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Space movies (possible spoilers)

Ben W

P85 #61, Roadster #108
Feb 27, 2009
647
534
Santa Barbara, CA
* I'm glad others brought up the wind-storm problem. That was a Large Helping Of Suspended Belief there, for me.

I had the opportunity to hear Andy Weir give a lunchtime talk at Google LA last month, and he addressed this pretty clearly. He had some alternative realistic scenarios for getting Watney stranded on Mars, but they felt too contrived and arbitrary to him, so it was a conscious decision to go for the more visceral and less realistic scenario of the windstorm. Perhaps he could have had the MAV positioned on unstable tilted terrain, where 175kph wind could actually blow it over, or undermine the sand under its landing legs.

Andy actually said that the LEAST realistic part of the entire book, in his opinion, was the supposition that NASA would actually fund something as staggeringly expensive as HERMES :)

The drama around the MAV intercept at the end was also, as others have pointed out, completely unnecessary; HERMES' ion engines would have allowed it to create its own additional intercepts a few hours later. This plot hole could have been easily worked around by giving Watney a more limited air supply, for instance. Or there could even have been an impending solar storm, to make time of the essence.

I haven't even seen the movie yet... very much looking forward to it. Even if there are some bones to pick, I think Andy did a truly amazing job.
 

Johan

Ex got M3 in the divorce, waiting for EU Model Y!
Feb 9, 2012
7,498
9,788
Drammen, Norway
I had the opportunity to hear Andy Weir give a lunchtime talk at Google LA last month, and he addressed this pretty clearly. He had some alternative realistic scenarios for getting Watney stranded on Mars, but they felt too contrived and arbitrary to him, so it was a conscious decision to go for the more visceral and less realistic scenario of the windstorm. Perhaps he could have had the MAV positioned on unstable tilted terrain, where 175kph wind could actually blow it over, or undermine the sand under its landing legs.

Andy actually said that the LEAST realistic part of the entire book, in his opinion, was the supposition that NASA would actually fund something as staggeringly expensive as HERMES :)

The drama around the MAV intercept at the end was also, as others have pointed out, completely unnecessary; HERMES' ion engines would have allowed it to create its own additional intercepts a few hours later. This plot hole could have been easily worked around by giving Watney a more limited air supply, for instance. Or there could even have been an impending solar storm, to make time of the essence.

I haven't even seen the movie yet... very much looking forward to it. Even if there are some bones to pick, I think Andy did a truly amazing job.

Thanks for those details!

However, I don't understand how the Hermes could have "created its on additional intercepts a few hours later" (in fact I don't quite understand the sentence). From the book and my other readings about ion thrust engines in reality my understanding is that acceleration/deceleration using these kinds of engines is a very slow process, hence they had to plot a new course a very long time before returning to mars, missing the earth, swinging around (gravity assist), going back to Mars, swing around Mars (gravity assist) then back to earth. Now I don't believe there is any plausible way they could have used the ion thrusters to quickly change that and swing around Mars twice for example? Also Watney in the MAV would keep going at a constant pace away from Mars after he got away from it's gravitational field, right? Or maybe he just got himself in to some kind of high orbit? Anyway, I think that if they didn't intercept with him on the first attempt it would have taken them weeks or months to get another attempt, right?
 

Ben W

P85 #61, Roadster #108
Feb 27, 2009
647
534
Santa Barbara, CA
Thanks for those details!

However, I don't understand how the Hermes could have "created its on additional intercepts a few hours later" (in fact I don't quite understand the sentence). From the book and my other readings about ion thrust engines in reality my understanding is that acceleration/deceleration using these kinds of engines is a very slow process, hence they had to plot a new course a very long time before returning to mars, missing the earth, swinging around (gravity assist), going back to Mars, swing around Mars (gravity assist) then back to earth. Now I don't believe there is any plausible way they could have used the ion thrusters to quickly change that and swing around Mars twice for example? Also Watney in the MAV would keep going at a constant pace away from Mars after he got away from it's gravitational field, right? Or maybe he just got himself in to some kind of high orbit? Anyway, I think that if they didn't intercept with him on the first attempt it would have taken them weeks or months to get another attempt, right?

The important thing to note is that both the MAV and HERMES are already on nearly-identical escape-velocity trajectories back to Earth. The MAV is not in Mars orbit. The difference between orbiting mars and escaping mars is about 1500 m/s; the velocity difference between the MAV and HERMES (before any course-correction) is only 11 m/s. That's nothing.

At 2mm/s^2, the HERMES' ion engines could correct those 11 m/s in about 90 minutes, and close their 67km gap in about 6 hours. (accelerating for the first half, decelerating for the second half). In the novel, HERMES uses 75% of its attitude-thruster fuel to give it a quick boost toward Watney's trajectory, where they will intercept him much sooner but at 42 m/s. It would have been better to use half that fuel to boost towards an intercept a couple hours later, and the other half to slow down when they get there. (with ion engines assisting all along.) The moment of closest approach of their original trajectories is irrelevant; the book treats it as if that moment is make-or-break. Better to make a different trajectory (for HERMES) to intercept at a later moment, at a tamer relative speed.

Of course, if Watney only has 1 hour of air in his EVA suit, then the drama is necessary to create the intercept ASAP. But I don't think the book mentions this. NASA's current spacesuits allow for 6-8 hour EVA's, plenty of time to allow for a less-dramatic and safer intercept in the Martian scenario.
 
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Johan

Ex got M3 in the divorce, waiting for EU Model Y!
Feb 9, 2012
7,498
9,788
Drammen, Norway
The important thing to note is that both the MAV and HERMES are already on nearly-identical escape-velocity trajectories back to Earth. The MAV is not in Mars orbit. The difference between orbiting mars and escaping mars is about 1500 m/s; the velocity difference between the MAV and HERMES (before any course-correction) is only 11 m/s. That's nothing.

At 2mm/s^2, the HERMES' ion engines could correct those 11 m/s in about 90 minutes, and close their 67km gap in about 6 hours. (accelerating for the first half, decelerating for the second half). In the novel, HERMES uses 75% of its attitude-thruster fuel to give it a quick boost toward Watney's trajectory, where they will intercept him much sooner but at 42 m/s. It would have been better to use half that fuel to boost towards an intercept a couple hours later, and the other half to slow down when they get there. (with ion engines assisting all along.) The moment of closest approach of their original trajectories is irrelevant; the book treats it as if that moment is make-or-break. Better to make a different trajectory (for HERMES) to intercept at a later moment, at a tamer relative speed.

Of course, if Watney only has 1 hour of air in his EVA suit, then the drama is necessary to create the intercept ASAP. But I don't think the book mentions this. NASA's current spacesuits allow for 6-8 hour EVA's, plenty of time to allow for a less-dramatic and safer intercept in the Martian scenario.

That makes sense. Very perceptive. The only caveat is we really don't get the details, from the book, on what kind of orbit or possibly escape vector the stripped down MAV is able to get, with the fab canvas slowing it down during the ascent and all.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,115
10,584
United States
The movie did feel a bit 'rushed'... even then it was nearly 2.5 hours long... no doubt there were a lot of hard decisions on which scenes to shorten.

- Restoring the HAB after decompression.
- He was stuck in the airlock for nearly a day... not <1 hour.
- Loss of communication with NASA when he fried pathfinder.
- The rollover on his road trip.
- The dust storm that nearly killed his solar recharging.
- Johansen and Beck sharing a bunk half-way back to Mars.
- Launching in the MAV crippled Whatney. Beck had to pull him from the seat.

It was a little irritating when they kept scenes that only made sense in the context of scenes they had cut...

Overall I enjoyed the movie; We need more films that at least make an honest attempt to get the science right to get more kids excited about science.
 

gg_got_a_tesla

Model S: VIN 65513, Model 3: VIN 1913
Jan 29, 2010
6,534
769
Redwood Shores, CA
I was a bit disappointed with the movie :( Not that the movie wasn't well made overall but, apart from not being able to capture the drama the way the book did (with Watney on the edge of danger constantly but, problem-solving his way out of it), the movie made silly caricatures out of some of the key characters such as Rich Purnell just for the sake of cheap laughs. The dynamic between members of the Hermes crew was very weak.

The seemingly-real-time comms between Hermes and Earth during the final rescue when they were really 12 light minutes apart (of which they do make a mention) was lame. The Iron Man routine by Watney with Lewis out to get hold of him was unnecessary when compared to Beck rescuing him from the MAV as in the book.

There were no compelling, sweeping vistas of Mars either, either from orbit or from the surface. A movie is the perfect platform to inspire folks about other celestial bodies.

A rather uninspiring space movie...
 

Cosmacelf

Well-Known Member
Mar 6, 2013
8,640
20,996
San Diego
I would agree. I wasn't as impressed by it as everyone else seemed to be. They didn't explain things very well (he was shown planting an entire potato to get back one potato plant. What's the point in that?). They made passing reference to using math, but never actually showed anyone even mentally calculating anything, or even writing down some numbers (other than counting things - is that the highest level of math they were comfortable showing, counting?). They spent too long in the beginning showing his despair, and not enough showing how he problem solved. Jeff Daniels was boring as the NASA administrator.

The ending was silly. The chemical bomb was thrown together in 10 minutes yet somehow managed to have a timer, beeping lights and a beeper? The ironman thing was ridiculous, and will someone please tell directors about the conservation of angular momentum? The movie Gravity had the same problem. When things are spinning around each other, they don't magically stop spinning unless you give a countervailing force.

The zero G sequences mostly weren't believable. Every time they had to turn, they just ... turned, without somehow canceling out their forward momentum.
 

Johan

Ex got M3 in the divorce, waiting for EU Model Y!
Feb 9, 2012
7,498
9,788
Drammen, Norway
I would agree. I wasn't as impressed by it as everyone else seemed to be. They didn't explain things very well (he was shown planting an entire potato to get back one potato plant. What's the point in that?). They made passing reference to using math, but never actually showed anyone even mentally calculating anything, or even writing down some numbers (other than counting things - is that the highest level of math they were comfortable showing, counting?). They spent too long in the beginning showing his despair, and not enough showing how he problem solved. Jeff Daniels was boring as the NASA administrator.

The ending was silly. The chemical bomb was thrown together in 10 minutes yet somehow managed to have a timer, beeping lights and a beeper? The ironman thing was ridiculous, and will someone please tell directors about the conservation of angular momentum? The movie Gravity had the same problem. When things are spinning around each other, they don't magically stop spinning unless you give a countervailing force.

The zero G sequences mostly weren't believable. Every time they had to turn, they just ... turned, without somehow canceling out their forward momentum.

It wasn't much of a mental effort to visually fill in the digitally removed wires they were hanging from... A bit too obvious. I wish they had done at least a few of the short zero G scenes in parabolic flight free fall. They could have done it against a green screen. It's easy to get at least 15 seconds of free fall per dive. However the actors would have to practice a bit to look believable.

Also did anyone else get annoyed by the sheer amount of junk he had laying around in the hab, like lots of pens and paper, including a paper map (!) of a large slice of Mars?
 

ecarfan

Well-Known Member
Sep 21, 2013
19,280
13,950
West Vancouver, British Columbia
Yes, there was a lot of stuff on Mars in the hab that would never have been sent there. Binders of blank sheets of paper? Really? Every gram counts.
Agree about the zero G scenes on Hermes, they looked ridiculous.
I still liked the film. Of course the book was better.
 
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AudubonB

One can NOT induce accuracy with precision!
Mar 24, 2013
8,192
28,168
Some people have no idea of how to leave their sense of reality at home when they go to movies....:biggrin:
 

StephenM

Active Member
Dec 23, 2012
1,192
93
I thought The Martian was fantastic. Ridley Scott did a fine job of capturing the essence/feel of the book IMO, technical aberrations notwithstanding.
 

doug

Administrator / Head Moderator
Nov 28, 2006
16,942
1,061
SF Bay Area
I've been avoiding this thread till after I saw the movie. Even though I read the book a while back, I don't like to be spoiled.

I'd say the movie was ok. Good, not great. Since I basically knew what was going to happen, I found myself bored in parts. I saw it in the theater hoping to be impressed by the visuals, but wasn't. Interstellar did a much better job at that. Overall, though, I was entertained and it was worth my free movie pass plus 4 bucks for 3D.

The science mistakes have mostly been covered (it was nowhere near as bad as Gravity), but I have to revisit the hab repair. Having designed and built a few vacuum chambers, and having had to fix many a leak in the middle of the night with whatever's available, that's the part that struck me the most.

Say the pressure inside the hab is 1 atm. Given the low pressure on Mars, the differential pressure is still about an atmosphere. If the diameter of the hab opening was 7 feet, then at 14.6 psi that means the repair would have to hold about 40 tons of force. Forty. Tons. Did that 4mil polyethylene sheeting with duct tape look like it could hold 40 tons? No, no it didn't.

(Aside: I once made a 2ft x 3ft vacuum chamber for optics that I needed to see inside of in order to do alignments. I used a 2 inch thick slab of clear acrylic to hold the roughly 6 tons of distributed force, and you could still see it flex under the pressure. Oh how easier it would have been if I could have just used some thin plastic sheeting and duct tape.)

Then they showed Matt Damon just on the other side of that flimsy sheeting, without his helmet on??? I chucked at what was supposed to be a poignant scene of him thinking he's going to starve to death in a couple months. Buddy you're about to go any second the way that "repair" is flapping about. Would it have been so much harder to show him hanging canvas and sealing it with some hand-wavy goop out of a shaving can?
 

Doug_G

Lead Moderator
Apr 2, 2010
17,881
3,351
Ottawa, Canada
I think the science errors were a rounding error compared to Gravity, which was so utterly ludicrous that it was continuously pulling me out of the movie. Seemed like every object in space was in nearly the same orbit, regardless of whether it was about to reenter or what. That and Clooney monkeying around in the untethered jet pack and everyone blathering on like they were at the beach. Geesh what a total mess. Visually fun to watch though.

I wasn't expecting The Martian to be as visually stunning, if it were anywhere near realistic. The one visual effect that I didn't like was the rocket plumes from the MAV. They should have been supersonic jets, not fluffy puffballs. To me it didn't look plausible that those rockets would be able to lift the craft an inch. Not nearly as bad as Buck Rogers, but in the same vein.

I was expecting the hab canvass to be something thick and heavy-duty, so yeah the polyethylene sheeting was absurd. And I was constantly expecting him to put a back-up sheet on the inside. And it should have been massively bulging outward under the pressure regardless of what the external winds were doing. (For the record, they don't pressurize spacecraft anywhere near 1 atm - more like being near the top of Mauna Kea.)

Once I convinced myself to ignore the plastic sheeting, I got back to enjoying the movie. But yeah, that took rather longer than the potato scene.
 

Johan

Ex got M3 in the divorce, waiting for EU Model Y!
Feb 9, 2012
7,498
9,788
Drammen, Norway
Yeah the plastic sheet was really annoying. To be the most annoying part was not just that it didn't bulge out like a ballon, but that as "the Mars winds" were howling outside it flapped inwards and outwards like a sail. Some winds it must have been, using an atmosphere thinner than 1/1000th of earths (close to vacuum so not a lot of particles) to push in against 1000 kPa of pressure. LOL.
 

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