Timeline for Person falling from space
Current License: CC BY-SA 4.0
29 events
| when toggle format | what | by | license | comment | |
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| Nov 26, 2023 at 9:10 | comment | added | ikrase | It is worth noting that the "two meter diameter flat plate" is a pretty good approximation of the MOOSE one-man reentry equipment | |
| Nov 22, 2023 at 23:03 | comment | added | Mark | @LorenPechtel, bigger is not uniformly better. Turns out there's an optimum around 10 square meters (depending on the person's mass). Below that, increasing speed at the start of aerobraking makes for a higher acceleration, above it, increased drag makes for a higher acceleration. | |
| Nov 22, 2023 at 9:11 | comment | added | scotty3785 | Randall Munroe would be proud of an answer like this! Add more stick people though :P | |
| Nov 22, 2023 at 4:53 | comment | added | Loren Pechtel | As for modifying the force field, the bigger the better--scale it up enough and she could land with it (landing with a big flat thing is common behavior--see "parachute". Nobody does it with fixed surfaces because it would weigh too much.) It can't be a plate, though, because that is unstable and will most likely flip. A gentle bowl would be optimum. | |
| Nov 21, 2023 at 20:24 | comment | added | chux | @Mark and John, Agree the magnitude of the acceleration builds after that peak velocity point. I tend to think of acceleration as a vector and building implies an increase (more positive), when the scenario you describe tells of a rapid negative increase in acceleration from 0. IAC, now it is clear what is meant - it increases in the opposite direction - and quite rapidly. | |
| Nov 21, 2023 at 20:08 | comment | added | Mark | @chux-ReinstateMonica, before, you're accelerating downwards. At the point of balance, you feel exactly 1 g of drag (you don't feel gravity, since it's acting uniformly on your body), with no net acceleration. After, you're accelerating upwards (but still moving downwards because of the velocity you've built up). | |
| Nov 21, 2023 at 16:52 | comment | added | John Dvorak | @chux-ReinstateMonica before that point, the acceleration is leisurely <1 g. At that exact point it's zero. Soon after you'll be going pretty fast through some thick atmosphere and your accelecation will go way up. If you're headed back-first when you hit those g's, you'll have a hard time. If you're oriented in any other way, you die. | |
| Nov 21, 2023 at 12:46 | comment | added | chux | @Mark "you hit your peak velocity of 2800 meters per second, with drag exactly balancing gravity. Acceleration is still building, though." Hmm, at this point, is not acceleration zero? and then one slows down later (deceleration, not building acceleration)? | |
| Nov 21, 2023 at 12:33 | comment | added | chux | @Mark "Head-first or feet-first is worse: you get deeper into the atmosphere before starting to slow down," implies a static posture. Maybe a change in posture at critical times to reduce the deceleration? | |
| Nov 21, 2023 at 9:44 | comment | added | AnoE | Awesome answer. You could add a little final info - what kind of speed does a real-world (military) skydiver hit the ground at, if trying to get down as quickly as possible without breaking anything? For comparison's sake? | |
| Nov 21, 2023 at 9:28 | comment | added | CapIsland | @eirikdaude, Thanks, but I am not a member there. I am a member here. The other question is no different from this one. Either this one should have been closed or that one should be opened. | |
| Nov 21, 2023 at 9:23 | comment | added | eirikdaude | @CapIsland You could try going to worldbuilding and ask there instead - I believe they do science-based answers... | |
| Nov 21, 2023 at 9:14 | comment | added | CapIsland | Thank you everyone for helping me so much with this question. I have no idea what I have done wrong with my other question and no one else seems to know either, or is willing to tell me. So I will stop here and wish you all the best. | |
| Nov 21, 2023 at 1:21 | comment | added | Lamar Latrell | I often find my intuition around jerk fails me. That number in other words is over 1km/s^3. One kilometre.. 😂. Thanks for looking it up 🙂👍 | |
| Nov 20, 2023 at 23:35 | comment | added | Mark | @LamarLatrell, maximum jerk in all scenarios is under 120 *g*/s, which Wikipedia suggests is tolerable in any orientation. | |
| Nov 20, 2023 at 22:17 | comment | added | vsz | @CapIsland : just barely over 20 g might be survivable if she is very fit and lucky. The world record (en.wikipedia.org/wiki/…) is above that. | |
| Nov 20, 2023 at 19:49 | comment | added | Lamar Latrell | Seems like the kind of analysis where jerk (rate of change of acceleration) would be relevant? I know that as you regress in to higher and higher derivative orders they become harder to predict/model (and where should you stop). But I think this is one of those cases where at least jerk could at least enter the discussion? | |
| Nov 20, 2023 at 16:35 | comment | added | CapIsland | My other question was closed because stupidly I used the word 'wormhole'. I am just interested in the physics, nothing else. I can write the novel: I not as good with the physics. | |
| Nov 20, 2023 at 14:48 | comment | added | Chris H | If you can modify the shape in real-time, you can start with a disc for maximum drag in the less dense regions (though of course this would be unstable) and go progressively smaller in cross-section to keep the drag tolerable, before going wide again to decelerate | |
| Nov 20, 2023 at 14:29 | comment | added | CapIsland | Can someone point me to a gravity and air resistance simulator so that I can do all this myself? I just need to know how air resistance works if you're shooting upwards. | |
| Nov 20, 2023 at 13:07 | comment | added | CapIsland | I have also added another part of the question here: space.stackexchange.com/questions/64809/… | |
| Nov 20, 2023 at 10:31 | vote | accept | CapIsland | ||
| Nov 20, 2023 at 10:31 | comment | added | CapIsland | @Mark, if it's not too much trouble, could you give me the advice the characters in the book would give to the woman on how to change her forcefield shape/cross-section, and how this would change what happens, stage by stage? | |
| Nov 20, 2023 at 7:53 | comment | added | gerrit | @Criggie Surface impact was explicitly excluded in the question. | |
| Nov 20, 2023 at 5:11 | comment | added | Criggie | "just 16 m/s" is still 57 km/h so guaranteed injury and and over 40% risk of death based on pedestrian/car impacts at 50 km/h. | |
| Nov 20, 2023 at 2:07 | history | edited | Mark | CC BY-SA 4.0 |
Add survivable scenario
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| Nov 20, 2023 at 1:51 | comment | added | Mark | @CapIsland Head-first or feet-first is worse: you get deeper into the atmosphere before starting to slow down, so the forces are higher (but briefer), while your tolerance is lower. If you can spread the forcefield out into a sphere (or even better, a plate), deceleration starts earlier, and forces drop to (barely) survivable levels. | |
| Nov 20, 2023 at 1:19 | comment | added | CapIsland | Thank you very much for that wonderful write up. So the woman would not survive the five seconds above 20gs even in the force field. The characters in the novel would have 333 seconds to say goodbye. I assume there is no way the woman could reduce the deceleration to survivable levels even with a head down streamlined forcefield? | |
| Nov 20, 2023 at 0:45 | history | answered | Mark | CC BY-SA 4.0 |