Pop quiz: diving on the moon

[Zept]

Two astronauts land on the moon. To the surprise of NASA, and the entire scientific community, their spacecraft settles alongside a large, deep lake of pure water. Fortunately the astronauts have their diving gear. Understandably, they are keen to dive, but, hmm...

Can they use their dive computers?

Can they plan their dive using tables?

Assume their drysuits will protect them from micrometeorites, solar radiation, freezing to death and/or overheating.


Z

Disclaimer -- This is just for fun. Diving on the moon is dangerous and requires specialist equipment and training.

 

[sumguy]

Well, I know MY computer wouldn't work. It would think it was at an altitude higher than 14000 feet (and it would be right) and it would shut itself off.
Being resourceful NASA types, I'm sure they'd whip up a formula to allow them to use standard diving tables.

 

[Newhampster]

One sixth the gravity means that if there were an atmosphere, atmospheric pressure (at "sea level") would be 2.45 psi.

Assuming the water was not frozen and not boiling, then...

Every 198 feet you descended would equal one earth atmosphere (14.7 psi).

So...(all of this is my quick speculation, no real thought involved...):

You could use your dive tables provided you compensated by "adjusting depth" readings.

Depth readings would be easy with a meaured rope. Just divide the measured depth you're at by 6 and look it up in the tables.

If you used an SPG (pressure gauge), it would automatically compensate for the change in gravity so...when it read 33 feet, you'd really be at a measured 198 feet but the pressure would be 14.7 psi...

Assuming your computer was properly hardened to deal with cosmic radiation, it would be "accurate" the same way the SPG would be.

So...what am I forgetting, eh?

 

[MikeS]

Even ignoring the temperature issue, with one-sixth earth’s gravity there would not be enough atmospheric pressure for water to stay in a liquid state. Water must be pressurized to stay in a liquid state; otherwise it will turn to a gas. The 14.7 psi at earth sea level is more than sufficient.

Sorry to be a party pooper but if you change the laws of physics to let water exist without pressure, the tables, based on the same laws of physics would no longer be valid.

Mike

 

[Rick Murchison]

Our Apollo astronauts used full pressure suits pressurized to 5psi, breathing pure oxygen. So, for deco purposes, there is no Nitrogen side of the problem, and no worry about DCS. There is, however, an oxygen side, exacerbated by the fact that our astronauts are breating oxygen at about .35 ATMe ("e" for "earth normal") all the time, and so are concerned with pulmonary (whole body) oxygen toxicity. Under the circumstances, I'd say they'd be looking at a max diving oxygen exposure of about 1.0 ATMe, and they'd probably want to limit that to less than an hour. So, at one sixth gravity, I'd put their max depth at about 130 feet.
Funny how that works out...
Rick
PS MikeS is correct that the vapor pressure of liquid water would cause it to evaporate immediately, but then this is a brain game, ain't it?

 

[devilfish]

It's too early in the morning but to start, if we understand high altitude diving, if on the moon the athmospehre pressure is 2.45 psi then according to Boyle's Law each athmosphere would increase every 5.54 ffw providing fresh water has the same density as on earth. At 5.54 ffw would be 2 ata, at 11.08 ffw would be 3 ata, at 16.62 ffw would be 3 ata, and so on.

 

[Rick Murchison]

Originally posted by devilfish
It's too early in the morning but to start, if we understand high altitude diving, if on the moon the athmospehre pressure is 2.45 psi then according to Boyle's Law each athmosphere would increase every 5.54 ffw providing fresh water has the same density as on earth. At 5.54 ffw would be 2 ata, at 11.08 ffw would be 3 ata, at 16.62 ffw would be 3 ata, and so on.

That is correct, however it is irrelevant - the depth/ATM importance has to do with inert gas bubble formation - e.g. DCS from Nitrogen when breathing air. American Apollo astronauts used pure oxygen, and oxtox is a function of absolute pressure, not ATM. We *use* ATM in diving because it is convenient - but for oxtox purposes when we say 1.0ATM exposure, we mean 14.7psi, not one actual atmosphere.
Rick

 

[Jef]

You folks are beginning to worry me.

 

[devilfish]

Of course its irrelevant, astronouts would not be diving on open circuit scuba. As for o2 breathing, what is the protocol for preox before spacewalk in suits. the last I heard was something like 45 min while exercising.
The whole question of diving on the moon I took it as theoretical and fun.

 

[Uncle Pug]

Zept... I am proud of you.... nice hijack....
And:
Sumguy... you got the right idea... sit this one out...
Newhampster... your 7th word is a key...
MikeS... poop on... pertinent observation...
Rick... way to hit the real issue!
Devilfish... have a latte on me... what atmosphere?

btw: there is evidence from what tenuous atmosphere exists on the moon that divers have indeed been there.... and techdivers at that!