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I just read a thought piece about what a war in space may look like, and it changed my thoughts on what orbit actually is. From what I read about orbits, it sounds like going faster in the velocity direction will cause you to get to a lower altitude, and going slower will cause you to get to a higher altitude orbit. This feels completely backwards to me, so I tried a thought experiment, but it led me to the questions below.

I'm standing on satellite in a circular low earth orbit, and I want to make my (indestructible) baseball go to the ground without waiting for months or years to de-orbit. If I threw the baseball in the velocity direction, I don't think I could cause enough delta V to make it go fast enough that it would go to a significantly lower orbit. Is that correct?

So instead of throwing it in the velocity direction, if I threw it straight at the earth (nadir), would it continue to go towards the earth, or would that just modify the baseball's orbit similar to throwing it in the velocity direction? I remember hearing about something "bouncing off the atmosphere". That wouldn't come into play with my baseball would it?

If I threw the baseball in the wake direction to try to take a bit of my orbital speed off of it, would it truly get to a higher orbit? Why wouldn't it just fall to the ground?

Bonus question: if I threw it anti-nadir, what happens?

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    $\begingroup$ Related: space.stackexchange.com/questions/38557/… $\endgroup$ – Nilay Ghosh Nov 19 '20 at 3:33
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    $\begingroup$ Youtube isn't ideal for answers, but about 40 seconds in, this video addresses your question with pictures. youtube.com/watch?v=wUgh8Y2JozI&feature=emb_title You can also, from a concept standpoint, think of what happens if you throw a ball from a high speed train (and ignore air resistance). $\endgroup$ – userLTK Nov 19 '20 at 4:31
  • $\begingroup$ Your opening is the other way around. Going down makes faster, not the opposite, as surprising as it can be. $\endgroup$ – Alchimista Nov 19 '20 at 8:58
  • $\begingroup$ play Kerbal Space Program and all will become clear :-) $\endgroup$ – Aaron F Nov 19 '20 at 23:56
  • $\begingroup$ Or Orbiter..... $\endgroup$ – James K Nov 20 '20 at 21:55
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Orbits are all ellipses, so when you throw a baseball you change the orbit of the base ball from your circular ellipse to another ellipse.

If you throw it prograde (in the velocity direction), then you baseball will have an elliptical orbit. It will be closest to the Earth at the point at which you threw it, and furthest from the Earth (and higher than the circular orbit) at 180 degrees. So throwing prograde will never make the baseball deorbit. The speed of the baseball will now not be constant. It will be faster than the circular orbit speed at the lowest point in the orbit, but slower than the circular orbit speed at the highest point.

This is your misconception: Adding velocity doesn't make the ball to a lower orbit. Instead, adding velocity makes the ball go to a higher orbit, which in turn reduces the speed of the ball.

Throwing retrograde (wake direction) has the opposite effect. The baseball will enter an elliptical orbit that is close to the Earth at 180 degree from the point at which you threw and is, on average at a higher speed. If you throw retrograde hard enough you can reduce the height at 180 degrees to less than 0, ie the baseball hits the ground. But you have to throw far far harder than is physically possible, because you and the baseball start out at orbital speeds, about 7km/s so throwing at 10m/s won't be enough to deorbit.

Throwing at the nadir would also just change the baseball's orbit into an elliptical orbit. The baseball would initially approach the Earth, but as it did it would gain speed and then move away from the Earth in an ellipse. The closest point would be at about 90 degrees ahead of the throwing point. This is actually not a very effective way of deorbiting. It takes a lot harder throw to reduce the height by the same amount that throwing retrograde would. As with the other throws, the ball will pass through the throwing point after going all around the Earth. But you won't be at the same point again because your orbital period will be different to that of the ball.

Throwing anti-nadir has a similar effect, except now the furthest point is at about 90 degrees, and the ball falls to the closest point at 270 degrees. It is equally ineffective at de-orbiting or gaining height. This is why nearly all spacecraft manoeuvres happen either in the prograde direction (to add height) or retrograde (to reduce height)

"Bouncing off the atmosphere" is a practical problem not directly connected to orbits. If you enter the atmosphere at the wrong angle, you can actually start to fly and so gain altitude. That's not really connected to the orbital manoeuvres here

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  • $\begingroup$ What speed would we need for the baseball to touch the earth surface when throwing retrograde (ignoring atmosphere)? Do have equations? $\endgroup$ – Ralf Kleberhoff Nov 19 '20 at 13:58
  • $\begingroup$ Yes we have equations. (It's not called rocket science for nothing) and no doubt the people at space.stackexchange would give you chapter and verse. Of course, it depends on exactly which low earth orbit you are in. But a retrograde dv of about 100m/s is in the right ball park. More than any human could throw, but you can de-orbit a bullet by fireing a gun backwards. $\endgroup$ – James K Nov 19 '20 at 17:48
  • $\begingroup$ The way I was reading that article, it made no sense whatsoever. But, if I understand you right, it's a two-step process, not just one. To make sure I get it, you speed up to get into a higher elevation, then when you get there, slow down to a proper orbital velocity for that orbit. Right? Thanks! $\endgroup$ – kmort Nov 20 '20 at 5:21
  • $\begingroup$ Yes, adding velocity raises your orbit, which causes your speed to decrease. A consequence of this is that atmospheric drag on a satellite will remove velocity, and cause the satellite's speed to increase. $\endgroup$ – James K Nov 20 '20 at 5:25
  • $\begingroup$ always good to reference relevant existing answers How hard do you have to throw something off the ISS to make it deorbit? and If you throw a baseball from the space station, will it return to you in 90 minutes? $\endgroup$ – uhoh Nov 22 '20 at 12:03

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