Lunar-orbit rendezvous required docking the lunar module withthe command module in lunar orbit. Arguably, the most demanding and sophisticated maneuvering during an Apollo mission was the rendezvous and docking of the LM ascent stage and the CSM. The lunar module (originally designated the lunar excursion module, known by the acronym LEM) was designed after NASA chose to reach the Moon via Lunar Orbit Rendezvous (LOR) instead of the direct ascent or Earth Orbit Rendezvous (EOR) methods. Since 2012, docking of 28 Russian vehicles (18 of them were Soyuz crew vehicles) has been accomplished using the 6-h and 4-orbit rendezvous profile. Both direct ascent and EOR would have involved landing a much heavier, complete Apollo spacecraft on the Moon.
Recently, the fast rendezvous profile trend is observed in the manned spaceflight domain. In his thesis on “Manned Orbital Rendezvous” he developed the technique for piloted rendezvous of two spacecraft in orbit.
Its dedication reads: In the hopes that this work may in some way contribute to their exploration of space, this is dedicated to the crew members of this country’s present and future manned space programs.

Earth orbit rendezvous (EOR) is a potential methodology for conducting round trip human flights to the Moon, involving the use of space rendezvous to assemble, and possibly fuel, components of a translunar vehicle in low Earth orbit. You can see this effect by the fact a spacecraft orbiting the earth at a 200 miles altitude takes roughly 90 minutes to orbit the earth and a spacecraft at 26,200 miles takes roughly 24 hours to orbit the earth (otherwise known as geosynchronous orbit). Often described as an orbital ballet, and invariably accompanied with the adjectives "dangerous" and "critical", the actual sequence of events is rarely explained in detail. Astronauts practiced the complextask of separating and uniting spacecraft to master dockingtechniques with Langley's Rendezvous and Docking Simulator, today aNational Historic Landmark, pictured.