Pack for a day trip to mars!

[KrazyHorse]

Originally posted by Geronimo


spiff think twice about that. The difference between earths atmospheric pressure at sea level and a total vacuum will be just one atmosphere. So how could the difference between earth and mars atmosphere be equivalent to a difference of 100 atmospheres?

For physiological considerations it will be absolute change in pressure not relative changes in pressure that are going to matter.

Actually, for physiological considerations the problem is the absolute pressure, period.

Human beings can withstand hyperbaric environments pretty well. At some point you start cutting down on the percent concentration of oxygen in the breathing mix and replacing it with inert gas to avoid oxygen poisoning. The problem with very low pressure is that human beings require at least a certain partial pressure of oxygen in the air they breathe. If the external pressure is much lower than that you can't survive. Period.

[KrazyHorse]

So all this bull**** about how well people can go from high pressure to regular atmospheric pressure if they take proper precautions has nothing to do with the problem at hand.

[KrazyHorse]

C'mon, geronimo: instead of arguing semantics with Spiffor explain to me how you plan to maintain a pressure differential between the lungs and the environment of at least 15 kPa

[Geronimo]

Originally posted by KrazyHorse
C'mon, geronimo: instead of arguing semantics with Spiffor explain to me how you plan to maintain a pressure differential between the lungs and the environment of at least 15 kPa

15 kPa = 112.5 mm Hg.

the minimum threshold for barotrauma is about 80 mm Hg

Someone who gradually builds up such a pressure difference for several weeks in preperation might conceviably endure the 15kPa difference for a few hours without permanent damage.

[DanS]

It might be possible, as Dan said, to wear a skintight suit which would, by its elasticity, provide sufficient, even pressure across the entire body. No such suit exists, AFAIK. The technical requirements to fit such a suit exactly and to have it provide even pressure under large expansions (such as breathing) are far greater than those required for a simple pressurised suit.

Actually, I can't confirm that this is true. The research on this point is modest, but what is out there seems to suggest that success has to do with fabric choice rather than exotic modifications. Personally, I wonder about the adequacy of the heating and cooling more than the idea of mechanical pressurization.

[Geronimo]

KH, do you know a way to calculate how much atmosphere a body with Mars's gravity could hold before it would start leaking off into space at an appreciable rate?

[DanS]

My second question is could we make a habitat for the day traveller to sleep in so that he can extend his stay. Once again using items that are commercially available or at least relatively cheap.

Taking a **** would be a problem. Other than that, you could probably eat liquid food that is heated and pressurized using a mechanical pressure cozy, just like the skintight suit.

Area heating might be a problem (like in a tent), although you might be able to work up a ground heat pump in some fashion.

[KrazyHorse]

Originally posted by Geronimo


You're underestimating the durability of the lungs. The minimum pressure difference required to risk pulmonary barotrauma is about 80 mm Hg .

80 mm Hg = 10 kPa

So we're 50% above that at least

That assumes the minimum oxygen level for survival and that we're operating in a 100% oxygen atmosphere.

the 300kg weight analogy doesn't seem right either. The pressure difference experienced by the aorta for example is on the order of 18 kPa and it's hard to imagine it would be equiped to hold back a 300kg weight.

My god. Force = pressure X area

The chest has a much larger area than the cross-section of the aorta. probably by a factor of 1000 or so. Thus for an equivalent pressure differential the chest experiences a force 1000 times greater.

[KrazyHorse]

Originally posted by Geronimo
KH, do you know a way to calculate how much atmosphere a body with Mars's gravity could hold before it would start leaking off into space at an appreciable rate?

IIRC the lifetime for an atmosphere comparable to the Earth's would be on the order of 10 000 years. Can't recall exactly.

[chequita guevara]

Originally posted by Geronimo
KH, do you know a way to calculate how much atmosphere a body with Mars's gravity could hold before it would start leaking off into space at an appreciable rate?

It's not the size of the body that's the problem. It's that Mars doesn't have a molten core, which would generate a magnetic field around the planet, which would deflect solar particles and keep them from blowing away the atmosphere. Consider that Venus has an atmospheric pressure 900 times that of Earth.

[DanS]

Mars does have at least a partially-molten core.

[KrazyHorse]

Originally posted by Geronimo
Someone who gradually builds up such a pressure difference for several weeks in preperation might conceviably endure the 15kPa difference for a few hours without permanent damage.

I truly doubt it. You're welcome to try, though.

Might be possible for a couple of minutes. Not for an hour.

Assuming everything went perfectly you're still exerting yourself heavily to breathe in a strong pressure diffential with very very little oxygen while your lung tissue is slowly being ripped, your blood vessels are becoming badly swollen etc.

You're 50% above the safe limit of pressure differential at best. That's not very bright.

[KrazyHorse]

Originally posted by chegitz guevara


It's not the size of the body that's the problem. It's that Mars doesn't have a molten core, which would generate a magnetic field around the planet, which would deflect solar particles and keep them from blowing away the atmosphere. Consider that Venus has an atmospheric pressure 900 times that of Earth.

Actually, chegitz, the size of the body is the problem. Mars would lose its atmospher something like 100 times faster than the Earth does if they had equivalent surface pressures (these are rough figures and I'm quoting them from a source I read something like 10 years ago, so they might be off).

So in addition to the fact that the Earth retains its atmosphere much better than Mars does, there is also the replenishment issue (the Earth replenishes its atmosphere at a much higher rate than Mars does too).

The difference between Venus and the Earth is solely due to the supply issue (there are geysers of sulfur dioxide etc. constantly being pumped out from the surface of venus at an incredible rate). Between the Earth and Mars it's due to both supply and loss.

As for the magnetic field slowing loss, it might have an effect, but the basic issue is one of diffusion. The smaller the potential well you trap the gas particles in the faster they escape.

[chequita guevara]

Originally posted by DanS
Mars does have at least a partially-molten core.

But it doesn't spin, which is what generates the magentic field.

[DanS]

Make up your mind about why there is no magnetic field.