launchwindow

A launch window is the period of time during which a launch must occur to achieve a mission’s objectives. It results from the geometry of orbital or interplanetary trajectories, the performance and limitations of the launch vehicle, and safety and operational constraints. If a launch misses the window, the mission may require significant delay or a different trajectory.

Key factors defining a launch window include the target orbit’s inclination, altitude, and phase, the launch site's geographic position, and the required alignment with celestial bodies or rendezvous targets. For missions to low Earth orbit, the window is often determined by the need to reach a specific orbital plane and to pass through a favorable launch azimuth relative to the ground track. For interplanetary missions, windows depend on the relative positions of the planets and the possibility of a feasible transfer orbit, such as a Hohmann transfer, which occurs at discrete synodic intervals.

Windows can vary in length from instantaneous (a very narrow, momentary alignment) to several hours or days, depending on mission constraints. They are usually planned with trajectory analyses and are published by space agencies or mission teams. Actual launches may be canceled or postponed due to weather, range safety restrictions, or air traffic control issues, even if a nominal window exists.

In practice, launch windows drive mission design, scheduling, and ground operations, ensuring that the vehicle can reach the intended trajectory while meeting safety and mission success criteria.