[forapurpose]

I wait and hope for someone with more planetary knowledge than I have to explain the lack of interest in Venus as a habitable planet and thus the center of NASA's attention ahead of Neptune, Uranus, and of course, Mars.

Based on what I've read, which includes a paper from a NASA (or was it JPL?) engineer, Venus' surface is not very hospitabl, but at a certain altitude it looks like an oasis in the Solar System:

Venus (at ~50-55 km altitude) / Mars (surface): (all stats from Wikipedia, and yes not always complete or comparable)

* Gravity: 0.9G / 0.38G

* Pressure: ~1 atm / 0.00628 atm (prevents liquid water)

* Temperature: 27-75 deg C / -63 deg C (mean)

* Shortest distance from Earth (for logistics): 40M km / 55M km

* Sunlight (energy): More than Earth / 43% of Earth

Also, oxygen and nitrogen are lighter than the CO2-heavy atmosphere, so a balloon of O2 and N2 would float conveniently at 50 km. The CO2 in the atmosphere also could be a valuable resource.

[vlovich123]

I'm not an expert, but the wikipedia page alone doesn't paint that bright a picture.

> Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid.

We know very little about it. Also, I'm sure you'll need to coat any probes/spacecraft to protect against the sulfuric acid.

> The water has probably photodissociated, and the free hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field.

So basically same chance of water (maybe worse) as Mars.

> Venus (at ~50-55 km altitude)

So we'd have to have floating habitats even if we knew this zone was actually habitable (it's still a sulfurous environment). This also means much higher energy costs along with other logistical challenges.

> Shortest distance from Earth (for logistics): 40M km / 55M km

Yeah, but you're fighting solar winds so the question is how much less are the energy costs. Also, from a logistics perspective, communication might be important & the unfriendly atmosphere may pose additional challenges/costs.

[cstross]

However, an interesting aspect of floating habitats in the Venusian stratosphere is that a terrestrial breathable gas mix (80% N2 / 18% O2 / 2% trace others) is a lifting gas that's about as effective as Helium here on Earth. (Venus's atmosphere is > 90% carbon dioxide, which has a significantly higher molecular weight than air.) And it's protected from solar UV and radiation to a considerable extent by the layers of atmosphere above it. So your entire balloon -- or, more likely, dirigible airship -- can be inhabited volume, rather than just a cramped gondola slung underneath.

Photovoltaic power might sound problematic at first in view of the long Venusian night (a single day lasts up to 116 Earth days), but at altitude there are strong jet streams and winds circulate around the equator roughly every hundred hours. So you're not stuck running on battery power for months on end, but you may need some maneuvering capability.

This is not to minimize the problems associated with activity in the Venusian atmosphere -- but it's not quite the impossible hell-hole it's been portrayed as.

[TheOtherHobbes]

You'd be floating in a haze of CO2 and sulphuric acid garnished with hydrogen sulphide, battered by raging convective winds which would make it very hard indeed to stay at a fixed altitude - which means the outer temperature would fluctuate by 10C to 50C or so without massively powerful altitude control.

You can't just drift there as if you're in a hot air balloon eating sandwiches and enjoying the view.

Venus might not be completely impossible, but it's still one of the less hospitable destinations in the solar system.

Also, smelly because of the H2S.

[azernik]

On the other hand, Mars requires you to live in a radiation-shielded pressure vessel.

I think the real killer is that it's hard to build and maintain infrastructure when floating on balloons - much easier to run a spaceport on Mars, or to get to all the useful surface resource deposits. On Venus you'd have to build literal castles in the air, using only only what you can pull out of the atmosphere or ship in from orbit.

Not to mention Mars is at the bottom of a much shallower gravity well.

[azernik]

Solar wind is a negligible factor in the trajectories of large-payload rockets - it's more of a radiation hazard that any interplanetary crewed mission has to deal with.

[justaaron]

It's not the solar wind I'm worried about re: uranus. The wind I'm concerned with portends very large payload rockets immanent arrival trajectories. It's definitely stinkier than any hazard any interplanetary crewed mission has had to deal with, hitherto.

[elsonrodriguez]

I can't speak to Neptune or Uranus, since they are so far out that even Jupiter and Saturn begin to feel more compelling due to Europa and Enceladus.

But in the debate about Mars vs Venus, for me two things stand out:

- We can kick off a Mars terraforming project with our current level of technology. I've heard it said that within a few hundred years we can get it so that all you need outside is thermal protection and an oxygen mask. Reversing the situation on Venus will basically take Star Trek level tech.

- You can leave your habitat on Mars, get some rocks, and pile those rocks up to make more habitat. On Venus, you will have to basically "drill" down to the surface to recover any materials, and I don't think you can easily build dirigibles out of rocks and atmosphere as easily as you can build a hut.

[jakeogh]

Outward Bound: Colonizing Venus: https://www.youtube.com/watch?v=BI-old7YI4I

Caution: don't click unless you have nothing else to do today.

[dizzystar]

I hope this is connected, but how much oxygen would it take to sustain these craft? A cursory look seems to suggest that the ISS generates oxygen from water electrolysis, which generates about 20lbs of oxygen a day.

The big difference is you can fire off a rocket and get water to the ISS in comparatively shorter time and less fuel, which makes it feel much more challenging to get in the sky of Venus.

I obviously have no idea what I'm talking about here, but I'm thinking the continued challenges of floating -vs- hard ground will be very high. Plus we don't really have any direct experience with that, right?

[Symmetry]

Water is on the order of 50 parts per million in that part of Venus's atmosphere which is pretty dry compared to Earth but still straightforward to extract from the air. In Venus's atmosphere you basically have all the Hydrogen, Nitrogen, Carbon, Oxygen, Sulfur, and Argon you need and pretty good access to Helium, Neon, Chlorine, and Florine. It's everything else that's the problem, like Silicon or metals.

[InclinedPlane]

There is practically no advantage to living on Venus other than that you get gravity. The only local resources available are the atmosphere, and you need to create a floating habitat that is also an interplanetary spacecraft port. Frankly, that's actually pretty far outside our realm of technology at present.

Mars has many more advantages in comparison. For one you can build on the surface of the planet. There are many resources on Mars that can be exploited almost immediately and many others that can be exploited over a longer term: the atmosphere can be used to help produce rocket propellant, water can be used to aid in that as well. Things like iron/steel, glass, plastics, concrete, etc. can all be produced on Mars with a minimal industrial base within the first decade of colonization, with increasing quality and throughput over time. These things are important because they significantly advantage Martian colonies in terms of their ability to be partially self-sufficient and partially self-reliant in regards to expansion.

On Venus practically every ounce of material in the colony needs to be shipped from Earth, it's scarcely better than an orbital station. On Mars you can rely on local supplies for water, for propellant for the return trip, for fuel and oxidizer for ground machinery (mining vehicles) and emergency backup power. You can grow crops using Martian sunlight, Martian CO2, Martian water, Martian Nitrogen, and Martian soil. You can use solar energy for power and sunlight to grow crops as on Earth, the lower light levels are slightly misleading, Mars doesn't have routine cloud cover and has a thinner atmosphere so the average amount of watt-hours per area per day on Mars are very similar to what they are on Earth. You can use regolith for radiation shielding and in construction (building roads, for example). You can manufacture concrete, steel, glass, and plastics using local materials so that you can begin building things like habitats, industrial facilities, etc. using substantially locally produced materials while relying on Earth-produced components for only a subset of the mass of the things that get built, and an ever decreasing subset at that.

A Mars colony would be one that should grow in size and capabilities by leaps and bounds year over year as local industry and agriculture ramps up, as exploitation of local resources increases and improves, as techniques for making use of those local resources scale up and become increasingly sophisticated.

Venus just doesn't rate in comparison. Nobody has a design for how you'd build a floating habitat on Venus that would be reliable enough to trust for decades. One that could also serve as a spaceport for spaceships.

We have the technology to tackle Mars colonization now, it only requires following through on doing it. And Mars has the resources to make colonization a feasible concern that increases its ability to support a population, increases its level of technological sophistication, increases its industrial and agricultural base substantially every year, year after year, indefinitely. That's why Mars is such an attractive target. You can plant a civilization there in a way that you can't, with our level of technology, on the Moon or Venus.

[forapurpose]

> There is practically no advantage to living on Venus other than that you get gravity.

Ambient pressure is a huge advantage: Liquid water doesn't boil away,

[InclinedPlane]

That just means you can build your pressure vessels much lighter. But you can't not have your habitat built out of pressure vessels, people can't breathe pure CO2.

[lostgame]

>> and you need to create a floating habitat that is also an interplanetary spacecraft port. Frankly, that's actually pretty far outside our realm of technology at present.

You just pretty much described the ISS, but I get your point. That's in orbit around Earth. :P

[InclinedPlane]

The ISS isn't floating, it's in freefall. We've been doing rendezvous in freefall for half a century. Launching out of a deep gravity well at 0.9g means a rocket operating with a tremendous amount of thrust and a launch pad (or area) for the rocket to take off from. Making a precision landing through atmosphere from interplanetary cruise onto a floating platform is also very difficult. SpaceX has managed to achieve something similar but much less challenging and with much lower stakes and it requires a vessel that uses thousands of tonnes of concrete and steel.

[Symmetry]

There are advantages to each and solid ground can be pretty useful. But Selenian Boondocks did an excellent series on how use Venus's resources a while back which I really have to share.

http://selenianboondocks.com/category/venus/page/2/