3 ms·

Its about the speed and not so much the height https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/

• CuriousCosmic 4y ago
  Well kind of but speed isn't a really useful metric until you have a circular orbit. Knowing speed won't be able to tell you whether you are suborbital (but it will tell you if you are on an escape orbit). However knowing your periapsis (elevation at lowest point in orbit) will tell you whether you are suborbital. It's only at the point where your periapsis is close to your apoapsis that speed is actually useful. Any metric other than periapsis will require 2 components to describe that the orbit isn't suborbital. Periapsis only gets away with it by implying that the second component is at least as high up as it is (apoapsis is always higher). The other useful metric would be velocity (speed + direction) but while that's something you can easily and immediately measure, periapsis & apoapsis (aka height) are far easier to visualize.