Ian Davies wrote:
Here's an interesting table, showing the mass (in metric tonnes) and
habitable volume (in cubic metres) of various space stations, and hence
how many cubic metres of habitable volume you get for each kilogram of
mass.

Mass Vol m3 per kg
Salyut 7 20 90 4.5
Skylab 76 361 4.75
MIR 124 350 2.82
ISS 246 425 1.72

So ISS is 12 times as massive as Salyut 7, but only provides about 5
times as much habitable volume. It's three times as massive as Skylab,
but only provides 18% more volume.

The trend seems to be that the newer or larger the space station, the
poorer the relationship of volume to mass.

So what is going on here?

More infrastructure. Look at the mass of the ISS truss, which provides
solar power and thermal control for the rest of the station. If you
compare power capacity in KW between the above stations, you'll see a
very different story.

Perhaps the modern craft are stuffed full of
more goodies (scientific equipment, coke machines, etc), but surely
1990's technology is more weight-efficient than 1960's technology.
Doubtlessly for electronics, but presumably for other things too.

I understand Skylab was exceptionally spacious, but there's four data
points here with a consistent trend.

It just goes to show that it is possible to draw erroneous conclusions
even with multiple data points.

Skylab had enough power for the science they attempted on it, but on the
other hand it was launched with all the science it ever did - it wasn't
"assembled" per se.

The Salyuts and Mir were, by most historical accounts, power-limited.
They literally had more habitable volume than they could put to use.

ISS was the first station designed with power to spare. It originally
had more habitable volume, but some (the US Hab module, most of the
Russian research modules) were cancelled, so now it has an even more
impressive power surplus (or habitable volume deficit, depending on how
you look at it).

Habitable volume is not the only, or even the best, figure of merit here.

Obviously there's some very unfortunate scaling going on which would
have ramifications for even larger stations. It also implies that for
the "space hotel" style projects, you'd be much better off launching 5
Salyut -style craft bolted together than one ISS-style.

Seems to me IIS really just a bunch of Salyuts bolted together (with the
odd CMG thrown in, valves for replenishment, etc)

Wow. What an extraordinarily ignorant statement.