Author Topic: Weir's The Martian.  (Read 44769 times)

Offline darren r

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Re: Weir's The Martian.
« Reply #15 on: June 08, 2015, 02:25:56 PM »
I don't know why - there's certainly no reference to it in the text - but when reading this book I always imagined that the Watney character was black. So as much as I like Matt Damon, I was a bit disappointed to find that they'd cast him instead of a black actor. Strange how your mind works sometimes.
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Offline LunarOrbit

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Re: Weir's The Martian.
« Reply #16 on: June 08, 2015, 08:51:13 PM »
I already knew Matt Damon was cast in the role when I read the book, so I guess I didn't really have a chance to imagine the character any other way.

They released a full trailer today. I'm pretty excited for the movie.

« Last Edit: June 08, 2015, 08:53:25 PM by LunarOrbit »
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Offline smartcooky

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Re: Weir's The Martian.
« Reply #17 on: June 09, 2015, 01:30:42 AM »
"..... I'm going to have to science the shit out of this!"


I love it!!!
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline onebigmonkey

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Re: Weir's The Martian.
« Reply #18 on: June 09, 2015, 03:14:10 PM »
I'm looking forward to seeing this, but I feel like I only have to bother with the last 20 minutes thanks to the trailer!

Offline smartcooky

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Re: Weir's The Martian.
« Reply #19 on: June 10, 2015, 08:36:51 PM »
An interesting issue has come up about a technical aspect of this story regarding Watney's breathing oxygen. A post on another forum has suggested that it would be hazardous to use pure oxygen for the hab over a long period

"Doesn't a long stay on Mars require lots of nitrogen gas? A person can't stay on pure oxygen the whole time right? There was mention of oxygen toxicity and making oxygen from CO2, but nothing of how the lost nitrogen was made up for. "

The answer to that should be that you don't need nitrogen or anything else to "make up the difference". You just breathe pure oxygen at a partial pressure equivalent to the % of oxygen in the atmosphere; 21% so that's about 3.1 psi.

However, the issue of the Apollo 1 fire then came up...

"Apollo One showed one problem with pure O2"

I fired off a quick reply to the effect that the real cause of Apollo 1 was an electrical spark, combined with the massive amount of flammables used inside the capsule, especially velcro and nylon netting, combined with the fact that the O2 level inside was at 16.7 psi, 2 psi higher than atmospheric pressure.

But now, I'm not so sure. Would the Apollo 1 fire have still happened if they had been breathing air, or breathing pure O2 at a partial pressure of 0.21 atm. 
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline ka9q

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Re: Weir's The Martian.
« Reply #20 on: June 11, 2015, 09:28:00 AM »
Aerobic organisms (like us) and fires both depend on oxygen, but respond differently.

Oxygen diffuses from the air through our lungs into the bloodstream in a "downhill" direction, i.e., from a high partial pressure in the air to a lower one in the blood. This won't work unless the oxygen has a minimum partial pressure. (One of the reasons you'd lose consciousness so quickly in a vacuum is that the oxygen already in your blood will diffuse back out through your lungs.) We also can't let that partial pressure get too high or the excess oxygen will become toxic, even fatal.

Adding inert gases to increase total air pressure has little or no effect (within reason) as long as they're not highly lipid soluble (which tends to make them anesthetic) or allowed to dissolve into body tissues and then rapidly released by a sudden drop in total pressure. That causes the bends.

Fires are different because nominally inert gases can carry away heat. This means pure oxygen is a greater fire hazard than air even when the partial pressures of oxygen are the same. Somewhere I saw a film of a Sealab mission in which the crew demonstrated the impossibility of striking a match in their high pressure helium/oxygen atmosphere. Even though there was plenty of oxygen for the crew, all that helium cooled the match head before it could ignite the match.

Some nominally inert gases also lose their inertness at high temperatures and interfere in the chemical reactions of a fire; this is how Halon worked.

« Last Edit: June 11, 2015, 09:33:01 AM by ka9q »

Offline BazBear

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Re: Weir's The Martian.
« Reply #21 on: June 11, 2015, 01:40:32 PM »
An interesting issue has come up about a technical aspect of this story regarding Watney's breathing oxygen. A post on another forum has suggested that it would be hazardous to use pure oxygen for the hab over a long period

"Doesn't a long stay on Mars require lots of nitrogen gas? A person can't stay on pure oxygen the whole time right? There was mention of oxygen toxicity and making oxygen from CO2, but nothing of how the lost nitrogen was made up for. "

The answer to that should be that you don't need nitrogen or anything else to "make up the difference". You just breathe pure oxygen at a partial pressure equivalent to the % of oxygen in the atmosphere; 21% so that's about 3.1 psi.

However, the issue of the Apollo 1 fire then came up...

"Apollo One showed one problem with pure O2"

I fired off a quick reply to the effect that the real cause of Apollo 1 was an electrical spark, combined with the massive amount of flammables used inside the capsule, especially velcro and nylon netting, combined with the fact that the O2 level inside was at 16.7 psi, 2 psi higher than atmospheric pressure.

But now, I'm not so sure. Would the Apollo 1 fire have still happened if they had been breathing air, or breathing pure O2 at a partial pressure of 0.21 atm.
From what I've read about the Apollo fire, a regular atmospheric mixture of gases would not have allowed the type pf conflagration that happened; I'm really not sure if that means a less intense fire or no fire at all.

I'm not sure about how much the fire hazard is reduced at partial pressure, but I am thinking the spacecraft might have imploded had you depressurized the CM to .21 atm at (virtually) sea level.
"It's true you know. In space, no one can hear you scream like a little girl." - Mark Watney, protagonist of The Martian by Andy Weir

Offline smartcooky

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Re: Weir's The Martian.
« Reply #22 on: June 14, 2015, 04:56:37 AM »
Aerobic organisms (like us) and fires both depend on oxygen, but respond differently.

Oxygen diffuses from the air through our lungs into the bloodstream in a "downhill" direction, i.e., from a high partial pressure in the air to a lower one in the blood. This won't work unless the oxygen has a minimum partial pressure. (One of the reasons you'd lose consciousness so quickly in a vacuum is that the oxygen already in your blood will diffuse back out through your lungs.) We also can't let that partial pressure get too high or the excess oxygen will become toxic, even fatal.

Adding inert gases to increase total air pressure has little or no effect (within reason) as long as they're not highly lipid soluble (which tends to make them anesthetic) or allowed to dissolve into body tissues and then rapidly released by a sudden drop in total pressure. That causes the bends

So 0.21 atm of pure oxygen (3 psi) would be too low, but it would not be necessary to "fill up" with inert gas all the way to 1 atm would it? Is there some lower pressure that would be sufficient and safe?
« Last Edit: June 14, 2015, 05:02:13 AM by smartcooky »
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline smartcooky

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Re: Weir's The Martian.
« Reply #23 on: June 14, 2015, 05:02:50 AM »
Adam Savage interview with Andy Weir.

Its 55min long and worth every minute of the time spent watching it..........

« Last Edit: June 14, 2015, 05:48:32 AM by smartcooky »
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline ka9q

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Re: Weir's The Martian.
« Reply #24 on: August 22, 2015, 02:49:07 AM »
I finally got and read the book, and it's every bit as good as everybody says.

I read most of it on a cross-country flight, and I didn't even mind that a jetbridge problem kept our flight at the arrival gate for a whole hour because it gave me enough time to finish it. Yes, it's that good.

The whole story is driven by a particularly perverse form of Murphy's Law: anything that can go wrong will go wrong -- but it won't actually kill you, and you'll still figure out a way. It's a little like the old Columbo TV series where there was never any mystery as to who the murderer was; the fun was in watching the battle of wits between Detective Columbo and the bad guy. And just as you know that Mark Watney must ultimately survive -- after all, this is fiction, and he is the hero -- the fun is in seeing how he survives.

Naturally, I'll soon have a long list of technical quibbles, but they're really quite minor given that nearly all of what passes for "science fiction" these days is really fantasy. This is hard science fiction of a quality I haven't seen in a very long time.
« Last Edit: August 22, 2015, 02:58:48 AM by ka9q »

Offline bknight

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Re: Weir's The Martian.
« Reply #25 on: August 22, 2015, 07:49:41 AM »
From what I've read about the Apollo fire, a regular atmospheric mixture of gases would not have allowed the type pf conflagration that happened; I'm really not sure if that means a less intense fire or no fire at all.

I'm not sure about how much the fire hazard is reduced at partial pressure, but I am thinking the spacecraft might have imploded had you depressurized the CM to .21 atm at (virtually) sea level.
While the hazardous nature of pure oxygen is reduced  by the partial pressure, it is certainly not eliminated.  The fire in Apollo 1 was a ticking time bomb as all ground tests of American spacecraft had used pure oxygen at an elevated pressure versus ambient pressures.  NASA was lucky for many years and grew complacent concerning fire.  Even with the partial pressures of 3.5-5 psi. fire is a concern.
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Offline ka9q

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Re: Weir's The Martian.
« Reply #26 on: August 22, 2015, 12:25:04 PM »
Even with the partial pressures of 3.5-5 psi. fire is a concern.
Yes, there were a whole bunch of post-fire tests that came to the same basic conclusion.

A diluent gas like nitrogen conducts heat away from a fire, reducing the hazard even when the ppO2 is the same.

Since helium has a much higher thermal conductivity (0.142 W/m-K) than nitrogen (0.024), I wonder if using it as the diluent might allow a lower total pressure. This is always desirable in a spacecraft for weight reasons. If the speech problem is intolerable, consider neon. Its thermal conductivity (0.046) is much lower than helium, but it's still twice as high as air. Argon is cheap, but at 0.016 it's even worse than air (that's why it's used to fill double-pane windows).

Hydrogen has an even greater thermal conductivity than helium, but...
« Last Edit: August 22, 2015, 12:31:20 PM by ka9q »

Offline bknight

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Re: Weir's The Martian.
« Reply #27 on: August 22, 2015, 12:33:07 PM »
...

Hydrogen has an even greater thermal conductivity than helium, but...
Hydrogen is even more flammable, a Zeppelin in outer space!
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Offline grmcdorman

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Re: Weir's The Martian.
« Reply #28 on: August 22, 2015, 12:34:56 PM »
Not if it's pure hydrogen. Get rid of all that nasty wasty oxygen! :P

Offline bknight

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Re: Weir's The Martian.
« Reply #29 on: August 22, 2015, 12:37:23 PM »
Not if it's pure hydrogen. Get rid of all that nasty wasty oxygen! :P

Seriously though, was there ever a small fire extinguisher in Apollo/Shuttle?  Seems like a reasonable piece of equipment even though it has mass(maybe not as bad for the Shuttle.
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan