4 ms·

> you won't even notice when you've gained intuitive understanding of basic orbital mechanics. You will, because every time you watch sci-fi where a ship drops

> you won't even notice when you've gained intuitive understanding of basic orbital mechanics. You will, because every time you watch sci-fi where a ship drops from orbit by accelerating towards the planet you’ll be screaming inside.

kaibee 7y ago
> you’ll be screaming inside. Just like the passengers.
TeMPOraL 7y ago
Fair. You will cringe hard. I haven't been to a cinema for a space movie since Interstellar, but I vividly remember watching The 100 at home, standing up and almost walking away from the computer screaming "THIS IS NOT HOW YOU DEORBIT A SPACE STATION". Other KSP side effects include: wondering how much Δv your car has, calling reverse "retrograde", calling right/left "normal"/"antinormal", calling up/down "radial-out"/"radial-in"...
Diederich 7y ago
> a ship drops from orbit by accelerating towards the planet you’ll be screaming inside Aww hell that'll work if you have sci-fi amounts of delta-v. (:
- DuskStar 7y ago
  There are even KSP mods that let you build honest-to-god, as-Clarke-would-have-recognized-them torchships [0] - so if you want to deorbit by burning radial-in, you can certainly try! You might end up with reentry heating issues, but that's what burning retrograde with your torchship is for. Who cares about making the landscape glow for the next century, we've got fusion! 0: http://www.projectrho.com/public_html/rocket/torchships.php http://www.projectrho.com/public_html/rocket/torchships.php
derefr 7y ago
What's wrong with accelerating toward the planet, if 1. your whole ship body is essentially one big jet engine impelling air through and out; 2. for the parts not covered by the impeller, you have a technobabble "deflector dish" bouncing off the dust that'd be ripping you to shreds; and 3. the existence of technobabble "inertial dampeners" implies that you can generate instantaneous gravitational fields† in any orientation you like (presumably both inside and outside the ship), to serve as a very fast drag chute? † Though, y'know, I've never heard a sci-fi story mention gravitomagnetism. Instantaneous change in gravitational force would imply a large gravitational flux, which would cause similarly improbable and interesting phenomena as the ability to instantaneously teleport magnets further together/apart would. With magnetism the weird things are monopoles; with gravitomagnetism... dipoles?
- wcoenen 7y ago
  > What's wrong with accelerating toward the planet It rotates the orbit, which is not the most efficient way to de-orbit. Instead, to de-orbit with minimal delta-v expended, you burn retrograde at the highest point of the orbit. This will lower the lowest point of the orbit into the atmosphere.
- raattgift 7y ago
  > I've never heard a sci-fi story mention gravitomagnetism. Out of curiosity, what would you want from the story? Astronaut in mid-altitude polar orbit around Earth notices at the end of a few [...thousand...] years that the vacuum-freefalling fuzzy dice art piece in the cockpit finally shows a different face to the entry hatch? Spooky stuff! ;) A low altitude polar orbit around a millisecond pulsar would certainly allow for plot twists (pardon the pun), but effects highlighted by the GEM formalism would be way down the list of post-Newtonian observables (and in any case you'd be far from the weak field limit in which the GEM formalism is reasonably reliable). Rather than cast about in the GEM formalism for ideas when departing dramatically from a slow stable orbit around a rotating spherical body, you might be happier going down the Equivalence Principle route directly, thinking about a pseudo-gravitational field popping up in response to acceleration. Michael Weiss's text at the link might give you some ideas: http://www.math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_gr.html http://www.math.ucr.edu/home/baez/physics/Relativity/SR/Twin... The rough sketch based on that is that an astronaut bouncing around in his reentry capsule, absent any view of the interactions between the outside of the capsule and the atmosphere, is free to think of the pseudo-forces he feels (he and the capsule both want to keep freely falling, but the capsule keeps interacting with the atmosphere, jostling the capsule around his free-fall trajectory) as pseudo-gravitational, much like riders of a vomit comet, roller coaster, fast car making a sharp turn, etc. and their experiences of changing weight. (Weight in the "contact" sense: the quantities piezo-electric bathroom scales would report if slipped between human body parts and surfaces bolted/welded to the inside of the capsule/car/roller-coaster/vomit-comet, with those scales essentially quantifying the feelings arising from stimulation of their skins' various sensory receptors like Merkel nerve endings and Pacini corpuscles). As a complete aside (I was thinking of dynamic neutral buoyancy for astronauts in your proposed situation, so fish came up), Kerbal probably doesn't simulate anything like the observations in this thread: https://www.reddit.com/r/askscience/comments/k0bdu/would_fish_in_an_aquarium_in_a_0_gravity/ https://www.reddit.com/r/askscience/comments/k0bdu/would_fis... and really you should be able to send simulated octopus astronauts on missions!
glandium 7y ago
OTOH, I don't remember the last time I saw Sci-fi where things were actually orbiting and then drop from orbit.

kaibee 7y ago

> you’ll be screaming inside. Just like the passengers.

TeMPOraL 7y ago

Fair. You will cringe hard. I haven't been to a cinema for a space movie since Interstellar, but I vividly remember watching The 100 at home, standing up and almost walking away from the computer screaming "THIS IS NOT HOW YOU DEORBIT A SPACE STATION". Other KSP side effects include: wondering how much Δv your car has, calling reverse "retrograde", calling right/left "normal"/"antinormal", calling up/down "radial-out"/"radial-in"...

Diederich 7y ago

> a ship drops from orbit by accelerating towards the planet you’ll be screaming inside Aww hell that'll work if you have sci-fi amounts of delta-v. (:

DuskStar 7y ago
There are even KSP mods that let you build honest-to-god, as-Clarke-would-have-recognized-them torchships [0] - so if you want to deorbit by burning radial-in, you can certainly try! You might end up with reentry heating issues, but that's what burning retrograde with your torchship is for. Who cares about making the landscape glow for the next century, we've got fusion! 0: http://www.projectrho.com/public_html/rocket/torchships.php http://www.projectrho.com/public_html/rocket/torchships.php

derefr 7y ago

What's wrong with accelerating toward the planet, if 1. your whole ship body is essentially one big jet engine impelling air through and out; 2. for the parts not covered by the impeller, you have a technobabble "deflector dish" bouncing off the dust that'd be ripping you to shreds; and 3. the existence of technobabble "inertial dampeners" implies that you can generate instantaneous gravitational fields† in any orientation you like (presumably both inside and outside the ship), to serve as a very fast drag chute? † Though, y'know, I've never heard a sci-fi story mention gravitomagnetism. Instantaneous change in gravitational force would imply a large gravitational flux, which would cause similarly improbable and interesting phenomena as the ability to instantaneously teleport magnets further together/apart would. With magnetism the weird things are monopoles; with gravitomagnetism... dipoles?

wcoenen 7y ago
> What's wrong with accelerating toward the planet It rotates the orbit, which is not the most efficient way to de-orbit. Instead, to de-orbit with minimal delta-v expended, you burn retrograde at the highest point of the orbit. This will lower the lowest point of the orbit into the atmosphere.
raattgift 7y ago
> I've never heard a sci-fi story mention gravitomagnetism. Out of curiosity, what would you want from the story? Astronaut in mid-altitude polar orbit around Earth notices at the end of a few [...thousand...] years that the vacuum-freefalling fuzzy dice art piece in the cockpit finally shows a different face to the entry hatch? Spooky stuff! ;) A low altitude polar orbit around a millisecond pulsar would certainly allow for plot twists (pardon the pun), but effects highlighted by the GEM formalism would be way down the list of post-Newtonian observables (and in any case you'd be far from the weak field limit in which the GEM formalism is reasonably reliable). Rather than cast about in the GEM formalism for ideas when departing dramatically from a slow stable orbit around a rotating spherical body, you might be happier going down the Equivalence Principle route directly, thinking about a pseudo-gravitational field popping up in response to acceleration. Michael Weiss's text at the link might give you some ideas: http://www.math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_gr.html http://www.math.ucr.edu/home/baez/physics/Relativity/SR/Twin... The rough sketch based on that is that an astronaut bouncing around in his reentry capsule, absent any view of the interactions between the outside of the capsule and the atmosphere, is free to think of the pseudo-forces he feels (he and the capsule both want to keep freely falling, but the capsule keeps interacting with the atmosphere, jostling the capsule around his free-fall trajectory) as pseudo-gravitational, much like riders of a vomit comet, roller coaster, fast car making a sharp turn, etc. and their experiences of changing weight. (Weight in the "contact" sense: the quantities piezo-electric bathroom scales would report if slipped between human body parts and surfaces bolted/welded to the inside of the capsule/car/roller-coaster/vomit-comet, with those scales essentially quantifying the feelings arising from stimulation of their skins' various sensory receptors like Merkel nerve endings and Pacini corpuscles). As a complete aside (I was thinking of dynamic neutral buoyancy for astronauts in your proposed situation, so fish came up), Kerbal probably doesn't simulate anything like the observations in this thread: https://www.reddit.com/r/askscience/comments/k0bdu/would_fish_in_an_aquarium_in_a_0_gravity/ https://www.reddit.com/r/askscience/comments/k0bdu/would_fis... and really you should be able to send simulated octopus astronauts on missions!

glandium 7y ago

OTOH, I don't remember the last time I saw Sci-fi where things were actually orbiting and then drop from orbit.