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### How many times do you have to circle the Earth to break orbit?

My science teacher asked us this, and nobody in my class knew. We guessed it would be three, but with no evidence. (Edit: The asker has not returned to clarify if they meant leaving the Earth-Moon ...
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### Why would a mission to Sun-Earth L1 have an instantaneous launch window?

I was watching the webcast for Falcon 9 Flight 15 (launching DSCOVR) when they scrubbed their first launch attempt due to some issues during the terminal countdown. Before the scrub, the narrator ...
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### What is a near rectilinear halo orbit?

A proposed option for the lunar orbit of a Lunar Orbital Platform-Gateway (formerly known as Deep Space Gateway) is a near rectilinear halo orbit, or NRHO. This excellent answer discusses the ...
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### Low Energy Transfer within Earth-Moon system

Practical aspects of a total low energy transfer to the Moon have been seen in missions like GENESIS, which uses Weak stability Boundary legs of Earth and Sun to reach ESL-2. This four body model ...
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### Why is a near rectilinear halo orbit proposed for LOP-G (formerly known as Deep Space Gateway?)

Why is a near rectilinear halo orbit a good place for a Lunar Orbital Platform-Gateway (formerly known as Deep Space Gateway)? Are there specific logistical and orbital-mechanical advantages over ...
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### How would you identify when an object in a Lissajous orbit needs station keeping?

Obviously, with the international space station you need to do some station keeping when you're falling into the atmosphere. However, I saw the following image showing the Halo orbit that the Deep ...
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### How many SpaceX 2nd stages are in heliocentric orbits?

I can think of one particularly famous SpaceX 2nd stage in heliocentric orbit that even has its own website: https://www.whereisroadster.com/ and I know one was used to send DSCOVR towards Sun-Earth ...
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### How do spacecraft reach Lagrange points?

As I understand, to reach a Lagrange point the spacecraft would need to slow down. Also, can spacecraft passing nearby Lagrange points get captured within the point?
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### Rendezvouses in halo or lissajous orbits

If a spacecraft was in an EM-L2 halo/lissajous orbit, and another craft would was going to approach EM-L2 a few days later, could they rendezvous immediately or is there a limitation when the second ...
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### Do Lissajous orbits have stable/unstable manifolds?

The question Did DSCOVR travel “along the stable manifold of it's future SE L1 Halo orbit” to get there? is specific to DSCOVR's trajectory from Earth to its primarily heliocentric orbit near Sun-...