On Paths Unknown discussion
BOOKS & FILMS: THE MARTIAN
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The Martian SCIENCE thread
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Trav said:
Nobody interested in Weir's obvious bit of showing off with "Hermes is powered by ion engines. They throw argon out the back of the ship really fast to get a tiny amount of acceleration. The thing is, it doesn’t take much reactant mass, so a little argon (and a nuclear reactor to power things) let us accelerate constantly the whole way there. You’d be amazed at how fast you can get going with a tiny acceleration over a long time."?
I wish my rocket science was good enough to really understand what he is saying there, compared to how spacecraft are currently driven forward. I know that orbital variables are carefully plotted, and it kind of goes without saying that once you are past the pull of gravity, that you won't need much to propel you forward - but... anyway, i suppose I'll have to try and read it up somewhere. Coz' i'm not just prepared to take his word for it - hoo boy, this might end up being a long read for me... XD
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Puddin Pt replied:
"Ion engines are very real, practical devices, and indeed very cool. If I remember my own rocket science correctly (which might be dicey, because I believe they're not rockets), his description is quite accurate: low acceleration, but extremely high fuel economy. This has made then useful for deep space missions in the 21st Century, and Earth satellites use them for station keeping as well. Today deep space missions are not powered by nuclear reactors, but by radioisotope thermoelectric generators, which use the heat of radioactive decay to generate electricity to propel the ions. A hypothetical manned mission might have to use a nuclear reactor, but to reach Mars photovoltaic arrays might be enough, too.
I love space science. Can you tell? ;) "
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Trav:
Next thing I'm wondering, is how realistic 124 days from Earth to Mars would be in today's terms.
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Puddin Pt :
How long a transit takes depends on the relative position of Mars from the Earth, of course, but also a lot of other factors including available fuels, yadda, yadda. The Interplanetary Transport Network can get you anywhere in the Solar System using remarkably little fuel, but takes a long time. So if a Mars-bound person's ship has a nuclear reaction and lots of xenon as fuel (and Mars is as close as it can possibly be.).. Maybe?
According to NASA 54.6M km is the closes approach of Mars, and the record speed for an ion thruster is 10km/s. My calculator says you could get there in 63 days. So 124 days sounds realistic.
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Thanks for that, Puddin!
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"There's just one thing on the science I am struggling with: In chapter one, a massive dust storm is threatening to topple the landing craft, and hurls some metal object into Watley's side, causing him to lose consciousness.
That, I do not think, could happen on Mars. Mars' atmosphere is 100 times thinner than Earth's, so to get to hurricane-force storms (~75mph for the weakest hurricane), you'd need a Martian wind moving at 7500 mph. That just does not exist on Mars.
But of course, I could just file that away under "artistic licence" - no biggie. The problem I am having is that towards the end of the book, the thinness of the atmosphere plays an explicit, and crucial, role in allowing Mark to get off the planet.
So basically, the plot is inconsistent in the way it makes use of scientific facts. Well, at least in that instance. The rest seems to work fine (not that I am in any way able to judge any of it, of course). Just to be clear - this is a minor niggle for me, but has been bothering me a bit ever since I read it. "
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But, Ted, have you not been curious to see for yourself now that everybody is raving about it so? I'm curious now as to the article, but you've obviously forgotten where it is. I must admit that I didn't even have this book on my radar at all, and that the ONLY reason I am reading it is:
1) Everyone is raving about it
2) I saw the trailer of the film and it looked... interesting. :P
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http://www.nasa.gov/feature/nine-real...
Traveller wrote: "I saw the trailer of the film and it looked... interesting. :P It did, or Matt Damon did? :)
I've read very little "hard" science fiction, probably because what I have read had a tendency to be really long-winded---not boring, just without a notion of when to step and call it a day. "The Martian"'s relatively short length encourages me, though, and I do love the science.
Traveller wrote: "Ted wrote: "[spoilers removed]"But, Ted, have you not been curious to see for yourself now that everybody is raving about it so? I'm curious now as to the article, but you've obviously forgotte..."
No, the raves don't mean much to me, it's just a popular novel. I've got way too many books to read anyway. I mean, if I thought this was one of the historically great SF novels I might be interested. But I don't think that.
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http://www.nasa.gov/feature/nine-real......"
That's very interesting, thank you, Amy, and there you have it from the horse's mouth...will check those out as I read - not there yet. (Reading 10 books at once again.) :P
@Puddin - nah, I've never found Matt hot, though a good actor, of course.
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I hear you. I always have at least two going, but this past couple of weeks I keep flipping channels and I can't settle down. (I'm driving me crazy.) The library is kicking me out, so I think I'll go home and read new short story collection. Or maybe the Calvino I just downloaded. Or maybe the ghost story I already started. Or the poetry. Who knows.
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I hear you. I always have at least two going, but this past couple of weeks I keep flipping channels and I can't settle down. (I'm driving me ..."
You've never had an urge to try out Borges?
I see you're reading quite a few ghost stories. Getting ready for Halloween well in advance? ;)
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Ted, I'm not a scientist, but I think this is mostly pretty good. There are two reasons:It was originally published online (possibly in parts), and Weir had many suggestions and correction from experts and enthusiastic amateurs.
NASA gave advice for the film. There was a private screening at JPL, and it was very well received by the real rocket scientists there.
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I must admit that the movie had got me onto thinking: Well, why DON't we try and terraform Mars? I realize there are huge temperature differences between night and day, but we already regulate temps here on Earth, so...
I was wondering how much influence the relative lack of gravity there would matter, and if one could perhaps somehow increase the gravity on areas of? of the planet to help an atmosphere to form. I realize that if you managed to change the entire planet's gravity, you would essentially be bumping it off-course...
I think that gravity is less an issue than is the lack of a magnetic field. The Earth's magnetosphere prevents the solar winds from stripping the atmosphere here at home; Mars doesn't have one, and its atmosphere is very thin indeed. I think this is borne our by e.g. Venus, which is much closer to the Sun than Mars (of course) and also has less mass (and thus weaker gravity), yet it has a thick atmosphere.
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See here : https://en.wikipedia.org/wiki/Terrafo...
Of course, the weaker gravity would be a problem for humans, just as it is on the ISS, with loss of bone density and all that. Reality sadly makes a lot of science-fiction improbable! :(
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Yes - well, we could still have certain areas with artificial gravity, and do a lot of weight-bearing activities. One would just have to take special care of that aspect.
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http://www.space.com/23017-weightless...
http://www.space.com/14876-astronaut-...
These are in regard to zero g, but we should keep in mind that the reduced gravity on Mars could also have long term effects we don't know about either. (I could swear there was a better article that actually had quotes from astronauts in it when this news first broke, but I'm not finding it right now.)
Otherwise, yes, magnetism, atmosphere, radiation, and other such related things are the big obstacle (in addition to just getting there).
http://www.sg1official.com/2015/04/ob...
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Phew, you pointed to a lot of obstacles, Amy!
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If only those who oppose birth control would think about the long-term consequences of global human overpopulation....
(Not to mention the poverty that extremely high birth rates create.)
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I feel urged to sound a more positive note :-) Check out this excellent talk by quantum physicist David Deutsch. It is uplifing, clearly about science, and also about space, so I thought it would make excellent viewing. It's a bit longish, so perhaps reserve the lunch break for it. One of my all-time favourite talks (I am a nerd).https://www.ted.com/talks/david_deuts...
Puddin' wrote: "Today deep space missions are not powered by nuclear reactors, but by radioisotope thermoelectric generators"I'll point out the difference here. Really, all a nuclear reactor is, is a way to create the radioisotopes for an RTG. All elements heavier than lead (and lots of the ones lighter) are radioactive. They give off particles, change into lighter elements, and in the process create heat. Fission splits relatively slow decayers into much more radioactive elements, creates quite a bit of heat in the process, and then even more from the decay of the fission elements.
Traveller wrote: ". Mars' atmosphere is 100 times thinner than Earth's, so to get to hurricane-force storms (~75mph for the weakest hurricane), you'd need a Martian wind moving at 7500 mph. That just does not exist on Mars."
Careful of that word "force". I was (mistakenly, it appears) of the belief that Mars actually has very high winds (not 7500mph, but maybe a tenth of that). "Force" = mass x acceleration, and I haven't a clue how I'd apply that... The "energy" of a storm, though, is ½ x mass x velocity². So for 1/100th of the mass of air, you'd need it to be ten times the speed to have the same energy. However, apparently, NASA hasn't measured speeds above 60mph—so call that, at most, 6.5% of the energy of a baby hurricane. Barely enough to go sailing.
Traveller wrote: "I was wondering how much influence the relative lack of gravity there would matter, and if one could perhaps somehow increase the gravity on areas of?"
iirc, experiments in the space labs have shown that "no" gravity affects some plants (but not all), but those that require gravity don't require much (less than on the moon, let alone Mars).
Puddin Pointy-Toes wrote: "The Earth's magnetosphere prevents the solar winds from stripping the atmosphere here at home; Mars doesn't have one, and its atmosphere is very thin indeed. "
Puddin Pointy-Toes wrote: "The Earth's magnetosphere prevents the solar winds from stripping the atmosphere here at home; Mars doesn't have one, and its atmosphere is very thin indeed. "
Of course, you can put up a pretty big dome in ⅓ gravity.
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Domes! ^_^ They seem to be a stock ingredient of SF shows, and I guess it makes sense.
If you fall in the latter category, (that is assuming you actually LIKE toast and peanut butter) then go no further. Come and camp out here and tell us(view spoiler)[(me):P (hide spoiler)] if you think Andy Weir has his science duckies in a row (and why you say so, of course).
Like a good little student, I'll be asking questions, and the science minded among you, can act as my.... (view spoiler)[(see, I'm being clever here - I'm too lazy to read all of this up, so I'm hoping somebody really smart and clued up will come along and save me the trouble. *evil laughter* (hide spoiler)] er... esteemed advisors.