Earth orbit rendezvous

Earth orbit rendezvous (EOR) is a method that has been proposed for space missions to the Moon. NASA considered an EOR mission profile for the Apollo program, but chose instead to use lunar orbit rendezvous (LOR). NASA currently plans to use both EOR and LOR for Project Constellation, which is intended to include human spaceflight missions to the Moon beginning around 2020.

Apollo

The EOR proposal for Apollo consisted of using a series of small rockets half the size of a Saturn V to put different components of a spacecraft to go to the Moon in orbit around the Earth, then assemble them in orbit. Experiments of Project Gemini involving docking with the Agena target vehicle were designed partly to test the feasibility of this program. In the end, NASA employed the Lunar Orbit Rendezvous for the Apollo Program, using the Saturn V to boost both the Apollo Command and Lunar Modules into low Earth orbit, and then firing again to send both spacecraft out to the Moon.

Constellation

This mode has been revived for Project Constellation as the Earth Departure Stage (EDS) and Altair (LSAM), which would be launched into low Earth orbit on the Ares V rocket. The EDS and Altair would be met by the separately launched Orion (CEV). Once joined in low Earth orbit, the three would then travel out to the Moon and the Orion/Altair combination would fly a lunar orbit rendezvous flight pattern.

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