14:00Target time
14:15Window closes
14:30
Illustrative UTC times. The target sits inside the permitted interval. An instantaneous window has a single opportunity.
The target is a moment; the window is an interval
A target time is the planned launch moment. A launch window is the interval in which the mission can depart under its trajectory constraints. Some missions have an instantaneous window: one scheduled opportunity rather than a broad interval.
Why the opportunity moves
Earth rotates and the destination moves. The launch must put the spacecraft on a useful path at the right time. Missing a window can require a later opportunity rather than a short countdown reset.
Read the precision before the clock
A month-only target is not a promise to fly at midnight on its last day. Spacian keeps uncertain dates out of precise countdowns. “Time pending” and “Date to be confirmed” are information, not missing countdown features.
Check your timezone
Spacian can display exact targets in your browser’s timezone or UTC. Near midnight, the same launch can fall on different calendar dates. The mission link stays the same when its target changes; refresh the details before making plans.
Sources & further reading
NASA · Launch windows ↗NASA · Basics of Space Flight: Launch ↗Explanations are reviewed separately from the live mission schedule. Follow the linked provider for current mission-specific information.