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. The Spacecraft Event Time of a singular event on the spacecraft can also be defined as equal to the ERT (Earth-Received Time) minus the OWLT (One-Way Light Time), or as TRM (transmission time) plus OWLT.

Spacecraft Event Time in UTC is also known as Orbiter UTC, and Earth-received time as Ground UTC.

References

• Basics of Space Flight Glossary, JPL/NASA