Nearorbital

Nearorbital is an informal or nonstandard term used to describe a trajectory, state, or object that lies very close to an orbital regime around a celestial body but does not form a stable, closed orbit.

Because orbital mechanics defines boundaries in terms of energy and angular momentum, a nearorbital path is typically understood as a route whose energy is near the threshold between bound and unbound motion, or whose geometry is near that of an ellipse but with perturbations that prevent completion of an orbit. Examples include highly eccentric orbits with perigee near the body's atmosphere, near-parabolic trajectories with eccentricities very close to 1, or temporary capture scenarios that do not last long enough to stabilise into a lasting orbit.

In spaceflight planning, nearorbital concepts may describe maneuvers or flight profiles that approach orbital conditions—such as low-perigee passes or gravity assists—that could lead to orbital insertion under different circumstances, but ultimately result in a suborbital or escape outcome due to constraints like delta-v or perturbations.

The term is not widely standardized in professional literature. When precision is important, authors typically specify the orbital elements (semi-major axis, eccentricity, perigee) or use established terms such as suborbital, quasi-orbital, or temporary capture.

Related topics include suborbital trajectories, orbital mechanics, trajectory design, temporary capture, and near-Earth objects.