Direct ascent is a method of landing a

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...

on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

or another

planetary surface A planetary surface is where the solid or liquid material of certain types of astronomical objects contacts the atmosphere or outer space. Planetary surfaces are found on solid objects of planetary mass, including terrestrial planets (includi ...

directly, without first assembling the vehicle in

Earth orbit Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes days (1 sidereal year), during which time E ...

, 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 A launch vehicle or carrier rocket is a rocket designed to carry a payload ( spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and sys ...

Apollo program

The Apollo program was initially planned based on the assumption that direct ascent would be used. This would have required developing an enormous

, either the

Saturn C-8 The Saturn C-8 was the largest member of the Saturn series of rockets to be designed. It was a potential alternative to the Nova rocket, should NASA have chosen a direct ascent method of lunar exploration for the Apollo program. The first st ...

or Nova rocket, to launch the three-man

Apollo spacecraft The Apollo spacecraft was composed of three parts designed to accomplish the American Apollo program's goal of landing astronauts on the Moon by the end of the 1960s and returning them safely to Earth. The expendable (single-use) 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 The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

considered required a somewhat smaller launch vehicle, either the

Saturn C-4 The Saturn C-4 was the fourth rocket in the Saturn C series studied from 1959 to 1962. The C-4 design was proposed in 1960 for a three-stage launch vehicle that could launch to low Earth orbit and send to the Moon via trans-lunar injection. It ...

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 A lunar lander or Moon lander is a spacecraft designed to land on the surface of the Moon. As of 2021, the Apollo Lunar Module is the only lunar lander to have ever been used in human spaceflight, completing six lunar landings from 1969 to 19 ...

spacecraft for flight between lunar orbit and the surface. LOR was the strategy used successfully in Apollo. The

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...

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 Soyuz () is a series of spacecraft which has been in service since the 1960s, having made more than 140 flights. It was designed for the Soviet space program by the Korolev Design Bureau (now Energia). The Soyuz succeeded the Voskhod spacecr ...

with a one-man LK lander. The Soviets attempted to launch the N1 rocket on 21 February and 3 July 1969, both of which failed, before NASA's

Apollo 11 Apollo 11 (July 16–24, 1969) was the American spaceflight that first landed humans on the Moon. Commander Neil Armstrong and lunar module pilot Buzz Aldrin landed the Apollo Lunar Module ''Eagle'' on July 20, 1969, at 20:17 UTC, ...

lifted off and made the first crewed lunar 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 firm OKB-52 continued to develop the UR-700 modular booster for the direct ascent LK-700 ship.

Science fiction Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel uni ...

movies such as '' Rocketship X-M'' and '' Destination 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).

References

Spaceflight concepts Apollo program {{Spacecraft-stub

Apollo program

See also

References