crazy as you might think and shouldn't be immediately dismissed.

[1]: https://space.stackexchange.com/questions/2156/does-a-missio...

[2]: https://qz.com/1105031/should-humans-colonize-mars-or-the-mo...

[3]: https://www.youtube.com/watch?v=BI-old7YI4I

[4]: https://www.extremetech.com/extreme/196114-nasa-is-developin...

I enjoy Isaac Arthur's YouTube channel where he explores topics like colonizing Venus. Here's the video: https://m.youtube.com/watch?v=BI-old7YI4I

Goes to get a snack.

> Venus is easier to reach than Mars. The Delta-V is 0.4km/s and 0.7km/s respectively

I'm not sure where those numbers are coming from. The Δv for reaching low earth orbit is already on the order of 10 km/s.

https://en.wikipedia.org/wiki/Delta-v_budget

Presumably these delta-v numbers are from some form of earth-orbit. These tend to make a lot more sense, because getting to LEO is mostly not about orbital mechanics, which is where delta-v is the most useful concept.

That said, looking at that wikipedia page these numbers don't match up with any kind of LEO-mars or LEO-venus transfer. Numbers seem to be off by an order of magnitude.

It's complicated:

https://en.wikipedia.org/wiki/Delta-v_budget

But no matter how you slice it, Venus is easier to get to than Mars, if for no other reason than that aerobraking is a lot easier when your destination has a thick atmosphere so you don't have to carry as much propellant for orbit insertion.

Mars has more than enough atmosphere for aerobraking on arrival (see all mars landers). After that, for subsequent orbit lowering, the density of the atmosphere doesn't matter as you only ever use the upper wisps anyway.

No, aerobraking at Mars is very difficult. It is used for orbit lowering but not for insertion. See e.g.:

https://mars.nasa.gov/mro/mission/timeline/mtmoi/

https://www.space.com/2439-tricky-task-aerobraking-mars.html

The reason is that you can do lowering incrementally across multiple orbits, but insertion requires a huge delta-V on a single pass. It might be possible in principle, but the engineering challenges are daunting. I don't believe it has ever been attempted.

>>It is used for orbit lowering but not for insertion.

It is not used for insertion of orbiters because strapping some rockets to them is easier/lighter than the heat shields and other equipment that would be needed for braking. They would also have to retract solar panels and do a bunch of other things. The martian atmosphere is more than thick enough to handle the ~1km/s for insertion. All the landers shed more than that (3km/s) on entry from orbit, a maneuver that only uses 1/2 the braking potential of the atmosphere.

OK, well, like I said originally, it's complicated.

Here are some more details:

https://space.stackexchange.com/questions/37250/is-aerobraki...

Turns out there's a distinction between aerocapture (which is possible but has never been done) and aerobraking (which has been done but it not common).

https://en.wikipedia.org/wiki/Aerocapture

So I guess I have to concede that my original claim about Venus being easier to attain because of its atmosphere was probably wrong.

But there is a place where you are correct. Atmospheric density does put an upper limit on payload density. Mars can slow down objects the size of cars or large trucks. But for very large things the heat shield needed to create enough drags becomes huge.

Think the scene from "2010: The Year We Made Contact" where very large spacecraft aerocaptures in Jupiter's atmosphere. That probably wouldn't be possible at mars, not without hitting the ground. Or 'Independence Day'. Those giant spacecraft arriving at earth surrounded by fire could not possibly have aerocaptured/braked in earth's atmosphere.

I believe humanity will colonise the open space way, way earlier than it would colonise another planet.

Really, if you are already in space with all that infrastructure, and economy needed to support settlement on another terrestial body, you would have to already have at least few megalopolises in the orbit.

Why? You don't have in space anything which you didn't bring there from a surface. On a planet you have resources at least. Also you have radiation shielding and no necessity to tie all small things from floating away.

In order to make anything in a space station, you have to bring something from outside. Not so on a planet.

The point is one of bootstrapping. IF you must build up a critical mass of space-based infrastructure in order to colonize a planet - do you still need to colonize the planet, or just continue on with the space based infra? Especially if you can capture sufficient resources from the asteroid belt.

Capturing resources from asteroids could be more expensive than from the planet, given the infrastructure on the planet.

So you may make an investment - spend initially to make a planet base, then enjoy smaller expenses.

Maybe the question is of comparison - how big space infrastructure one need to colonize the planet comparing to returns from planet base. Is it obvious that planet returns are smaller?

Considering the difficulty of aerial operations on Earth (namely balloons/zeppelins are vulnerable to weather and using airships as aircraft carriers extremely risky and tricky) I think you're underselling the practical difficulty of living in the Venusian atmosphere. We should be able to master these matters on Earth before trying it on another planet.

Agreed. One interesting idea in my mind is to colonize the oceans. Floating ships with agriculture.

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