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At 17:11, Watney says that NASA designed the habitat to last for only 31 days on the surface of Mars.

Why did they not design something to last longer?

  • Because the mission was specifically limited to 31 sols (Mars days) – Shreedhar Feb 27 '18 at 20:05
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    He also jokes about a ziplock bag costing $50,000 because... NASA. Consider payload weight, fuel, all the math. Every ounce comes at a cost. The hab may not have been designed to last exactly 31 days, but more like a range where 31 days is well within the safe zone. Maybe the next level would have added a whole ton of extra weight and cost substantially more for a mission with a strict budget, both in time and money – Kai Qing Feb 27 '18 at 20:26
  • Because it would cost more, weigh more, and take longer to build. – Organic Marble Feb 27 '18 at 20:56
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    Watney is a character with a strong tendency to dark humour and hyperbole. I don't think he'd mind exaggerating exactly how fragile the hub was to get his point (how low his chances of survival were) across. – Sean Condon Feb 27 '18 at 21:26
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    It wasn't designed to last only 31 days, the books say they were supplied for 56 days, and the mission only lasted for 31. Doesn't say anything about the hab only lasting 31 days – CBredlow Feb 27 '18 at 22:01
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This is explained slightly later in the novel. The mission was only intended to last that long.

The surface mission was supposed to be thirty-one days. For redundancy, the supply probes had enough food to last the whole crew fifty-six days. That way if one or two probes had problems, we’d still have enough food to complete the mission.

The Martian: Andy Weir

Assuming the NASA in the books operates in the same way that our own NASA do, they will have used Reliability Engineering Analysis to make sure that there is a near-zero-percent chance of a critical equipment failure (mission-affecting or life-affecting) occurring within those 31 days.

NASA’s Reliability and Maintainability (R&M) program ensures that the systems within NASA’s spaceflight programs and projects perform as required throughout their life cycles to satisfy mission objectives. Mission objectives include safety, mission success and sustainability criteria.

NASA - Reliability and Maintainability Program

Typically the best way to ensure that a piece of equipment has the lowest possible chance of breaking during its projected mission is to massively over-engineer it, hence why Mark has so much redundancy in his equipment and why most of his kit lasts years instead of weeks. Note, for example that he has multiple additional valves. They aren't likely to be needed, but scrubbing a multi-billion dollar mission for the want of a $2 valve isn't something that NASA would countenance.

Getting the tubing through the balloon canvas wasn’t too hard. I have several spare valve patches. Basically they’re ten-by-ten-centimeter patches of Hab canvas with a valve in the middle. Why do I have these? Consider what would happen on a normal mission if the regulator valve broke. They’d have to scrub the whole mission. Easier to send spares.

The Martian: Andy Weir

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    That doesn't indicate the Hab was designed to last only 31 days. – Edlothiad Feb 27 '18 at 20:19
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    @Edlothiad That might depend on how you interpret "designed for". It could be seen as meaning "designed to last long enough for a 31 day mission". If part of that design includes overengineering it so that it has an expected lifespan of much more than 31 days, that could still be seen as being "designed to last 31 day". Or taken another way, it could be implied that it was designed to last at least 31 days. – Todd Wilcox Feb 27 '18 at 20:25
  • @ToddWilcox that's all well and dandy, but that doesn't support the fact it was designed to last only 31 days. – Edlothiad Feb 27 '18 at 21:01
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    @Edlothiad - The HAB was rated to last at least 31 days. Beyond that point the chances of it breaking go from near-zero to more-than-near-zero – Valorum Feb 27 '18 at 21:02
  • @Edlothiad This is par for the course of NASA though, it's designed to work a short time, but greatly exceeds it's original mission. The Voyager probes, and the Opportunity rover are good examples of this. – CBredlow Feb 27 '18 at 21:10

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