Trends in space station design, weight versus volume

On Fri, 22 Feb 2008 14:31:22 +1100, Ian Davies
wrote:

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.

In the case of ISS, the reduction is due to habitable modules being
cancelled while the heavy power system remained intact. The truss
structure and its solar arrays/radiators/batteries were intended to
provide power for the large-ish U.S. Hab module and the Centrifuge
Accomodation Module, both of which were cancelled due to budget cuts.

And at what point in time do your figures represent? If that is
current ISS mass/volume, then the heavy Truss is close to complete,
while two JEM modules and Node 3 have yet to be added.

Brian

Each station had a certain volume, and weighed what it weighed. Trying to
derive some meaning based on ratios is not productive. Each one was built
differently.

When looking at the various structures and parts on ISS, usually while a
space walk is going on, it seems to me that they use a lot of thick
metal.... a strong machine. The drive unit for the solar arrays is a good
example. The thing is massive.



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Revision wrote:

Each station had a certain volume, and weighed what it weighed. Trying to
derive some meaning based on ratios is not productive. Each one was built
differently.

When looking at the various structures and parts on ISS, usually while a
space walk is going on, it seems to me that they use a lot of thick
metal.... a strong machine. The drive unit for the solar arrays is a good
example. The thing is massive.




The structural strength is driven by launch loads, since each truss was
launched pre-assembled. The old 5-meter truss (sticks-n-balls) would have
been a lot lighter, as it would have been assembled in orbit. Considering
the problem they have with docking loads now, it would have been
interesting to see how a lighter, more flexible station would have fared.

Mike Ross

Jorge R. Frank wrote:
Ian Davies wrote:


As it happens, I'm still ignorant as to the reason. All you've told me
is ISS is a bunch of bolted-together modules with over-engineered
power supply.

If you think that's all I've told you, you've understood nothing.


Ok - that bit where I said the arrogance was unbecoming ... I retract that.

Rand Simberg wrote:
On 22 Feb 2008 01:11:32 -0500, in a place far, far away, Jim Kingdon
made the phosphor on my monitor glow in such a way
as to indicate that:

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
It is hard to prove anything from only 4 data points (which have
hard-to-control-for differences such as nationality, whether the
purpose was quick-and-dirty or "optimally" designed, etc), but if I
had to guess, I'd say that people have gradually figured out that big
stations have a lot of air drag and thus require a lot of reboost
fuel.

Only if at low altitudes. This is a function of launch costs. If
costs of reaching it weren't a consideration (and earth observation
weren't an issue), a station would like to be much higher than ISS is,
with an upper limit as it gets into the belts. The altitude is
constrained by the increasing reduction of payload to reach it with
the Shuttle (a problem that could be solved by a station-based tug).

Not just the shuttle. Soyuz/Progress have a rendezvous ceiling of 425 km.

On Tue, 26 Feb 2008 23:16:35 -0600, in a place far, far away, "Jorge
R. Frank" made the phosphor on my monitor glow
in such a way as to indicate that:

Rand Simberg wrote:
On 22 Feb 2008 01:11:32 -0500, in a place far, far away, Jim Kingdon
made the phosphor on my monitor glow in such a way
as to indicate that:

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
It is hard to prove anything from only 4 data points (which have
hard-to-control-for differences such as nationality, whether the
purpose was quick-and-dirty or "optimally" designed, etc), but if I
had to guess, I'd say that people have gradually figured out that big
stations have a lot of air drag and thus require a lot of reboost
fuel.

Only if at low altitudes. This is a function of launch costs. If
costs of reaching it weren't a consideration (and earth observation
weren't an issue), a station would like to be much higher than ISS is,
with an upper limit as it gets into the belts. The altitude is
constrained by the increasing reduction of payload to reach it with
the Shuttle (a problem that could be solved by a station-based tug).

Not just the shuttle. Soyuz/Progress have a rendezvous ceiling of 425 km.

Indeed. But that remains a function of expensive launch. If it were
cheaper, we'd like to have a higher station.