A City on Jupiter

In the last chapter we tried to put people on Mercury, and Venus, but Jupiter poses an even greater challenge. Technically, we can't put people on Jupiter, because it has no surface. It is a "gas giant". We must place our city in Jupiter's atmosphere, floating among the clouds, like Stratos on Star Trek.

There's no such thing as antigravity, so our city has to float, hover, or fly. Hovering takes more energy than flying, I don't know why. I asked a hummingbird and he told me it just does, in between sips of nectar. Thus a helicopter can't fly across the ocean. So hovering isn't feasible.

How about a flying city, avoiding the Great Red Spot and other nasty storms. Can we fly using the power of the sun? We have built solar powered drones that can fly for a long time, almost continuously, but these are light craft with no payload, and the sun is ten times as strong on earth as it is at Jupiter, and our city spends half its time in darkness, so let's agree that solar power won't be sufficient. Chemical fuels would quickly run out, so it's nuclear or fusion. Both are heavy reactors, and they must be carried aloft along with the city. Fusion power is tempting, because the whole atmosphere is hydrogen. It's fuel everywhere you look! But fusion power is centuries away, if it can be done at all. In the 70's I read articles in Scientific American: fusion power was coming, and would solve all our energy needs. Now I read articles in the same magazine on why it is a profound engineering challenge, and it's easier to harvest energy from the sun.

Whether fusion or nuclear, there is risk in a flying city. If the reactor fails, even for a few minutes, or if the engines fail, or if a wing breaks off, or if anything goes wrong, the city falls into the thicker, hotter layers below, where it is crushed and baked simultaneously, killing all life on board.

That won't work, so assume the city floats. The city is a grid of modules connected by flexible tunnels, so people can move from module to module. Some are living quarters, some are kitchens, some are science stations, some have airlocks to the outside to perform maintenance as needed. One module is a movie theater so our residence can watch a movie. One module is sickbay, and one module has showers and most of the water facilities. Tunnels are flexible, so a sudden updraft jostles the city and moves the modules about, but doesn't snap the city in half. This is the same way we earthquake proof large buildings, they flex and bend. Ok, that was the easy part, now there are 3 almost unsolvable problems, even looking millennia into the future.

No desert on earth, or Mars, or Venus, is as dry and barren as the atmosphere of Jupiter. It's hydrogen, with minute traces of helium, methane, ammonia, and water. Unlike the space station in low earth orbit, there aren't any supply ships coming. Oh maybe one every 10 or 20 years, that's it. If you lose even a milligram of carbon, it's going to be difficult to glean another milligram of carbon (via methane) out of the atmosphere. Even harder for the heavier elements. If a bolt comes loose and drops away, it might take ten thousand years to pull enough iron atoms out of the atmosphere to make another one. Supply ships will have to replace the metallic items, and in the meantime, every molecule has to be recycled. We don't vent or waste anything! Every metabolic byproduct is broken down and recycled, not just for the water, but for every atom of carbon and nitrogen and sulfur and oxygen. A machine that we can't even imagine today, something like Star Trek's replicator, takes our breath and our waste and turns it back into food we can eat, and products that we use, so that the city is entirely closed. Ok that's nearly impossible; let's move on.
Gravity is 2.5 times that of earth. If you're 200 pounds on earth, you are effectively 500 pounds on Jupiter. With practice and care you might learn to walk about, I suppose, but a slip & fall almost certainly leads to a broken arm, or broken ribs, or some other injury. It's not just the added weight, but also the speed of the fall. There's less time to put your arms down and brace. Beyond this, months or years of this gravity probably strains the heart to the point of failure, pumping all that heavy blood around. I'd be surprised if a human could live for more than a few months in that gravity.
How does the city float? Each module is supported by a dozen large balloons, so if one balloon fails, or if the string breaks, the remaining balloons still support the city. We put a new balloon in place as time permits. This is a stable equilibrium. If the city drifts up, the "air" is thinner, the balloons less buoyant, and the city settles back down again. Similarly, the city cannot descend too far down, as the air is thicker and pushes the city back up. So there's time to repair or replace a broken balloon; you'll just be 100 meters lower for the interim. But I've skirted around the main problem, the elephant in the room; what is in the balloons? On earth, our blimps are filled with helium. That works because helium is lighter than air; but it's not lighter than hydrogen. Nothing is lighter than hydrogen! There is literally no substance we can put into a balloon that is lighter than the atmosphere of Jupiter. Well how bout a vacuum? Each balloon is a metal shell with nothing inside. Ok, but the metal shell weighs a lot more than a mylar balloon. We could make the shell bigger, so it encloses more and more vacuum, but the shell has to be stronger to stand up to more and more pressure. That makes it heavier. There's no way to win here.
The last possibility is a hot air balloon, but now we need lots of energy pumped continuously into the system. Here comes that nuclear or fusion reactor again. Sure, it isn't as fragile as flying. We don't have wings and flaps and mechanical engines to fail, and we can store energy in case the reactor is off line, and the balloons have thermal inertia, so if we don't pump heat into them for a couple hours we'll probably survive, but still it's a complex system. If something goes wrong, and we don't fix it in 6 to 8 hours, we're probably drifting down to our deaths, into a hot thick soup of hydrogen.

With all that in mind, I predict that we will never, not in a billion years, and no matter how much technology we develop, establish a colony in the hydrogen atmosphere of Jupiter. We could however build a science plane that flies through the Jovian atmosphere for a couple days, gathering data, until its fuel runs out. Its fuel is, of course, oxygen. Oxygen plus hydrogen produces water and lots of energy.

Saturn, Uranus, and Neptune are no better. They are all gas giants with no surface to stand on. However, they all have plenty of interesting moons we can visit.

Venus provides a more inviting atmosphere for a floating city. (Lord knows we can't put people on the surface.) Problems 2 and 3 are easily solved. Gravity is the same as on earth, and hydrogen balloons will hold the city aloft in the carbon dioxide atmosphere, which is denser than ours. Also, if there is a leak, hydrogen does not burn in the presence of CO₂.