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Distant retrograde orbit

A distant retrograde orbit (DRO) is a highly stable, periodic orbit around the Moon in which a spacecraft travels in a direction opposite to the Moon's orbital motion around Earth, typically at a high altitude of approximately 40,000 miles (64,000 kilometers) from the lunar surface.^[1] This orbit forms within the circular restricted three-body problem, resembling a large quasi-elliptical path around the Earth-Moon L1 or L2 libration points, with orbital periods ranging from 6 to 28 days depending on the distance from the Moon.^[2] DROs exhibit Lyapunov stability due to the balanced gravitational perturbations from Earth and the Moon, allowing spacecraft to remain in orbit for extended periods—potentially hundreds of years—with minimal fuel consumption for station-keeping.^[3] The stability and fuel efficiency of DROs make them particularly advantageous for deep-space missions, as demonstrated by NASA's Artemis I mission in 2022, where the Orion spacecraft entered a DRO for about six days to test spacecraft systems in a distant lunar environment without crew risk.^[1] These orbits have also been proposed for long-duration applications, such as lunar GNSS constellations combining DROs with halo orbits to provide consistent equatorial coverage and global navigation support on the Moon's surface.^[2] In the Hill three-body problem framework, which approximates the Earth-Moon system, DROs can incorporate three-dimensional out-of-plane motion, enabling precise modeling of their dynamics for mission planning.^[3]

Fundamentals

Definition and characteristics

A distant retrograde orbit (DRO) arises in the context of the circular restricted three-body problem (CR3BP), a model in celestial mechanics where two massive primary bodies—such as Earth and the Moon—orbit their common center of mass in circular paths, while a third body of negligible mass is influenced by the gravitational fields of both primaries without affecting their motion.^[4] In this framework, the DRO represents a family of stable, periodic orbits around the secondary body, classified as the "f-family" in classical literature.^[5] Specifically, a DRO is a retrograde, nearly circular trajectory around the smaller secondary body in a three-body system, where the spacecraft circumnavigates the secondary in the direction opposite to its orbital motion around the primary.^[6] For the Earth-Moon system, this means the spacecraft orbits the Moon in a retrograde sense relative to the Moon's prograde revolution around Earth. The orbit is "distant" due to its large extent, typically positioned beyond the secondary's Hill sphere—the approximate boundary of the secondary's gravitational dominance—yet remaining within the overall influence of the three-body dynamics.^[7] Key characteristics of a lunar DRO include a high inclination approaching 180° to indicate the retrograde direction, a low eccentricity that maintains its near-circular shape, and a large semi-major axis ranging from approximately 60,000 to 100,000 km from the Moon's center.^[6] These orbits exhibit periods on the order of several weeks, such as 25 to 27 days for representative cases, and demonstrate inherent stability due to the balanced gravitational perturbations in the CR3BP, allowing prolonged mission durations with minimal station-keeping fuel.^[7] While primarily studied in the Earth-Moon system, DROs are applicable to other planetary-moon pairs, such as those involving Jupiter's satellites, where similar three-body dynamics enable stable distant orbits around the moons.

Orbital parameters and geometry

Distant retrograde orbits (DROs) are characterized by specific orbital elements in the circular restricted three-body problem (CRTBP), typically defined relative to the secondary body such as the Moon in the Earth-Moon system. The inclination is approximately 180°, indicating a retrograde motion coplanar with the orbital plane of the secondary body. The argument of pericenter is approximately 0° or 180°, aligning the closest approach with the line connecting the primary and secondary bodies. The semi-major axis (a) is typically on the order of 60,000–80,000 km from the secondary body's center, making the orbit "distant" compared to low lunar orbits. Eccentricity (e) is low, often less than 0.01, resulting in near-circular paths that maintain periodicity over extended durations.^[9]^[6] Geometrically, a DRO forms a large, elongated loop around the secondary body within its orbital plane, with the spacecraft executing retrograde motion that appears as a quasi-elliptical path encircling the Moon while the entire structure slowly precesses relative to the primary body like the Moon's orbit around Earth. The orbit's distant nature positions it beyond the L1 and L2 Lagrange points, allowing the spacecraft to maintain distances of approximately 60,000–80,000 km from the Moon's center throughout the orbit, with low variation between perilune and apolune due to low eccentricity, and farther excursions toward the primary, without crossing the Lagrange points directly. This configuration provides a stable, repeating trajectory with a synodic period matching the secondary's orbital period, approximately 27 days for lunar DROs, during which the spacecraft completes about two loops around the Moon.^[9]^[6] Insertion into a DRO requires targeted maneuvers, with delta-v costs varying by transfer trajectory. From low lunar orbit, insertion delta-v is approximately 100–180 m/s, achieved via a retrograde burn to establish the initial velocity vector. Insertion into a DRO from a suitable lunar approach trajectory requires approximately 100–200 m/s delta-v. The trans-lunar injection from low Earth orbit adds approximately 3.1–3.2 km/s, for a total delta-v of over 3.2 km/s depending on the transfer design. These values reflect efficient transfers in the CRTBP model, minimizing fuel while leveraging gravitational assists.^[9] Diagrams of DRO geometry often depict the path in the synodic rotating frame, illustrating the retrograde ellipse around the secondary body offset from the barycenter, with the L1 and L2 points marked for contrast—highlighting how DROs extend beyond these collinear equilibria without equilibrating at them. Such visualizations, like those in trajectory design analyses, show the orbit's amplitude (~70,000 km radius) and its distinction from near-Lagrange halo orbits, emphasizing the distant, looping enclosure of the secondary.^[9]

Dynamics and stability

Retrograde motion mechanics

In the synodic frame of the circular restricted three-body problem (CR3BP), where the two primary bodies are fixed along the x-axis, a distant retrograde orbit (DRO) encircles the secondary body in a direction opposite to the frame's rotation, effectively countering the secondary's prograde orbital motion around the primary.^[10] This retrograde circulation interacts with the Coriolis force, which acts as a stabilizing influence by deflecting the third body away from close approaches to the secondary, unlike in prograde motion where it promotes destabilization.^[11] Consequently, tidal perturbations from the secondary's non-spherical gravity and the primary's distant pull are mitigated, as the orbit maintains a relatively uniform distance without resonant close encounters.^[7] Perturbation analysis in the CR3BP reveals that the retrograde direction minimizes chaotic interactions near the secondary's sphere of influence by avoiding secular energy exchanges that amplify instabilities.^[12] The Jacobi integral, a conserved quantity analogous to energy in the rotating frame, governs this behavior: C = x^2 + y^2 + 2(1-\mu)/r_1 + 2\mu/r_2 - (\dot{x}^2 + \dot{y}^2 + \dot{z}^2), where \mu is the mass ratio, r_1 and r_2 are distances to the primaries, and dots denote time derivatives.^[7] For DROs, high Jacobi constants (near those of the L1 or L2 Lagrange points) confine motion to bounded regions, preserving the orbit's integrity against perturbations while enabling retrograde paths to align with invariant manifolds that channel stable trajectories around the secondary.^[10] The equations of motion in the CR3BP synodic frame capture these dynamics through the effective potential \Omega = \frac{1}{2}(x^2 + y^2) + \frac{1-\mu}{r_1} + \frac{\mu}{r_2}:

\ddot{x} - 2\dot{y} = \frac{\partial \Omega}{\partial x}, \quad \ddot{y} + 2\dot{x} = \frac{\partial \Omega}{\partial y}, \quad \ddot{z} = \frac{\partial \Omega}{\partial z}.

The Coriolis terms (-2\dot{y} and +2\dot{x}) highlight how retrograde velocities oppose the frame rotation, enhancing orbital coherence.^[12] In contrast to prograde distant orbits, which succumb to instabilities from orbital resonances with the secondary's motion—leading to rapid energy dissipation and ejection—retrograde DROs evade these resonances, sustaining periodic loops with minimal deviation.^[7]

Stability mechanisms and advantages

The stability of distant retrograde orbits (DROs) in the circular restricted three-body problem (CR3BP), such as the Earth-Moon system, arises primarily from bounded motion influenced by third-body gravitational perturbations that create a "sticky" region in phase space, where trajectories remain confined without escaping to infinity.^[13] This stickiness is evident in Poincaré sections, which reveal dense coverage of quasi-periodic orbits near resonant regions, preventing chaotic diffusion over long timescales.^[13] Numerical integrations of DROs at various altitudes (e.g., 60,000–80,000 km from the Moon) demonstrate Lyapunov stability, characterized by all Floquet multipliers having magnitude equal to 1, ensuring no exponential divergence from initial conditions.^[6] In the Earth-Moon system, such orbits exhibit Lyapunov stability for over 100 years without active control, as confirmed by high-fidelity simulations incorporating solar perturbations.^[14] To quantify and map these stable structures, computational methods like pseudo-arclength continuation are employed to trace families of invariant tori that underpin the quasi-periodic nature of DROs. These techniques adaptively adjust integration steps (e.g., from 11 to 791 nodes) to navigate singularities at resonance boundaries, representing the tori via Fourier series for accurate long-term predictions.^[13] Such approaches, building on earlier work by Hénon (1970), reveal that retrograde configurations inherently resist destabilizing influences compared to prograde orbits, leading to extended bounded motion. Key advantages of DROs include exceptional fuel efficiency, with station-keeping requirements effectively negligible (approaching 0 m/s per year for nominal cases) due to their inherent dynamical stability, far surpassing the 5–50 m/s annual costs of libration point orbits.^[15] This allows for long-duration missions without propulsion, reducing mass and complexity. Additionally, DROs offer persistent visibility from the primary body (e.g., Earth) for communication and tracking, as well as halo-like continuous views of the secondary (e.g., Moon) over orbital periods of about 27 days.^[6] Certain configurations may provide partial radiation shielding by leveraging the secondary body's position, mitigating exposure in cislunar space.^[16] Despite these benefits, DRO insertion after trans-lunar injection typically requires low Δv of about 100-200 m/s, which is less than the 600-800 m/s needed for low lunar orbit insertion; the total Δv from low Earth orbit is approximately 3.2-3.3 km/s, comparable to other lunar transfers.^[17] They are also vulnerable to non-gravitational perturbations, such as solar radiation pressure, which can induce gradual drift in low-mass spacecraft over decades, particularly at higher altitudes.^[6]

Historical development

Theoretical foundations

The theoretical foundations of distant retrograde orbits (DROs) originate in the late 19th-century developments of the circular restricted three-body problem (CR3BP), which models the motion of a negligible-mass body under the influence of two larger primaries in circular orbits around their common center of mass. Henri Poincaré's seminal work on periodic orbits, outlined in Les Méthodes Nouvelles de la Mécanique Céleste (1892–1899), demonstrated the existence of an infinite number of such solutions in the CR3BP, including retrograde configurations that encircle the secondary primary in the opposite direction to its orbital motion around the primary. Poincaré's analysis of variational equations and surfaces of section revealed the intricate structure of these orbits, laying the conceptual groundwork for understanding their bounded, non-chaotic paths in three-body dynamics. Building on this, George William Hill's lunar theory, first presented in 1878 and refined in subsequent publications through the 1890s, provided analytical approximations for retrograde solutions in the CR3BP by considering the Moon's motion relative to the Earth-Sun system. Hill's variational equations captured the essential dynamics near the collinear libration points, identifying retrograde paths as stable, elongated orbits around the secondary body that avoid resonance with the primaries' orbital period. These approximations emphasized the non-resonant character of such orbits, where the orbital frequency differs significantly from the system's mean motion, enabling persistent circulation without periodic alignment. An early analytical description of retrograde satellite orbits appeared in John Jackson's 1913 study, which explored their stability and geometry in the restricted three-body problem.^[18] In the 1960s, researchers advanced concepts for lunar libration point orbits in the CR3BP. Robert Farquhar proposed halo and Lissajous orbits near the Earth-Moon L1 and L2 points, highlighting their potential for bounded motion. Concurrently, numerical and analytical techniques confirmed the existence of the retrograde family of orbits as specific solutions in the pre-computational era. These efforts established DROs as a distinct class of periodic orbits amenable to theoretical prediction.

Discovery and early proposals

The computational discovery of distant retrograde orbits (DROs) as a distinct family of periodic solutions in the circular restricted three-body problem (CR3BP) emerged from numerical explorations in the late 1960s. Roger Broucke's 1968 cataloging of planar periodic orbits using single-shooting methods provided early evidence of these retrograde trajectories in the Earth-Moon system.^[19] Shortly thereafter, Michel Hénon identified them as family "f" in his 1969 numerical study of the planar restricted three-body problem, confirming their existence through extensive integration of initial conditions across a range of energies and mass ratios. These orbits, characterized by large, stable loops encircling the secondary body in retrograde motion relative to the rotating frame, were distinguished from other families like halos and Lissajous by their vertical symmetry and relative isolation from chaotic regions. While early analytical work on three-body dynamics, such as that by George Hill and George Darwin in the late 19th and early 20th centuries, laid theoretical groundwork, it was the advent of digital computing that enabled the revelation of DROs as a computationally identifiable class.^[19] In the 1980s, numerical studies further illuminated DRO characteristics using advanced techniques like Poincaré maps to analyze stability and bifurcation in the CR3BP. Researchers employed these maps to section the phase space, revealing DROs as fixed points or invariant curves within bounded regions of retrograde motion, separate from prograde families.^[19] John V. Breakwell's 1984 work on vertical periodic orbits in the Earth-Moon system extended these insights, though focused primarily on halo extensions.^[20] By the 1990s, the term "distant retrograde orbit" was coined by C. A. Ocampo and G. W. Rosborough in their 1993 analysis of transfer trajectories to such orbits in the Sun-Earth system.^[21] The concept was subsequently applied to lunar DROs in the Earth-Moon system for long-duration missions, positioning them as alternatives to geostationary Earth orbits (GEO) for cislunar communications and observation due to their natural stability and low station-keeping demands. Key milestones in DRO development included stability confirmations through long-term simulations in the early 2000s. Jeffrey S. Parker and Rodney L. Anderson's 2001 ephemeris model integrations over 500 years validated the quasi-stable nature of lunar DROs under solar perturbations, showing minimal drift and confirming their suitability for extended missions with annual delta-v costs below 10 m/s.^[19] This built on prior numerical catalogs, shifting DROs from theoretical curiosities to practical candidates. In the 2010s, proposals for Artemis-like architectures explicitly leveraged DROs; for instance, NASA's 2013 Asteroid Redirect Mission concept designated a lunar DRO as a stable parking site for captured asteroids, enabling crewed inspections with reduced propulsion needs.^[22] The evolution toward practicality accelerated with improved computational power for trajectory design in the 2000s and 2010s. Enhanced numerical integrators and manifold-based methods, as in Koon et al.'s 2000 work on invariant manifolds, facilitated precise DRO insertions via low-energy transfers, reducing delta-v requirements by up to 50% compared to direct lunar orbits.^[19] These advances, coupled with high-fidelity ephemeris models like DE421, transformed DROs into a cornerstone for sustainable cislunar exploration, emphasizing their role in multi-body dynamics beyond the foundational three-body framework.^[19]

Real-world examples

Chang'e 5 orbiter

The Chang'e 5 mission, launched on November 23, 2020, by the China National Space Administration (CNSA), marked China's first lunar sample-return effort, successfully retrieving approximately 1.731 kilograms of lunar regolith from the Oceanus Procellarum region. Following the sample delivery to Earth on December 16, 2020, the orbiter module—retaining unused propellant—embarked on an extended mission phase to demonstrate advanced orbital technologies while avoiding direct reentry risks into Earth's atmosphere. This phase included a temporary halo orbit around the Earth-Sun L1 point from March to September 2021, after which the spacecraft returned to the Earth-Moon system and transitioned into a distant retrograde orbit (DRO) around the Moon by early 2022, as confirmed by amateur satellite trackers and orbital analyses.^[23]^[24]^[25] The orbiter's insertion into the lunar DRO occurred via low-thrust maneuvers utilizing the remaining propellant, positioning it in a stable, quasi-elliptical path interacting with the Earth-Moon L1 and L2 Lagrange points. The DRO configuration allowed the spacecraft to maintain visibility of both Earth and the lunar surface without frequent corrections, leveraging the orbit's inherent dynamical stability derived from third-body gravitational influences.^[26] The mission demonstrated long-term orbital stability in the DRO, with the spacecraft operating without significant station-keeping maneuvers for extended periods, providing valuable telemetry, tracking, and control data essential for future CNSA endeavors such as the Chang'e 7 south polar relay satellite. Observations confirmed minimal fuel consumption, highlighting the DRO's advantages for extended cislunar operations and contributing to astrodynamics models for low-energy trajectories. As the first operational spacecraft to utilize a lunar DRO, Chang'e 5's implementation validated the orbit's practicality, paving the way for sustainable infrastructure in the Earth-Moon system; the orbiter remained in stable lunar orbit as of November 2025, supporting ongoing technology verifications.^[24]^[23]^[27]

Orion spacecraft

The uncrewed Artemis I mission, launched on November 16, 2022, utilized NASA's Orion spacecraft to demonstrate deep space operations by placing it into a lunar distant retrograde orbit (DRO) following an initial lunar flyby. This test flight aimed to simulate extended human exploration scenarios beyond low Earth orbit, with Orion entering DRO on November 25, 2022, after a powered flyby maneuver approximately 130 km above the Moon's surface. The orbit insertion involved an 88-second burn of the European Service Module's main engine, adjusting Orion's velocity by about 110 meters per second to achieve the retrograde path.^[28]^[1] Orion's DRO had an average distance of approximately 70,000 km from the Moon, with perigee altitudes around 64,000 km and apogee reaching up to 92,000 km above the lunar surface, providing a stable, fuel-efficient environment for system testing. The spacecraft remained in this orbit for six days before a departure burn on December 1, 2022, initiating the return trajectory that culminated in a Pacific Ocean splashdown on December 11, 2022, after a total mission duration of 25 days and 10 hours. This configuration allowed Orion to travel as far as 432,000 km from Earth, exceeding previous Apollo mission distances.^[29]^[30]^[31] Key outcomes included validation of DRO stability for a human-rated spacecraft, confirming its low station-keeping requirements due to balanced gravitational influences from Earth and the Moon, which supports prolonged lunar vicinity operations. Radiation sensors aboard Orion measured exposure levels during the DRO phase, revealing that the vehicle's shielding effectively limited doses to below NASA career limits for astronauts on similar missions, with variations depending on detector locations inside the crew module. Navigation and guidance systems performed nominally, enabling precise trajectory adjustments and data collection on deep space communication blackouts. As the first crew-capable vehicle to enter DRO, these results directly informed risk assessments and operational planning for subsequent crewed Artemis II and beyond missions, including integration with the Lunar Gateway station.^[32]^[33]^[34]

DRO A/B objects

DRO-A and DRO-B are a pair of Chinese lunar test satellites developed by the Microsatellite Innovation Institute of the Chinese Academy of Sciences (CAS), launched on March 13, 2024, aboard a Long March 2C rocket with a YZ-1S upper stage from Xichang Satellite Launch Center. With a combined mass of 581 kg, the mission aimed to demonstrate distant retrograde orbit (DRO) operations, including communication, navigation, and orbital dynamics testing for future cislunar infrastructure. However, the upper stage failed to perform its planned burn, placing the satellites into an unintended low-energy transfer orbit.^[35]^[36] Mission engineers executed a complex rescue operation involving 167 minutes of maneuvers using the satellites' onboard propulsion to reconstruct the trajectory, enabling both to reach lunar DRO by April 2024. DRO-A was inserted into a stable lunar DRO with an orbital period of approximately 27 days, while DRO-B operates in complementary Earth-Moon maneuver orbits to support relay functions. Together with the earlier-launched DRO-L satellite (February 2024, in heliocentric orbit), they formed the world's first three-satellite constellation in the DRO regime by April 2025, achieving milestones such as the first lunar-distance satellite laser ranging and validating low-fuel entry into deep lunar orbits.^[37]^[38] As of November 2025, the DRO A/B satellites continue operations, providing data on long-term stability and minimal station-keeping needs in DRO, with DRO-A remaining in its primary orbit. This mission highlights China's advancements in cislunar space utilization, supporting upcoming endeavors like the Chang'e series and potential lunar GNSS networks. No natural minor bodies have been confirmed in lunar DROs to date, though theoretical studies suggest possible dust or ejecta accumulations.^[39]^[40]

Proposed applications

Earth-Moon system missions

The Lunar Gateway, a key component of NASA's Artemis program, is primarily planned for a near-rectilinear halo orbit (NRHO) around the Moon, with initial elements launching no earlier than 2027, though a fiscal year 2026 budget proposal released in May 2025 seeks to cancel the project.^[41] Full operational capability, if the project proceeds, is targeted for the Artemis IV mission no earlier than September 2028.^[42] However, distant retrograde orbits (DROs) have been proposed as alternative or complementary orbits for cislunar stations due to their exceptional stability, requiring minimal station-keeping fuel over extended periods. This stability arises from the balanced gravitational influences of Earth and the Moon, making DROs attractive for long-duration human-tended platforms that could support lunar surface operations without frequent orbital adjustments.^[43]^[44] One significant advantage of DROs for Earth-Moon missions is their potential to enable continuous communications with the lunar surface, where a constellation of three equally phased satellites in DRO can provide coverage to 99.8% of the Moon's surface at all times. This coverage supports real-time data relay for surface explorers, including high-definition video and navigation signals, which is critical for Artemis-era landings at the lunar south pole. Additionally, DROs offer low-latency links to Earth, with line-of-sight visibility for most of the orbital period, facilitating efficient command and control from ground stations. To mitigate periodic solar eclipses that can last up to four hours in nominal DROs—posing risks to power systems—mission planners employ targeted maneuvers, such as slight orbital perturbations, to avoid shadow regions while keeping total delta-v costs low.^[45]^[46]^[47] The Asteroid Redirect Mission (ARM), proposed by NASA from 2013 to 2017, exemplified early DRO applications by planning to capture a small near-Earth asteroid boulder and place it in a stable lunar DRO at approximately 70,000 km altitude above the Moon for subsequent crewed study. This orbit was selected for its long-term stability, allowing the asteroid to remain accessible for up to several years without significant drift, and for providing safe rendezvous opportunities for Orion spacecraft. Insertion into such a DRO parking orbit typically requires a delta-v budget of approximately 60 m/s, leveraging lunar gravity assists to minimize propulsion needs during transfer from Earth orbit. ARM's DRO concept integrated with broader Artemis timelines by enabling precursor technology demonstrations for resource utilization, though the mission was ultimately canceled in favor of other priorities. Beyond ARM, DROs are envisioned for cislunar infrastructure like propellant depots or observation platforms, enhancing sustainable Earth-Moon logistics.^[48]^[49]

Outer solar system concepts

The Jupiter Icy Moons Orbiter (JIMO), a proposed NASA mission from the early 2000s that was ultimately canceled, envisioned using a nuclear-powered spacecraft to explore Jupiter's icy moons, including Europa, Ganymede, and Callisto, through a series of orbital insertions and tours. A key element of the mission design involved employing distant retrograde orbits (DROs) around these moons, particularly Europa, to leverage their inherent stability for long-duration observations without significant fuel expenditure on station-keeping maneuvers.^[50] These DROs, analyzed in the context of the Jupiter-Europa circular restricted three-body problem, allow a spacecraft to maintain a quasi-periodic path at distances of approximately 100,000 to 200,000 km from the moon, enabling repeated flybys and data collection across multiple targets while mitigating perturbations from Jupiter's massive gravity field.^[50] The European Space Agency's Jupiter Icy Moons Explorer (JUICE), launched in April 2023, represents a realized effort to study Jupiter's Galilean moons, with Ganymede as its primary target for an extended orbital phase beginning around 2034.^[51] While JUICE's baseline trajectory includes elliptical orbits around Ganymede, mission concepts have explored incorporating DRO phases to enhance stability during the Jupiter system tour, particularly for prolonged remote sensing of the moon's surface and magnetic interactions.^[10] Studies of DROs in the Jupiter-Ganymede system demonstrate linear stability over mission-relevant timescales, even under perturbations from other moons and solar gravity, allowing the spacecraft to remain in a distant, retrograde configuration for months with minimal delta-V adjustments.^[10] This approach supports JUICE's objectives by facilitating efficient transitions between observation windows of Ganymede, Europa, and Callisto, reducing overall propulsion demands in the harsh Jovian environment.^[10] Beyond the Jovian system, DRO concepts have been proposed for navigation and stability in the asteroid belt, particularly as extensions to missions like NASA's canceled Asteroid Redirect Mission (ARM), which originally planned to relocate captured material to a lunar DRO but inspired ideas for analogous stable orbits around near-Earth or main-belt asteroids.^[52] In these extensions, DRO-like trajectories in the Sun-asteroid three-body framework could enable low-energy parking for sample return or resource prospecting, allowing spacecraft to loiter near multiple belt objects with reduced fuel for corrections against solar perturbations.^[53] Similarly, for the Saturn-Titan system, resonant periodic orbits including DRO families have been identified as viable for future probe designs, offering stable configurations around Titan for atmospheric and surface studies amid Saturn's ring-plane hazards.^[54] These orbits, computed in the restricted three-body model, exhibit enhanced stability compared to prograde paths, supporting long-term missions like potential successors to Cassini or Dragonfly by minimizing exposure to Saturn's intense radiation belts.^[55] In the outer solar system, DROs provide critical advantages for robotic missions, including substantial reductions in fuel requirements for orbit maintenance—often near zero over years—due to their dynamical stability in perturbed three-body environments.^[10] This efficiency is particularly beneficial for long-duration explorations, where propulsion resources are limited, enabling extended science operations without frequent maneuvers.^[50] Additionally, the distant nature of these orbits allows strategic placement to manage radiation exposure, positioning spacecraft outside intense magnetospheric belts around gas giants like Jupiter and Saturn, thereby preserving sensitive instruments and extending operational lifetimes.^[10]

Depictions in fiction

Scientific accuracy in media

In media portrayals, distant retrograde orbits (DROs) are often depicted as inherently "hidden" or stealthy paths for spacecraft, allowing undetected surveillance or ambushes in space, a trope seen in various science fiction video games where unusual orbital inclinations enable tactical advantages without radar detection. However, this inaccurately suggests invisibility; in reality, DROs offer extended visibility windows from Earth-based observatories due to their periodic alignment with the Earth-Moon line, making them trackable via standard astronomical methods.^[44] A notable accurate representation appears in the video game Kerbal Space Program (KSP), where players can manually insert vehicles into retrograde orbits, demonstrating the mechanics of inclination changes and fuel costs associated with counter-rotational paths around celestial bodies. While stock KSP accurately simulates basic orbital dynamics like prograde versus retrograde insertions—requiring additional delta-v for retrograde due to gravitational drag effects—it simplifies multi-body perturbations, leading to artificial long-term stability that does not fully replicate real DRO persistence without mods like Principia. This portrayal highlights DRO stability benefits for prolonged missions, such as reduced station-keeping needs, aligning with their use in conceptual lunar bases.^[56]^[57] Common inaccuracies in fictional media include the effortless insertion into DROs without accounting for substantial delta-v requirements, often showing instantaneous orbital flips via minimal propulsion, which overlooks the energy-intensive maneuvers needed to achieve retrograde inclination from typical launch trajectories. Such depictions prioritize dramatic tension over physics, contrasting with real insertions that demand precise low-thrust transfers over days or weeks.^[58] Media like KSP has positively influenced public understanding of advanced orbits, serving as an educational tool that builds intuition for concepts like orbital stability and retrograde motion through interactive trial-and-error gameplay. Studies confirm KSP effectively trains users in orbital mechanics, with players gaining practical knowledge comparable to introductory aerospace curricula, though it emphasizes conceptual grasp over precise numerical modeling. Astronauts, including Scott Kelly, have used the game to illustrate these principles, enhancing its role in demystifying DRO-like trajectories for broader audiences.^[59]^[60]

Notable fictional uses

In video games emphasizing realistic orbital mechanics, distant retrograde orbits (DROs) have gained prominence as a stable configuration for lunar missions. Kerbal Space Program (KSP), developed by Squad and released in 2015, allows players to simulate DROs around the Mun (the game's Earth-Moon analog), where the orbit's inherent stability enables long-duration stays without frequent corrections, mirroring real-world applications like asteroid capture.^[61] Players often employ DROs for strategic positioning in mission planning, such as establishing temporary bases or parking captured asteroids, which underscores the orbit's utility in narrative-driven exploration scenarios.^[57] In broader science fiction media, retrograde orbits—though not always explicitly termed DROs—appear for tactical advantages around moons.

References

[1]
Orion Will Go the Distance in Retrograde Orbit During Artemis I - NASA
Apr 18, 2022 · The orbit is “distant” in the sense that it's at a high altitude from the surface of the Moon, and it's “retrograde” because Orion will travel ...
[2]
Multi-orbit lunar GNSS constellation design with distant retrograde ...
Jun 22, 2023 · The DRO is a stable circular retrograde orbit, in which the satellites running around the L1 and L2 points in a direction opposite to that of ...
[3]
Analysis of a distant retrograde orbit in the Hill three-body problem
When the secondary body moves in a circular orbit whose center is the primary body, a distant retrograde orbit (DRO) exists on the plane of revolution of the ...
[4]
[PDF] low-thrust transfers from distant retrograde orbits to l2 halo
2.3. Distant retrograde orbits. DROs are a type of orbit that have received increased attention in the past few years because of the unique characteristics ...
[5]
[PDF] Transfer to Distant Retrograde Orbits via Rideshare to Sun-Earth L1 ...
Distant retrograde orbits (DRO), often classified as the f-family in the literature, are stable periodic orbits around the secondary body in the circular ...
[6]
Results of Long-Duration Simulation of Distant Retrograde Orbits
The term Distant Retrograde Orbit (DRO) was introduced by O'Campo and Rosborough [1] to describe a set of trajectories that appeared to orbit the Earth–Moon ...
[7]
[PDF] aas 14-467 various transfer options from earth into distant ...
Distant retrograde orbits are well-known trajectory types. 3,4,5,6,7 Such orbits have also been the focus of a number of investigations concerning transfers. ...
[8]
[PDF] Trajectory Design Considerations for Exploration Mission 1
In the two-body rotating frame, Distant Retrograde Orbits move in the retrograde direction around the secondary body, appearing as large quasi-elliptical orbits ...
[9]
Orbital Stability and Invariant Manifolds on Distant Retrograde Orbits ...
This section introduces the dynamical model used in this work, the numerical methods employed to compute the families of periodic solutions in the CR3BP, and ...
[10]
[PDF] Generalized Hill-Stability Criteria for Hierarchical Three-Body ... - arXiv
Dec 1, 2016 · Thus, the Coriolis force is a stabilizing force for retrograde orbits and destabilizing force for prograde orbits.
[11]
[PDF] 16 AAS/AIAA Space Flight Mechanics Meeting - Anil Hirani
Distant retrograde orbits (DROs) are a family of periodic orbit solutions of the equations of motion in the. Circular Restricted Three Body Problem (CR3BP).
[12]
Family of 2:1 resonant quasi-periodic distant retrograde orbits in ...
Sep 1, 2024 · This paper investigates the existence of quasi-periodic orbits near the 2:1 resonant DRO in the circular restricted three-body problem (CR3BP).
[13]
None
### Summary of Distant Retrograde Orbit (DRO) Information
[14]
[PDF] Options for Staging Orbits in Cis-Lunar Space
Oct 21, 2015 · The Distant Retrograde Orbit's (DRO's) are orbits that exist in the Circular Restricted Three Body Problem (CRTBP) that appear to orbit the ...
[15]
Transfer to long term distant retrograde orbits around the Moon
A distant retrograde orbit (DRO) is a stable orbit found in the circular restricted three-body problem (CR3BP). This kind of stable orbit was first found by ...
[16]
Transfer to Distant Retrograde Orbit Using Finite Time Lyapunov ...
Aug 5, 2025 · However, transfers designed by Vaquero, Folta, and Capdevila offer short durations, insertion maneuvers into DROs consistently exceed 300 m/s.
[17]
[PDF] 19670017192.pdf - NASA Technical Reports Server (NTRS)
A review of NASA sponsored research which was held on 5 January. 1967 at MIT is summarized in this report. A list of meeting attendees is included as Appendix A ...
[18]
[PDF] LOW-ENERGY LUNAR TRAJECTORY DESIGN - DESCANSO
Feb 16, 2013 · orbits, distant prograde orbits, distant retrograde orbits, symmetric resonant orbits, and a variety of other classes of symmetric periodic ...
[19]
[PDF] ALMOST RECTILINEAR HALO ORBITS - KC HOWELL* and JV ...
The values of at a re- crossing of the x-z plane are used to assist (see Breakwell and Brown,. 1979) the convergence toward an orbit with a second perpendicular ...Missing: vertical retrograde
[20]
[PDF] Potential Cislunar and Interplanetary Proving Ground Excursion ...
Currently, ARRM is targetting a. DRO (Distant Retrograde Orbit) about the moon for its final orbit. It is in this orbit that the asteroid is currently assumed.
[21]
A Chinese spacecraft is testing out a new orbit around the moon
### Summary of Chang'e 5 Orbiter's Distant Retrograde Orbit (DRO)
[22]
What is China Doing at the Lunar Distant Retrograde Orbit?
Jun 1, 2023 · China's Chang'e 5 (CE-5) orbiter, which as of January 2022 has likely moved to the lunar Distant Retrograde Orbit (DRO), is probably conducting enabling ...Missing: parameters insertion outcomes
[23]
Chang'e-5 (China's Lunar Sample Return Mission) / CE-5 - eoPortal
Nov 24, 2020 · ... Chang'e-5's travels through space and provide evidence for the new lunar orbit following months of observations. - A distant retrograde orbit ...Missing: parameters outcomes
[24]
What is China doing at the lunar distant retrograde orbit?
Apr 11, 2022 · China's Chang'e 5 (CE-5) orbiter, which as of January 2022 has likely moved to the lunar distant retrograde orbit (DRO), is probably conducting ...Missing: parameters insertion outcomes
[25]
Artemis 1 in flight: What's next for the epic NASA moon mission?
Nov 16, 2022 · 25) to insert the spacecraft into a distant retrograde orbit (DRO), where it will spend a week at an altitude of about 38,000 miles (61,000 km) ...
[26]
Chang'e-5: China's Moon sample return mission
China's Chang'e-5 spacecraft returned Moon samples to Earth in 2020. The samples are a relatively young 2 billion years old. They will help scientists ...Missing: semi- axis insertion
[27]
Orion enters lunar distant retrograde orbit - SpaceNews
Nov 25, 2022 · The maneuver changed the velocity of the spacecraft by about 110 meters per second, placing the spacecraft into a distant retrograde orbit (DRO) ...
[28]
Orion capsule enters distant retrograde orbit, breaks Apollo distance ...
Nov 26, 2022 · In the DRO, the Orion spacecraft will have an average distance of about 43,000 miles (70,000 kilometers) from the moon.
[29]
Artemis I Press Kit - NASA
Over the course of the mission, it will travel 280,000 miles (450,000 kilometers) from Earth and 40,000 miles (64,000 kilometers) beyond the far side of the ...
[30]
Artemis-I (Exploration Mission-1) - eoPortal
Orion will fly about 62 miles (100 km) above the surface of the Moon, and then use the Moon's gravitational force to propel Orion into a new deep retrograde, or ...
[31]
Celebrating the Past: Artemis I and Orion, One Year Later
Nov 16, 2023 · Orion was the first human spacecraft to enter a Distant Retrograde Orbit (DRO), a highly stable orbit around the Moon where little fuel is ...Missing: details parameters
[32]
Artemis I Radiation Measurements Validate Orion Safety for Astronauts
Oct 9, 2024 · Researchers found that Orion's design can protect its crew from potentially hazardous radiation levels during lunar missions.Missing: DRO outcomes navigation
[33]
[PDF] AAS 23-363 TRAJECTORY OPERATIONS OF THE ARTEMIS I ...
Nov 28, 2022 · A Distant Ret- rograde Orbit (DRO), chosen as the Artemis I ... semi-major axis of 384,400 kilometers. Burn plans in the EMRP frame ...
[34]
Retrograde co-orbital orbits in the Earth–Moon system - ResearchGate
Aug 7, 2025 · This paper explores a stability region near the 1:1 retrograde resonance with the Moon in the planar bicircular restricted four-body problem ...
[35]
Distribution of dust ejected from the lunar surface into the Earth ...
In this work, we focus on the dynamics and distribution of particles ejected from the surface of the Moon that escape the Moon's gravity.
[36]
[PDF] Distribution of dust ejected from the lunar surface into the Earth ...
Apr 3, 2022 · About 3.6 × 10−3 kg/s (∼ 2%) particles ejected from the lunar surface escape the gravity of the Moon, and they form an asymmetric torus between ...
[37]
NASA Shares Progress Toward Early Artemis Moon Missions with ...
Jan 9, 2024 · Artemis IV, the first mission to the Gateway lunar space station, remains on track for 2028. “We are returning to the Moon in a way we never ...
[38]
Gateway Space Station - NASA
On-orbit assembly of the fully realized Gateway space station will commence with the Artemis IV mission that will launch no earlier than September 2028. Artemis ...
[39]
Robust Intelligent Guidance Method for Distant Retrograde Orbit ...
Oct 1, 2025 · Earth–moon distant retrograde orbits (DROs) periodically circle around the moon with high stability, suitable for the deployment of a ...
[40]
Coverage Analysis of Lunar Communication/Navigation ...
Mar 24, 2020 · It is found that three satellites equally phased on a DRO can continuously cover 99·8% of the lunar surface. An obvious fact from Figure 13 ...
[41]
[PDF] A COMMUNICATIONS PLATFORM FOR LUNAR EXPLORATION
lunar Distance Retrograde Orbit (DRO). ... Gateway supports relaying multiple real-time HD video channels from. Lunar Systems to Earth using the Lunar System- ...
[42]
Active solar eclipse avoidance on the distant retrograde orbit of the ...
Feb 1, 2025 · This study proposes a solar eclipse avoidance strategy for DRO missions. First, the lighting condition on a stable nominal DRO is analyzed.
[43]
[PDF] Asteroid Redirect Mission Reference Concept Description - NASA
An additional ~60 m/s is provided by the SEP system to transfer the asteroid to the long-term-stable, lunar distant retrograde storage orbit. The asteroid size.
[44]
Asteroid Redirect Mission - Wikipedia
The Asteroid Redirect Mission (ARM), also known as the Asteroid ... Lunar Distant Retrograde Orbit (DRO) encompassing Earth-Moon L1 and L2, is ...Objectives · Spacecraft overview · Proposed timeline · Target asteroid
[45]
Artemis I mission overview – Orion blog
Aug 27, 2022 · This so-called distant retrograde orbit insertion requires only 149 m/s of delta-v using the gravity of the Moon to position Orion on an oval- ...
[46]
(PDF) Exploration of distant retrograde orbits around Europa
... inclination of 180° and a thrust acceleration of < 0.5 mm/s2. The result of ... 180 deg inclination) it becomes necessary to perform maneuvers to ...
[47]
ESA - Juice - European Space Agency
ESA's Jupiter Icy Moons Explorer, Juice, will make detailed observations of the giant gas planet and its three large ocean-bearing moons.Missing: DRO | Show results with:DRO
[48]
[PDF] Solar System Exploration Augmented by Lunar and Outer Planet ...
The outer planets offer enormous amounts of energetic gases such as H2, 3He, CH4, and ammonia. By using these in-situ resources, robotic precursor missions can ...Missing: advantages DRO
[49]
Strategies to capture asteroids to distant retrograde orbits in the Sun ...
... m/s have been defined as Easily Retrievable Objects (EROs) [30]. Following ... Among these periodic orbits, distant retrograde orbit (DRO) may provide ...<|control11|><|separator|>
[50]
Leveraging Resonant-Orbit Manifolds to Design Transfers Between ...
Feb 10, 2014 · All members in the 4∶3 resonant family in the EM system are unstable; in contrast, most of the 4∶3 resonant orbits in the. Saturn–Titan family ...
[51]
Stability analysis of first order resonant periodic orbit - ScienceDirect
Nov 15, 2022 · First–order resonant periodic orbits for the Saturn–Titan system are presented by Patel et al. (2021). In this work, the oblateness of Saturn is ...
[52]
orbital mechanics - How realistic is Kerbal Space Program?
May 9, 2014 · The orbit simulation is quite accurate, including how to change inclination, raise/lower orbits, leave a planet, and approach a new planet. · The ...
[53]
TIL: Distant Retrograde Orbit. But, does it apply in KSP? - Reddit
Nov 21, 2014 · DRO is not applicable in KSP because a long term stable orbit is not a problem you have in KSP. Unstable orbits are a result from n-body physics which KSP does ...
[54]
Are retrograde orbits bad in real life too? - Science & Spaceflight
Oct 15, 2018 · Hi!! I know in ksp orbiting retrograde from Kerbin requires more fuel due to something gravity related. What exactly is this, and does it exist ...Retrograde or Prograde Orbit? - Kerbal Space Program ForumsRetrograde orbit (from east to west) is it a thing?More results from forum.kerbalspaceprogram.comMissing: accuracy | Show results with:accuracy
[55]
[PDF] Effective Orbital Mechanics Knowledge Training Using Game ...
For this purpose, this paper examines the learning outcome of playing the computer game Kerbal Space Program (KSP). [18]. The game indicates a strong potential ...
[56]
Video: Astronaut Scott Kelly teaches orbital mechanics with Kerbal ...
Dec 28, 2018 · Though silly and fun, KSP also works as a reasonably solid and wonderfully interactive demonstration of the vagaries of orbital mechanics—and ...
[57]
Capture Asteroid in Distant Retrograde Orbit Around Moon
Apr 9, 2014 · Kerbal Space Program 1 · KSP1 Gameplay and Technical Support · KSP1 ... Capture Asteroid in Distant Retrograde Orbit Around Moon. Share.Lagrange points, Rectilinear Halos, & the Retrograde Square Moon ...Artemis: To the Moon and beyond! - Kerbal Space Program ForumsMore results from forum.kerbalspaceprogram.com
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Is This New Rocket Simulator Worth Buying? Juno New Origins V1.0!
Jan 30, 2023 · Comments ; What Is Distant Retrograde Orbit, And Why Is Artemis 1 Using It? Scott Manley · 253K views ; Apollo 11 REMAKE | Juno: New Origins - ...<|control11|><|separator|>
[59]
Triton | The Expanse Wiki - Fandom
It orbits Neptune in a retrograde orbit ... Take your favorite fandoms with you and never miss a beat. Fandom App logo. Store icon. The Expanse Wiki is a Fandom ...