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The Earth-Moon Lagrange points

A distant retrograde orbit (DRO), as most commonly conceived, is a spacecraft orbit around a moon that is highly stable because of its interactions with two Lagrange points (L₁ and L₂) of the planet–moon system.

In more general terms, an object of negligible mass can be in a DRO around the smaller body of any two-body system, such as planet–Sun or exoplanet–star.

Using the example of a spacecraft in a DRO around a moon, the craft would orbit in the direction opposite to the direction in which the moon orbits the planet. The orbit is "distant" in the sense that it passes above the Lagrange points, rather than being near the moon. Considering more and more distant orbits, the synodic period (the period between two moments when the craft passes between the planet and the moon) gets longer and approaches that of the moon going around the planet. The sidereal period (the time it takes for the craft to come back to a given constellation as viewed from the moon) can then become much longer than the orbital period of the moon. A hypothetical example with Europa has a sidereal period about eight times the orbital period of Europa.^[1]

DROs have been researched for several decades. In April 2022, CNSA's Chang'e 5 orbiter^[2] became the first to enter the orbit, followed by NASA's Orion Spacecraft during the Artemis 1 mission which entered in November 2022.^[3] Two more CNSA spacecraft, DRO A and B, attempted in 2024, but were left in lower orbits due to a failure of the YZ-1S upper stage.^[4]

Description

The stability of a DRO is defined in mathematical terms as having very high Lyapunov stability, where an equilibrium orbit is "locally stable if all solutions which start near the point remain near that point for all time".^[1]

List of objects in distant retrograde orbit

Chang'e 5 orbiter

Chang'e 5 spacecraft with orbiter at bottom

After dropping off return samples for Earth, China's Chang'e 5 (CE-5) orbiter first moved to Sun-Earth Lagrange point 1 (L1) in March 2021 for solar observations.^[5] In January 2022, CE-5 left L1 point for the lunar distant retrograde orbit (DRO) to conduct very-long-baseline interferometry tests in preparation for the next stage of China's lunar exploration program.^[5]^[6] According to The Space Review (TSR), this maneuver was depicted in Chinese government and academic documents.^[2] In February 2022, multiple amateur satellite trackers observed CE-5 had entered DRO, making it the first spacecraft in history to utilize the orbit.^[5]

Orion spacecraft

On 16 November 2022, the Space Launch System was launched from Complex 39B as part of the Artemis 1 mission carrying Orion to the Moon.^[7]^[8] On 25 November it entered DRO and orbited the Moon in that orbit.^[9]^[10]

DRO A/B

Yuanzheng 1S upper stage failed to deliver these two CAS spacecrafts (not under CLEP) into correct orbit. The satellites were intended to test Distant retrograde orbit.^[11] Tracking data appears to show China is attempting to salvage spacecraft and they appear to have succeeded in reaching their desired orbit.^[12]^[13]

Space concepts proposed to use a DRO

Jupiter Icy Moons Orbiter

A distant retrograde orbit was one of the proposed orbits around Europa for the Jupiter Icy Moons Orbiter—principally for its projected stability and low-energy transfer characteristics—but that mission concept was cancelled in 2005.^[1]

Asteroid Redirect Mission (ARM)

A distant retrograde orbit was considered to be used for the proposed Asteroid Redirect Mission. Although the mission would end up getting cancelled, the research done with DRO in-mind, lead to the orbit being used for Artemis 1.^[14]

NASA Lunar Gateway

Two system requirements for the NASA Lunar Gateway, as published in the Baseline DSG-RQMT-001^[15] published in June 2019, mention the use of lunar DROs. Requirement L2-GW-0029, Single Orbit Transfer, states "the Gateway shall be capable of performing a single round trip transfer to Distant Retrograde Orbit (DRO) and back within 11 months". Requirement L2-GW-0026, Propulsion System Capability, states "the Gateway shall provide a fuel capacity that would support performing a minimum of two round-trip uncrewed low-energy cislunar orbit transfers between a near-rectilinear halo orbit (NRHO) and a distant retrograde orbit (DRO) and orbit maintenance for a period of 15 years between refueling". Although the selected orbit for the Gateway has been confirmed to be NRHO^[16] instead of DRO.

DRO orbits in fiction

In the 2019 Daniel Suarez novel Delta-v, a 560-tonne crewed asteroid-mining ship Konstantin is constructed in a lunar DRO approximately 40,000 km (25,000 mi) above the Moon.^[17]

References

^ ^a ^b ^c Johnson, Kirstyn (18 December 2014). "Understanding NASA's Asteroid Redirect Mission: Distant Retrograde Orbits". Archived from the original on 11 January 2015. Retrieved 3 May 2015.
^ ^a ^b Burke, Kristin (11 April 2022). "The Space Review: What is China doing at the lunar distant retrograde orbit?". The Space Review. Archived from the original on 2022-04-12. Retrieved 2022-04-12.
^ Foust, Jeff (25 November 2022). "Orion enters lunar distant retrograde orbit". SpaceNews.
^ Jones, Andrew (28 March 2024). "China appears to be trying to save stricken spacecraft from lunar limbo". SpaceNews. Retrieved 2 July 2024.
^ ^a ^b ^c Jones, Andrew (15 February 2022). "A Chinese spacecraft is testing out a new orbit around the moon". Space News.
^ "Chang'e-5: China's Moon sample return mission". Planetary.
^ Artemis I Launch to the Moon (Official NASA Broadcast) - Nov. 16, 2022. NASA. 16 November 2022. Archived from the original on 29 November 2022. Retrieved 2 December 2022 – via YouTube.
^ NASA (8 November 2022). "NASA Prepares Rocket, Spacecraft Ahead of Tropical Storm Nicole, Re-targets Launch". Retrieved 8 November 2022.
^ NASA (27 November 2015). "The Ins and Outs of NASA's First Launch of SLS and Orion". Archived from the original on 22 February 2020. Retrieved 3 May 2016. This article incorporates text from this source, which is in the public domain.
^ Foust, Jeff (2022-11-25). "Orion enters lunar distant retrograde orbit". SpaceNews. Retrieved 2022-11-29.
^ Jones, Andrew (2024-03-14). "Surprise Chinese lunar mission hit by launch anomaly". SpaceNews. Retrieved 2024-03-14.
^ Jones, Andrew (2024-08-20). "Chinese spacecraft appear to reach lunar orbit despite launch setback". SpaceNews. Retrieved 2024-08-20.
^ Jones, Andrew (2024-03-28). "China appears to be trying to save stricken spacecraft from lunar limbo". SpaceNews. Retrieved 2024-03-29.
^ NASA [@NASA] (19 November 2022). "@JVendl @NASA_Orion We first studied the DRO to support the proposed Asteroid Redirect Mission (ARM) which paralleled early SLS and Orion development. The plan for ARM was to capture a near Earth asteroid and redirect it to a lunar DRO. (1/4)" (Tweet). Retrieved 2 December 2022 – via Twitter.
^ NASA (2019). "DSG-RQMT-001 – Gateway Program System Requirements Document (SRD)" (PDF). NASA Technical Reports Server. p. 25. Archived (PDF) from the original on 11 April 2020. Retrieved 11 April 2020.
^ Zaid, Christina (2022-05-16). "A unique halo orbit is the road less traveled around the Moon". NASA. Retrieved 2022-11-29.
^ Suarez, Daniel (2019). Delta-v. New York: Penguin Random House. pp. 189–198. ISBN 978-1524742416.

[johnson2014-1] Johnson, Kirstyn (18 December 2014). "Understanding NASA's Asteroid Redirect Mission: Distant Retrograde Orbits". Archived from the original on 11 January 2015. Retrieved 3 May 2015.

[tsr20220411-2] Burke, Kristin (11 April 2022). "The Space Review: What is China doing at the lunar distant retrograde orbit?". The Space Review. Archived from the original on 2022-04-12. Retrieved 2022-04-12.

[3] Foust, Jeff (25 November 2022). "Orion enters lunar distant retrograde orbit". SpaceNews.

[4] Jones, Andrew (28 March 2024). "China appears to be trying to save stricken spacecraft from lunar limbo". SpaceNews. Retrieved 2 July 2024.

[ce5_extend-5] Jones, Andrew (15 February 2022). "A Chinese spacecraft is testing out a new orbit around the moon". Space News.

[ce5_ov-6] "Chang'e-5: China's Moon sample return mission". Planetary.

[7] Artemis I Launch to the Moon (Official NASA Broadcast) - Nov. 16, 2022. NASA. 16 November 2022. Archived from the original on 29 November 2022. Retrieved 2 December 2022 – via YouTube.

[nasa-20221108-8] NASA (8 November 2022). "NASA Prepares Rocket, Spacecraft Ahead of Tropical Storm Nicole, Re-targets Launch". Retrieved 8 November 2022.

[Nov15-9] NASA (27 November 2015). "The Ins and Outs of NASA's First Launch of SLS and Orion". Archived from the original on 22 February 2020. Retrieved 3 May 2016. This article incorporates text from this source, which is in the public domain.

[10] Foust, Jeff (2022-11-25). "Orion enters lunar distant retrograde orbit". SpaceNews. Retrieved 2022-11-29.

[11] Jones, Andrew (2024-03-14). "Surprise Chinese lunar mission hit by launch anomaly". SpaceNews. Retrieved 2024-03-14.

[12] Jones, Andrew (2024-08-20). "Chinese spacecraft appear to reach lunar orbit despite launch setback". SpaceNews. Retrieved 2024-08-20.

[13] Jones, Andrew (2024-03-28). "China appears to be trying to save stricken spacecraft from lunar limbo". SpaceNews. Retrieved 2024-03-29.

[14] NASA [@NASA] (19 November 2022). "@JVendl @NASA_Orion We first studied the DRO to support the proposed Asteroid Redirect Mission (ARM) which paralleled early SLS and Orion development. The plan for ARM was to capture a near Earth asteroid and redirect it to a lunar DRO. (1/4)" (Tweet). Retrieved 2 December 2022 – via Twitter.

[15] NASA (2019). "DSG-RQMT-001 – Gateway Program System Requirements Document (SRD)" (PDF). NASA Technical Reports Server. p. 25. Archived (PDF) from the original on 11 April 2020. Retrieved 11 April 2020.

[16] Zaid, Christina (2022-05-16). "A unique halo orbit is the road less traveled around the Moon". NASA. Retrieved 2022-11-29.

[17] Suarez, Daniel (2019). Delta-v. New York: Penguin Random House. pp. 189–198. ISBN 978-1524742416.

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@@ Line 1: / Line 1: @@
-{{Short description|Elliptical path around a celestial object encircling the first two Lagrange points}}
+{{Short description|Type of spacecraft orbit}}
+{{CSS image crop
-[[File:Lagrange points simple.svg|thumb|upright=1.35|Lagrange points L1 and L2 in the Sun–Earth system (not to scale).]]
+|Image = Lagrange Earth Moon Sun.svg
-A '''distant retrograde orbit''' (DRO), as most commonly conceived, is a spacecraft [[orbit]] around a moon<!-- it would be overly narrow to say "... is an orbit around a moon..." Why? While a moon/planet/spacecraft can work for a DRO orbit in our Solar System and the orbit will be "around" a moon; technically, the orbit of the "smallest body" (M3) is "around" the middle-sized body (M2) in a three-body problem where, for the three masses, M1>>M2>>M3. So DRO is a general three-body problem solution.  It's just that most practical near-term uses for the concept at three-body problems in our Solar System where M1 = a planet, and M2 = a moon of that planet, and M3 = a human-made spacecraft. --> that is highly stable because of its interactions with two [[Lagrange point]]s ({{L1}} and {{L2}}) of the planet-moon system.
+|bSize = 1024
+|cWidth = 282
+|cHeight = 273
+|oTop = 0
+|oLeft = 388
+|Location=right
+|Description=The Earth-Moon Lagrange points
+}}
+A '''distant retrograde orbit''' (DRO), as most commonly conceived, is a spacecraft [[orbit]] around a moon<!-- it would be overly narrow to say "... is an orbit around a moon..." Why? While a moon/planet/spacecraft can work for a DRO orbit in our Solar System and the orbit will be "around" a moon; technically, the orbit of the "smallest body" (M3) is "around" the middle-sized body (M2) in a three-body problem where, for the three masses, M1>>M2>>M3. So DRO is a general three-body problem solution.  It's just that most practical near-term uses for the concept at three-body problems in our Solar System where M1 = a planet, and M2 = a moon of that planet, and M3 = a human-made spacecraft. --> that is highly stable because of its interactions with two [[Lagrange point]]s ({{L1}} and {{L2}}) of the planet–moon system.
 In more general terms, an object of negligible mass can be in a DRO around the smaller body of any two-body system, such as planet–Sun or exoplanet–star.
-Using the example of a spacecraft in a DRO around a moon, the craft would orbit in the direction opposite to the direction in which the moon orbits the planet. The orbit is "distant" in the sense that it passes above the Lagrange points, rather than being near the moon. If we consider more and more distant orbits, the [[synodic period]] (the period between two moments when the craft passes between the planet and the moon) gets longer and approaches that of the moon going around the planet, so that the [[sidereal period]] (the time it takes for the craft to come back to a given constellation as viewed from the moon) can become much longer than the orbital period of the moon. A hypothetical example with [[Europa (moon)|Europa]] has a sidereal period about eight times the orbital period of Europa.<ref name=johnson2014/>
+Using the example of a spacecraft in a DRO around a moon, the craft would orbit in the direction opposite to the direction in which the moon orbits the planet. The orbit is "distant" in the sense that it passes above the Lagrange points, rather than being near the moon. Considering more and more distant orbits, the [[synodic period]] (the period between two moments when the craft passes between the planet and the moon) gets longer and approaches that of the moon going around the planet. The [[sidereal period]] (the time it takes for the craft to come back to a given constellation as viewed from the moon) can then become much longer than the orbital period of the moon. A hypothetical example with [[Europa (moon)|Europa]] has a sidereal period about eight times the orbital period of Europa.<ref name=johnson2014/>
+DROs have been researched for several decades. In April 2022, CNSA's [[Chang'e 5]] orbiter<ref name=tsr20220411/> became the first to enter the orbit, followed by NASA's [[Orion (spacecraft)|Orion Spacecraft]] during the [[Artemis 1]] mission which entered in November 2022.<ref>{{cite web|url=https://spacenews.com/orion-enters-lunar-distant-retrograde-orbit/ |title=Orion enters lunar distant retrograde orbit |website=SpaceNews |date=25 November 2022 |first=Jeff |last=Foust }}</ref> Two more CNSA spacecraft, [[DRO (spacecraft)|DRO A]] and B, attempted in 2024, but were left in lower orbits due to a failure of the [[Yuanzheng|YZ-1S]] upper stage.<ref>{{Cite news |last=Jones |first=Andrew |date=28 March 2024 |title=China appears to be trying to save stricken spacecraft from lunar limbo |url=https://spacenews.com/china-appears-to-be-trying-to-save-stricken-spacecraft-from-lunar-limbo/ |access-date=2 July 2024 |work=SpaceNews}}</ref>
-DROs have been researched for several decades, but as of 2021, no spacecraft had used such an orbit for an actual flight. In early 2022, it was speculated that the [[Chang'e 5]] orbiter may have now done so.<ref name=tsr20220411/>
 == Description ==
-The stability of a DRO is defined in mathematical terms as having very high [[Lyapunov stability]], where an equilibrium orbit is "[[Local maxima|locally stable]] if all solutions which start near the point remain near that point for all time."<ref name=johnson2014/>
+The stability of a DRO is defined in mathematical terms as having very high [[Lyapunov stability]], where an equilibrium orbit is "[[Local maxima|locally stable]] if all solutions which start near the point remain near that point for all time".<ref name=johnson2014/>
-==List of Objects in Distant retrograde orbit==
+==List of objects in distant retrograde orbit==
 ===Chang'e 5 orbiter===
+[[File:Chang-e-5-zh-2.png|thumb|Chang'e 5 spacecraft with orbiter at bottom]]
-China's [[Chang'e 5]] (CE-5) orbiter, which according to [[The Space Review]] (TSR) may have moved to a lunar distant retrograde orbit by January 2022, could be conducting [[very-long-baseline interferometry]] (VLBI) tests to support Chinese preparations for the next stage of China's Lunar Exploration Program (CLEP). The analysis by TSR was based on statements made by Chinese government information and Chinese academics.<ref name=tsr20220411>{{cite news |title=The Space Review: What is China doing at the lunar distant retrograde orbit? |url=https://www.thespacereview.com/article/4365/1 |last=Burke |first=Kristin |date=11 April 2022 |access-date=2022-04-12 |work=[[The Space Review]] |archive-date=2022-04-12 |archive-url=https://web.archive.org/web/20220412050808/https://www.thespacereview.com/article/4365/1 |url-status=live }}</ref>{{update after|2022|8|29}}<!-- any source to say this was actually done? rather than it might be done? --> If the move to DRO was actually made, then Chang'e 5 would be the first spacecraft to actually enter a distant retrograde orbit to test the DRO theoretical result.
+After dropping off return samples for Earth, China's [[Chang'e 5]] (CE-5) orbiter first moved to Sun-Earth Lagrange point 1 (L1) in March 2021 for solar observations.<ref name="ce5_extend" /> In January 2022, CE-5 left L1 point for the lunar distant retrograde orbit (DRO) to conduct [[very-long-baseline interferometry]] tests in preparation for the next stage of China's [[Chinese Lunar Exploration Program|lunar exploration program]].<ref name="ce5_extend">{{cite web|url=https://spacenews.com/a-chinese-spacecraft-is-testing-out-a-new-orbit-around-the-moon/ |title=A Chinese spacecraft is testing out a new orbit around the moon |website=Space News |date=15 February 2022 |first=Andrew |last=Jones }}</ref><ref name="ce5_ov">{{cite web|url=https://www.planetary.org/space-missions/change-5 |title=Chang'e-5: China's Moon sample return mission |website=Planetary }}</ref> According to [[The Space Review]] (TSR), this maneuver was depicted in Chinese government and academic documents.<ref name=tsr20220411>{{cite news |title=The Space Review: What is China doing at the lunar distant retrograde orbit? |url=https://www.thespacereview.com/article/4365/1 |last=Burke |first=Kristin |date=11 April 2022 |access-date=2022-04-12 |work=[[The Space Review]] |archive-date=2022-04-12 |archive-url=https://web.archive.org/web/20220412050808/https://www.thespacereview.com/article/4365/1 |url-status=live }}</ref> In February 2022, multiple amateur satellite trackers observed CE-5 had entered DRO, making it the first spacecraft in history to utilize the orbit.<ref name="ce5_extend" />
+=== Orion spacecraft ===
-== Space concepts proposed to use a DRO ==
+{{main|Orion (spacecraft)}}
-=== NASA Asteroid Redirect Mission (ARM) ===
+[[File:Orion Artemis I Selfie 1.jpg|thumb|Orion spacecraft prior to arriving at the Moon, where it would later get into DRO]]
-By 2014, a lunar DRO was the preferred alternative under consideration for the NASA-proposed [[Asteroid Redirect Mission]] (ARM).  This orbit would have had a lunar orbital altitude of approximately {{cvt|61500|km}}, a distance somewhat greater than the distance from the Moon to either of the Earth-Moon {{L1}} or {{L2}} [[Lagrangian point]]s.<ref name=johnson2014/>  NASA subsequently cancelled work on ARM in 2017 and never funded the build of flight hardware nor issued any space launch contracts.<ref name=sn20170614>{{cite news |last=Foust |first=Jeff |title=NASA closing out Asteroid Redirect Mission |url=http://spacenews.com/nasa-closing-out-asteroid-redirect-mission/ |date=14 June 2017 |access-date=3 November 2019 |work=[[SpaceNews]] |archive-date=15 June 2017 |archive-url=https://wayback.archive-it.org/all/20170615143924/http://spacenews.com/nasa-closing-out-asteroid-redirect-mission/ |url-status=live }}</ref>
+On 16 November 2022, the [[Space Launch System]] was launched from Complex 39B as part of the [[Artemis 1]] mission carrying Orion to the Moon.<ref>{{cite AV media |date=16 November 2022 |url=https://www.youtube.com/watch?v=CMLD0Lp0JBg |title=Artemis I Launch to the Moon (Official NASA Broadcast) - Nov. 16, 2022 |publisher=[[NASA]] |via=[[YouTube]] |access-date=2 December 2022 |archive-url=https://web.archive.org/web/20221129101304/https://www.youtube.com/watch?v=CMLD0Lp0JBg |archive-date=29 November 2022 |url-status=live}}</ref><ref name="nasa-20221108">{{cite web |url=https://blogs.nasa.gov/artemis/2022/11/08/nasa-prepares-rocket-spacecraft-ahead-of-tropical-storm-nicole-re-targets-launch/ |title=NASA Prepares Rocket, Spacecraft Ahead of Tropical Storm Nicole, Re-targets Launch |author=[[NASA]] |date=8 November 2022 |access-date=8 November 2022}}</ref> On 25 November it entered DRO and orbited the Moon in that orbit.<ref name="Nov15">{{cite web |date=27 November 2015 |title=The Ins and Outs of NASA's First Launch of SLS and Orion |url=http://www.nasa.gov/feature/the-ins-and-outs-of-nasa-s-first-launch-of-sls-and-orion |access-date=3 May 2016 |author=[[NASA]] |archive-date=22 February 2020 |archive-url=https://web.archive.org/web/20200222201819/https://www.nasa.gov/feature/the-ins-and-outs-of-nasa-s-first-launch-of-sls-and-orion |url-status=live }} {{PD-notice}}</ref><ref>{{Cite web |last=Foust |first=Jeff |date=2022-11-25 |title=Orion enters lunar distant retrograde orbit |url=https://spacenews.com/orion-enters-lunar-distant-retrograde-orbit/ |access-date=2022-11-29 |website=SpaceNews }}</ref>
+===DRO A/B===
+[[Yuanzheng|Yuanzheng 1S]] upper stage failed to deliver these two [[China Academy of Sciences|CAS]] spacecrafts (not under [[Chinese Lunar Exploration Program|CLEP]]) into correct orbit. The satellites were intended to test Distant retrograde orbit.<ref>{{Cite web |last=Jones |first=Andrew |date=2024-03-14 |title=Surprise Chinese lunar mission hit by launch anomaly |url=https://spacenews.com/surprise-chinese-lunar-mission-hit-by-launch-anomaly/ |access-date=2024-03-14 |website=SpaceNews |language=en-US}}</ref> Tracking data appears to show China is attempting to salvage spacecraft and they appear to have succeeded in reaching their desired orbit.<ref>{{Cite web |last=Jones |first=Andrew |date=2024-08-20 |title=Chinese spacecraft appear to reach lunar orbit despite launch setback |url=https://spacenews.com/chinese-spacecraft-appear-to-reach-lunar-orbit-despite-launch-setback/ |access-date=2024-08-20 |website=SpaceNews |language=en-US}}</ref><ref>{{Cite web |last=Jones |first=Andrew |date=2024-03-28 |title=China appears to be trying to save stricken spacecraft from lunar limbo |url=https://spacenews.com/china-appears-to-be-trying-to-save-stricken-spacecraft-from-lunar-limbo/ |access-date=2024-03-29 |website=SpaceNews |language=en-US}}</ref>
+== Space concepts proposed to use a DRO ==
 === Jupiter Icy Moons Orbiter ===
-A distant retrograde orbit was one of the proposed orbits around [[Europa (moon)|Europa]] for the [[Jupiter Icy Moons Orbiter]]—principally for its projected stability and low-energy transfer characteristics—but that mission concept was cancelled in 2005.<ref name=johnson2014>{{cite web |url=http://ccar.colorado.edu/asen5050/projects/projects_2013/Johnson_Kirstyn/finalorbit.html |last=Johnson |first=Kirstyn |title=Understanding NASA's Asteroid Redirect Mission : Distant Retrograde Orbits |date=18 December 2014 |archive-url=https://web.archive.org/web/20150111224722/http://ccar.colorado.edu/asen5050/projects/projects_2013/Johnson_Kirstyn/finalorbit.html |archive-date=11 January 2015 |access-date=3 May 2015 |url-status=dead }}</ref>
+A distant retrograde orbit was one of the proposed orbits around [[Europa (moon)|Europa]] for the [[Jupiter Icy Moons Orbiter]]—principally for its projected stability and low-energy transfer characteristics—but that mission concept was cancelled in 2005.<ref name=johnson2014>{{cite web |url=http://ccar.colorado.edu/asen5050/projects/projects_2013/Johnson_Kirstyn/finalorbit.html |last=Johnson |first=Kirstyn |title=Understanding NASA's Asteroid Redirect Mission: Distant Retrograde Orbits |date=18 December 2014 |archive-url=https://web.archive.org/web/20150111224722/http://ccar.colorado.edu/asen5050/projects/projects_2013/Johnson_Kirstyn/finalorbit.html |archive-date=11 January 2015 |access-date=3 May 2015 |url-status=dead }}</ref>
-=== NASA Lunar Gateway ===
+=== Asteroid Redirect Mission (ARM) ===
+A distant retrograde orbit was considered to be used for the proposed Asteroid Redirect Mission. Although the mission would end up getting cancelled, the research done with DRO in-mind, lead to the orbit being used for [[Artemis 1]].<ref>{{cite tweet |author=NASA |author-link=NASA |user=NASA |number=1593769483507830787 |date=19 November 2022 |title=@JVendl @NASA_Orion We first studied the DRO to support the proposed Asteroid Redirect Mission (ARM) which paralleled early SLS and Orion development. The plan for ARM was to capture a near Earth asteroid and redirect it to a lunar DRO. (1/4) |language=en |access-date=2 December 2022}}</ref>
-Two system requirements for the [[NASA]] [[Lunar Gateway]] mention{{when|date=June 2020}}<!-- what was the year (and version of the spec) that these rqmts were laid down? --> the use of lunar DROs. Requirement L2-GW-0029, Single Orbit Transfer, states "the Gateway shall be capable of performing a single round trip transfer to Distant Retrograde Orbit (DRO) and back within 11 months." Requirement L2-GW-0026, Propulsion System Capability, states "the Gateway shall provide a fuel capacity that would support performing a minimum of two round-trip uncrewed low-energy [[cislunar space|cislunar]] orbit transfers between a [[near-rectilinear halo orbit]] (NRHO) and a distant retrograde orbit (DRO) and orbit maintenance for a period of 15 years between refueling."<ref>{{cite web |title=DSG-RQMT-001 - Gateway Program System Requirements Document (SRD) |year=2019 |pages=25 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190029153.pdf |website=NASA Technical Reports Server |publisher=National Aeronautics and Space Administration (NASA) |access-date=11 April 2020 |archive-date=11 April 2020 |archive-url=https://web.archive.org/web/20200411005107/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190029153.pdf |url-status=live }}</ref>
+=== NASA Lunar Gateway ===
-NASA will test the theory of DRO in November 2022, on the initial [[test flight]] for the NASA [[Space Launch System]] (SLS) launch vehicle (in development since 2010<ref name=spo20110915>{{cite news |url=http://www.spacepolicyonline.com/news/new-nasa-crew-transportation-system-to-cost-18-billion-through-2017 |title=New NASA Crew Transportation System to Cost US$18 Billion Through 2017 |work=Space Policy Online |date=14 September 2011 |access-date=15 September 2011 |first=Marcia|last=Smith |archive-date=2 April 2015|archive-url=https://web.archive.org/web/20150402133411/http://www.spacepolicyonline.com/news/new-nasa-crew-transportation-system-to-cost-18-billion-through-2017 |url-status=live}}</ref>) and the NASA [[Orion space capsule]] (in development since 2005),<ref name=nasa200511>{{cite web |url=http://www.nasa.gov/pdf/140649main_ESAS_full.pdf|title=Exploration Systems Architecture Study – Final Report |publisher=[[NASA]] |date=November 2005 |id=NASA-TM-2005-214062 |access-date=July 6, 2009 |archive-url=https://web.archive.org/web/20061013112649/http://www.nasa.gov/pdf/140649main_ESAS_full.pdf|archive-date=October 13, 2006}}</ref>) where NASA has selected a DRO as a part of the first Orion deep space test mission, named [[Artemis 1]]. Previously planned to use a [[circumlunar trajectory]] for its lunar test flight, by late 2015 NASA had replanned the first deep space test of the uncrewed Orion capsule to use a distant retrograde orbit, with the Orion spacecraft slated to spend approximately three weeks in space, including six days in a DRO around the Moon.<ref name=nasa20151127>{{cite web |title=The Ins and Outs of NASA's First Launch of SLS and Orion |url=http://www.nasa.gov/feature/the-ins-and-outs-of-nasa-s-first-launch-of-sls-and-orion |date=27 November 2015 |url-status=live |archive-url=https://web.archive.org/web/20200222201819/https://www.nasa.gov/feature/the-ins-and-outs-of-nasa-s-first-launch-of-sls-and-orion |archive-date=22 February 2020 |access-date=3 May 2016 |publisher=NASA}}</ref><!-- according to the Artemis 1 article on 29 Aug 2022, it's planned (now delayed) launch day, Artemis 1 will spend 6 days in a DRO, and it uses this 2015 source.  Seems it needs a better/more recent source; but that is current article prose. -->
+Two system requirements for the NASA [[Lunar Gateway]], as published in the Baseline DSG-RQMT-001<ref>{{cite web |title=DSG-RQMT-001 – Gateway Program System Requirements Document (SRD) |year=2019 |pages=25 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190029153.pdf |website=NASA Technical Reports Server |author=[[NASA]] |access-date=11 April 2020 |archive-date=11 April 2020 |archive-url=https://web.archive.org/web/20200411005107/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190029153.pdf |url-status=live }}</ref> published in June 2019, mention the use of lunar DROs. Requirement L2-GW-0029, Single Orbit Transfer, states "the Gateway shall be capable of performing a single round trip transfer to Distant Retrograde Orbit (DRO) and back within 11 months". Requirement L2-GW-0026, Propulsion System Capability, states "the Gateway shall provide a fuel capacity that would support performing a minimum of two round-trip uncrewed low-energy [[cislunar space|cislunar]] orbit transfers between a [[near-rectilinear halo orbit]] (NRHO) and a distant retrograde orbit (DRO) and orbit maintenance for a period of 15 years between refueling".  Although the selected orbit for the Gateway has been confirmed to be NRHO<ref>{{Cite web |last=Zaid |first=Christina |date=2022-05-16 |title=A unique halo orbit is the road less traveled around the Moon |url=http://www.nasa.gov/feature/a-lunar-orbit-that-s-just-right-for-the-international-gateway |access-date=2022-11-29 |website=NASA}}</ref> instead of DRO.
 == DRO orbits in fiction ==
-In the 2019 [[Daniel Suarez (author)|Daniel Suarez]] novel ''Delta-v'', a 560-tonne crewed asteroid-mining ship ''The Konstantin'' is constructed in a lunar DRO approximately {{cvt|40000|km}} above the Moon.<ref>{{cite book |last=Suarez|first1=Daniel |authorlink=Daniel Suarez (author) |title=Delta-v |location=New York |publisher=Penguin Random House |year=2019 |pages=189-198 |isbn=978-1524742416 }}</ref>
+In the 2019 [[Daniel Suarez (author)|Daniel Suarez]] novel ''Delta-v'', a 560-tonne crewed asteroid-mining ship ''Konstantin'' is constructed in a lunar DRO approximately {{cvt|40000|km}} above the Moon.<ref>{{cite book |last=Suarez|first1=Daniel |authorlink=Daniel Suarez (author) |title=Delta-v |location=New York |publisher=Penguin Random House |year=2019 |pages=189–198 |isbn=978-1524742416 }}</ref>
 == See also ==