On 8 Nov 2017 at 13:41, Grimmund wrote:

> Back to my earlier point.  Big air tanks in the cargo hold, and pump
> most of the ship's air into the tanks for storage.  (Run it through a
> desiccator and a filter, so you don't get anything growing in the
> tanks.)

dehumdifier shouldn't be needed as high pressure air is *very*
hostile environment for most bacteria and the like (that's why
hyperbaric chambers are a good treatment for a number of nasty
infections.

Also, what exactly would the organisms be using to grow? All there
would be would be O2, N2, H2O and maybe some CO2. and no energy
sources.

But storing the air on the ship makes no sense because high pressure
tanks will leak faster than normal atmosphere in compartments. At
least over long periods of timee.

Just pump replace the ship's atmosphere with dry nitrogen (done in
some kinds of mothballing even here on earth). The air yopu remove
can be used by other ships or the mothballing facility.

> Inert gas would make sense for long term storage, but only if you have
> an bottomless budget and a substantial supply.  (I have no idea how
> much is available at the local gas giant.).  I would also suggest
> that N2 would be fine for storage if you wanted to use an inert
> atmosphere mix.  But inert atmosphere mixes also make it much more
> dangerous to do anything on board the stored hulks, as any failure of
> your breathing gear is likely to be fatal.  

The whole point of mothballing is that you aren't planning to do
anything on board for a long time.

Also, given that they've had space travel for longer than we've had
writing, I dare say that their suit protocols are up[ to it.

> Storage with low pressure breathing mix would probably be fine, and
> while not fabulous to breathe, unlikely to be immediately fatal.  I
> suspect "minimum survivable breathing mix/pressure" would be the
> standard storage atmosphere, just to make the job less risky for the
> yard crews.  

Sorry, but low pressure breathing "mix" is pretty much pure O2 at 3
psi. and transitioning to it requires an hour or so of pre-breathing
and other thiungs to avoid the bends.

And you *don't* want oxygen in there for long term storage because
oxygen is corrosive. At the low pressure it's not too much of a fire
hazard, but it'll still run counter to the purpose.

Lower pressure  does mean there'd be less "strain" on seals, but
there are going to be sealed systems  that will be more likely to
leak at the lower pressure (because the pressure inside them is
higher than the outside now).

And low pressure makes various items containing volatiles (like a lot
of plastics) more likely to outgass, which can make them brittle.

That's the whoile *point* of maintaining normal pressure or even
slightly elevated pressure when mothballing.

> Likewise, venting to vacuum for long term storage still means you need
> to bring air to resupply the ship if you want to put it back in
> operation.  That may be challenging, particularly for a large ship.
> Plus, the risks of all the various mechanical problems that vacuum
> storage may generate.  

Venting to vacuum guarantees the outgassing problem. It'd also
require testing to make sure the seals are still good.

If you have normal or normal+ pressure in the ship, you'll *know* if
seals have gone bad because the pressure in a compartment with bad
seals will be siginificantly lower than when it was mothballed.

Replacing the atmosphere isn't that big a deal. Not for a culture
that has larger space habitats and planets with breathable atmospher.

Also, if you use nitrogen, you can just fill the oxygen tankage and
turn on the air recycling system and soon enough the "excess"
nitrogen will have been extracted and stored while the necessary
oxygen has been added. that's the sort of thing the air system is
*designed* to do.

Ditto for adding humidity.
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com