Incoming!!!

Henry Spencer wrote:
In article ,
Josh Gigantino wrote:

Would water available on orbit be the opposite situation? Fuel, water
and atmosphere are all vital and easily (relative...) derived from
cometary& NEO ices. Especially in the next 10-20 years, any onorbit
delivery of water in quantity could be immediately used there -
perhaps in the later life of ISS, maybe on a Bigelow-built or MirCorp
hotel or for a Mars shot.


Careful here. Relatively pure water (which in itself is a significant
assumption) would have a modest LEO market, perhaps tons per year, for
life-support uses. It won't get a lot bigger than that soon unless the
LEO tourist business really booms.

The fuel market is much less certain, because turning water into fuel is
actually a difficult and expensive process. It's *conceptually* simple,
but the engineering is not as easy as it looks. Electrolysis is grossly
energy-intensive, and then you get into the difficulties of orbital
storage of LH2. And there is no current market, none, for LOX/LH2 in LEO,
because the current users are not set up to take on fuel there. Future
bulk users, like Mars expeditions, are all highly speculative.

Besides water ice, comets are thought to have methane ice.

I'm not sure how much methane an accessible NEO comet would have, though.

--
Hop David
http://clowder.net/hop/index.html

Joseph Hertzlinger m.retro.com wrote in message ...
On 9 May 2004 07:45:42 -0700, Mike Miller wrote:

The hoop stress in the sphere would be a piddly 29000psi, well within
the range of metals to resist. Pure aluminum is almost up to the task.
That stress should increase linearly with increasing radius of the
vacuum balloon, assuming wall thickness stays the same. By 60m, you
should have a lot of net lift.

We're not dealing with tensile strength, we're dealing with resisting
buckling.

Is the term "hoop stress" exclusive to tensile strength? If so, I used
the wrong term. The numbers don't change, except to urge a bit more
fudge room to fit in some orthogonal stiffener mass.

Mike Miller, Materials Engineer