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?
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.
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.
- 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.
- Spirit was active from 4 January 2004 through 22 March 2010, for a total of more than 6 years.
- Opportunity landed 25 January 2004 and remained operational until 10 June 2018, for a total of almost 15 years.
- 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.
Mars may not be the most friendly place anybody can dream of, but it's absolute paradise compared to Venus.
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.
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.
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.
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.”
Further sources at the quote.