Weir's The Martian.

[smartcooky]

The book actually plays looser with partial pressures than with most of the chemistry presented. It talks about relative percentages but doesn't really go into ppO2 being the critical value at all. In the book the astronauts are breathing mixed N2/O2 at ~100 kPa in the fabric-constructed hab as well as on EVAs; I have no idea if that would be considered on an actual mission but it seems unlikely.

* * * * * SPOILER * * * * *

OK, so I think my question #3 earlier

3. Would taping some plastic sheeting over the gapiing hole left by the malfuntion of the HAB airlock have been enough to keep the HAB pressurised?

Definitely had some validity.

The hole was at least 8ft in diamater, its area given by πr²

R = 48" , so
a = 7238 in² at 14.83 lb in²

Thats a force of 107,342 lb (nearly 48 tons) pushing out on that plastic sheeting.

Surely, it would puff out tight like a baloon and not flap around in the breeze like to did. I was anly held in place with a few strips of duct tape so I would not be trusting that enough to wander around inside the HAB without a spacesuit on.

[Dalhousie]

Does Weir actually mention the pressure/partial pressure the Ares crew would be breathing in their suits on the surface and in the HAB? I haven't read the book, and if it was mentioned in the movie, or there was a graphic showing it, I missed it.

The book actually plays looser with partial pressures than with most of the chemistry presented. It talks about relative percentages but doesn't really go into ppO2 being the critical value at all. In the book the astronauts are breathing mixed N2/O2 at ~100 kPa in the fabric-constructed hab as well as on EVAs; I have no idea if that would be considered on an actual mission but it seems unlikely.

I think you are right.

[Dalhousie]

The book actually plays looser with partial pressures than with most of the chemistry presented. It talks about relative percentages but doesn't really go into ppO2 being the critical value at all. In the book the astronauts are breathing mixed N2/O2 at ~100 kPa in the fabric-constructed hab as well as on EVAs; I have no idea if that would be considered on an actual mission but it seems unlikely.

* * * * * SPOILER * * * * *

OK, so I think my question #3 earlier

3. Would taping some plastic sheeting over the gapiing hole left by the malfuntion of the HAB airlock have been enough to keep the HAB pressurised?

Definitely had some validity.

The hole was at least 8ft in diamater, its area given by πr²

R = 48" , so
a = 7238 in² at 14.83 lb in²

Thats a force of 107,342 lb (nearly 48 tons) pushing out on that plastic sheeting.

Surely, it would puff out tight like a baloon and not flap around in the breeze like to did. I was anly held in place with a few strips of duct tape so I would not be trusting that enough to wander around inside the HAB without a spacesuit on.

I got similar numbers.  I don't think it would work.  In the book he uses "hab canvas" and much more robust sealants.

[Dalhousie]

There is the very common failure in heltent design (about as common as sound in space) - lights in the helmet.  This was first shown in Outland I think.  It would never work, because it would blind the wearer's night vision.  The reason for it in films is obvious of course, it is to show the astronaut's face

[Dalhousie]

On another board someone asked why people were so obsessively picking technical nits with this movie, when technobabble and worse in star wars or star trek gets off almost scott free.  One reply was intriguing, there is an equivalent of "uncanny valley" in depiction of humans, as one gets very close to reality people notice the technological issues more and are more upset by them. 

There might be something in this.  It got to the point with Gravity that people think it was a very bad movie, when it's not.  I would be very sorry if that happened here.  Not only is it a more positive movie that Gravity, I think, like it, the film as a good chance of a Hugo and an Oscar.

[ka9q]

If someone had told me beforehand, the type of music they would use in this movie, I would have said WTF? However, it workeds really well.

As running gags in space movies go, that wasn't a bad one.

But if I had been selecting the rest of the music, I would definitely have used Ralph Vaughan-Williams' Sinfonia Antartica. He originally wrote it as the score for the 1947 movie Scott of the Antarctic and later turned it into a complete symphony (his 7th). I think it is one of the most vivid tone poems ever written, and it's just as good at conjuring up images of Mars as of the Antarctic. It would have been ideal for those outstanding wide CGI shots of Watney's long treks.

[ka9q]

On another board someone asked why people were so obsessively picking technical nits with this movie, when technobabble and worse in star wars or star trek gets off almost scott free.  One reply was intriguing, there is an equivalent of "uncanny valley" in depiction of humans, as one gets very close to reality people notice the technological issues more and are more upset by them. 

I've been saying exactly that for some time -- sure it wasn't me?

Don't get me wrong, it's because The Martian is such an excellent movie overall that we enjoy picking nits in it, just as generations of fans have been picking nits in Star Trek. If I thought it was a bad movie I wouldn't be talking about it.

[ka9q]

WARNING: BEYOND THIS POINT THERE BE SPOILERS
Just a couple of nitpicks and questions

1. the obvious one was the storm that injured Watney at the beginning. As has been stated, it could not have caused the damage it did due to the low pressure of Mars' atmosphere.

Right. He might have picked some other plot device that required the crew to make a fast getaway and leave Watney behind for dead. Maybe an unstoppable leak in the fuel system that forced them to launch immediately or be stranded.

2. When the HAB airlock malfunctioned and blew off, Watney's helment visor was punctured, and he lost pressure, it seemed to take about 30 secoinds to get down to 5% pressure, but once he taped over the cracks and the small hole, it was almost instantly restored to nominal. Really? That quickly, and what anout the bends?

That wasn't too unrealistic. A PLSS automatically adds O₂ through a pressure regulator to replace metabolic consumption, and it will also keep a suit pressurized against leaks if the max regulator flow rate is high enough -- until your high pressure oxygen supply runs out. It might well maintain survival pressure against the leaks depicted for some time, especially if the PLSS was augmented with an Apollo-style OPS. (The flow of a pressurized gas through a small hole is generally Mach 1.) But I don't remember if the warning was for low suit pressure or a low oxygen supply. The former would cause him to pass out quickly; the latter would require him to get to shelter quickly before he exhausted what was left of his oxygen supply.

3. Would taping some plastic sheeting over the gapiing hole left by the malfuntion of the HAB airlock have been enough to keep the HAB pressurised?

Absolutely not, as others have already shown. It sure looked like HDPE to me, nothing magical. And the Martian wind even depresses it inward at one point. No way.

4. Could they really have accurately calculated the deceleration effect of blowing the front airlock off the Hermes

Maybe. The whole bit with blowing off the airlock door was over the top. The reason for doing it, as I recall, was that an interlock prevented both doors from being opened at the same time. It would have been far more realistic (if not as dramatic) for one of the crew to just hotwire the damn thing. But the story has you on the edge of your seat by that point so you can sort of excuse it.

5. Would puncturing his glove really have worked the way it was depicted? How was he able to stop it leaking, once Lewis caught him, long enough to get him into Hermes?

Seems unlikely. He does kinda forget about the leak later, doesn't he?

I noticed another "physics failure" in that sequence (one of several). At one point Lewis and Watney are wrapping themselves in Lewis's tether, which draws them toward the airlock and each other. That should have had them spinning like a neutron star due to angular momentum conservation. Maybe Lewis' maneuvering unit was better than I thought.

[ka9q]

A few more nits not already mentioned (SPOILERS):

Scavenging Hydrazine

Watney apparently drains surplus descent stage hydrazine through the engine nozzles. Strange, anybody who knew liquid rockets would use the fill-and-drain valves provided for exactly that purpose.

Straight hydrazine (N2H4) freezes at +1C. No way it would still be liquid on Mars. Although a large rocket would more likely use UDMH, MMH or Aerozine-50 (50-50 UDMH + N2H4) with lower freezing points (but which would still probably freeze on Mars) he uses a catalyst to decompose it. That only works with straight hydrazine.

Not sure why he couldn't just burn the fuel directly. Also, it's incredibly toxic and I very seriously doubt he could burn it completely enough to avoid all sorts of noxious byproducts (NH3, etc).

The RTG Space Heater

Use of a Pu-238 RTG as space heater is entirely plausible and wouldn't be dangerous at all unless you deliberately cut it open (as he does concede). Many pictures exist of workers (some in ordinary clothes) around fueled RTGs at launch sites. I had that idea way back during Apollo 13 when I heard how cold they were. But it would have required a hazardous EVA for which they had not trained, and it wasn't truly necessary anyway.

There's no plausible reason you'd ever want to throw away something as valuable as several kg of Pu-238 on Mars, especially when you have a habitat that needs a lot of heating.

Burying a fueled RTG in deep sand would almost certainly insulate it so well that the fins would melt, if not the whole thing.

Martian Dust
Not sure a spacecraft would be totally buried by dust after only 2 decades or so. (The setting isn't specified, but the JPL Pathfinder guys didn't look that old.) I think the orbiting cameras have spotted the two Vikings that have been there 40 years now.

JPL and JSC
I've been to both places several times; they look nothing like their gleaming, modern depictions in the movie. Think 1960's University Institutional.

[ka9q]

While picking nits I should be fair and cite elements of the story that I think worked really well.

The real standout is that great, nail-biting rescue sequence. You must match position and velocity in a rendezvous, and because you don't have the fuel to decelerate into Mars orbit and escape again, it has to be a flyby. And that means you get only one shot at the rescue, which creates an enormous amount of suspense. It was a perfect example of working with physical laws to drive your story instead of just dismissing them with lame handwaving.

After Gravity I was so delighted to see some realistic trajectory physics that I was willing to overlook the more unrealistic, over-the-top elements like using an IED to blow off an airlock door and puncturing Watney's suit to act as a maneuvering jet. That kind of seat-of-the-pants space physics is very unlikely to work in real life. But it was still great fun. That's the section I was reading when my plane got stuck at the arrival gate for an hour, and I was so engrossed I didn't mind.

[ka9q]

Does Weir actually mention the pressure/partial pressure the Ares crew would be breathing in their suits on the surface and in the HAB? I haven't read the book, and if it was mentioned in the movie, or there was a graphic showing it, I missed it.

Yes in both places. In the movie it frequently shows up as on-screen telemetry in his video recordings. We were seated toward the left side of the theater and they were almost in front of us on the left side of the screen. It was ordinary air slightly below sea level pressure.

I was surprised that he didn't seem to research this one very well. He was supposedly talking to lots of NASA guys and other space geeks, so one of them should have explained that even after 5 decades of work, nobody has yet produced a really comfortable suit that operates at ~0.22 bar, much less a full 1 bar. And because the crews were doing frequent EVAs, that would call for the habitat also being pure or nearly pure O₂ at reduced pressure to avoid decompression sickness ("the bends"). That would also greatly reduce the stress on the structure (which we find is an actual problem).

There is at least one confirmed case of decompression sickness during flight in the US program: Michael Collins during Gemini X. He didn't report this at the time for fear of never flying again, but he did write about it in his book Carrying the Fire. He was more careful to follow the prebreathing protocols before his Apollo 11 flight and didn't have a problem.

[sts60]

There is the very common failure in heltent design (about as common as sound in space) - lights in the helmet.  This was first shown in Outland I think.  It would never work, because it would blind the wearer's night vision.  The reason for it in films is obvious of course, it is to show the astronaut's face

This always reminds me of Mad's long-ago spoof of the original Battlestar Galactica, specifically a scene where Baltar is glowering from his throne and the oily Cylon henchman asks him, "Is there anything else I can do for you, Imperious One?"*

"Yes! You can turn off these lights that are always shining up into my face to make me look evil!  They're driving me crazy!"

* dialog recall not guaranteed; Mad's exact wording was of course much funnier.

[Zakalwe]

How come a storm was strong enough to tilt the MAV over to critical levels, thus enforcing a rapid take-off, yet NASA was happy to send a similar design to sit in Schiaperalli or a number of years?

[ka9q]

How come a storm was strong enough to tilt the MAV over to critical levels, thus enforcing a rapid take-off, yet NASA was happy to send a similar design to sit in Schiaperalli or a number of years?

Just...Because....

You could also ask why NASA never heard of guy wires.

I suppose NASA would think it a very unlikely occurrence, especially since it's impossible in reality, but this being fiction the author has the right to cause all sorts of unlikely things to happen.

Kinda like the opening scene in Rosencranz And Gildenstern Are Dead, when they're flipping a coin and it comes up heads 92 times in a row. They realize the extreme unlikeliness of this according to the laws of probability, and begin to speculate that they're not real or that somebody is controlling everything that happens.

[Dalhousie]

On another board someone asked why people were so obsessively picking technical nits with this movie, when technobabble and worse in star wars or star trek gets off almost scott free.  One reply was intriguing, there is an equivalent of "uncanny valley" in depiction of humans, as one gets very close to reality people notice the technological issues more and are more upset by them. 

I've been saying exactly that for some time -- sure it wasn't me?

Don't get me wrong, it's because The Martian is such an excellent movie overall that we enjoy picking nits in it, just as generations of fans have been picking nits in Star Trek. If I thought it was a bad movie I wouldn't be talking about it.

Not unless your haunt the nasa spaceflight forum under a different name.....