View source for Astronomy:Lunar lander

{{short description|Spacecraft intended to land on the surface of the Moon}}

[[File:Apollo 11 Lunar Module Eagle in landing configuration in lunar orbit from the Command and Service Module Columbia.jpg|thumb|upright=1.3|Apollo Apollo Lunar Module-5 ''Eagle'' as seen from CSM-107 ''Columbia'']]
A '''lunar lander''' or '''Moon lander''' is a [[Engineering:Lander (spacecraft)|spacecraft]] designed to [[Astronomy:Moon landing|land on the surface of the Moon]]. As of 2023, the [[Engineering:Apollo Lunar Module|Apollo Lunar Module]] is the only lunar lander to have ever been used in human spaceflight, completing six lunar landings from 1969 to 1972 during the {{wipe|United States}} [[Astronomy:Apollo program|Apollo Program]]. Several robotic landers have reached the surface, and some have returned [[Astronomy:Moon rock|samples]] to Earth.

The design requirements for these landers depend on factors imposed by the [[Engineering:Payload|payload]], flight rate, propulsive requirements, and configuration constraints.<ref>[https://space.nss.org/media/Lunar-Bases-conference-2-113-Lander-Stage-Requirements.pdf Lunar Lander Stage Requirements Based on the Civil Needs Data Base] {{Webarchive|url=https://web.archive.org/web/20211001045958/https://space.nss.org/wp-content/uploads/Lunar-Bases-conference-2-113-Lander-Stage-Requirements.pdf |date=2021-10-01 }} (PDF). John A. Mulqueen. NASA Marshall Space Flight Center. 1993.</ref> Other important design factors include overall energy requirements, mission duration, the type of mission operations on the lunar surface, and [[Engineering:Life support system|life support system]] if crewed. The relatively high [[Physics:Gravity|gravity]] (higher than all known asteroids, but lower than all Solar System planets) and lack of [[Astronomy:Atmosphere of the Moon|lunar atmosphere]] negates the use of [[Astronomy:Aerobraking|aerobraking]], so a lander must use propulsion to decelerate and achieve a [[Engineering:Soft landing (rocketry)|soft landing]].

==History==
(In order to avoid unnecessarily lengthy citations in this section, please see the relevant hyperlinked Wikipedia pages for extensive sources for each historical item).

===1958-1976===
The [[Astronomy:Luna programme|Luna program]] was a series of robotic impactors, flybys, orbiters, and landers flown by the [[Place:Soviet Union|Soviet Union]] between 1958 and 1976. [[Astronomy:Luna 9|Luna 9]] was the first spacecraft to achieve a soft landing on the Moon on February 3, 1966, after 11 unsuccessful attempts. Three Luna Spacecraft returned lunar soil samples to Earth from 1972 to 1976. Two other Luna spacecraft soft-landed the Lunokhod robotic lunar rover in 1970 and 1973. Luna achieved a total of seven successful soft-landings out of 27 landing attempts.

The {{wipe|United States}} [[Astronomy:Surveyor program|Surveyor program]] first soft-landed [[Astronomy:Surveyor 1|Surveyor 1]] on June 2, 1966, this initial success was followed by four additional successful soft-landings, the last occurring on January 10, 1968. The Surveyor program achieved a total of five successful soft landings out of seven landing attempts through January 10, 1968.

The [[Engineering:Apollo Lunar Module|Apollo Lunar Module]] was the lunar lander for the United States' [[Astronomy:Apollo program|Apollo program]]. As of 2022, it is the only crewed lunar lander. The Apollo program completed six successful lunar soft-landings from 1969 until 1972; a seventh lunar landing attempt by the Apollo program was aborted when [[Engineering:Apollo 13|Apollo 13]]'s service module suffered explosive venting from its oxygen tanks.

The [[Engineering:LK (spacecraft)|LK]] lunar module was the lunar lander developed by the Soviet Union as a part of several [[Astronomy:Soviet crewed lunar programs|Soviet crewed lunar programs]]. Several LK lunar modules were flown without crew in [[Astronomy:Low Earth orbit|low Earth orbit]], but the LK lunar module never flew to the Moon, as the development of the [[Engineering:N1 (rocket)|N1 Rocket]] [[Engineering:Launch vehicle|Launch Vehicle]] required for the lunar flight suffered setbacks (including several launch failures), and after the first human [[Engineering:Apollo 11|Moon landings]] were achieved by the {{wipe|United States}}, the Soviet Union cancelled both the N1 Rocket and the LK Lunar Module programs without any further development.

===2013-2023===
The [[Astronomy:Chinese Lunar Exploration Program|Chinese Lunar Exploration Program]] (also known as the Chang'e project) includes robotic lander, rover, and sample-return components; the program realized an initial successful lunar soft-landing with the [[Astronomy:Chang'e 3|Chang'e 3]] spacecraft on 14 December 2013. As of 2023, the CLEP has achieved three successful soft-landings out of three landing attempts, namely [[Astronomy:Chang'e 3|Chang'e 3]], [[Astronomy:Chang'e 4|Chang'e 4]] and [[Astronomy:Chang'e 5|Chang'e 5]]. 
Chang'e 4 made history by making humanity's first ever soft-landing on the far side of the moon.

Israel's [[Engineering:SpaceIL|SpaceIL]] attempted a robotic lunar landing by its [[Astronomy:Beresheet|Beresheet]] lander on 4 April 2019; the attempt failed. As of 2023, SpaceIL has plans for another soft-landing attempt using a follow-up robotic lander named [[Astronomy:Beresheet 2|Beresheet 2]].

India's Chandrayaan Programme conducted an unsuccessful robotic lunar soft-landing attempt on 6 September 2019 as part of its [[Astronomy:Chandrayaan-2|Chandrayaan-2]] spacecraft with the lander crashing on  the Moon's surface.<ref>{{cite web |title=India Admits Its Moon Lander Crashed, Cites Problem with Braking Thrusters |url=https://www.space.com/india-admits-moon-lander-crash.html|date=26 November 2019 |access-date=10 January 2024}}</ref> On 23 August 2023, the program's follow-up [[Astronomy:Chandrayaan-3|Chandrayaan-3]] lander achieved India's first robotic soft-landing.

Japan's [[Company:Ispace (Japanese company)|ispace]] (not to be confused with China's i-Space) attempted a lunar soft-landing by its [[Astronomy:Hakuto-R Mission 1|Hakuto-R Mission 1]] robotic lander on 25 April 2023. The attempt was unsuccessful and the lander crashed into the lunar surface. The company currently has plans for another landing attempt in 2024.

Russia's [[Astronomy:Luna-Glob|Luna-Glob]] program, the successor program to the Soviet Union's [[Astronomy:Luna programme|Luna program]], launched the [[Astronomy:Luna 25|Luna 25]] lunar lander on 10 August 2023; the probe's intended destination was near the lunar south pole, but on 19 August 2023 the lander crashed on the Moon's surface.<ref>{{cite news |title=Luna-25 crashes into moon after orbit maneuver |last=Jones|first=Andrew |url=https://spacenews.com/luna-25-crashes-into-moon-after-orbit-maneuver/ |work=SpaceNews |date=20 August 2023 |access-date=20 August 2023}}</ref>

Japan's [[Astronomy:Smart Lander for Investigating Moon|Smart Lander for Investigating Moon]] launched on 6 September 2023. The probe made a successful lunar landing on 19 January 2024, near the Shioli crater on the lunar near side; the lander carries two small rovers on board.<ref>https://global.jaxa.jp/press/2023/12/20231205-1_e.html</ref> It landed on 19 January 2024 at 15:20 UTC, making Japan the 5th country to soft land on the moon.<ref>{{Cite web |last=Chang |first=Kenneth |date=2024-01-19 |title=Japan Becomes Fifth Country to Land on the Moon |url=https://www.nytimes.com/live/2024/01/12/science/japan-moon-landing-slim |work={{wipe|The New York Times}}}}</ref> Although it landed successfully, its in wrong attitude, because the solar panels are oriented westwards facing opposite the Sun at the start of [[Astronomy:Lunar day|lunar day]], thereby failing to generate enough power. The lander operated on internal battery power, which was fully drained that day.<ref>{{Cite web |title=According to the telemetry data, SLIM’s solar cells are facing west. So if sunlight begins to shine on the lunar surface from the west, there is a possibility of generating power, and we are preparing for recovery. #SLIM can operate with power only from the solar cells. #JAXA |url=https://x.com/SLIM_JAXA/status/1749320575103995954?s=20 |website=X (Formerly Twitter)}}</ref> The mission's operators hope that the lander will wake up after a few days when sunlight should hit the solar panels.<ref name=":8">{{Cite news |last=Sample |first=Ian |date=2024-01-19 |title=Japan’s Slim spacecraft lands on moon but struggles to generate power |url=https://www.theguardian.com/science/2024/jan/19/japan-slim-spacecraft-lands-on-moon-but-struggles-to-generate-power |access-date=2024-01-20 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref> 

Irrespective of this solar array issue on lander, the two LEV 1 and 2 rovers, deployed during hovering just before final landing are working as expected and LEV-1 communicating independently to the ground stations.<ref name=":8" /> LEV-1 conducted six hops on lunar surface. Images taken by LEV-2 show the wrong attitude landing with loss of an engine nozzle during descent and even possible sustained damage to lander's Earth bound antenna, that is not pointed towards Earth.<ref>{{Citation |title=小型月着陸実証機（SLIM）および小型プローブ（LEV）の月面着陸の結果・成果等 の記者会見 |url=https://www.youtube.com/watch?v=U61i0wN01Uk |access-date=2024-01-25 |language=en}}</ref>  Irrespective of wrong attitude and loss of communication with the lander, the mission is already successful after confirmation of its primary goal landing within {{cvt|100|m}} of its landing spot was already achieved.<ref>{{Cite web |last=Jones |first=Andrew |date=2024-01-22 |title=Japan’s moon lander forced to power down but may yet be revived |url=https://spacenews.com/japans-moon-lander-forced-to-power-down-but-may-yet-be-revived/ |access-date=2024-01-25 |website=SpaceNews |language=en-US}}</ref><ref>{{Cite web |title=SLIM Project Press Kit |url=https://global.jaxa.jp/countdown/slim/SLIM-mediakit-EN_2308.pdf |website=JAXA}}</ref><ref>{{Citation |title=小型月着陸実証機（SLIM）および小型プローブ（LEV）の月面着陸の結果・成果等 の記者会見 |url=https://www.youtube.com/watch?v=U61i0wN01Uk |access-date=2024-01-25 |language=en}}</ref>

===2024-Present===
On 8 January 2024, the first mission of the NASA-funded [[Astronomy:Commercial Lunar Payload Services|CLPS]] program, [[Astronomy:Peregrine Mission One|Peregrine Mission One]], was placed into an elliptical High Earth orbit; the mission's lunar lander was expected to execute a number of propulsive maneuvers to achieve a low lunar orbit prior to making a lunar landing attempt on 23 February 2024. However, a fuel leak was detected on the spacecraft several hours after launch with the result that it will lose its ability to maintain attitude control and to charge its battery, thereby rendering the acquisition of lunar orbit unlikely and precluding a landing attempt.<ref>{{cite news |title=Peregrine lander suffers anomaly after launch |last=Foust|first=Jeff |url=https://spacenews.com/peregrine-lander-suffers-anomaly-after-launch/ |work=SpaceNews |date=8 January 2024 |access-date=8 January 2024}}</ref>

==Landing outcomes==
The following table details the success rates of past and on-going lunar soft-landing attempts by robotic and crewed lunar-landing programs. Landing programs which have not launched any probes are not included in the table; they are added as their initial robotic and/or crewed landers are launched from Earth.

Due to prior usage in this article, the term "landing attempt" includes any mission that was launched with the intent to land on the moon, including all missions which failed to reach lunar orbit for any reason.
{| class="wikitable" style="max-width:1200px; text-align: left;"
! scope="col" | Program
! scope="col" | Country/Orgs.
! scope="col" | Time-span{{efn|"Time-span" in this case begins in the year that the relevant program launched its first lunar landing attempt.}}
! scope="col" | Type
! scope="col" | Landing attempts
! scope="col" | Soft-landed
! scope="col" | Outcome pending
! scope="col" style="width:40%;" | Notes
|-
! scope="row" style="text-align: left;" | [[Astronomy:Luna programme|Luna]]
| {{flagicon|USSR}} USSR
| 1963-1976
| robotic
! scope="row" | 27
! scope="row" | 7
! scope="row" | <small>not applicable</small>
| <small>Historical program; Russia's Luna 25 (2023) is part of successor program</small>
|-
! scope="row" style="text-align: left;" | [[Astronomy:Surveyor program|Surveyor]]
| {{flagicon|USA}} [[Organization:NASA|NASA]]
| 1966-1968
| robotic
! scope="row" | 7
! scope="row" | 5
! scope="row" | <small>not applicable</small>
| <small>Historical program</small>
|-
! scope="row" style="text-align: left;" | [[Astronomy:Apollo program|Apollo]]
| {{flagicon|USA}} [[Organization:NASA|NASA]]
| 1969-1972
| {{yes|{{hs|4}}crewed}}
! scope="row" | 7
! scope="row" | 6
! scope="row" | <small>not applicable</small>
| <small>Historical program</small>
|-
! scope="row" style="text-align: left;" | [[Astronomy:Soviet crewed lunar programs|Soviet crewed lunar programs]]
| {{flagicon|USSR}} USSR
| N/A
| {{yes|{{hs|4}}crewed}}
! scope="row" | 0
! scope="row" | 0
! scope="row" | <small>not applicable</small>
| <small>Historical programs; 3 uncrewed T2K variant of the [[Engineering:LK (spacecraft)#Testing|LK]] lunar lander were tested in Earth orbit between November 1970 and August 1971</small>
|-
! scope="row" style="text-align: left;" | [[Astronomy:Chinese Lunar Exploration Program|Chang'e]]
| {{flagicon|CHN}} CNSA
| 2013-present
| robotic
! scope="row" | 3
! scope="row" | 3
! scope="row" | 
| <small>landers/rovers, sample-returns, future ISRU missions</small>
|-
! scope="row" style="text-align: left;" | [[Astronomy:Beresheet|Beresheet]]
| {{flagicon|ISR}} [[Engineering:SpaceIL|spaceIL]]
| 2019-present
| robotic
! scope="row" | 1
! scope="row" | 0
! scope="row" | 
| 
|-
! scope="row" style="text-align: left;" | Chandrayaan
| {{flagicon|IND}} [[Astronomy:ISRO|ISRO]]
| 2019-present
| robotic
! scope="row" | 2
! scope="row" | 1
! scope="row" | 
| 
|-
! scope="row" style="text-align: left;" | [[Company:Ispace (Japanese company)#Hakuto-R program|Hakuto-R]]
| {{flagicon|JPN}} [[Company:Ispace (Japanese company)|ispace]]
| 2022-present
| robotic
! scope="row" | 1
! scope="row" | 0
! scope="row" | 
| 
|-
! scope="row" style="text-align: left;" | [[Astronomy:Luna-Glob|Luna-Glob]]
| {{flagicon|RUS}} [[Company:Roscosmos|Roscosmos]]
| 2023-present
| robotic
! scope="row" | 1
! scope="row" | 0
! scope="row" | 
| <small>Successor program to the Soviet [[Astronomy:Luna programme|Luna programme]].</small>
|-
! scope="row" style="text-align: left;" | [[Astronomy:Smart Lander for Investigating Moon|JAXA programs]]
| {{flagicon|JPN}} JAXA
| 2023-present
| robotic
! scope="row" | 1
! scope="row" | 1
! scope="row" | 
| <small>[[Astronomy:Smart Lander for Investigating Moon|SLIM]] (successful "pinpoint landing" within {{cvt|100|m}} of target with incorrect attitude; power problems post landing)<ref>{{Citation |title=小型月着陸実証機（SLIM）および小型プローブ（LEV）の月面着陸の結果・成果等 の記者会見 |url=https://www.youtube.com/watch?v=U61i0wN01Uk |access-date=2024-01-25 |language=en}}</ref></small>
|-
! scope="row" style="text-align: left;" | [[Astronomy:Commercial Lunar Payload Services|CLPS]]
| {{flagicon|USA}} [[Organization:NASA|NASA]]
| 2024-present
| robotic
! scope="row" | 1
! scope="row" | 0
! scope="row" | 
| <small>CLPS-1 [[Astronomy:Peregrine Mission One|Peregrine lander]] (spacecraft failure)</small>
|}

==Proposed landers and research craft==

===Uncrewed===
* ESA [[Engineering:Lunar Lander (spacecraft)|Lunar Lander]]
* Under the [[Astronomy:Luna-Glob|Luna-Glob]] program of lunar exploration undertaken by the Russian Federal Space Agency
** [[Astronomy:Luna 27|Luna 27]] "Luna-Resurs 1" - lunar south pole lander
** [[Astronomy:Luna 28|Luna 28]] "Luna-Resurs 2" - lunar south pole lander and sample return
* [[Engineering:Blue Moon (spacecraft)|Blue Moon Mark 1]], from [[Company:Blue Origin|Blue Origin]]
* Under NASA's [[Astronomy:Lunar CATALYST|Lunar CATALYST]] program and eligible to bid on [[Astronomy:Commercial Lunar Payload Services|Commercial Lunar Payload Services]] contracts to support NASA's crewed Artemis Program:
** XL-1 and XEUS from [[Engineering:Masten Space Systems|Masten Space Systems]] and [[Company:United Launch Alliance|United Launch Alliance]] (XEUS was dual use as crewed, but cancelled)
** Griffin Lander from [[Company:Astrobotic Technology|Astrobotic Technology]]
** MX-1 from [[Engineering:Moon Express|Moon Express]]

===Crewed===
{{main|Engineering:List of crewed lunar landers|Astronomy:Lunar module}}
* [[Engineering:Altair (spacecraft)|Altair]], a proposed spacecraft for the [[Astronomy:Constellation program|Constellation program]], previously known as the Lunar Surface Access Module
* Under [[Organization:NASA|NASA]]'s [[Astronomy:Artemis program|Artemis program]], multiple vendors were selected to supply spacecraft for the [[Astronomy:Human Landing System|Human Landing System]] role:
** [[Engineering:Starship HLS|Starship HLS]], lunar variant of [[Engineering:SpaceX Starship|SpaceX Starship]], chosen as the first HLS vendor<ref>{{Cite web|last=Brown|first=Katherine|date=2021-04-16|title=NASA Picks SpaceX to Land Next Americans on Moon|url=http://www.nasa.gov/press-release/as-artemis-moves-forward-nasa-picks-spacex-to-land-next-americans-on-moon|access-date=2021-06-23|website=NASA|archive-date=2021-04-22|archive-url=https://web.archive.org/web/20210422144134/https://www.nasa.gov/press-release/as-artemis-moves-forward-nasa-picks-spacex-to-land-next-americans-on-moon/|url-status=live}}</ref>
** [[Engineering:Integrated Lander Vehicle|Integrated Lander Vehicle]], chosen as the second HLS vendor ([[Company:Blue Origin|Blue Origin]], [[Company:Lockheed Martin|Lockheed Martin]], [[Company:Northrop Grumman|Northrop Grumman]] and [[Organization:Draper Laboratory|Draper Laboratory]])
** [[Engineering:Lockheed Martin Lunar Lander|Lockheed Martin Lunar Lander]] and Mars Precursor, based on [[Engineering:Orion (spacecraft)|Orion]] technology; partially incorporated into the Integrated Lander Vehicle
** [[Engineering:Blue Moon (spacecraft)|Blue Moon Mark 2]], from [[Company:Blue Origin|Blue Origin]]; not selected, but partially incorporated into the Integrated Lander Vehicle
** [[Engineering:Boeing Lunar Lander|Boeing Lunar Lander]], not selected
* As part of the [[Astronomy:Chinese Lunar Exploration Program#Crewed mission phase|crewed mission phase]] of its [[Astronomy:Chinese Lunar Exploration Program|Chinese Lunar Exploration Program]], China has introduced a staged-descent concept for a [[Engineering:Chinese crewed lunar lander|crewed lunar landing]] attempt by 2030. The staged-descent concept would use a propulsion stage to handle most of the deceleration, after which the lander segment would separate and complete the powered descent with a soft-landing on the moon; the lander would also serve as the ascent vehicle.<ref name=AJ27022023>{{cite news | author=Andrew Jones | title=China unveils lunar lander to put astronauts on the moon | url=https://spacenews.com/china-unveils-lunar-lander-to-put-astronauts-on-the-moon/ | work=spacenews.com | date=27 February 2023 | access-date=24 July 2023}}</ref>

===Research craft (earthbound)===
* Several were produced for the [[Engineering:Lunar Lander Challenge|Lunar Lander Challenge]], a competition to produce VTVL vehicles with sufficient delta-v to fly from the Moon to orbit
* [[Astronomy:Mighty Eagle|Mighty Eagle]] lander<ref>[http://www.nasa.gov/mission_pages/lunarquest/robotic/index.html Robotic Lunar Lander] {{Webarchive|url=https://web.archive.org/web/20111227065456/http://www.nasa.gov/mission_pages/lunarquest/robotic/index.html |date=2011-12-27 }}, [[Organization:NASA|NASA]], 2010, accessed 2011-01-10.</ref>
* Morpheus Lander, part of NASA's [[Astronomy:Project Morpheus|Project Morpheus]] (results used for [[Astronomy:Lunar CATALYST|Lunar CATALYST]])

==Challenges unique to lunar landing==
Landing on any Solar System body comes with challenges unique to that body. The [[Astronomy:Moon|Moon]] has relatively high gravity compared to that of asteroids or comets—and some other [[Astronomy:Natural satellite|planetary satellites]]—and no significant atmosphere. Practically, this means that the only method of descent and landing that can provide sufficient thrust with current technology is based on [[Engineering:Rocket engine|chemical rockets]].<ref name="smad">{{cite book |last1=Wertz |first1=James |last2=Larson |first2=Wiley |title=Space Mission Analysis and Design |date=2003 |publisher=Microcosm Press |location=California |isbn=1-881883-10-8 |edition=3rd}}</ref> In addition, the Moon has a long solar day. Landers will be in direct sunlight for more than two weeks at a time, and then in complete darkness for another two weeks. This causes significant problems for thermal control.<ref name=Okishio>{{cite journal |last1=Okishio |first1=Shogo |last2=Nagano |first2=Hosei |last3=Ogawa |first3=Hiroyuki |title=A proposal and verification of the lunar overnight method by promoting the heat exchange with regolith |journal=Applied Thermal Engineering |date=December 2015 |volume=91 |issue=5 |pages=1176–1186 |doi=10.1016/j.applthermaleng.2015.08.071 |hdl=2346/64545 |hdl-access=free }}</ref>

===Lack of atmosphere===
{{As of|2019|post=,}} space probes have landed on all three bodies other than Earth that have solid surfaces and atmospheres thick enough to make aerobraking possible: [[Astronomy:Mars|Mars]], [[Astronomy:Venus|Venus]], and [[Astronomy:Titan (moon)|Saturn's moon Titan]]. These probes were able to leverage the atmospheres of the bodies on which they landed to slow their descent using parachutes, reducing the amount of fuel they were required to carry. This in turn allowed larger payloads to be landed on these bodies for a given amount of fuel. For example, the 900-kg [[Engineering:Curiosity (rover)|''Curiosity'' rover]] was landed on Mars by [[Organization:Mars Science Laboratory|a craft]] having a mass (at the time of Mars atmospheric entry) of 2400&nbsp;kg,<ref>{{Cite web|url=https://spaceflight101.com/msl/msl-landing-special/|title=MSL Landing Special – MSL – Mars Science Laboratory|access-date=2021-10-01|archive-date=2021-02-26|archive-url=https://web.archive.org/web/20210226184539/https://spaceflight101.com/msl/msl-landing-special/|url-status=live}}</ref> of which only 390&nbsp;kg was fuel. In comparison, the much lighter (292&nbsp;kg) [[Astronomy:Surveyor 3|Surveyor 3]] landed on the Moon in 1967 using nearly 700&nbsp;kg of fuel.<ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1967-035A|title=NASA - NSSDCA - Spacecraft - Details|access-date=2019-03-09|archive-date=2019-09-04|archive-url=https://web.archive.org/web/20190904165614/https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1967-035A|url-status=live}}</ref> The lack of an atmosphere, however, removes the need for a Moon lander to have a heat shield and also allows [[Physics:Aerodynamics|aerodynamics]] to be disregarded when designing the craft.

===High gravity===
Although it has much less gravity than Earth, the Moon has sufficiently high gravity that descent must be slowed considerably. This is in contrast to a small asteroid, in which "landing" is more often called "docking" and is a matter of rendezvous and matching velocity more than slowing a rapid descent.

Since rocketry is used for descent and landing, the Moon's gravity necessitates the use of more fuel than is needed for asteroid landing. Indeed, one of the central design constraints for the Apollo program's Moon landing was mass (as more mass requires more fuel to land) required to land and take off from the Moon.<ref>{{cite journal |last1=Cole |first1=E.G. |title=Design and Development of the Apollo Three‐Man Spacecraft With Two‐Man Lunar Excursion Module (LEM) |journal=Annals of the New York Academy of Sciences |volume=134 |issue=1 |date=November 1965 |pages=39–57 |doi=10.1111/j.1749-6632.1965.tb56141.x |bibcode=1965NYASA.134...39C |s2cid=86244382 }}</ref>

===Thermal environment===
The lunar thermal environment is influenced by the length of the lunar day. Temperatures can swing between approximately {{convert|-250|to|120|C|F}} (lunar night to lunar day). These extremes occur for fourteen Earth days each, so thermal control systems must be designed to handle long periods of extreme cold or heat.<ref>{{cite journal |last1=Hager |first1=P |last2=Klaus |first2=D |last3=Walter |first3=U |title=Characterizing transient thermal interactions between lunar regolith and surface spacecraft |journal=Planetary and Space Science |date=March 2014 |volume=92 |pages=101–116 |doi=10.1016/j.pss.2014.01.011 |bibcode=2014P&SS...92..101H }}</ref> Most spacecraft instruments must be kept within a much stricter range of between {{convert|-40|and|50|C|F}},<ref>{{cite book |last1=Gilmore |first1=D. G. |title=Spacecraft Thermal Control Handbook |date=2003 |publisher=Aerospace Press |location=Segundo, California |isbn=1-884989-11-X |edition=2nd}}</ref> and human comfort requires a range of {{convert|20|to|24|C|F}}. This means that the lander must cool and heat its instruments or crew compartment.

The length of the lunar night makes it difficult to use solar electric power to heat the instruments, and nuclear heaters are often used.<ref name=Okishio/>

==Landing stages==
Achieving a soft landing is the overarching goal of any lunar lander, and distinguishes landers from impactors, which were the first type of spacecraft to reach the surface of the Moon.

All lunar landers require rocket engines for descent. Orbital speed around the Moon can, depending on altitude, exceed 1500&nbsp;m/s. Spacecraft on impact trajectories can have speeds well in excess of that.<ref name="nssdc.gsfc.nasa.gov">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-045A|title=NASA - NSSDCA - Spacecraft - Details|access-date=2019-03-08|archive-date=2019-09-27|archive-url=https://web.archive.org/web/20190927153246/https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-045A|url-status=live}}</ref> In the vacuum the only way to decelerate from that speed is to use a rocket engine.

The stages of landing can include:<ref>{{cite web|url=https://www.nasa.gov/mission_pages/apollo/missions/apollo11.html|title=Apollo 11 Mission Overview|date=2015-04-17|access-date=2019-03-09|archive-date=2018-02-09|archive-url=https://web.archive.org/web/20180209204039/https://www.nasa.gov/mission_pages/apollo/missions/apollo11.html|url-status=live}}</ref><ref>{{Cite web|url=https://spaceflight101.com/change/change-3/|title=Chang'e 3 – Change|access-date=2021-10-01|archive-date=2021-07-25|archive-url=https://web.archive.org/web/20210725024644/https://spaceflight101.com/change/change-3/|url-status=live}}</ref>

# Descent orbit insertion – the spacecraft enters an orbit favorable for final descent. This stage was not present in the early landing efforts, which did not begin with lunar orbit. Such missions began on a lunar impact trajectory instead.<ref name="nssdc.gsfc.nasa.gov"/>
# Descent and braking – the spacecraft fires its engines until it is no longer in orbit. If the engines were to stop firing entirely at this stage the spacecraft would eventually impact the surface. During this stage, the spacecraft uses its rocket engine to reduce overall speed
# Final approach – The spacecraft is nearly at the landing site, and final adjustments for the exact location of touchdown can be made
# Touchdown – the spacecraft achieves soft landing on the Moon

===Touchdown===
Lunar landings typically end with the engine shutting down when the lander is several feet above the lunar surface. The idea is that engine exhaust and lunar regolith can cause problems if they were to be kicked back from the surface to the spacecraft, and thus the engines cut off just before touchdown. Engineers must ensure that the vehicle is protected enough to ensure that the fall without thrust does not cause damage.

The first soft lunar landing, performed by the Soviet [[Astronomy:Luna 9|Luna 9]] probe, was achieved by first slowing the spacecraft to a suitable speed and altitude, then ejecting a payload containing the scientific experiments. The payload was stopped on the lunar surface using airbags, which provided cushioning as it fell.<ref>{{Cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-006A|title=NASA - NSSDCA - Spacecraft - Details|website=nssdc.gsfc.nasa.gov|access-date=2019-03-08|archive-date=2017-11-20|archive-url=https://web.archive.org/web/20171120175210/https://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1966-006A|url-status=live}}</ref> [[Engineering:Luna 13|Luna 13]] used a similar method.<ref>{{cite web|url=https://www.drewexmachina.com/2016/12/24/the-mission-of-luna-13-christmas-1966-on-the-moon/|title=The Mission of Luna 13: Christmas 1966 on the Moon|date=2016-12-24|access-date=2019-03-08|archive-date=2019-03-03|archive-url=https://web.archive.org/web/20190303213956/https://www.drewexmachina.com/2016/12/24/the-mission-of-luna-13-christmas-1966-on-the-moon/|url-status=live}}</ref>

Airbag methods are not typical. For example, NASA's [[Astronomy:Surveyor 1|Surveyor 1]] probe, launched around the same time as Luna 9, did not use an airbag for final touchdown. Instead, after it arrested its velocity at an altitude of 3.4m it simply fell to the lunar surface. To accommodate the fall the spacecraft was equipped with crushable components that would soften the blow and keep the payload safe.<ref name="nssdc.gsfc.nasa.gov"/> More recently, the Chinese [[Astronomy:Chang'e 3|Chang'e 3]] lander used a similar technique, falling 4m after its engine shut down.<ref>{{cite news|url=https://www.bbc.com/news/science-environment-25356603|title=China puts Jade Rabbit rover on Moon|work=BBC News|date=2013-12-14|last1=Rincon|first1=Paul|access-date=2019-03-08|archive-date=2019-03-27|archive-url=https://web.archive.org/web/20190327001052/https://www.bbc.com/news/science-environment-25356603|url-status=live}}</ref>

Perhaps the most famous lunar landers, those of the Apollo Program, were robust enough to handle the drop once their contact probes detected that landing was imminent. The landing gear was designed to withstand landings with engine cut-out at up to {{Convert|10|ft|m}} of height, though it was intended for descent engine shutdown to commence when one of the {{Convert|67|in|cm|adj=on}} probes touched the surface. During [[Engineering:Apollo 11|Apollo 11]] Neil Armstrong however touched down very gently by firing the engine until touchdown; some later crews shut down the engine before touchdown and felt noticeable bumps on landing, with greater compression of the landing struts.<ref name="ALSJ 1">{{cite web|date=1995|editor-last=Jones|editor-first=Eric M.|title=The First Lunar Landing|url=http://www.hq.nasa.gov/alsj/a11/a11.landing.html|access-date=June 13, 2013|work=Apollo 11 Lunar Surface Journal|publisher=NASA|archive-date=December 27, 2016|archive-url=https://web.archive.org/web/20161227230604/http://www.hq.nasa.gov/alsj/a11/a11.landing.html|url-status=live}}</ref><ref>{{Cite web|url=http://heroicrelics.org/info/lm/lunar-surface-probe.html|title=Lunar Surface Sensing Probes|website=heroicrelics.org|access-date=2019-03-08|archive-date=2019-03-16|archive-url=https://web.archive.org/web/20190316205213/http://heroicrelics.org/info/lm/lunar-surface-probe.html|url-status=live}}</ref>

==Notes==
{{notelist}}

==See also==
* [[Astronomy:List of artificial objects on the Moon|List of artificial objects on the Moon]], a list of objects that have been left, landed, or crashed on the Moon
* [[Engineering:List of crewed lunar lander designs|List of crewed lunar lander designs]]
* [[Astronomy:Lunar module|Lunar module]]

==References==
{{Reflist}}

[[Category:Exploration of the Moon]]
[[Category:Landers (spacecraft)|Moon]]

{{Sourceattribution|Lunar lander}}