Space Shuttle Folly of Our AgeThe space shuttle.

Derek Lyons wrote:
"Jeff Findley" wrote:
5 tons may be a bit tight to develop a pressurized people carrier for a
dozen people, but I'd think 6 to 8 people ought to be doable.


So what do you think Derek? Sound reasonable to you?

5 tons as a weight seems like a reasonable starting point - but the
sticky part is (as I point out to George), 5 tons of what? (I.E. when
you get beyond Power Point, volume matters.) A cargo bay 1 meter by 2
is a different matter than one that is 2 meters by 10, even if both
are limited to five tons gross capacity.

This matters in the 5 tons and orbital assembly scenario greatly.

There are some reasonable bounds we can put on the problem,
at least.

Minimum acceptable volume would start somewhere around
the density of water. I don't know of any spacecraft
parts or propellants significantly denser than that (peroxide
and nitrogen tetroxide and nitric acid are, but not by a
large factor). So at least that much volume.

Maximum credible volume would be something like the density
of a tank full of liquid hydrogen, which is roughly 13.5 cubic
meters per ton (assume 12 cu m/ton including a tank).

Real tanks are going to have endcaps and the like,
but let's for now simplify to those numbers.

See, easy, we already almost got it to within an order of
magnitude range, in two easy paragraphs ;-)

5 tons at 12 cu m/ton would be 60 cu m. In rough terms,
3 m diameter by 9 or 10 m cargo bay, or 4 m diameter by 5 m
long.

5 tons at 1 cu m/ton is 5 cubic meters, which is only
going to be something like 1.5 m diameter by 3 m long.

If you're putting people in, a seated person plus access
space is no less than 1 cu m, more like 2 cu m. You could
credibly put at least 1 person per 500 kilograms, perhaps
as good as 1 person per 250 kilograms. 5 tons therefore
is 10 to 20 people. 10 people at 1 cubic meter per is
10 cubic meters; 20 people at 2 cubic meter per is 40
cubic meters. I think that range is a more reasonable
lower bound range. Reasonable realistic minimum is
probably somewhere around 20 cubic meters, or say a
2 m diameter 6 m long volume.

2 m is also likely the minimum credible diameter to
get berthing module / hatch assemblies which are
big enough for people and racks to get through.

Where you go from here depends a lot on the RLV
design issues.

Keep in mind that the Fluffy Capsule arguments work
as well on most RLV designs: low density is good,
and larger cargo volume may not be a weight or
design problem as much as you might think on first
analysis of the problem.


-george william herbert