Launch Window

A launch window is the period during which a rocket can depart its launch site and reach the desired orbit with acceptable propellant efficiency. The window is determined by the target orbit's geometry relative to the launch site. For ISS rendezvous missions, the launch site must rotate directly under the ISS orbital plane — creating an instantaneous (zero-duration) or very short window. For GEO missions, windows are typically 1–4 hours long. For interplanetary missions, windows depend on planetary alignment and may occur as rarely as once every 26 months (Mars) or 13 years (Jupiter gravity assist to outer planets).