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I'm no expert but this part seems to stretch science into hollywood sensationalism: "At the right angle and velocity, you might even fall back into Earth’s atmo

I'm no expert but this part seems to stretch science into hollywood sensationalism: "At the right angle and velocity, you might even fall back into Earth’s atmosphere and burn up." There is a Scott Manley video that describes orbital mechanics well where he covers if someone could throw a ball from orbit back to earth. https://www.youtube.com/watch?v=cxNJoaBLLNM https://www.youtube.com/watch?v=cxNJoaBLLNM It is pretty clear that the best one can do is throw the ball directly backwards which would slightly decrease the orbital height on the opposite side of the earth. I can't imagine someone drifting off a structure faster than someone could hit a golf ball so it seems extremely unlikely that falling back to earth and burning up would be an outcome. I love Kerbal Space Program and find orbital mechanics interestingly counterintuitive so please correct me if I am wrong.

fennecfoxen 5y ago
The thing to remember is in a low earth orbit, your orbit has you moving around 8 kilometers per second. So even before we start getting to the counterintuitive parts (higher is slower, lower is faster, etc) take a moment and think about that 8km/s figure by itself. Consider a token 1% of that amount: 80 m/s (~180 mph). Do you think your orbit has more than a 1% margin before your craft plunges into the atmosphere? (I certainly expect it does). Does this seem like a reasonable speed you could get to using your personal astronaut propulsion device? I don't actually know, but it certainly challenges my image of astronauts zooming around a space station at speeds that would make a kick-scooter look fast.
- jkelleyrtp 5y ago
  Since there's no drag, you can accelerate as much as you want given the fuel in your pack. In fact, propellant is talked about in terms of Detla-V (delta in velocity). It seems like the first models of cosmonaut suits gave about 70 m/s of DV while the most recent astronaut MMUs give about 25m/s [1]. So, I don't think an astronaut could de-orbit themselves with just their suit alone. [1] https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit
  - kayodelycaon 5y ago
    There is drag on the International Space Station.
    - fennecfoxen 5y ago
      There is, but the drag is so small that they operate an entire space station in that orbit. It'll be quite some time before it starts to make a difference.
      - deleted 5y ago
        [deleted]
  - inglor_cz 5y ago
    There is non-0 drag at this distance from Earth and it is the main reason for orbital decay. https://en.wikipedia.org/wiki/Orbital_decay https://en.wikipedia.org/wiki/Orbital_decay But from a POV of an astronaut fiddling around with his propulsion unit, this drag is low.
js8 5y ago
> the best one can do is throw the ball directly backwards What if you had a really good pitch, do this, and then waited until it comes around the Earth (several months, I guess) hurling back at you, and threw another ball against it? They would collide and fall?
- scrumbledober 5y ago
  it wouldn't come back around to you. you're moving at over 17000 mph. if you threw the ball backwards it would be in a slightly different orbit that wouldn't meet back up with you. The two orbits would look like a spirograph
  - js8 5y ago
    I think you're right, they can't collide.
- thaumasiotes 5y ago
  What kind of model are you working with? Suppose you're orbiting at 10,000 units per second. You throw a ball backwards at -20 units per second, giving it a velocity of +9,980 units per second. Later, you throw another ball at the first ball with the same velocity. Traveling at +9,980 units per second, it will... obviously never be able to hit the first ball. But if the two balls did somehow collide, how could they end up falling to earth as a result? If your idea is that you sneak up on the first ball from behind (after all, you are going faster) and throw the second ball at it from behind, now you have a ball traveling at v = +10,020 colliding with another ball traveling at v = +9,980. Here at least the collision is possible, but how does falling become a possibility?
- btilly 5y ago
  Thanks to the satellite paradox, when your orbits meets up again it would be ahead of you. If after some number of orbits the objects meet up, the golf ball will still be moving backwards relative to the satellite.
seventytwo 5y ago
They would fall back to earth and burn up eventually, but the oxygen would run out much faster.

fennecfoxen 5y ago

The thing to remember is in a low earth orbit, your orbit has you moving around 8 kilometers per second. So even before we start getting to the counterintuitive parts (higher is slower, lower is faster, etc) take a moment and think about that 8km/s figure by itself. Consider a token 1% of that amount: 80 m/s (~180 mph). Do you think your orbit has more than a 1% margin before your craft plunges into the atmosphere? (I certainly expect it does). Does this seem like a reasonable speed you could get to using your personal astronaut propulsion device? I don't actually know, but it certainly challenges my image of astronauts zooming around a space station at speeds that would make a kick-scooter look fast.

jkelleyrtp 5y ago
Since there's no drag, you can accelerate as much as you want given the fuel in your pack. In fact, propellant is talked about in terms of Detla-V (delta in velocity). It seems like the first models of cosmonaut suits gave about 70 m/s of DV while the most recent astronaut MMUs give about 25m/s [1]. So, I don't think an astronaut could de-orbit themselves with just their suit alone. [1] https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit
- kayodelycaon 5y ago
  There is drag on the International Space Station.
  - fennecfoxen 5y ago
    There is, but the drag is so small that they operate an entire space station in that orbit. It'll be quite some time before it starts to make a difference.
    - deleted 5y ago
      [deleted]
- inglor_cz 5y ago
  There is non-0 drag at this distance from Earth and it is the main reason for orbital decay. https://en.wikipedia.org/wiki/Orbital_decay https://en.wikipedia.org/wiki/Orbital_decay But from a POV of an astronaut fiddling around with his propulsion unit, this drag is low.

js8 5y ago

> the best one can do is throw the ball directly backwards What if you had a really good pitch, do this, and then waited until it comes around the Earth (several months, I guess) hurling back at you, and threw another ball against it? They would collide and fall?

scrumbledober 5y ago
it wouldn't come back around to you. you're moving at over 17000 mph. if you threw the ball backwards it would be in a slightly different orbit that wouldn't meet back up with you. The two orbits would look like a spirograph
- js8 5y ago
  I think you're right, they can't collide.
thaumasiotes 5y ago
What kind of model are you working with? Suppose you're orbiting at 10,000 units per second. You throw a ball backwards at -20 units per second, giving it a velocity of +9,980 units per second. Later, you throw another ball at the first ball with the same velocity. Traveling at +9,980 units per second, it will... obviously never be able to hit the first ball. But if the two balls did somehow collide, how could they end up falling to earth as a result? If your idea is that you sneak up on the first ball from behind (after all, you are going faster) and throw the second ball at it from behind, now you have a ball traveling at v = +10,020 colliding with another ball traveling at v = +9,980. Here at least the collision is possible, but how does falling become a possibility?
btilly 5y ago
Thanks to the satellite paradox, when your orbits meets up again it would be ahead of you. If after some number of orbits the objects meet up, the golf ball will still be moving backwards relative to the satellite.

seventytwo 5y ago

They would fall back to earth and burn up eventually, but the oxygen would run out much faster.