# Flight Architectures

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There are many ways to get to the moon. Some are:

A) Direct : Take-off from earth, land on the moon, come home again. -This was the original Apollo program.

B) Earth Orbit Rendezvous: Ship up pieces of out vehicle to low earth orbit, put it together, go to the moon and return. -This was the revised Apollo program when they realized just how bit the Launch vehicle would have to be.

C) Lunar Orbit (Return) Rendezvous: Launch from the earth, fly to Lunar Orbit, land in a seperate vehicle, meet back up on the way home, and land on the earth. -This is what the Apollo program finally did with the launch vehicle they had.

There are all sorts of mixing and matching, There can be multiple rendezvous, multiple parallel flights, Rendezvous around earth on the way home, etc. But they all need to do the same things.

1) Leave Earth surface (generally to orbit)................Launch

2) Leave earth for the moon (orbit or otherwise)......Trans Lunar Injection (TLI)

3) Slow down at the moon (into orbit?).....................Lunar Orbit Injection (LOI)

4) Descend to the lunar surface................................Lunar Descent

5) Ascend from the surface (maybe to orbit)............Lunar Ascent

6) Leave the Moon (orbit or otherwise) for earth.......Trans Earth Injection (TEI)

7) Land on the earth (or slow into Low Earth Orbit)...Re-entry

Generally there is some coasting time between these actions (rocket burns), but some can be combined.(1&2, 3&4, and 5&6). There are reasons both for and against these combinations, but it's easier to do the math in separate steps.