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With all the speculation of manned missions to Mars, there is very little talk of a manned mission to Venus (whose orbit is closer to the orbit of Earth than mars is). That being said, would it be easier to put humans on Venus? If so, how & why?

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    $\begingroup$ Perhaps you should enlighten up what you consider "putting humans on Venus" and a chosen measure of relative "easiness". $\endgroup$ – Mithoron Aug 17 at 14:07
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    $\begingroup$ In particular, are you talking about just "delivering a human payload to that location" or also keeping them alive? $\endgroup$ – chrylis -cautiouslyoptimistic- Aug 17 at 18:19
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    $\begingroup$ @J..., yes, but then it stops being easy... $\endgroup$ – I'm with Monica Aug 17 at 19:43
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    $\begingroup$ Have you done any research about Venus at all? It's a hellish nightmare. Mars is just cold and dead. $\endgroup$ – user91988 Aug 18 at 14:21
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    $\begingroup$ Venus is a terrible place. (Source: Obligatory xkcd.) The summary: "Unfortunately, X-Plane is not capable of simulating the hellish environment near the surface of Venus. But physics calculations give us an idea of what flight there would be like. The upshot is: Your plane would fly pretty well, except it would be on fire the whole time, and then it would stop flying, and then stop being a plane." $\endgroup$ – reirab Aug 19 at 10:41
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Technically, yes, it would be easier to put people on Venus. You need less of a kick for the interplanetary trip and slowing down is trivial with that dense atmosphere...one of the Pioneer Multiprobe sub-probes made a soft landing despite only being designed as atmospheric probes.

However, the surface temperature stays close to 464 °C, with over 90 atmospheres of pressure. There's no way we could keep someone alive more than perhaps a few hours, and rockets will be practically non-functional under those conditions. Landing would be a death sentence. You might live longer by deploying a balloon that keeps you in the upper atmosphere, but Venus is nearly as large as Earth, and leaving it would require a rocket as big as the one you used to reach it, except launched from the upper atmosphere. This is far beyond our current capabilities, so you'd only be delaying your trip to the surface.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage Aug 18 at 11:32
  • $\begingroup$ Actually the HAVOC mission plans to fly a crew on an airship within Venus' atmosphere and launching them back from Venus in the same craft. So "far beyond our current capabilities" is wrong. An airlaunch is much more efficient and on Venus more doable anyway. youtube.com/watch?v=bcHkWKp9e4Y $\endgroup$ – Giovanni Aug 20 at 8:02
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    $\begingroup$ @Giovanni HAVOC is a concept outlining the capabilities we would need to develop in order to put people in the atmosphere of Venus and bring them back. We are currently at the level of doing studies for determining how we might perform the earliest robotic missions. None of it is actually planned. $\endgroup$ – Christopher James Huff Aug 20 at 12:25
  • $\begingroup$ @ChristopherJamesHuff Perhaps a crewed flyby mission with Artemis' Orion should be performed first. Like the one concepted for Apollo. $\endgroup$ – Giovanni Aug 21 at 6:05
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As others have already pointed out, getting humans to Venus would be marginally easier than getting them to Mars.

Let's consider survival on Venus in a little more detail though. Although there haven't been any manned missions to either Mars or Venus, there have been unmanned missions to both. So let's consider how long those unmanned missions have survived.

The United States has sent four rovers to Mars.

  1. Pathfinder was active on Mars from 4 July 1997 until communication was lost 27 September 1997. That gives a little under 3 months during which it was in active use.
  2. Spirit was active from 4 January 2004 through 22 March 2010, for a total of more than 6 years.
  3. Opportunity landed 25 January 2004 and remained operational until 10 June 2018, for a total of almost 15 years.
  4. Curiosity landed on Mars on 6 August 2012, and remains operational today just over 8 years later.

So, 3 months minimum, and 15 years maximum (so far), though Curiosity could pretty easily set a new record.

Now let's consider Venus. The two longest lasting probes were Venera 13 and 14, both launched by the Russians. Venera 14 lasted only 57 minutes. Venera 13, however is the record holder: it lasted a whopping 127 minutes. Even being generous and rounding up, that gives a total of 3 hours and 5 minutes between the two of them.

Given Venus' atmosphere, lasting almost an hour was an impressive accomplishment and lasting two whole hours was almost mind-boggling. People who've studied them probably have ideas about how to design something better--but even so, I doubt even the most cocksure young whippersnapper would be bold enough to claim that they could design something that would last a whole day, not to mention lasting for months.

Summary

Mars may not be the most friendly place anybody can dream of, but it's absolute paradise compared to Venus.

Reference

https://www.space.com/18551-venera-13.html#:~:text=The%20Soviet%20Union%20sent%20three,information%20between%201983%20and%201984.

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    $\begingroup$ Real numbers and actual experiments put things in perspective, interesting contribution. $\endgroup$ – Exocytosis Aug 18 at 9:03
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    $\begingroup$ Minor note. It is likely that the Venera missions actually lasted a bit longer, except the spacecraft that was relaying their signals went over the horizon. Still, we are talking at most another hour or two, far from a day... $\endgroup$ – PearsonArtPhoto Aug 25 at 13:18
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The atmospheric pressure of Venus would crush any human. Mars would therefore be a slight more hospitable. It may be red and dry, but it doesn't rain acid!

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  • $\begingroup$ This is a good point! Presumably "put humans on Venus" includes doing it in a way that allows them to stay alive for a while :-) $\endgroup$ – uhoh Aug 18 at 0:33
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    $\begingroup$ Don't worry, you won't get rained on if you're on the surface of Venus. The ground level temperatures are much too high for sulfuric acid to be liquid, it all evaporates well before it reaches the ground. $\endgroup$ – Christopher James Huff Aug 18 at 2:12
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    $\begingroup$ Note though that the pressure would not crush you, unless you were rapidly exposed without a chance for your body to come to equilibrium. It's fluid pressure, applied equally from all directions, and bodily tissues are basically incompressible. The problems are more to do with gases dissolving in your blood and reaching levels that have toxic or narcotic effects...surface pressures are somewhat higher than those encountered in the deepest dives ever done on Earth. $\endgroup$ – Christopher James Huff Aug 18 at 2:29
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    $\begingroup$ While it is a gas, at the pressures at the surface, the atmosphere is so dense it's perhaps better to think of it as a liquid for these purposes. Even assuming some magical material to construct a spacesuit out of, walking through the atmosphere would be as much work as walking underwater on Earth is. And breezes would knock you over like a truck. $\endgroup$ – Exasperation Aug 18 at 17:14
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    $\begingroup$ @ChristopherJamesHuff In a twist that should surprise nobody, there doesn't seem to be a whole lot of active research on the bulk modulus of human flesh. I'm probably on several watchlists now for searching that. $\endgroup$ – probably_someone Aug 19 at 23:55
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While Mars is more expensive to reach than Venus (it requires more delta-v, thus your payload-to-fuel ratio is smaller on a Mars mission than a Venus mission, everything else being the same), we have all of the technologies needed to put humans on Mars and sustain them for a substantial period of time. Sure, we have to build the spaceships and refine some technologies for adaption to Mars, but there's nothing substantially new required.

Venus, on the other hand, requires new technologies to be developed before we can put humans anywhere inside its atmosphere. Building a base on the surface would require exotic construction materials and techniques that we don't possess. Floating a base in the upper atmosphere would be easier (it would basically be a giant airtight blimp with a human-friendly atmosphere in the cabin), but it would have to be capable of launching rockets back into space again (at least into low-Venus orbit to rendezvous with a spaceship capable of returning to Earth), and "landing" them back on the base again, which is outside our current capabilities for the moment (maybe not far outside, an air-launched rocket could do it, maybe something like Virgin Galactic's White Knight).

In the short-term, Mars has more interesting science goals, because we have good reason to believe that there was once liquid water on its surface, which could have hosted some form of primitive life before the atmosphere was lost and the water boiled away. While Venus could also have had liquid water in the past, its entire surface was "repaved" in a cataclysmic event in the geologically-recent past, which would have erased any signs of life that might have been there. Venus' surface is also so much more inhospitable than Mars' that doing any research that requires a human presence on the planet is not yet technologically feasible.

In the longer-term, when these problems have been solved, Venus is perhaps a more viable candidate for human colonization than Mars. Venus' surface gravity is much closer to Earth's than Mars' is, so the long-term health effects of living in a low-gravity environment are likely to be less on Venus (if they are even a problem there at all) compared to Mars. You also get the benefit of Venus' atmosphere for shielding against cosmic rays and radiation from the Sun.

TL;DR

Yes, when sending a payload to Venus, you need less delta-v. That means you can do it with a larger payload-to-fuel ratio than a Mars trip. The total travel time is also shorter, so you less of your payload is dedicated to life-support for the crew on the trip there and back, so your mission payload mass can be larger. But until we have significant technological advancements, there's nothing we need humans for on Venus, while Mars allows us to do more science than we could with just rovers.

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  • $\begingroup$ FWIW, there was an Apollo-era proposal to do a manned Venus flyby mission: en.wikipedia.org/wiki/Manned_Venus_flyby If you can do that, then of course you could use aerobraking to actually enter the atmosphere, though I'm not taking bets on whether the occupants of a manned spacecraft would survive long enough to reach the surface. $\endgroup$ – jamesqf Aug 19 at 0:29
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    $\begingroup$ Yeah, getting humans to Venus isn't the problem, it's getting them back alive. $\endgroup$ – asgallant Aug 19 at 3:34
  • $\begingroup$ Would landing on a blimp in Venus’ upper atmosphere be that much harder than landing on a barge in the ocean? One could even catch the rocket in mid air like RocketLab is planning for their Electron. I think deploying/construction the blimp would be the hardest part and relatively pointless since there are no resources to exploit and you are stuck in yet another gravity well (a space habitat in Venus’s orbit would be easier). $\endgroup$ – Michael Aug 19 at 7:05
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    $\begingroup$ Building a blimp (or similar neutral buoyancy craft) that is stable enough to serve as a launch and landing platform for rockets feels outside our current capabilities to me, but maybe someone with knowledge of airship construction could prove me wrong. Catching rockets might be viable in the near future, but you'd better be really damn good at catching them if you want to catch rockets with human passengers. $\endgroup$ – asgallant Aug 19 at 15:19
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There are some concept missions for manned missions to a high altitude city/research station using balloons. https://ntrs.nasa.gov/citations/20160006329 (Thanks to @eps to finding the reference)

At the high altitude the temperatures and pressures are not so crazy. However the difficulty of constructing a site and have rockets landing and taking off is tricky. Another question is how useful would such as mission be where they cannot reach the surface, the crew could better control remote probes that were sent down from their balloon station. But again while Venus is less understood than Mars we understand it to be less interesting for a was there life on the planet perspective. It was possible Venus was much nicer in the distance past but the current conditions would likely have obliterated much of the evidence.

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    $\begingroup$ So, is your answer to the question that was asked yes or no? $\endgroup$ – Organic Marble Aug 18 at 12:51
  • $\begingroup$ The question was asking is it easier to put humans on venus than mars and importantly the how and why. yes: the delta-v and aerobreaking is easier, and to get them to the upper atmosphere the conditions are less harsh than mars in some ways no: the surface conditions are much worse $\endgroup$ – Alex Dawn Aug 19 at 14:16
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    $\begingroup$ Which concept missions? (Just edit your answer instead of tacking on comments -- that's easier for others to read.) $\endgroup$ – Camille Goudeseune Aug 19 at 19:47
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    $\begingroup$ @CamilleGoudeseune ntrs.nasa.gov/citations/20160006329 $\endgroup$ – eps Aug 19 at 22:33
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    $\begingroup$ The upper atmosphere of Venus is probably the most hospitable place for human life beyond Earth apart from the lack of a solid surface! At around 50km altitude give or take the pressure, temperature and radiation levels are acceptable and a balloon inflated with an oxygen nitrogen atmosphere would act as a lifting gas so people could live inside the envelope. Going outside would even be possible for short periods (minutes) in just a face mask with oxygen supply, although for safety a sealed suit would be needed as low levels of sulphur trioxide would damage the skin with prolonged exposure. $\endgroup$ – Slarty Aug 20 at 9:13
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I love this bit from the WaitButWhy Blog, where it is posited that while landing and staying on the surface of Venus is hell, there might be a layer of the atmossphere where there is earth-like air.

Curiously, though, if you got all the way to the top of Venus’s miserable atmosphere, you’d be rewarded with—shockingly—pleasant, livable conditions. Randomly, at the top of Venus’s clouds is a layer where the temperature and pressure are similar to those on Earth, and because oxygen and nitrogen both rise in Venus’s dense atmosphere (like helium does on Earth), the air in that layer might actually be close to breathable. That’s led some scientists to actually discuss human colonization of Venus’s high atmosphere, building “cities designed to float at about fifty kilometer altitude in the atmosphere of Venus.”

Source: https://waitbutwhy.com/2015/08/how-and-why-spacex-will-colonize-mars.html/2#part2

Further sources at the quote.

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    $\begingroup$ "close to be breathable" means: temperature and pressure are roughly pleasant, but... nearly 100% CO2, with some N2. Vapor and sulfur dioxide, some sulfuric acid. O2 not even in traces. This is about 60km height above the surface. $\endgroup$ – peterh - Reinstate Monica Aug 25 at 14:38
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    $\begingroup$ What @peterh-ReinstateMonica said. The relevance of oxygen and nitrogen being buoyant isn't that they'd form a layer of breathable air (there's far too much mixing for that to ever happen), it's that a breathable oxynitrogen atmosphere at near-ambient pressure would be a workable lift gas for buoyant structures. And really, dangling from a balloon over a lethal high-pressure furnace with no available resources other than the sulfuric acid clouds and CO2 atmosphere around you is its own kind of hell. $\endgroup$ – Christopher James Huff Aug 25 at 20:11
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    $\begingroup$ @ChristopherJamesHuff Right! I imagine ordinary Zeppelins. The O2 could be produced in situ from the atmosphere. H2 production would be likely far more harder, maybe it could have somehow sucked from the atmosphere, too (there is very little). $\endgroup$ – peterh - Reinstate Monica Aug 25 at 20:54
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    $\begingroup$ @peterh-ReinstateMonica You're most of the way to CHONPS: you've got carbon and oxygen from the CO2 atmosphere, there's a couple percent nitrogen there too, and some sulfur and hydrogen from the clouds. You could in principle produce hydrocarbon polymers, fabricate buoyant structures, and fill them with breathable lift gas. You're short quite a few things needed to fill them with anything living, though...never mind building more of the machinery needed to make them. $\endgroup$ – Christopher James Huff Aug 25 at 21:20
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    $\begingroup$ Probably N2 would be better for bouyant, it is inert and a little bit lighter than O2. It can be produced from the Venusian atmosphere by simple freezing, because CO2 solidifies at -70C. A whole civilization could be built there. Although I think, colonizing the Moon with the "ordinary" method would be easier. And the easiest would to colonize the Sahara desert. Although the problems here are not on the engineering, but on the politics + $$$ side. $\endgroup$ – peterh - Reinstate Monica Aug 25 at 21:52

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