4 ms·

The speed of Rosetta's comet at perigee is, I think, significantly grater than the max speed of this dwarf planet. The dwarf planet has a much higher apogee, o

The speed of Rosetta's comet at perigee is, I think, significantly grater than the max speed of this dwarf planet. The dwarf planet has a much higher apogee, of course, but escape velocity, corresponding to infinite apogee, is finite and not that large, and Rosetta had to go much deeper into the Sun's gravity well. So, as a non-expert who hasn't done the numbers, I'd guess matching pace with the dwarf planet would be easier (requiring less delta V and/or gravity assists) than Rosetta with the comet.

messe 5y ago
Somewhat unintuitively, thanks to the Oberth effect, it can be easier to reach escape velocity closer to an object, (Humorously portrayed in https://xkcd.com/1242 https://xkcd.com/1242). Aside: if you are looking to learn more, I cannot recommend Kerbal Space Program enough.
- thoughtsimple 5y ago
  I think you meant: https://xkcd.com/1244/ https://xkcd.com/1244/
  - messe 5y ago
    Whoops. Yep, that’s the one. Maybe I’ll be vindicated when it turns out the planetoid is made out of grey goo.
- perl4ever 5y ago
  I've been aware of people talking about Kerbal Space Program for years and years, but I lost interest in playing it when I heard it didn't do real N-body gravitational calculations because they were too intensive. I still find that inexplicable. To me, it sounds like saying "our calculator only does basic arithmetic on four core machines, square roots are too slow".
  - messe 5y ago
    Not really that inexplicable, it’s a video game. It’s not for computational reasons, but to make gameplay easier to reason about; because again, it’s a video game. The mechanics are simplified, yes, but patched conics is quite a good approximation for many cases, and great for developing an intuition for the basics. There is a mod that includes n-body calculations called Principia if you’re interested in that.
    - deleted 5y ago
      [deleted]
  - garaetjjte 5y ago
    There's mod though! https://forum.kerbalspaceprogram.com/index.php?/topic/162200-wip181-191-1101-and-1110%E2%80%932-principia%E2%80%94version-gr%C3%B6bner-released-2021-06-10%E2%80%94n-body-and-extended-body-gravitation/ https://forum.kerbalspaceprogram.com/index.php?/topic/162200...
    - ericbarrett 5y ago
      It’s quite good as well, written in C++ for speed with new versions released every lunar cycle (!). I’ve done some Lagrange orbits with it in the Kerbol solar system. Doing it with Realism Overhaul and Real Solar System is a bit harder…
  - perihelions 5y ago
    I'd push back against that interpretation of the developer's design choices. Kerbal's use of patched conic approximations greatly lowers the difficulty of the game (it is a game) for most players; it enables a simple and coherent UI/UX; and it guarantees fixed orbits that make difficult in-space rendezvous like the Apollo program's accessible. Like Minecraft cubes, it creates a reliable foundation of simple abstractions that people can reason about, and build complicated strategies on top of. (Wouldn't Minecraft be unplayable if instead of cubes, it was arbitrary user-defined convex polyhedra? It's like that). Upping the realism lowers the playability: games and simulators are subtly different things. Otherwise we'd all be playing STK/Astrogator instead of Kerbal, and AutoCAD instead of Minecraft, and sitting in city hall basements debugging spreadsheets in place of Cities: Skylines. The type of limitations that distinguish games from serious simulators are not accidents and not laziness, but deliberate design choices. I concede this makes certain interesting topics like Lagrange points / halo orbits, masscons, and orbital precession inaccessible. That's part of the tradeoff.
- pyuser583 5y ago
  Are you sure that the right xkcd link?
  - messe 5y ago
    Already noted in a comment below. Too late to edit. It’s 2 off. It should be xkcd.com/1244.

messe 5y ago

Somewhat unintuitively, thanks to the Oberth effect, it can be easier to reach escape velocity closer to an object, (Humorously portrayed in https://xkcd.com/1242 https://xkcd.com/1242). Aside: if you are looking to learn more, I cannot recommend Kerbal Space Program enough.

thoughtsimple 5y ago
I think you meant: https://xkcd.com/1244/ https://xkcd.com/1244/
- messe 5y ago
  Whoops. Yep, that’s the one. Maybe I’ll be vindicated when it turns out the planetoid is made out of grey goo.
perl4ever 5y ago
I've been aware of people talking about Kerbal Space Program for years and years, but I lost interest in playing it when I heard it didn't do real N-body gravitational calculations because they were too intensive. I still find that inexplicable. To me, it sounds like saying "our calculator only does basic arithmetic on four core machines, square roots are too slow".
- messe 5y ago
  Not really that inexplicable, it’s a video game. It’s not for computational reasons, but to make gameplay easier to reason about; because again, it’s a video game. The mechanics are simplified, yes, but patched conics is quite a good approximation for many cases, and great for developing an intuition for the basics. There is a mod that includes n-body calculations called Principia if you’re interested in that.
  - deleted 5y ago
    [deleted]
- garaetjjte 5y ago
  There's mod though! https://forum.kerbalspaceprogram.com/index.php?/topic/162200-wip181-191-1101-and-1110%E2%80%932-principia%E2%80%94version-gr%C3%B6bner-released-2021-06-10%E2%80%94n-body-and-extended-body-gravitation/ https://forum.kerbalspaceprogram.com/index.php?/topic/162200...
  - ericbarrett 5y ago
    It’s quite good as well, written in C++ for speed with new versions released every lunar cycle (!). I’ve done some Lagrange orbits with it in the Kerbol solar system. Doing it with Realism Overhaul and Real Solar System is a bit harder…
- perihelions 5y ago
  I'd push back against that interpretation of the developer's design choices. Kerbal's use of patched conic approximations greatly lowers the difficulty of the game (it is a game) for most players; it enables a simple and coherent UI/UX; and it guarantees fixed orbits that make difficult in-space rendezvous like the Apollo program's accessible. Like Minecraft cubes, it creates a reliable foundation of simple abstractions that people can reason about, and build complicated strategies on top of. (Wouldn't Minecraft be unplayable if instead of cubes, it was arbitrary user-defined convex polyhedra? It's like that). Upping the realism lowers the playability: games and simulators are subtly different things. Otherwise we'd all be playing STK/Astrogator instead of Kerbal, and AutoCAD instead of Minecraft, and sitting in city hall basements debugging spreadsheets in place of Cities: Skylines. The type of limitations that distinguish games from serious simulators are not accidents and not laziness, but deliberate design choices. I concede this makes certain interesting topics like Lagrange points / halo orbits, masscons, and orbital precession inaccessible. That's part of the tradeoff.
pyuser583 5y ago
Are you sure that the right xkcd link?
- messe 5y ago
  Already noted in a comment below. Too late to edit. It’s 2 off. It should be xkcd.com/1244.