Inflatable propellant tanks

I just came across the following link:
http://www.marshome.org/files2/Space-Inflatables
Which seems to back up some of my own thinking.

It looks like one can use PCTFE, (Kel-F), for a flexible liner for LOX,
CH4, RP-1, etcetera, inflated tanks. Kevlar seems good to such
temperatures and it would seem that by surrounding such a liner in a
Kevlar net, (refer to how Bigelow inflated modules are constructed),
inflatable cryogenic propellant tanks are quite possible.

The primary advantage of such inflatable tanks is that they can have
much greater specific strength than even composite tanks, (no resin mass
or minium gauge buckling constraints). Tank mass fractions as low as
0.1% might be possible. This can make a huge difference to the ease of
design of an SSTO, and other space transports besides. Due to minimum
gauge constraints, inflatable tanks also scale down to smaller sizes
much better.


An approach that this brings to light is to use a light weight cabin
shell which is good for one atmosphere, with the inflatable tanks
mounted internally. This serves a number of functions, including the
protection of the inflatable tanks.

Considering such a long cylinder with rocket engines mounted at one end,
(VTOL or HTHL), the inflatable tanks could be longitudinally displaced
with one end at the rocket engine so as to be structurally self
supporting.

With a barrier curtain between the LOX tanks and cabin area ice build up
on the LOX tanks can be prevented, (air dehumidification), such that
insulation is not necessarily required.

With a positive cabin pressure the inflatable tanks can be pumped out to
the last. Once empty the available space can become extra cabin space.
This might be particularly useful for longer trips.

While the increased size of the cabin pressure vessel shell weighs more,
this can add to propellant pressure and so is somewhat mitigated. This
allows for a fluffy re-entry design.

The internal inflatable tank layout is very flexible enabling variations
to accommodate unusually shaped payloads. It would suit a growing
rotovator where tankage wants to be progressively swapped for payload.
One might also swap the tanks out for use as inflatable habitats,
radiators, farms, etcetera. By terminating each inflatable tank at the
tail, the need for intertank structures and long feed lines is also
avoided.


Pete.