The physics and engineering of moving a spacecraft from one orbit to another and keeping it there: orbital mechanics itself along with the specific maneuvers, quantities and hazards spacecraft designers and mission planners work with, including delta-v, escape velocity, geostationary orbit, gravity assist, the Hohmann transfer orbit, orbital eccentricity and inclination, the Roche limit, sphere of influence, the Tsiolkovsky rocket equation, aerobraking and the orbital-debris hazard of Kessler syndrome. Belongs here: a concept describing how spacecraft move through space or the practical engineering constraints of doing so. Does not belong here: a concept about the universe's large-scale structure or origin, grouped under Cosmology and the Early Universe, or a concept about the search for life, grouped under Astrobiology and the Search for Life.