Direct ascent

Direct ascent is a method of landing a spacecraft on the Moon or another planet directly, without first assembling the vehicle in Earth orbit, or carrying a separate landing vehicle into orbit around the target body. It was proposed as the first method to achieve a crewed lunar landing in the United States Apollo program, but was rejected because it would have required developing a prohibitively large launch vehicle.

Apollo program

The Apollo program was initially planned based on the assumption that direct ascent would be used.[1] This would have required developing an enormous launch vehicle, either the Saturn C-8 or Nova rocket, to launch the three-man Apollo spacecraft, with an attached landing module, directly to the Moon, where it would land tail-first and then launch off the Moon for the return to Earth. The other two options that NASA considered required a somewhat smaller launch vehicle, either the Saturn C-4 or C-5. These were Earth Orbit Rendezvous, which would have involved at least two launches to assemble the direct-landing and return vehicle in orbit; and Lunar Orbit Rendezvous (LOR), which carried a smaller two-man lunar lander spacecraft for flight between lunar orbit and the surface. LOR was the strategy used successfully in Apollo.[1]

The Soviet Union also considered several direct ascent strategies, though in the end they settled on an approach similar to NASA's: two men in a Soyuz spacecraft with a one-man LK lander. The failure of the Soviets' N1 rocket delayed their lunar program substantially, however, and they were nowhere close to a successful N1 launch when Apollo 11 lifted off and made the first crewed lunar landing. The Soviets had planned to use an LK, which looked much like a smaller version of the spider-like Lunar Module, although OKB-52 continued to develop the UR-700 modular booster for the direct ascent LK-700 ship.

Science fiction movies such as Destination Moon had frequently depicted direct ascent missions.

See also


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