Dapproche

Dapproche, typically written in French as distance d’approche or simply d’approche, is a term used in astronomy and spaceflight to describe the distance between two moving bodies at their closest approach during an orbital encounter. The concept is most often applied to the minimum separation between a spacecraft and a planet or moon, or between two celestial objects such as a near-Earth asteroid and Earth.

In practice, d’approche refers to the closest distance reached during a defined time window as the bodies follow their gravitational trajectories. It is a key quantity for assessing encounter geometry, collision risk, and communication or navigation considerations for missions. Distances are derived from orbital elements and refined ephemerides, sometimes expressed as a radial distance (kilometers or astronomical units) or as a line-of-sight separation depending on the context.

The term is primarily used in French-language technical literature. In English, the equivalent expression is usually “distance of closest approach” or “closest-approach distance.” While d’approche is informative within its linguistic context, there is no single universal standard spelling in non-Francophone sources, and care should be taken to translate or interpret it according to the surrounding scientific framework.

See also: close approach, orbital mechanics, ephemeris, collision risk assessment.