Spacecraft Event Time
Spacecraft Event Time (SCET) is the time an event occurs at a spacecraft. Since it takes time for a radio transmission to reach the spacecraft from the Earth, the usual operation of a spacecraft is done via an uploaded commanding script containing SCET markers to ensure a certain timeline of events. Real-time commanding of spacecraft is done rather rarely, mostly in case of time constraints during an emergency event like going into safe mode for an Earth-pointed CME of the Sun. [why?]
The Spacecraft Event Time of a singular event on the spacecraft can be defined as equal to the ERT (Earth-Received Time) minus the OWLT (One-Way Light Time), or for sent-from-Earth events as TRM (transmission time) plus OWLT.
Spacecraft Event Time in UTC is also known as Orbiter UTC, and Earth-received time as Ground UTC.
- Basics of Space Flight Glossary; JPL/NASA
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