What is the best design for docking onto a rotating space-station?
In the distant future, space-stations use centrifugal force to emulate gravity, effectively being a cylinder (or something similar like a wheel) spinning around a central axis at high speeds.
A spacecraft is coming up to dock, but how can it dock to such a fast, spinning object?
The possible approaches I could think of would be:
The dock being positioned on the side of the station, hooks (or tractor beams or what-have-you) are locked onto the craft, swinging it around at break-neck speeds while pulling it in to dock. (Doesn't sound so great for the passengers or the ship.)
The dock being positioned on the top/bottom of the station, the craft nears the dock, spinning around its own axis to match the speed of the station before closing in. (Sounds pretty plausible, since the speeds in the center would be slower. Perhaps some dizzy passengers, nothing more.)
Same as the previous idea, but the dock rotates instead of the ship. (No-one notices a thing.)
The dock being positioned anywhere, and the space station transfers its momentum to another body, causing weightlessness inside the station and allowing the craft to dock without using additional fuel. The momentum would then be transferred back onto the station, causing the apparent 'gravity' to return. (If done slowly, no-one should mind.)
There is a docking structure that doesn't move relative to spacecraft, perhaps a core around which the station rotates or additional rings rotating at various speeds.
I am particularly interested in the fourth idea. Perhaps it could be done using a sealed flywheel or something of the sorts, potentially reducing the complexity of the problem by reducing the skill required to synchronise the movement of the craft with that of the station, perhaps even reducing overall fuel consumption or other neat side-effects.
My question is one of engineering. Which of these solutions would be the most realistic or practical, based on engineering difficulty, crew safety, reliability and fuel consumption?
Should there be any inaccuracies or other approaches that come to mind, please leave them in the comments below.
This post was sourced from https://worldbuilding.stackexchange.com/q/134530. It is licensed under CC BY-SA 4.0.
1 answer
I think this is option #3.
There is a problem with centrifugal gravity, rotating things want to rotate around their center of gravity; so if the weight is not distributed quite evenly around the rim, then the center of rotation moves and the "rotation" becomes chaotic. i.e. it won't work, the structure will start tumbling (albeit in place).
For this reason you need automatic compensation, massive devices that can keep the ring balanced so as people and things move around inside your ring, they move in counter-point to keep the center of gravity (the balance point) in the center of the spin.
I think your best docking solution is to dock at the center point of the ring, around which everything is rotation. Imagine a bicycle tire with thick spokes. The rubber ring is the habitable area, the spokes are both travel tubes and "rails" carrying automatically moving counter weights. The hub is the docking station.
Let us add to the hub a transfer cylinder which can spin opposite the direction of the entire tire spinning. Now, to those inside the hub, this cylinder appears to be spinning, but to the ship outside the hub, the cylinder appears to be stationary while the station appears to be spinning.
So the ship approaches the stationary-for-it transfer cylinder, and can make an airlock with it. Objects (people and things) leave the ship to enter the hub; they are weightless inside it. They take seats or are otherwise secured to the walls. The airlock is closed. The transport ship can depart.
Then, from the space station's point of view, this spinning transfer cylinder is "slowed down" until it is fully spinning with the station, has centrifugal gravity (pointing out to its walls), and the passengers and cargo can exit the cylinder into the hub proper, where they can then take an elevator "down" one of the spokes to the habitable areas. The computers for the space station will automatically move counterweights up and down the outside of the spokes to maintain the balance with the new weights moving around.
All of this, to the passengers, would seem pretty similar to the modern experience of airlines. Waiting, strapping in, acceleration, waiting, deceleration for landing, waiting, departing the aircraft, collecting your luggage, navigating through your destination (finding the right spoke, floor, etc).
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