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In my novel, I want to feature a large (>5km) centrifuge space station that was built on/into a comet, and is in the comet’s tail whenever it passes close to the sun. It is home to many criminal elements and is generally regarded as a lawless place, but is also a safe haven for political dissidents who would be persecuted in other parts of the system and in other star systems. However, more than those plot elements, I just think it would be really cool to have a station in the tail of a comet.

However, I also want most things in my novel to have an element of believability, and this station is no exception. So how could I explain why this shady space station is in a comet of all places, and why part of it sticks out into the comet’s tail? What practical advantages would this location have, and what disadvantages might it also face, if any?

Another thing to consider is that the setting of my novel is based on 70s retrofuturism, and cannot go too crazy with technology, especially not in terms of IT and computation where it is basically still stuck in the 70s. Otherwise, any modern or near-future technology could be used help explain the practicality of this space station.

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    $\begingroup$ As for why on a comet, as most people are talking about being in the tail, the answer is simple: water ice is heavy and valuable. $\endgroup$
    – jdunlop
    Mar 22, 2023 at 18:34

5 Answers 5

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The station is anchored to the comet

Image composited from Creative Commons and Public domain sources. https://www.flickr.com/photos/simonov/3181656147/in/photostream/ , https://www.flickr.com/photos/kevinmgill/32370930490/

A comet's tail orients away from the star, and its size and properties change based on how close it is to the star. Because of a comet's elliptical orbit, there is actually no way you can orbit a space station around a comet in such a way that it will always line up with the tail, and using thrusters to arbitrarily keep yourself in the tail is quite wasteful, difficult, and unduly hazardous.

However, a space station is mostly empty spaces filled with air meaning that its average density to surface area is going to be much lower than that of the ice of the comet; so, if you mount a large, mostly empty space station to a comet, the space station will act like a giant fletching or a parachute always dragging itself into alignment with the "wind" created by the comet's tail every time it passes into the sun's melt radius.

enter image description here

This means that as the comet passes close to the sun that the tail will basically capture the station the first time it drifts into the tail. So, instead of trying really hard to force your station to always be inside of the tail treating this as a 2-body problem, it sorts itself out when talking about it as a 1-body problem.

Mounting a station to a comet could also be seen as a biproduct of necessity. Comets are full of water which is hard to come by in space. Your space station could use this water to feed its agricultural needs, and maybe even break it up so your crew have oxygen to breath and hydrogen to power some fusion reactors; so, even though the comets tail is a rather big hazard to have to engineer around, it could be worth it from a realism perspective to have all that easy access to water.

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    $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Mar 23, 2023 at 20:05
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The thing about the tail is, it's not in the same orbit as the comet. So you would need to use rockets (or whatever you use to move in space under the rules in your story) to stay in the tail.

A comet's tail is driven off the comet by solar wind. There are often two tails.

enter image description here

The tail points away from the sun. Dust and small particles follow one path. Gas follows a different path. This is because the larger the mass of the object the more it tends to follow an orbit rather than be driven in front of the solar wind.

So you need to work to stay in the tail. Ordinary rockets will then leave a wake in the tail. Each time you fire them you will leave a ripple in the material of the tail. That will flow out from the comet, pretty much acting as a giant arrow pointing at Something Interesting Here.

After that you have the issue of getting whacked in the head by various larger chunks that split off the comet. These arrive unpredictably, straight down the tail, and so obscured by the material of the tail and the shadow of the main comet.

So, hanging out in the tail is probably not too good an idea, at least close to the comet.

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The tail of a comet, with its constant flow of gas and ions evaporating from the comet surface, can be a difficult place to land on or take off.

Also communications can be more easily disturbed by the flow of ions.

These would be nice added safety features to avoid unwanted attention from nosy agencies.

However keep in mind that the tail is always pointing away from the Sun: so, during the approach to the Sun it would be in the back of the comet's trajectory, but when the comet is moving away from the Sun the tail would precede it. This would require some maneuvering for the station to be always in the tail.

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You want the shadow

There is a very good reason that you might want to position a station in the tail of a comet: shadow. The reasons for hitching your wagon to a comet isn't hard. It's a good source of water and minerals. Heck, you could probably fund a mining operation using near-slave prisoner labor. However, it has a problem in that it swings back and forth between the deep cold of the Oort cloud and the hot inner orbits. This can cause all sorts of engineering stress on the hull of the station as it heats up.

The simple solution: put the station in the shadow of the comet. You might know that the Webb telescope uses six layers of mylar to allow its telescope to achieve extremely low temperatures. With the shadow of a comet, you don't need to engineer your hull for regular heating and cooling cycles, you can just keep it one standard temperature, which is probably cold on the outside and cozy on the inside.

A cometary tail is a side effect of the solar wind that blows from the sun, so it's guaranteed to be surrounding the shadowy side.

As a side note, @Nosajimiki's answer is a good one, but if you're using the comet for shade, you don't want the edges to peek out. You'd probably want shuttlecock-like screens to do that work.

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The comet's coma (head) and the tail don't differ much in properties. It's the same gas and dust cloud - the tails are formed when the photon pressure, the solar wind and the tidal deformation extend the coma in one direction or another.

This is why one could orbit a comet at tens or even hundreds of kilometers away from the core without getting much visibility.

Problem 1: Be aware that a lot of comet particles (some of them quite large) will orbit the main core in the same region. Be ready to evade them.

Problem 2: dust, dust, dust, dust. Unhealthy amount of black sooty dust adhering to everything.

Problem 3: getting in and out of the habitable zone. Profoundly different heat management.

Problem 4: Comets with short periods are not a great number and as of today, they attract a great deal of attention.

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