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I am not a NASA employee or a scientist, but why do we fly to the moon when it looks easier to fly away from it and wait for it to approach the craft. Then put something permanently in a polar orbit so it's always in view with radio contact. I've only done it on a simulation, but got to thinking if it was easier if you wanted all the components of a space station and build it and wait for the moon. Imagine twenty rockets, all parts of a station flying away from earth and as they flew they connected in space then stopped and waited. Sorry if it's dumb but no one is in a hurry to have a moon base, so just thought I'd ask.

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  • $\begingroup$ A polar orbit is not particularly helpful, because it's expensive to get to and expensive to get out of when you are close to the Moon. You might want to have a look how spacecraft are captured by Mars after a transfer from Earth, which is roughly similar to what you have in mind. $\endgroup$
    – asdfex
    Aug 19, 2022 at 11:03
  • $\begingroup$ Does a polar orbit ensure constant radio contact throughout the moon month ? $\endgroup$
    – AJN
    Aug 19, 2022 at 11:34
  • $\begingroup$ A polar orbit would not automatically guarantee constant contact either. it would have to be an earth synchronous orbit but I doubt that there is an orbit like that around the moon. $\endgroup$
    – TrySCE2AUX
    Aug 19, 2022 at 13:00
  • $\begingroup$ @AJN Not all polar orbits do, but whether some might is actually an intriguing question $\endgroup$
    – TooTea
    Aug 19, 2022 at 13:02
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    $\begingroup$ This seems like driving 1000 miles and then waiting for a friend to show up, rather than just driving 1000 miles with the plan to arrive when they do. If you're going to the moon, just go to the moon - I don't see the proposed benefit of going to where the moon will be and waiting. If you had just left later, you'd have a near-identical trip but would arrive at the moon with no wait. $\endgroup$ Aug 19, 2022 at 14:21

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Orbital mechanics works differently. You can't just "stop" somewhere (or you'd need to spend a huge amount of energy to do that.)

"Flying up there and letting the moon catch the spacecraft" is basically what is done already every time we send something to the moon. But keep in mind that an "trajectory" that comes from somewhere "outside" will also go "outside" again (hyperbolic trajectory). So if you want to be captured into an orbit around a body in space, you'll always need to get rid of some energy (that's how the "free return trajectory" of the Apollo missions worked).

If you want to get a feel for orbital mechanics there is a simple way. Play Kerbal Space Program...

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I want to emphasize this point: They always do that. Except that they don't "wait". They always figure out where the moon is going to be and fly directly to that point. They do one big push to get out of low earth orbit and change to a much skinnier orbit that reaches up to the distance of the moon. Basically they throw the spaceship up to the height of the moon, but they aim for the point where the moon will be when the spaceship gets there. Just as the spacecraft is about to turn around and fall back to the earth, the moon catches up to it. At that point, you need to use the rocket to match speeds with the moon or you will swing by it rather than going into orbit around it.

It is also true that you can't just "wait" at a point in space. With enough fuel, you could come to a stop (relative to the earth) at the distance of the moon's orbit and then use a little more fuel to hover there a while. But you are throwing away fuel the whole time you hover. It is much better to time it for when the moon is going to be there and use its gravity to help you change direction so you're orbiting the moon and not just the earth.

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One problem with "just waiting for the Moon" (or by flying away from Earth in a long elliptical orbit that will intersect the Moon's orbit as you can't actually just wait in space) is that Moon will arrive at 2,300 mph and if that wasn't bad enough will start pulling you towards it at a faster and faster rate the closer you get. So your fine up until a moment before impact.

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