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I have been making a future colonization scenario where people have vast colonies on Mars and cloud top bases on Venus. These things are unbelievably large. I've already thought of a way to travel between these on Mars, but Venus is another issue. Could you use a common passenger jet (most likely modified to use solar power, however) to traverse these large expanses of atmosphere? How about any other form of common air travel? Helicopters? Gliders?

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    $\begingroup$ There is no oxygen (or other oxidizer) in Venus' atmosphere. Pressure and temperature are extremely high for any kind of Earth aircraft. So your plane has to be very, very deeply modified. $\endgroup$ – Alexander Nov 5 '19 at 22:49
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    $\begingroup$ what-if.xkcd.com/30 Choice excerpt: "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." $\endgroup$ – Halfthawed Nov 5 '19 at 22:54
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    $\begingroup$ @Alexander OP specified cloud top bases, meaning pressure probably something more convenient than on the surface $\endgroup$ – JollyJoker Nov 6 '19 at 8:19
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    $\begingroup$ @JollyJoker The absence of oxygen in the atmosphere makes jets a non-starter (literally) since the purpose of jet intakes is to gather oxygen to burn with the fuel. $\endgroup$ – Vince O'Sullivan Nov 6 '19 at 9:53
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    $\begingroup$ @jasper Above the clouds is fine as long as you can handle the constant category 5 hurricane level winds. Venus really isn't a good place to live. $\endgroup$ – Shadur Nov 6 '19 at 13:15
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While in theory the atmospheric pressures and temperatures in the upper regions of Venus' atmosphere are more conducive to the operation of aircraft, you still have a problem; sulphur dioxide. This is one of the emissions that grounds planes during volcanic eruptions meaning that even if you can fly the plane there, the maintenance costs are likely to be prohibitive.

That said, given the density and the nature of the gases in the Venusian atmosphere, you don't need aircraft to fly between bases. You could literally float.

The idea behind the cloud cities of Venus is that molecular oxygen, nitrogen and other gases that humans need for a healthy life, particularly at the temperatures we operate at, would actually float in the atmosphere at a particular altitude because the density of the super heated CO2 is sufficient to support it. So, you basically can build a lightweight 'bubble' of the gases we breathe and put a city on the floor of it and it would float around Venus. Obviously this is a simplification, but it's functionally correct.

The point being, you could do the same thing with your aircraft or transport vehicles. Basically create a series of mobile bubbles, fill them with breatheable air, give them propellers and the like to move about, and you've literally got an airship in which the crew, passengers and goods can all safely reside in the air envelope - you don't need hydrogen or helium to make the craft lighter, because in that environment normal air is already lighter.

This would actually be a failsafe for all but catastrophic breaches of the air envelope because even if you run out of power, you float until someone picks you up or tows you in.

The other advantage of this of course is that your airships are likely to be capable of moving larger cargoes and passenger lists than a conventional 747. They would be more like the trains of the Venusian sky.

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  • $\begingroup$ How correct am I in imagining Cloud City from Star Wars? $\endgroup$ – Parrotmaster Nov 6 '19 at 11:14
  • $\begingroup$ @Parrotmaster not very. That city would be far too heavy. Think more like giant zepplins but instead of being airships they are aircities. The lift factor of the atmosphere isn't going to support a lot of heavy metal structures and the like so your inner environment is more likely going to be some form of lightweight cubical farm inside a robust balloon style structure would be my guess. Most likely hundreds of population would be the absolute limit rather than tens or hundreds of thousands running heavy industrial equipment. The proposed models are more research bases, akin to the ISS. $\endgroup$ – Tim B II Nov 6 '19 at 11:47
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    $\begingroup$ You may also want to mention the category five hurricane level winds that are constant at that altitude, as well as the high concentrations of sulfuric acid that will corrode any exposed metal in minutes. Venus is much nicer at high altitudes than on the surface, but "much nicer than a place that is consistent with most descriptions of hell" is a fairly low bar to set. $\endgroup$ – Gryphon Nov 6 '19 at 14:11
  • $\begingroup$ @Parrotmaster Also, Cloud City had its buildings supported by tall poles attached to the ground, rather than floating. This would probably be impossible on Venus with any currently known materials, as the sulfuric acid rain would eat away the support poles and cause your buildings to crash to the ground (where they too would be destroyed by acid rain in addition to the damage from gravity). $\endgroup$ – Darrel Hoffman Nov 6 '19 at 14:32
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    $\begingroup$ @DarrelHoffman, What? Cloud City is located on a gas giant planet called Bespin. There is no ground and no support poles. The city does have a long tube that extends into the planet to "mine" a rare gas found there, but it is a totally floating city. $\endgroup$ – JPhi1618 Nov 6 '19 at 15:23
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Obvious problem number 1: there's no free oxygen in Venus' atmosphere, so you can't run any kind of combustion engine. Lets assume you're using some other kind of engine though, though I won't specify which.

Venus at low altitude is very, very hot and has very high air pressure. Your aircraft would disintegrate in short order. Once you get to an altitude of 50km though, atmospheric pressure is nearly the same as that found on the surface of Earth... about 1.07 atmospheres, though it is a little warm at 75 degrees C. Go a few kilometres higher and you'll get half an atmosphere of pressure and a balmy 27 degrees air temperature. At 60km conditions start to look a little more like they would for a Boeing 747 at cruising altitude on earth, though quite a lot warmer.

You'd still have to contend with a possibly very corrosive atmosphere though... there's quite a lot of sulphuric acid in Venus' atmosphere, but if you avoid clouds you might be OK but it would be best to thoroughly corrosion-proof everything. Wind speeds are quite strong up there too, but windspeeds at high altitude on Earth can also be pretty brisk and that hasn't stopped commercial flights being entirely practical and largely safe.

Any form of flight that would work on earth and not need oxygen for the engines to work should function just fine.

I'm not sure a solar powered passenger jet would work, though... I'm not about to run the numbers myself, but I think the available surface area is too low to provide the same amount of power those four big gas turbines would on Earth, and even at 60km altitude there can be thick cloud cover. If you don't have compact and lightweight fusion power, you'll have to scale back the cruising speeds of your aircraft somewhat. Maybe electric props or fans with fuel cells as the power source might work. At 50km you can make bouyant balloons filled with human-breathable gas, so as long as you have some good air conditioning maybe zeppelins would work for you...

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    $\begingroup$ The numbers don't stack up for solar power. This thread over at aviation stackexchange suggests that the engine power of a 747 is around $\mathrm{88MW}$. Cruising power might be half or even a quarter of that; but the surface area of the 747 wings is $\mathrm{525 m^2}$ and the solar irradiance on Venus is only $\mathrm{2622 W/m^2}$, so solar power would be more like $\mathrm{1.3MW}$. $\endgroup$ – Stephen Nov 6 '19 at 10:17
  • $\begingroup$ @Stephen thanks for that. I'm not surprised. I tried to work out if you could do it with a microwave powersat a while back, and even that didn't work out well with a safe microwave power density at the target. Still, a megawatt or two isn't to be sneezed at; it'll do well enough for zepellin propulsion. $\endgroup$ – Starfish Prime Nov 6 '19 at 10:22
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In a direct answer to your question no you could not use a common passenger jet unmodified.

Firstly the atmosphere would contain a lot of sulphur dioxide and a small amount of water creating sulphuric acid which would rapidly corrode the structure of the jet. That said a jet could reasonably easily be modified to incorporate plastic coatings such as polytetrafluorethylene to resolve that issue. But a bigger issue would be propulsion. How would the structure be moved in the atmosphere as no oxygen is present for combustion?

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    $\begingroup$ The obvious answer would be to carry its own oxidant supply as well, much like rockets currently do. Of course, that means a lot more weight, which means a significant redesign of the entire aircraft, and at that point it probably wouldn't be a jet engine anymore, so... $\endgroup$ – Shadur Nov 6 '19 at 13:19
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At the altitude the cloud cities would be situated the atmospheric density is similar to that at ground level, or ,say, the troposphere, the lack of oxygen knocks out any possible jet aircraft.

While solar-powered aircraft can be possible. They will be too light and too fragile. This is a major potential problem. Remember the Hellish abyss of the Venusian atmosphere lies down below.

The most probable aircraft for travelling between cloud cities will be nuclear-electric powered helicopters or propeller-driven fixed wing aircraft. Pressurization and airtight compartments will be an absolutely necessary to ensure they can breath air containing oxygen. This will keep out the sulphuric acid in the clouds and aircraft will have be acid-proof.

Not totally infeasible, But Boeing 747's cruising Venusian skies, definitely not. Jets are also definitely out. But propeller or rotor aircraft with suitable power sources, presumably nuclear instead of solar, are quite feasible.

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  • $\begingroup$ This answer, too, neglects to warn about the Cat5 hurricane level storms that are a constant feature in the upper Venusian atmosphere and which I can't help but feel would significantly complicate any attempted regular air travel... $\endgroup$ – Shadur Nov 6 '19 at 13:17
  • $\begingroup$ @Shadur phys.org/news/2016-12-weather-venus.html "Closer to the equator, the wind speeds die down to almost nothing." It also appears those winds are steady circling the planet, kinda like the jet stream. You could probably float along in them without issues - hurricanes are an issue more when those winds hit an immovable object like a house. $\endgroup$ – ceejayoz Nov 6 '19 at 14:01
  • $\begingroup$ @ceejayoz Or a 'cloud city' ? Aside from that, I specifically mentioned 'regular' air travel, because while your suggestion of floating along in them might be viable, that means all travel will have to be in a single direction... $\endgroup$ – Shadur Nov 6 '19 at 15:17
  • $\begingroup$ @Shadur A cloud city would float along with the prevailing winds - it'd be silly to try anchoring it to a fixed spot. Ground speed might be hundreds of kilometers per hour, but that doesn't really matter. A fast enough aircraft could fly into the winds, but might find suborbital hops or going the longer way around to be a more efficient approach. $\endgroup$ – ceejayoz Nov 6 '19 at 15:22
  • $\begingroup$ @Shadur travel in the upper atmosphere relative to the surface would have to be in the same direction but relative to other habitats it need not be. $\endgroup$ – Slarty Nov 6 '19 at 17:22

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