Author Topic: Help me make sure I'm not getting it all wrong  (Read 10011 times)

Offline ceswiedler

Hi! I'm hoping this is the right place to ask this. I'm writing a novel for middle-school age kids in the vein of THE MARTIAN, and I'd like to make sure I'm not getting any major facts wrong. I'm pretty confident about most of these, but I'm in the middle of writing an afterword explaining some of the actual science behind various parts of the story, and it occurs to me that I'd really, really rather not publish a book where I tell kids that "Mars is X" when actually Mars is Y. If anyone here sees anything majorly wrong with these statements, can you let me know?

1. Mars doesn't have a significant magnetic field, and so colonists on the surface would be exposed to dangerous radiation, especially during solar flares / CMEs. Also, compasses won't work.

2. Without an ionosphere, radio signals won't travel over the horizon, or even over large obstacles like a mountain (?). You would either need line-of-sight or would need to relay your signal through a satellite.

3. Phoenix found some of the first evidence for water ice in the soil on Mars. (Follow-up, though: we did know before Phoenix that the actual ice caps contained water ice, right?).

4. Airplanes and helicopters won't work because of the thin atmosphere.

5. An efficient mode of long-distance flight would be rockets, which would basically travel in ballistic arcs. During a trajectory like this, the occupants would be weightless on the way down. They would still experience normal gravity up until the highest point of the ballistic arc.

6. In theory, an air filter that sucked in CO2 from the atmosphere and converted it to O2 to breathe, meaning a person in an environment suit would only need to have a backup source of oxygen. I know rebreathers currently exist for SCUBA, but they seem to have a lot of limitations. My super-basic calculations are: Mars atmosphere is 0.5% Earth pressure; humans metabolize 5% of Earth air as oxygen and 'ignore' the rest by exhaling it; a perfect air filter would then need to suck in 10 liters of CO2 to get 1 liter of breathable air. I'm super-handwavy on this, I just want to make sure I'm not insane.

7. The most likely long-term source of oxygen for colonists would be water ice.

8. Mars doesn't have a north star, but in theory someone on the surface could tell true north by finding the point between several stars in certain constellations.

9. A dust storm of any significance would block out all (nearly all?) stars.

10. Stars on Mars don't twinkle because of the thin atmosphere.

11. Normal voices on Mars would sound extremely low-pitched because of the thin atmosphere. Humans could communicate acoustically suit-to-suit (via speakers/microphones), but they would need to modify the pitch of the sound to compensate.

Thanks for any help on this!

chris
« Last Edit: 03/15/2019 01:17 pm by ceswiedler »

Offline zhangmdev

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Re: Help me make sure I'm not getting it all wrong
« Reply #1 on: 03/15/2019 01:28 pm »
Point4 ?

https://science.nasa.gov/science-news/science-at-nasa/2003/02may_bigblue/
https://www.nasa.gov/press-release/mars-helicopter-to-fly-on-nasa-s-next-red-planet-rover-mission

Helicopter and glider (dropped from high altitude) is workable on Mars. Airplanes, at least the normal ones, need runway to takeoff and land. So before there is a runway on Mars, airplanes are out of the question.

Offline freddo411

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Re: Help me make sure I'm not getting it all wrong
« Reply #2 on: 03/15/2019 01:48 pm »
Hi! I'm hoping this is the right place to ask this. I'm writing a novel for middle-school age kids in the vein of THE MARTIAN, and I'd like to make sure I'm not getting any major facts wrong. I'm pretty confident about most of these, but I'm in the middle of writing an afterword explaining some of the actual science behind various parts of the story, and it occurs to me that I'd really, really rather not publish a book where I tell kids that "Mars is X" when actually Mars is Y. If anyone here sees anything majorly wrong with these statements, can you let me know?

1. Mars doesn't have a significant magnetic field, and so colonists on the surface would be exposed to dangerous radiation, especially during solar flares / CMEs. Also, compasses won't work.

Some radiation.  The ground blocks roughly 50%, and the thin atmosphere blocks a bit too.
Quote


2. Without an ionosphere, radio signals won't travel over the horizon, or even over large obstacles like a mountain (?). You would either need line-of-sight or would need to relay your signal through a satellite.

Probably true about the radios.   If Mars has an ionosphere (you'd expect some ionization of the top of the atmosphere) it will be very thin
Quote

3. Phoenix found some of the first evidence for water ice in the soil on Mars. (Follow-up, though: we did know before Phoenix that the actual ice caps contained water ice, right?).

That caps existed was known; CO2 was indicated but the question of water ice as well was unconfirmed.   Ground truth hasn't been done yet.
Quote

4. Airplanes and helicopters won't work because of the thin atmosphere.

False.   You'll need much larger aero surfaces, and different engines however.
Quote

5. An efficient mode of long-distance flight would be rockets, which would basically travel in ballistic arcs. During a trajectory like this, the occupants would be weightless on the way down. They would still experience normal gravity up until the highest point of the ballistic arc.


You'll experience acceleration due to rocket thrust.   No thrust and you'll be weightless

Quote

6. In theory, an air filter that sucked in CO2 from the atmosphere and converted it to O2 to breathe, meaning a person in an environment suit would only need to have a backup source of oxygen. I know rebreathers currently exist for SCUBA, but they seem to have a lot of limitations. My super-basic calculations are: Mars atmosphere is 0.5% Earth pressure; humans metabolize 5% of Earth air as oxygen and 'ignore' the rest by exhaling it; a perfect air filter would then need to suck in 10 liters of CO2 to get 1 liter of breathable air. I'm super-handwavy on this, I just want to make sure I'm not insane.


What about pressure suits?   You'll need those; it's close enough to a vacuum. 

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7. The most likely long-term source of oxygen for colonists would be water ice.


Maybe.   Cracking O2 from CO2 might be easier.

Quote

8. Mars doesn't have a north star, but in theory someone on the surface could tell true north by finding the point between several stars in certain constellations.

Yes.
Quote

9. A dust storm of any significance would block out all (nearly all?) stars.

Yes
Quote

10. Stars on Mars don't twinkle because of the thin atmosphere.

Maybe.   What about the dust?
Quote

11. Normal voices on Mars would sound extremely low-pitched because of the thin atmosphere. Humans could communicate acoustically suit-to-suit (via speakers/microphones), but they would need to modify the pitch of the sound to compensate.

Not sure about this.   I suspect that sound doesn't vary by pressure, as people on mountain tops sound normal on Earth, with 1/2 the pressure of sea level.      But, different gases make voices sound different.  However, the gas involved with your voice and lungs will (MUST) stay as mostly O2.   Maybe people will breath O2 and argon instead of O2 and nitrogen ??
Quote

Thanks for any help on this!

chris

Offline CuddlyRocket

Re: Help me make sure I'm not getting it all wrong
« Reply #3 on: 03/15/2019 02:02 pm »
2. Without an ionosphere, radio signals won't travel over the horizon, or even over large obstacles like a mountain (?). You would either need line-of-sight or would need to relay your signal through a satellite.

False. Below 3 MHz, radio waves hug the ground due to diffraction effects and can follow the planet's curvature. They're called ground waves. AM stations on Earth use this effect to increase the range, and therefore audience, of their broadcasts.

Offline whitelancer64

Re: Help me make sure I'm not getting it all wrong
« Reply #4 on: 03/15/2019 02:25 pm »
1. Generally correct, however, there are remnants of magnetic field in some areas. Radiation levels at the Martian surface were measured by the Curiosity rover as similar to those at the ISS. Worthwhile to note that radiation shielding is easily accomplished by burying habitats with a few meters of dirt, and an early warning system for CMEs would need to be in place for people to get to shelter.

2. Mars does have an ionosphere, but it is quite different from Earth's. It is much weaker and is only one layer, but that layer could be used to direct radio waves over the horizon! However, this would only be possible on the day side (the ionosphere is much less stable on the night side of Mars) and only with specific radio frequencies, and dust storms would also cause interference. Much of this is uncertain because, of course, there are no experimental results as of yet :D

In my opinion, and my opinion only, relay satellites would be more reliable and effective.

3. The Phoenix lander directly observed water ice just below the surface, yes. The polar caps were known to be primarily water ice prior to that thanks to various orbiters, though they also contain frozen carbon dioxide.

4. zhangmdev covered this. As a side note, NASA is planning to send a small quadcopter on the next rover mission to Mars.

5. You're half right. As long as the rockets are firing, the riders experience acceleration. When the rockets cut off, then the vehicle is ballistic, so they are in free-fall while both ascending and descending.

6. Beyond my area of expertise.

7. Almost certainly yes. There'd be a major industry working with the Sabatier reaction and Oxygen is something that could be extracted during that process.

8. Mars’ North Pole points to a spot in the sky that’s about midway between Deneb, the brightest star in the constellation Cygnus the Swan, and Alderamin, the brightest star in the constellation Cepheus. Also, as in Andy Weir's "The Martian" it would be easy to determine East-West by the rise and set of Phobos every 8 hours.

9. My gut instinct is that it would need to be a severe dust storm to obscure bright stars. Faint stars would be obscured by lesser dust storms of course.

10. They would probably twinkle a little bit if there's a lot of water vapor in the air, but yes it would be very much less pronounced than it is on Earth.

11. Also beyond my area of expertise, but there is another way to talk more or less normally, by touching faceplates and letting the sound propagate through the helmets.
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Offline Slarty1080

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Re: Help me make sure I'm not getting it all wrong
« Reply #5 on: 03/15/2019 05:45 pm »
Note the stars and constellations would appear as they do on Earth but would not rotate about the same point in the sky.

I’m not sure that voices would sound much lower on Mars. They might a bit, but although voices would sound lower in a 1bar CO2 atmosphere, lower pressure might counteract this to some extent and lower temperature would also have an effect. More importantly any sound waves would be very weak so would probably not be heard at all unless very loud like a Starship landing close by.

https://physics.stackexchange.com/questions/133333/atmospheric-pressures-effect-on-sound
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Offline ccdengr

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Re: Help me make sure I'm not getting it all wrong
« Reply #6 on: 03/15/2019 07:03 pm »
The polar caps were known to be primarily water ice prior to that thanks to various orbiters, though they also contain frozen carbon dioxide.
There's a permanent cap, mostly H2O, and a seasonally-varying cap of CO2.  Under current conditions the CO2 cap at the south pole never completely goes away.  The presence of CO2 has been known since at least the Mariner 4 flyby, and possibly before from Earth-based observations.  https://en.wikipedia.org/wiki/Martian_polar_ice_caps

In general, I'd avoid plot points that make flat declarative statements about things that we aren't that sure about, like twinkling, what it looks like in a dust storm, whether aircraft make good engineering sense, what sounds are like, etc.

Offline ceswiedler

Re: Help me make sure I'm not getting it all wrong
« Reply #7 on: 03/16/2019 01:04 pm »
Thank you!

Out of all of these bits, the only one that concerns me, because it's a major plot point, is the question of whether communications over the horizon are possible in the absence of satellites. In the story, two kids are stranded during a solar flare that's destroyed all communication satellites. Eventually the kids find a radio with a directional antenna and climb to the top of a mountain so they can communicate with a colony that's just over the horizon.

I'm fine that there are some obvious problems with this -- why do they need a separate antenna if normally their suits can talk to satellites? How could future satellite makers not shield well enough to protect from a flare? The main point is to get kids thinking about how ionospheres and the curvature of planets affect radio. But I would like to include an afterword that tells readers the parts that are farfetched or completely wrong.

So, because I'm still not quite clear: if I'm in a pressure suit with a radio that normally communicates with satellites (or people nearby) and my friend is over the horizon, can the two of us talk? CuddlyRocket mentioned ground waves as a phenomenon that allows propagation even without an ionosphere. Is that enough to rely on when on Mars? Or, to put it another way: if you read a book with this idea, would you think "that's plausible, Mars's ionosphere does mean over-the-horizon communications might be impossible" or would you think "oh, boy, this author doesn't have a basic grasp of physics?"

Regarding flight/ballistics: I didn't realize helicopters might work, thank you. I had read up on how airplanes would need enormous wings and/or need to fly ridiculously fast. So in my story, everyone flies in rockets in ballistic arcs. It's very amusing to me to think of 'normal' flight between cities/colonies involving weightlessness, especially since I can hardly stand to ride on fast roller-coasters. I appreciate the point about weightlessness after rockets shut off. I actually have it in the book this way, and then recently decided I must have misunderstood when I researched. My thought was that people on airplanes experience gravity when flying, and as long as the nose is pointed up, you could think of the plane as being in some kind of ballistic arc. I guess the difference is because of the lift exerted on the wings? Or is there something else I'm missing?

I appreciate all of the input! If anyone happens to want to read the book, or pass it along to a 12-ish-year-old who might like it, email me at [email protected] and I can send you an electronic copy. Otherwise, wait for it to come out early next year, and then buy lots of copies... ;-)

chris

Offline ceswiedler

Re: Help me make sure I'm not getting it all wrong
« Reply #8 on: 03/16/2019 01:13 pm »
One more thing. My question about ice was to make sure I was reasonably correct in my afterword when I say this:

"Fortunately for future Earthlings, we now know that there are large deposits of water ice on Mars. The first proof of underground ice was discovered in 2008 by the Phoenix lander..."

Thanks for the clarification that we knew the ice caps had both water and CO2 ice before Phoenix. I think what I say about Phoenix is still correct? I bring it up in the afterword because the characters (almost literally) run into the now-ancient Phoenix lander at one point in the story, and I'd like to point out its contributions.

Offline ccdengr

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Re: Help me make sure I'm not getting it all wrong
« Reply #9 on: 03/16/2019 02:16 pm »
In the story, two kids are stranded during a solar flare that's destroyed all communication satellites.
It's a pretty poorly designed satellite that could be destroyed by a solar flare.  I guess it's just barely possible that a huge flare could destroy even hardened electronics in space but leave electronics on the surface still functional -- the atmosphere of Mars does provide a fair amount of shielding.

I don't know enough about radio but I think there are over-the-horizon mechanisms that don't require the ionosphere -- "ground waves".  On Earth, one can bounce radio signals off the Moon for long-distance comm (maybe you could bounce a signal off Phobos).  https://en.wikipedia.org/wiki/Radio_propagation

IMHO Phoenix's contributions were pretty minimal and mostly about soil chemistry.

Offline zhangmdev

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Re: Help me make sure I'm not getting it all wrong
« Reply #10 on: 03/16/2019 02:29 pm »
Lower frequency radio communication has longer range, but needs larger antenna. kHz AM radio can be heard farther away than MegaHz FM radio. Small mobile device works on high frequency needs line-of-sight, or its effective range is quite limited. Walkie-talkie often could not work during Korean War because of the undulating terrain. If all comm sats are down, I'm afraid beyond horizon comm on Mars is not workable, at least not with hand-held devices, like those on the EVA suits.

People on airplane experience gravity when the plane is accelerating, i.e. engine thrust > drag, and when its weight is supported by lift from the wings. If the plane stalls, i.e. loss of lift, everything is in free-fall. People will feel weight-less, and in general panic. If the plane is in a steep dive, i.e. minimal lift pointing to the wrong direction, people will be weight-less too.

People use sat comm and rocket around on Mars seems quite farfetched  to me.

Offline MATTBLAK

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Re: Help me make sure I'm not getting it all wrong
« Reply #11 on: 03/20/2019 02:15 am »
Cracking CO2 to make oxygen is easy, but my reading tells me it's power intensive. The radiation levels on the Martian surface would be high, but not as high as the Lunar surface for instance. Next to Earth; probably Titan and Venus would be the safest places to hide from radiations from space, be it solar or cosmic. Venus has the super thick atmosphere but big, secondary thermal radiation problem of all that trapped infra-red from the Sun, making it a bloody hot place. The magnetic field of Venus is poor compared to Earth's.

Titan has a really thick atmosphere and it would also get some shielding from the Saturnian magnetic field. Mars is the safest relatively habitable place in the solar system, next to Earth. No one will live on Venus and no one on Titan; at least for a very long time.
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Offline Wicky

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Re: Help me make sure I'm not getting it all wrong
« Reply #12 on: 03/21/2019 03:52 pm »
You could inoke a Solar Storm of similar strength to the recently discovered one that occured in 660 BC

https://phys.org/news/2019-03-uncover-additional-evidence-massive-solar.html

https://physicsworld.com/a/ice-cores-reveal-huge-solar-storm-struck-earth-around-660-bc/

"According to the team, the storm in 660 BC was comparable to the 775 event, which is the strongest solar storm known to date. Furthermore, the ancient storm was ten times more intense than any solar storm that has occurred over the past 70 years – including storms that have disrupted electricity grids and telecommunications."


Offline whitelancer64

Re: Help me make sure I'm not getting it all wrong
« Reply #13 on: 03/21/2019 04:17 pm »
Thank you!

Out of all of these bits, the only one that concerns me, because it's a major plot point, is the question of whether communications over the horizon are possible in the absence of satellites. In the story, two kids are stranded during a solar flare that's destroyed all communication satellites. Eventually the kids find a radio with a directional antenna and climb to the top of a mountain so they can communicate with a colony that's just over the horizon.

I'm fine that there are some obvious problems with this -- why do they need a separate antenna if normally their suits can talk to satellites? How could future satellite makers not shield well enough to protect from a flare? The main point is to get kids thinking about how ionospheres and the curvature of planets affect radio. But I would like to include an afterword that tells readers the parts that are farfetched or completely wrong.

So, because I'm still not quite clear: if I'm in a pressure suit with a radio that normally communicates with satellites (or people nearby) and my friend is over the horizon, can the two of us talk? CuddlyRocket mentioned ground waves as a phenomenon that allows propagation even without an ionosphere. Is that enough to rely on when on Mars? Or, to put it another way: if you read a book with this idea, would you think "that's plausible, Mars's ionosphere does mean over-the-horizon communications might be impossible" or would you think "oh, boy, this author doesn't have a basic grasp of physics?"

Regarding flight/ballistics: I didn't realize helicopters might work, thank you. I had read up on how airplanes would need enormous wings and/or need to fly ridiculously fast. So in my story, everyone flies in rockets in ballistic arcs. It's very amusing to me to think of 'normal' flight between cities/colonies involving weightlessness, especially since I can hardly stand to ride on fast roller-coasters. I appreciate the point about weightlessness after rockets shut off. I actually have it in the book this way, and then recently decided I must have misunderstood when I researched. My thought was that people on airplanes experience gravity when flying, and as long as the nose is pointed up, you could think of the plane as being in some kind of ballistic arc. I guess the difference is because of the lift exerted on the wings? Or is there something else I'm missing?

I appreciate all of the input! If anyone happens to want to read the book, or pass it along to a 12-ish-year-old who might like it, email me at [email protected] and I can send you an electronic copy. Otherwise, wait for it to come out early next year, and then buy lots of copies... ;-)

chris

In writing my answer to you, I referred to a paper published by NASA in 2002, called "Radio Wave Propagation Handbook for Communication On and Around Mars" which I have attached for your reading pleasure.

In short, it is possible for radio waves below 4.5 MHz (the paper concludes that around 4 MHz is ideal) to be bounced over the horizon on Mars' ionosphere, but Mars' ionosophere is pretty variable, and dust storms may cause significant interference, so such communication would be unreliable. Also NASA has little data on the night-side condition of Mars' ionosphere, which is probably extremely unstable or non-existent based on current measurements.
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Offline Paul451

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Re: Help me make sure I'm not getting it all wrong
« Reply #14 on: 04/06/2019 04:28 am »
5. An efficient mode of long-distance flight would be rockets, which would basically travel in ballistic arcs. During a trajectory like this, the occupants would be weightless on the way down. They would still experience normal gravity up until the highest point of the ballistic arc.

To clarify what others have said: You are in freefall the moment the rocket shuts off. It doesn't matter which direction you are travelling, you are in free-fall. (Although a small amount of air resistance will create an tiny amount of upward acceleration.)

6. In theory, an air filter that sucked in CO2 from the atmosphere and converted it to O2 to breathe, meaning a person in an environment suit would only need to have a backup source of oxygen. I know rebreathers currently exist for SCUBA, but they seem to have a lot of limitations.

I was surprised to see this slip by so many people.

No. There is no such thing as a "filter" that turns CO₂ into O₂. Such chemical cracking of CO₂ into CO + O₂ is hugely energy intensive and will not be something done by a spacesuit. Think about it, you are basically trying to reverse carbon or hydrocarbon burning in oxygen, you have to put all that energy back in. (And the current record, AIUI, is less that 15% efficiency. So you have to put about 7 times as much energy back in as you would have gotten out.)

It is also not how rebreathers work. Rebreathers absorb CO₂ via a "scrubber", into sodium & calcium hydroxide, allowing just bottled oxygen instead of the bottled air of regular SCUBA. All spacesuits use the same kind of CO₂ absorption. They do not crack CO₂ back into oxygen.

Seriously, you could put ancient alien ruins in your story and it would be more realistic than putting a CO₂-to-O₂ "filter" in EVA suits.

However, NASA does 12hr EVAs routinely, and it might be possible that a specialised and mature Mars-suit ECLSS-pack [PLSS] would allow users to swap out scrubbers and O₂ bottles while wearing the suits.
« Last Edit: 04/06/2019 06:48 pm by Paul451 »

Offline speedevil

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Re: Help me make sure I'm not getting it all wrong
« Reply #15 on: 04/06/2019 12:58 pm »
I was surprised to see this slip by so many people.

No. There is no such thing as a "filter" that turns CO₂ into O₂. Such chemical cracking of CO₂ into CO + O₂ is hugely energy intensive and will not be something done by a spacesuit.
For pure CO2, this is true.
The atmosphere of Mars is not pure CO2, it has ~0.15% oxygen.
Assuming for the moment that the process of filtering this gas is as efficient as my home oxygen concentrator, which multiplies by 5 oxygen in the air at the physiological requirement for about 50W, this gives us a requirement for 3 or 4 stages (depending on if it needs to be at 20% or 100%) of between 150 and 200W or so. (with an added 40W or so for the initial compression)

A proper calculation of the above would need to look at exactly what the sorbent(s) used is in the above hypothetical device,  and its selectivity between CO and O2 (CO is at about the same volume), and how does N2 and Ar play into your desired breathing mix.
(N2/Ar are both tenfold what O2 is).

But a device to produce breathable air using 250W of power per person does not seem flat out ridiculous.



Offline Slarty1080

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Re: Help me make sure I'm not getting it all wrong
« Reply #16 on: 04/06/2019 06:58 pm »
You might find this article of interest:

https://www.researchgate.net/publication/242525435_Perchlorate_on_Mars_A_chemical_hazard_and_a_resource_for_humans

Oxygen can be released from the Martian regolith by treting it with an aqueous solution of enzymes that breakdown the perchlorate and release oxygen.


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Offline punder

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Re: Help me make sure I'm not getting it all wrong
« Reply #17 on: 04/06/2019 07:14 pm »
Just a nit. Airplanes technically don't need runways, they only need a way to get to flying speed, and runways are a convenient way of doing that.

Another way is the catapult, used by electric RC jet modelers, through military drone operators, all the way up to the U.S. Navy. So, if there was a need for launching airplanes on Mars (extreme loiter time, say) it could definitely be done without having to build a runway.

P.s. IMHO some of the best SF is in the "juveniles" so I look forward to your book with interest!

P.p.s. Wright Brothers didn't have a runway at Kitty Hawk, they had... a catapult! 

Couple examples


Money shot about 2:40 in
« Last Edit: 04/06/2019 07:41 pm by punder »

Offline punder

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Re: Help me make sure I'm not getting it all wrong
« Reply #18 on: 04/06/2019 07:56 pm »
A runway would come in very handy for landing...   ;D  depends on the type of aircraft I guess. The glider pilot would be SOL, and while drones are recovered by parachute on Earth, that probably won't work at Martian air pressure. An arresting net might work, or an in-air snag by a copter-type drone. So... yeah. Problematic after all.

But remember runways don't have to be paved. They only have to be adequately smooth, adequately flat, and adequately long for the expected traffic. Plenty of grass, dirt, and gravel runways all over the world. Bush pilots routinely land on unprepared sand bars and hill tops.

Sorry, sometimes I have to think things through in real time...
« Last Edit: 04/06/2019 08:07 pm by punder »

Offline Paul451

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Re: Help me make sure I'm not getting it all wrong
« Reply #19 on: 04/06/2019 08:02 pm »
There is no such thing as a "filter" that turns CO₂ into O₂.
For pure CO2, this is true. The atmosphere of Mars is not pure CO2, it has ~0.15% oxygen.
[...]But a device to produce breathable air using 250W of power per person does not seem flat out ridiculous.

At 0.15% O₂, you would need to absorb around a tonne of CO₂ per day, at greater than 95% purity in the final output. Given that the alternative is "they made sure to grab spare 8-hour oxygen and scrubber kits from the recharge station before...", insisting on augmenting breathable O₂ from Mars' atmosphere in a space-suit seems "flat out ridiculous" to me.

Tags: Mars 
 

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