Editing Lunar orbit rendezvous (section)

==Advantages and disadvantages==
===Advantages===
[[File:LOR Gravity Well.png|thumb|Representation of the lunar [[gravity well]], illustrating how resources needed only for the trip home don't have to be carried down and back up the "well"]]
The main advantage of LOR is the spacecraft payload saving, due to the fact that the propellant necessary to return from lunar orbit back to Earth need not be carried as dead weight down to the Moon and back into lunar orbit. This has a multiplicative effect, because each pound of "dead weight" propellant used later has to be propelled by more propellant sooner, and also because increased propellant requires increased tankage weight. The resultant weight increase would also require more thrust for lunar landing, which means larger and heavier engines.{{sfnp|Reeves|2005}}

Another advantage is that the lunar lander can be designed for just that purpose, rather than requiring the main spacecraft to also be made suitable for a lunar landing. Finally, the second set of life support systems that the lunar lander requires can serve as a backup for the systems in the main spacecraft; this redundancy saved the crew of [[Apollo 13]] when their command module's systems failed.

===Disadvantage===
Lunar-orbit rendezvous was considered risky in 1962, because [[space rendezvous]] had not been achieved, even in Earth orbit. If the LM could not reach the CSM, two astronauts would be stranded with no way to get back to Earth or survive [[atmospheric entry|re-entry into the atmosphere]]. Rendezvous was successfully demonstrated in 1965 and 1966 on six [[Project Gemini]] missions{{refn|group=Note|[[Gemini 6A]], [[Gemini 8]], [[Gemini 9A]], [[Gemini 10]], [[Gemini 11]], and [[Gemini 12]]}} with the aid of radar and on-board computers. It was also successfully done each of the eight times it was tried on Apollo missions.{{refn|group=Note|[[Apollo 9]] in Earth orbit; in lunar orbit on [[Apollo 10]], [[Apollo 11]], [[Apollo 12]], [[Apollo 14]], [[Apollo 15]], [[Apollo 16]], and [[Apollo 17]].}}