Direct ascent is a method of landing a spacecraft on the Moon or another planetary surface directly, without first assembling the vehicle in Earth orbit, or carrying a separate landing vehicle into orbit around the target body. It was the first method proposed 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
thumb|right|190px|Artist's conception of an early Apollo spacecraft that would have used direct ascent
The Apollo program was initially planned based on the assumption that direct ascent would be used. 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.