Planetside shipyards, like the one for the Enterprise in Star Trek (2009), never really made much sense to me. You'd expend a lot of energy and put a lot of stress on the ship trying to get it into orbit. It might make sense for something like an Intrepid class or a runabout, but it makes little sense for a capital ship. (I realize the JJ-prise flew around in every planetary environment but lava, but I guess we can assume they were using 24th Century future-tech.) Anyway, since it's the future, and the materials of a ship's hull are probably resistant to things like corrosive gases like the one in the atmosphere of Venus, why not just have a shipyard in the upper atmosphere of Venus. After all, much of the internal volume of a ship is going to be breathable air, and in the Venusian atmosphere, that's a lifting gas, so your spaceship will basically be an airship. Well, not completely, but enough that you can get to orbit with far less thrust than you'd need to get off the Earth's surface. It helps that the gravity of Venus is only about 89% that of Earth. I was thinking floating shipyards, kept buoyant by the massive internal volume they'd need to construct ships internally. The ships would be built suspended from support structures above a massive door. The doors would open and the support structure would slide down and release the completed ship, allowing it to exit the shipyard without loosing precious breathable air that doubles as your lifting gas. The doors close, and any atmosphere that manages to seep into the interior is processed out of the air by the life support systems. Plus you can run the entire operation on solar panels covering the entire surface of the shipyard, due to the high albedo of the atmosphere and proximity to the Sun. You're basically getting bright sunlight from every direction.
Or just put it out toward the asteroid belt. No gravity or pesky corrosive atmosphere to deal with, and the bonus of ready access to plenty of raw materials.
Neptune floating drydocks (was used in the third Space Battleship Yamato series to make emergency repairs on an alien ship
The asteroid belt is actually pretty sparse. Moving an asteroid to Mars orbit would take about as much time as moving it to a specific location in the asteroid belt. So basically you're arguing for Utopia Planitia, which is a reasonable argument, I suppose. The problem with Mars, and space facilities in general, though, is there's no protection against solar radiation and cosmic rays. You'd have to shield your facility. Also, if you can protect your mining equipment from the heat and pressure, Venus probably has vastly more raw materials to build with. No reason to fly around the Solar System for raw materials when they're just a few miles below you. Heck, this is Star Trek, so just use phasers to drill below the surface and tractor the materials up. The atmosphere of Neptune is almost entirely Hydrogen and Helium. Your only potential lifting gas is really hot hydrogen. You'd probably need some form of propulsion or anti-gravity to keep the drydocks at the proper altitude. Also, there's little solar radiation to use for power generation, though I suppose you could always use fusion. It's not like you'd be hurting for the hydrogen, after all.
So who says the dock would just be drifting in empty space? Obviously, you put it in orbit of Ceres or Vesta or some other large asteroid. Or you go out, stick thrusters on other small asteroids, and bring them to your shipyard where you can mine them at your convenience. The Main Asteroid Belt is "sparse" in the sense that it's nothing like your standard Empire Strikes Back fictional asteroid belt; the typical separation between asteroids is something like 16 times the Earth-Moon distance and you could drift in it for a hundred years before getting hit by anything larger than a speck of dust. But in terms of its total quantity of resources, it has dozens of times as much mineral wealth as you could get by strip-mining the Earth's entire crust down to the mantle. It's not sparse at all in that respect, just widely distributed. You just have to do what miners always do and go to the specific places where the ore can be found. Presumably that's the reason for the enclosed Spacedock in ST III. In the Belt, you could easily coat your facility in asteroidal rock and ice for radiation shielding. (A lot of fiction has portrayed space stations/docks inside hollowed-out asteroids, but it's now known they tend to be pretty loose and brittle, so that might not be very structurally sound.) The thing is, lifting mass up out of a planetary gravity well is a lot more energy-intensive than just moving it around in interplanetary space. Robert Heinlein once said that if you can get into Earth orbit, you're already halfway to anywhere else in the Solar System, because moving that first hundred or so kilometers out into space is at least as hard as moving hundreds of millions of kilometers to some other planet. After all, in space, you can mostly just coast. As long as you're not in a rush, you just need to point yourself onto the right course and then just drift until you get to your destination. So since Venus's surface gravity is about 90% of Earth's, it might actually be less energy-intensive to mine material from the asteroids and use a mass-driver to fire it toward Venus orbit than it would be to haul ores from Venus's surface up into its upper atmosphere. It would take more time, but if it's an ongoing operation anyway, that's not really an issue.
An orbital shipyard is the most logical approach to building ships designed to operate pretty much 99.999999% of the time.
...Operate in space, you mean? That's the thing, though: in Star Trek, operating in space is so demanding that it makes occasional forays onto planetary surfaces or into black holes pretty trivial in comparison. The ships routinely handle accelerations and other stresses that put the environmental challenges a planet (any planet, including Venus and her like) can offer to shame. Which is consistently shown in modern Trek, aptly enough: when a starship and a mountain meet, the ship wins by a landslide! On the other hand, when a spacecraft and a volcano meet, contaminants nearly make the spacecraft crash; Venus might be inconvenient that way, too. But probably no worse than the Class Y world that an Intrepid class starship low on power, a Type 6 shuttle, and a pair of standard spacesuits handled with apparent ease. And we have little reason to think that the hardware of spinoff show X would fare worse than that of spinoff movie Y. Whether gravity wells are a thing in Trek is currently unknown. Might be the transporter ignores said, just like it ignores angular momentum when beaming stuff or folks from planetary surfaces to high orbits. Might be the Newtonian potential energy is there, but is listed in the same budget paragraph as complimentary salted peanuts for visitors, considering how massively more significant energies the starships themselves handle daily, without any comment on economy. So hauling stuff from surface to orbit for construction (and then twice back and up again due to odd bureaucracy) is practical and affordable. But so would be the hauling of entire starships, under their own essentially unlimited power. Timo Saloniemi
And yet, we do not build submarines underwater. For me, there are at least three over-lapping items to consider: How automated is the construction process? What are the hazards to the humanoids involved, what is needed to mitigate them, and how is that best accomplished? What advanced tech exists to facilitate the process?
Airship Enterprise? Spoiler: Airship Enterprise The rare exception is seen in the two-part "In a Mirror, Darkly" story of ENT where a construction facility is inside a large asteroid. Probably protects you from harmful solar radiation.
Orbital shipyards would appear to make sense. It's easier to get stuff to your ship, you don't have to worry about rats and cockroaches helping themselves on board as much (messy compartment? expose it to void) I seem to remember the novelistation maybe mentioning why it happened, but I could be wrong, and I don't have it. The building of Enterprise in Iowa in the 2009 movie was mostly for visual spectacle, I know (and a good way to get Kirk to that bar to get beat up by the field-trip cadets) and it worked very well for that. Thinking about the op, I can think of a great reason to use Venusian orbit for ship building: you can dump all your construction garbage to the surface and not worry about it. Venus is already basically hell, so you're not really going to make it any worse.
For the Venus idea, upper level winds would be a factor, averaging around 300 km/h (184 mph) in the tropics.
This is Star Trek, so you "Could" have a shipyard in Venus, but it goes to .. why? You'd have to deal with gravity, noxious gases, and wind. If it was more habitable, where the construction workers could go "short sleeved" then theres a maybe. Bigest problem is the gravity well, unless you complete the ship totally on the ground, and it can get up on its own power, ..( which you would also need to support the ship with scafolding, etc from its own weight) It just makes more sense to make a ship in orbit than on the ground. As for the asteroid field.. Seen an article.. Way back.. That to make a rotating habitate, that you take your average Nikel/iron asteriod, and heat it up, then add water to the center, and you bassically, "Blow It Up" like a baloon, creating a center cavity. You could do that here.. "Blow Up" a moderate asteroid, and then you won't have to worry about it being loose or crumbly. and you'll have a huge cavern to build whatever you'd like.
As already mentioned, a standard oxygen-nitrogen mix is a lifting gas in the mostly CO2 upper atmosphere of Venus, so gravity is dealt with. And since it's enclosed, toxic gases and wind aren't issues either. At the altitude being discussed here, the temperature and pressure are about Earth-normal anyway. I actually portray aerial cities like this on a Venus-type Class-N planet in my new TOS novel The Captain's Oath. Realistically, that's true, but Trek has magic antigrav technology. If you can nullify gravity, getting into orbit is easy. Yup, that's one method.
Might have some to add later but this is great discussion! I geek out on these type of things in my own head all the time. Thanks!
Asteroids I see being used for "Harvesting" for resources by mining vessels. Gas Planets like Venus I see would be used by Orbital mining vessels / facilities for harvesting the components in the atmosphere. Somebody will need the basic components of the Atmosphere of Venus (CO2 & Nitrogen) for something.