Quasi-Satellite Orbit (QSO)
Author: Tianjiang Shuo
Website: https://cislunarspace.cn
Definition
A quasi-satellite orbit is a family of periodic orbits around the secondary primary in the restricted three-body problem, discovered by Hénon in 1969 (in his study of periodic orbits in Hill's case). Its hallmarks are linear stability (stability index |ν|≤1, holding over the entire altitude range) and very close proximity to the secondary (candidate orbits reach periapsis distances as low as tens of kilometers) (Fu 2024).
Relation to the DRO
The QSO and the Earth–Moon distant retrograde orbit (DRO) belong to the same Hénon 1969 periodic-orbit family: the small-body exploration community (mission concepts such as MMX at Phobos, DePhine at Deimos, JIMO at the Jovian moons) calls it QSO, while the cislunar community calls it DRO (the QSO provenance cited by Fu 2024 and the DRO provenance cited by He 2026 both point to Hénon 1969). See Distant Retrograde Orbit (DRO) and Moon-Centered Orbit.
Mission Applications and Station-Keeping
QSOs are listed as candidate science orbits by several small-body close-proximity missions: ESA's DePhine (Deimos) and NASA's JIMO (Jovian moons); JAXA's MMX mission examined five QSOs at low altitude around Phobos as working orbits for the proximity phase (Fu 2024). Taking the MMX baseline QSO as an example, the high-order target phase approach (TPhA) station-keeping method costs about 1 m/s per month in a high-fidelity model (Fu 2024).
Related Concepts
References
- Hénon, 1969, Numerical exploration of the restricted problem. V. Hill's case
- Fu et al., 2024, A high-order target phase approach for the station-keeping of periodic orbits
- He et al., 2026, A review of cislunar constellation design and optimization