17

At the beginning of the film The Martian, part of the dialogue implies that one of the crew has the job of monitoring the MAV to check it is still upright. The importance of this job is clearly shown when a storm hits.

Later we find out about another MAV which will be in place for a significant period of time before it is needed, yet no one shows any concern that it may also be at risk of toppling.

So given the importance of this escape craft, why wasn't any plan in place to tether the first craft? And were NASA just gambling on the weather that the latter MAV didn't topple before it was needed?

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    That is an excellent question. I wonder if the topography gave more protection to the Ares IV MAV? – Lexible Oct 12 '15 at 16:24
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    Guesswork: If the MAV toppled before the Ares IV mission started, the mission would have to be aborted. They never planned for it to be used as a lifeboat like this. Presumably, storms of the necessary ferocity are uncommon on Mars. – Kevin Oct 12 '15 at 16:33
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    Notably, the site of the Ares IV landing would be (in reality) wholly unsuitable. jpl.nasa.gov/spaceimages/details.php?id=PIA19914 – Valorum Oct 12 '15 at 17:30
  • ... the two locations were also pretty distant from each other... were they not? Perhaps the storm didn't even hit where the Ares IV was. – Catija Oct 12 '15 at 18:34
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    The second MAV was probably built later. It could have had design changes to make it more stable in high winds. – Kenster Oct 12 '15 at 18:36
17

Well, they said the MAV could handle up to 150kph winds before it started to tilt. The storm they experienced reached (or exceeded) 175kph winds.

However:

The maximum wind speeds recorded by the Viking Landers in the 1970's were about 30 meters per second (60 miles an hour) with an average of 10 m/s (20 mph). Just as on Earth, at certain latitudes, the winds tend to blow in certain directions. - NASA Mars facts

60 miles per hour is about 96 kilometers per hour. So the winds would have to exceed their maximum recorded values (for where ever Viking landed) by 50% in order to reach the maximum tolerance of tilting, but NASA doesn't expect those wind speeds. It was bad luck that the Ares III mission experienced what might be called a "storm of the century" given its severity.

Also, from the book:

The MAV was soft-landed (as opposed to the balloon bounce-fest the other supplies had). Of course, it was in constant communication with Houston, and if there had been any problems with it, we would have passed by Mars and gone home without ever landing. - The Martian, ch. 1

One wonders though, with such a massive storm, how did the air clear so quickly?

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    Interesting thought occured to me when I read the comment above "how did the air clear so quickly?". I was going to point out that the atmospheric pressure on Mars is so low as to almost be non-existent. Therefore you would expect particles to settle quickly. However that also implies that, even at high velocities, there would be very little force exerted by Martian "winds". Intriguing concept. – Nathan Oct 13 '15 at 2:31
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    @Nathan The author has gone on record stating that the initial storm would not have been powerful to cause the problems it did in the book, but made a rare concession to drama in order to get Watney stranded. – DavidS Oct 13 '15 at 11:21
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Ares 3 landed on Acidalia Planitia wich is a plain... When a wind blows on a plain there is no resistance. It sweeps everything in its path and can cause tipping of a lander.

Ares 4 landed on Schiaparelli crater. Given, the crater is 286 miles in diameter but it is still more protected as the high walls of the crater would break up the wind and give the lander more protection.

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In addition to @JackBNimble's answer, note that the MAV IV was full of cargo (witness the montage of all the unloading of it, plus the whole point of the presupply mission). If you have an object with the same cross-section, and significantly more weight, it will be much more stable against tipping.

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    That wasn't cargo, that was just the equipment onboard. They had to take the extraordinary steps of stripping out most of it to lighten the craft to get Mark into a higher orbit than usual. Both MAVs were largely the same. – user1027 Oct 12 '15 at 19:39
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    @Keen: Didn't he unload a bunch of movable stuff first? – ThePopMachine Oct 12 '15 at 20:46
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    @Keen, forget the montage. You believe the MAV was landed totally empty with no supplies? – ThePopMachine Oct 12 '15 at 21:24
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    Why would it have any cargo? The only purpose of the MAV is to get the exploration team and their samples back to the "mothership". Since it was designed to be soft-landed, they'd want to keep it as light as possible commensurate with it's mission. – Joe L. Oct 12 '15 at 21:33
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    @Joe: Yet, there it was, with cargo. Big white packages were the first things he removed. That being said, they didn't seem all that heavy, so... probably irrelevant. – Lightness Races in Orbit Oct 12 '15 at 21:53

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