Author: CislunarSpace
Website: https://cislunarspace.cn
Cislunar spacecraft orbits (hub)
Spacecraft in cislunar space are poorly approximated by a single Keplerian center: Earth–Moon (and often solar) gravity couples into restricted multi-body dynamics. Orbit families multiply, and operations must respect longer light times, tracking geometry, and often maneuver-heavy maintenance or transfers. This hub establishes shared vocabulary before you dive into papers and tools.
How it differs from LEO
- Gravity model: From two-body intuition to Earth–Moon (and sometimes Sun-dominated) models; libration points and periodic/quasi-periodic orbits become central.
- Tracking & time: Large ranges make delay and pass scheduling part of the design.
- Stability & maneuvering: Some classes are sensitive to state errors or require station-keeping; trades involve time, fuel, and launch windows.
Common mission orbit classes (conceptual)
| Class | What it is (intro) | Where to read more |
|---|---|---|
| Earth–Moon transfer | From LEO or staging to lunar sphere of influence | Mission reports on TLI, mid-course correction |
| Lunar orbits | Circular/elliptical/polar classes for remote sensing, landing prep | Lunar gravity field, frozen orbits |
| Libration-point & halo families | Periodic/quasi-periodic motion near Earth–Moon libration points | See glossary; NRHO/DRO entries mirror the Chinese section over time |
| DRO | Distant retrograde class in the Earth–Moon rotating frame | Same as above |
Detailed design needs ephemerides, force models, and program constraints. See resources & tools for datasets and libraries, and the orbit simulation lab for interactive experiments.
Deep Dives: Three Key Topics
NRHO (Near-Rectilinear Halo Orbit)
NRHO (Near-Rectilinear Halo Orbit) is a class of periodic orbits near the Earth-Moon libration points, named for their elongated "near-linear" appearance in the rotating frame. These orbits offer favorable communication visibility to the lunar south pole and require relatively low delta-v to reach the lunar surface, making them the preferred operational orbit for NASA's Lunar Gateway station in the Artemis program. NRHOs are solutions to the restricted three-body problem—they are not asymptotically stable and require periodic station-keeping—but their dynamical properties have been validated by numerous missions and remain a hot research topic in cislunar operations.
DRO (Distant Retrograde Orbit)
DRO (Distant Retrograde Orbit) refers to quasi-periodic orbits that are retrograde in the rotating frame and located at considerable distances from the Earth-Moon barycenter. Compared to NRHOs, DROs are farther from the Moon, demand less station-keeping, and serve well as long-duration parking orbits or deep-space mission outposts. Their forgiving dynamical structure makes DROs attractive for demonstrating multi-body transfer concepts and for studying chaos and orbital stability in cislunar space.
Earth-Moon Transfer Orbits
Earth-Moon transfer orbits bridge the gap between low-Earth parking orbits and lunar orbit or the Moon's sphere of influence. Common transfer strategies include Hohmann transfers, low-energy transfers (Lunar Transfer Orbit, LTO), and the increasingly studied multi-body gravity-assist transfers. Each approach trades off propellant, transfer time, and launch window flexibility—fast transfers consume more fuel, while low-energy transfers can take months but require much less delta-v. Mission planners weigh these factors against schedule, launch vehicle capacity, and tracking coverage to select the best fit.
Suggested reading order
- What is cislunar space and the environment page.
- Glossary for abbreviations (e.g. CR3BP).
- Research frontiers for active topics and references.
Deep-dive articles and worked examples are expanding—contributions via the repository are welcome.
Simulation Lab
Explore the dynamical characteristics of various orbit classes interactively in the Satellite Orbit Simulation Lab.