Questions about Mars series

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Rikkitic

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#207337 19-Dec-2016 21:14

Nat Geo has been running a partially fictionalised series about the colonisation of Mars. Several things in the episodes bother me and I wonder what the more knowledgeable here think. I assume an organisation like National Geographic is not going to allow inaccuracies to creep in, but I have a hard time believing some of the things they have portrayed. There are actually several that I have noticed, but I will stick to just two here (I don't fault them for the inaccurate gravity, by the way; that would be difficult and expensive to reproduce so I will let that one go).

My first question is about the helicopter drones. They look a lot like earth toys, but surely in the extremely thin atmosphere the blades would have to be a lot bigger and spin a lot faster to generate lift. Are these credible?

My real issue is with the depressurisation episode. Surely no rational engineer is going to design a door that is capable of opening directly to the outside, and no air lock is going to allow one door or the other to open if the pressures are not equal. This seems so basic that it is hardly worth mentioning, except in that episode a gentleman having a nervous breakdown is in fact able to open a door directly to the outside with no alarms going off or safety mechanisms kicking in. This hardly seems possible.

There are some other things but I will leave it here for the moment. What do others think?

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geocom

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#1692480 19-Dec-2016 22:16

I have not been watching the series but will attempt to answer your first question. Although i don't know the exact designs on the series JPL did release a video on youtube about drones on mars and included test they did in simulated atmosphere.

https://www.youtube.com/watch?v=vpBsFzjyRO8&feature=youtu.be

Geoff E

Rikkitic

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#1692511 19-Dec-2016 22:46

Thanks for the link. That helicopter looks a lot like the one in the series so I guess they got that right. I still wonder about the door to the outside, through.

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geocom

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#1692528 19-Dec-2016 23:23

There are a few reasons I can think of why an engineer would not choose a plug door to the outside that would require the pressure on the inside to be the same as the outside. The main one being Fire. In the event that fire did happen a decompression actually makes a lot of sense.

With water being in short supply there may just simply not be enough water to put out a fire so in this case a decompression would be the quickest and safest option to put it out.

The issue with this of cause is it needs to be short as it would not be good for any life left in the open. You would also need to make sure that any oxygen supplies are shut off before decompression otherwise all your oxygen would be lost as well.

So while there are risks there could be just as many by not allowing decompression.

NASA or whoever run the operation would have to weigh up the weight cost and risk of anything going this far out. Do you take many more ton's worth of doors to make each compartment sealable or convert that weight to food/water/chemicals?

Geoff E

meesham

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#1692611 20-Dec-2016 10:12

I was thinking that the door was there for future expansion of the building, ie it later becomes an internal door capable of sealing off a part of the habitat in case of emergency.

Fred99

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#1692644 20-Dec-2016 10:28

I'm amazed that JPL managed to get that drone flying in a vacuum chamber with atmosphere density similar to Mars.

Still, I'm not yet convinced that they'd be able to do anything useful with it, by the time it was carrying some payload and presumably "ruggedised" so that it could withstand high winds, dust storms etc. Also the more miniaturised the electronics, the more prone the electronics are to being "nuked" by primary or secondary cosmic radiation.

Rikkitic

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#1692645 20-Dec-2016 10:31

Both good reasons that make sense. I hadn't considered either of those. I still would think there ought to be better safety mechanisms, though. If anyone can just open a door to the outside by pushing a couple of buttons then that doesn't seem like particularly good engineering to me. Maybe it makes sense for two people in the lunar lander, but not in a large community costing untold billions to establish and maintain. If the door is for future expansion, there ought to be a locking mechanism so it can't be opened until it is needed. If it is for firefighting, it makes more sense but you wouldn't need an actual door for that. In any case, I would think there would be better ways to do it, especially as everything has to be brought from earth. Mars air is free and mostly carbon dioxide and that could be compressed and used to fight fire.

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meesham

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#1692650 20-Dec-2016 10:36

Rikkitic:

Both good reasons that make sense. I hadn't considered either of those. I still would think there ought to be better safety mechanisms, though. If anyone can just open a door to the outside by pushing a couple of buttons then that doesn't seem like particularly good engineering to me. Maybe it makes sense for two people in the lunar lander, but not in a large community costing untold billions to establish and maintain. If the door is for future expansion, there ought to be a locking mechanism so it can't be opened until it is needed. If it is for firefighting, it makes more sense but you wouldn't need an actual door for that. In any case, I would think there would be better ways to do it, especially as everything has to be brought from earth. Mars air is free and mostly carbon dioxide and that could be compressed and used to fight fire.

** Warning, potential spoilers ahead **

I'm in two minds about the safety mechanisms, I was thinking there should have been central system to allow the opening of the doors but then you have a situation like what happened with the original engineering habitat that they were using where they needed to get the fire out fast and she had to break the window. My main problem with what happened is he was obviously not thinking rationally, I'm guessing opening the door and overriding the safety mechanisms was quite a complex task yet he was able to do it while thinking he was back on earth.

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geocom

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#1692678 20-Dec-2016 10:55

Fred99:

I'm amazed that JPL managed to get that drone flying in a vacuum chamber with atmosphere density similar to Mars.

Still, I'm not yet convinced that they'd be able to do anything useful with it, by the time it was carrying some payload and presumably "ruggedised" so that it could withstand high winds, dust storms etc. Also the more miniaturised the electronics, the more prone the electronics are to being "nuked" by primary or secondary cosmic radiation.

The winds on mars are not as bad as you would think. Because the atmosphere is less dense there is less impact than in air on earth.

NASA released a fact and fiction piece after the martian came out snippet below from https://www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-storms

It is unlikely that even these dust storms could strand an astronaut on Mars, however. Even the wind in the largest dust storms likely could not tip or rip apart major mechanical equipment. The winds in the strongest Martian storms top out at about 60 miles per hour, less than half the speed of some hurricane-force winds on Earth.

Focusing on wind speed may be a little misleading, as well. The atmosphere on Mars is about 1 percent as dense as Earth’s atmosphere. That means to fly a kite on Mars, the wind would need to blow much faster than on Earth to get the kite in the air.

“The key difference between Earth and Mars is that Mars’ atmospheric pressure is a lot less,” said William Farrell, a plasma physicist who studies atmospheric breakdown in Mars dust storms at Goddard. “So things get blown, but it’s not with the same intensity.”

But yes radiation is the key issue.

The other interesting thing is power. Because they need to spin at a higher speed to get airborne you would think that the power consumption would increase. However because the atmosphere is less there is less resistance on the blades meaning that you can spin faster without sucking anywhere near as much battery power as you would think meaning that with a combination of the lower gravity you could add more mass for radiation protection.

Geoff E