Orbital mechanics dictate precisely when a spacecraft can depart Earth to intercept a moving target like a planet or space station. If a rocket lifts off before or after this strictly calculated timeframe, it will lack the fuel required to correct its trajectory. Interplanetary missions often have periods lasting just a few weeks, while trips to the International Space Station might have an instantaneous opening of a single second.
We lost the launch window due to high upper level winds, so we've to scrub and try again on Tuesday.
A missed opening for a deep space mission can mean waiting months or years for planetary alignments to reset.
Related terms
Transfer window
A specific timeframe when a spacecraft can depart one body to intercept another using minimal fuel.
T-minus
A countdown protocol indicating the time remaining before a scheduled launch or major sequence.
Countdown
A strict backward schedule of tasks leading up to the launch of a rocket or spacecraft.