[Spaceships] Gas Giant Habitats

[AlexanderHowl]

I was wondering how you would design gas giant habitats? Aerostats are a popular suggestion, but GURPS limits them to SM+9. In any case, four gasbags should be sufficient for a gas giant like Saturn, Uranus, or Neptune, though I would think that you would want a couple of spares just in case of damage. After all, it is not like you will have time to repair damaged gasbags...

With that in mind, I suggest the following design for a modest homestead:

Gas Giant Home (TL9)

Size: SM+8 (1,000 metric tons)

Components: Front Hull - AML Armor, External Clamp, Gasbags (x2), Hanger Bay (x2); Central Hull - AML Armor, Control Room (Core), Fuel Tank, Gasbags (x2), and Habitat (x2); Rear Hull - AML Armor, Engine Room (Core), Gasbags (x2), Open Space (x2), and Smaller System (NTR, Fission Reactor, and Refinery).

Features: Ram-rocket and Total Automation (x1)

A gas giant home is a mobile homestead that mostly floats with the winds. When needed, it uses its ram-rocket NTR to maneuver, but its automated systems tend to just follow the winds. It uses its refinery to refill its gasbags and to extract helium-3 from the atmosphere of the planet (5 metric tons of gases per hour produces 32 grams of helium-3 per hour). It is mostly a retreat for the wealthy though, and it is capable of sustaining twelve people in modest comfort for a prolonged period of time (generally six family members and six guests).

[Anthony]

Originally Posted by AlexanderHowl

In any case, four gasbags should be sufficient for a gas giant like Saturn, Uranus, or Neptune

The way gasbags work depend on the gas inside the balloon being less dense than the gas outside the balloon. There are two ways of doing this:

1. Use a lower molar weight gas than what is outside. Earth's atmosphere has an average molar weight of 29, so helium and hydrogen (at 4 and 2) are plenty light enough. Gas giant atmospheres have an average molar weight of about 2.2.
2. Use hot gas. This can work on gas giants, but hot gas balloons are a lot less efficient than lifting gas.

[dataweaver]

In other words, you want to focus on lift engines (e.g., rotors or vertical jets), aerodynamic lift (your habitat doesn't float; it flies) or some sort of contragravity. Most of these are going to be energy-intensive, and there's a real question of what benefit you'd get from them vs. an orbital habitat with dropships.

EDIT: another possibility would be a “vacuum bag”, a hollow chamber filled literally with nothing but made or if the sturdiest yet lightest material you can manage. That gives you a “molar weight” of zero, plus however much the Shell weighs. And that's the catch: you need to keep the Shell's weight down, or else it will plummet like a lead balloon.

[kdtipa]

If you're looking for your building to float at a depth in the atmosphere that resembles Earth's atmospheric pressure, wouldn't hydrogen and helium be about right for what you want? It's probably not breathable air, but you might not need as hardy a pressurized building.

[dataweaver]

Since a gas giant's atmosphere is largely composed of hydrogen and helium, no: they don't make good lifting gasses in that atmosphere. They work in Earth's atmosphere because it's composed mainly of nitrogen, which is much denser than hydrogen.

[William]

Could you take advantage of atmospheric features? Jupiter's winds can reach 100 m/s and its cyclones, which surround areas of low pressure and hence updrafts, can last for years. A small, light habitat surrounded by wings and sails worked by an autopilot seems like it might be able to stay aloft indefinitely with a decent safety margin. Add some solar panels to run the occasional jet boost when needed. (Failure of weather, or of weather prediction, would necessitate abandoning the station of course.)

Alternative proposal, although extremely high-tech: instead of gas bags, nail the habitat to the sky as the lower end of a space elevator. A quick Google tells me I'm not the first to think of this idea.

[dcarson]

Clouds of Saturn by Michael McCollum is a SF novel that deals with this. There are several other SF novels that have city sized aerostats and Geoffrey Landis has written proposals for NASA to build one in the Venusian atmosphere. That would be one about a kilometer in diameter. Square cube law means that the weight of the shell is low proportionate to the volume and keeping the air at normal room temperature would be enough to give plenty of lift.

[Anthony]

Originally Posted by dcarson

Square cube law means that the weight of the shell is low proportionate to the volume and keeping the air at normal room temperature would be enough to give plenty of lift.

Square/cube law doesn't actually much affect bag weight; yes, a bigger bag has less surface area relative to its volume, but it needs to be thicker to not rupture, so overall weight is nearly constant in volume (the square/cube law does help with the energy requirements for hot gas, though. On the minus side, thermal conductivity of gas giant atmosphere is nearly 4x that of a terrestrial atmosphere).

[scc]

First ask yourself this: Why are people living inside a gas giant?

[AlexanderHowl]

Hypothetically, it would be to harvest rare gases like helium-3. Right now, helium-3 is worth approximately $20,000/gram and, if it was not for price restrictions by the US government, it would be worth even more. Even in societies that have solved fusion (helium-3 is a byproduct of half the DD fusion reactions), it would likely be worth $345/gram due to its potential energy content, as every gram can produce around 34.5 MW-H of electricity without any neutrons through fusing with itself (D-He-3 fusion is actually quite difficult because the D will fuse with itself at a million times higher rate that it will with He-3). At $345/gram, the above facility would earn around $93 million per year, which would produce a modest return after all the associated costs.