Is there an upper limit for the internal size of space stations?

Question

I was reading about the various TransHab proposals (at http://www.astronautix.com/craft/traodule.htm, among others), and I started to think about pushing the idea to its limits. Assuming you had a large enough payload area on a rocket (or space shuttle - once upon a time), you could launch some pretty big modules. Most of the plans called for multi-"story" modules, with different levels. But a much bigger, simpler version would, of course, simply have no levels, and be just one giant cavity. Reminiscent of Star Wars landing bays, right?

But there's a catch. Most (okay, all) of the modules for space stations over the years are tight, cramped, and not for the overly claustrophobic. One upside is that you can pull yourself around using bars on the "walls". In a large, cavernous module, that would be hard (unless you plan on using an MMU all the time!). Artificial gravity could make this even worse, by trapping any astronauts on a single side!

So my question is this: Is there an upper limit to the interior of space stations because it becomes impossible to move around in a controlled fashion? Are space station modules doomed to be thin and cramped forever?

Note: I don't think that this is a duplicate of Are there any theoretical size limits of man-made space stations/structures?, simply because I am interested in the interior of such a space station - my hypothetical module could simply be the size of a gymnasium and still be of a problematic scale, as opposed to the miles-long structures discussed in the other question.

Answer 1

Have you seen tours of the space station? The modules are not particularly cramped. Some parts are, especially where they connect with other modules, but most seem quite spacious actually.

Kibo, the Japanese module and also the largest module on the station, has seemed somewhat too spacious for the astronauts, as they could get stuck in the middle. [1]

From wikipedia, these are Kibo's dimensions, and thus a version of an answer to your question:

Length: 11.19 m (36.7 ft)
Diameter: 4.39 m (14.4 ft)

Since they could to get stuck in Kibo, I'd bet that it would be tough to build a module much larger without "levels" or some kind of infrastructure to get around.

[1] http://www.universetoday.com/14967/space-station-astronauts-could-get-stranded-in-kibo/

Answer 2

With respect to "getting stuck" in a large open space in an orbiting space station, I believe the dangers have been exaggerated.

First: A "stuck" astronaut would need to work pretty hard to get stuck. If he/she is moving from the wall of the compartment to the middle, it's tricky to stop in mid-air. There could be a line run from one side to the other, then removed. Or fellow astronauts could do it to a unsuspecting victim. Sort of the orbital equivalent to being stuffed in a high-school locker...

OK, say you are stuck. This means that you are in your own orbit around the earth, unaffected by anything the space station does. The center of mass of the space station is following its orbit, and all the parts of the station (except you) are pulled along in the same orbit by the structural integrity of the station.

If the center of mass of the space station is located inside the large space, and that's where you're stuck, well, then you are stuck (except see below). As a bonus, you'll still be stuck if someone changes the station's orientation.

Picture the line traced by the center of mass of the station as it orbits and how this line passes through the structure of the space station. You can only be stuck, motionless, if you are located on this line. You can only be stuck, with oscillations, if you are located close to this line. The oscillations get bigger, around the line, as you get farther from the line. If the oscillations are too big, you'll get close enough to something to grab it.

Finally, if you are stuck, you are no longer affected by any decay in the space station orbit. The ISS changes speed, and thus altitude, because of the slight amount of air friction, and must be periodically boosted back up. Eventually the space station will come to meet you. The time scale for rescue would depend on the state of the earth's atmosphere and the shape and orientation of the station.

Then, you could always sneeze, or ...But I digress...

Answer 3

As Nickolai suggested, this is more of a technical problem, and so there are several imaginable technical solutions. Reading the article he linked, it seems to be a temporary annoyance in Kibo, rather than a serious problem.

"Swimming" might work for relatively small distances. If modules get bigger, you would of course need a more sophisticated solution, such as a small hand-held cold gas thruster. Although it would take practice to operate in a way that doesn't send the astronaut spinning wildly. (This solution appears in the anime "Planetes", which is excellent, btw)

A simpler solution would be to create an air draft in the station that pushes the astronauts towards one side. This approach is of course limited in how large the module can be, because the required energy to create such a draft would become unreasonable.

Obviously some draft always has to exist in a space station, or the CO2 that the Astronauts produce wouldn't get transported away from them. So you could rescue yourself by sending the air conditioning into overdrive.