The period of time over which conditions are suitable for the launching of a SATELLITE or spacecraft into the desired ORBIT. Many different conditions determine the duration and frequency of such windows. For example, it may be possible to launch a spacecraft to MARS on any day out of a period of several weeks (provided the rocket vehicle has sufficient reserves of fuel), and this period would constitute the launch window; but this window would only recur at intervals of about 780 days. The long interval arises because suitable relative configurations of the Earth and a target PLANET arise at times separated by the SYNODIC PERIOD of that PLANET.
