Near-rectilinear halo orbit

An NRHO is a member of a family of periodic orbits associated with the gravitational dynamics of a two-body system, such as the Earth–Moon system. The path is highly elliptical in appearance and is called near-rectilinear because portions of the trajectory pass relatively close to the Moon while other portions extend much farther away. In the Earth–Moon case, the orbit is shaped by the combined gravitational influence of both bodies; it is not simply a Keplerian ellipse around the Moon. Specific NRHO trajectories and periods depend on the selected member of the orbit family.

NASA and its partners planned Gateway for a lunar NRHO. In NASA's published explanation, that choice was intended to combine relatively convenient access to the lunar surface with lower orbit-maintenance demands than a low lunar orbit, while keeping Earth in continuous view for communications. The orbit's distant arcs also expose spacecraft to the deep-space environment, useful for science and technology demonstrations. These are design trade-offs, not a claim that NRHO is best for every mission: closer lunar orbits can make surface transfers shorter, while more distant trajectories may offer different stability and access characteristics.

A spacecraft in an NRHO must navigate a dynamical environment influenced by the Earth and Moon, and operators must plan transfers, station keeping, communications and rendezvous around the orbit's changing distance and velocity. NASA's CAPSTONE mission was sent to test navigation and operational aspects of a lunar NRHO ahead of the planned Gateway. Its path demonstrated that a small spacecraft could operate in the selected orbit, while also providing experience relevant to future cislunar missions.

NRHO became widely known because it was selected for the planned Gateway lunar outpost, not because Gateway has already been assembled in lunar orbit. NASA and ESA pages describe the station as a multi-partner project, but ESA's current Gateway overview states that NASA paused Gateway in its previous form in 2026 while focusing on lunar-surface operations and that studies are examining how partner contributions might be repurposed. The orbit's scientific and engineering characteristics can be discussed separately from the changing status of the station project.