Direct ascent is a method of landing aspacecraft on theMoon or anotherplanetary surface directly, without first assembling the vehicle inEarth 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 StatesApollo program, but was rejected because it would have required developing a prohibitively largelaunch vehicle.

TheApollo program was initially planned based on the assumption that direct ascent would be used.^[1] This would have required developing an enormouslaunch vehicle, either theSaturn C-8 orNova rocket, to launch the three-manApollo 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 thatNASA considered required a somewhat smaller launch vehicle, either theSaturn C-4 orC-5. These wereEarth Orbit Rendezvous, which would have involved at least two launches to assemble the direct-landing and return vehicle in orbit; andLunar Orbit Rendezvous (LOR), which carried a smaller two-manlunar lander spacecraft for flight between lunar orbit and the surface. LOR was the strategy used successfully in Apollo.^[1]

TheSoviet Union also considered several direct ascent strategies, though in the end they settled on an approach similar to NASA's: two men in aSoyuz spacecraft with a one-manLK lander. The Soviets attempted to launch theN1 rocket on 21 February and 3 July 1969, both of which failed, before NASA'sApollo 11 lifted off and made the first crewedlunar landing on 20 July 1969. The Soviets would make two more attempts to launch the N1, in 1972 and 1974, but neither was successful. The Soviet engineering firmOKB-52 continued to develop theUR-700 modular booster for the direct ascentLK-700 ship.

Science fiction movies such asRocketship X-M andDestination Moon have frequently depicted direct ascent missions, although the first was a two-stage vehicle which accidentally, and successfully landed on Mars, but failed to successfully return to Earth (crashed in Nova Scotia), and the second was a single-stage vehicle which successfully landed on the Moon, and speculatively returned to Earth (return not shown).

• Lunex Project
• List of crewed lunar lander designs