Lunar orbit rendezvous

Lunar orbit rendezvous (LOR) is a way to land people on the Moon and bring them back to Earth. It was used during the Apollo program missions in the 1960s and 1970s.

In this method, a main spacecraft and a lunar lander both travel to lunar orbit. The lunar lander goes down to the Moon's surface by itself, while the main spacecraft stays in orbit. After the work on the Moon is done, the lander comes back up to meet, or rendezvous, with the main spacecraft and connects to it again. Only the main spacecraft then comes back to Earth.

The idea of lunar orbit rendezvous was first suggested in 1919 by a Ukrainian engineer named Yuri Kondratyuk. He thought it was the best way to send a person to the Moon and back without using too much fuel.

The most well-known example of this was in the Apollo missions, where the command and service module and the lunar module were both sent to the Moon on one big rocket. There are also ideas where the lander and the main spacecraft could travel separately, like some plans from the Shuttle-Derived Heavy Lift Launch Vehicle, Golden Spike, and China's plans for sending people to the Moon.

Advantages and disadvantages

The main advantage of lunar orbit rendezvous is that it saves weight. The spacecraft does not need to carry all the fuel to return from the Moon to Earth. This makes the spacecraft lighter and easier to handle.

Another advantage is that the lunar lander can be built just for landing on the Moon. The life support systems in the lunar lander can act as a backup for the main spacecraft. This helped the crew of Apollo 13 when their main systems stopped working.

Lunar-orbit rendezvous was thought to be risky in 1962 because space rendezvous had not yet been done. If the lunar lander could not meet up with the main spacecraft, astronauts could be stuck. But rendezvous was tested successfully in 1965 and 1966 during Project Gemini missions. It was also done in all eight Apollo missions where it was tried.

Apollo mission mode selection

When the Apollo Moon landing program began in 1961, people thought the three-person spacecraft would take off from the Moon and return to Earth using a very big rocket. This would need an extremely large spacecraft to land on the Moon.

There were two other ideas. One was to use one very large rocket to go straight to the Moon. The other was to launch many rockets from Earth and join them together in space before going to the Moon.

In 1958, some experts suggested another idea called lunar orbit rendezvous. This idea let one rocket launch both the main spacecraft and a smaller Moon lander. When they reached the Moon, one astronaut would stay in the main spacecraft while two went down to the Moon in the lander. After exploring, they would go back up and meet the main spacecraft, then return to Earth together. This way, the lander could be smaller and easier to build.

Dr. John Houbolt strongly believed this idea was the best way to reach the Moon quickly. He felt that other ideas were too hard and would take too long. In 1961, he wrote a letter to a top NASA leader explaining why this idea should be used. After reading his letter, NASA decided to pay more attention to this idea.

Soon after, NASA chose this method because it would save time and money. The smaller lander made it easier to land on the Moon. In July 1962, NASA officially chose this method to land on the Moon by 1969.

Other plans using LOR

The Soviet Union wanted to land people on the Moon using a similar method. They planned to use their N1 rocket, LK Lander, and Soyuz 7K-LOK. The Constellation program wanted to use two different ways for Moon landings. The Artemis program plans to meet in a special orbit near the Moon to land people in the lunar south pole area. The Chinese Lunar Exploration Program has talked about using this same method for their Moon landing mission.

In popular culture

In the 1998 television miniseries From the Earth to the Moon, an episode called "Spider" tells how John Houbolt worked hard to convince NASA to use the Lunar Orbit Rendezvous method for the Apollo Program in 1961. The episode also shows the development of the lunar lander up to its first test flight with people on board, Apollo 9, in 1969. The episode is named after the Apollo 9 Lunar Module.