T-time, on the other hand, can be stopped and started.ĭuring a launch, t-time will be used for specific tasks that need to be completed before the rest of the launch can proceed, whereas l-time is used as a countdown to the end of the overall mission. L-time consists of actual time that has elapsed, meaning that it is a continuous countdown that cannot be modified. When conducting space launches, the United States National Aeronautics and Space Administration (NASA) uses what are called l-time and t-time.
