93:, the usual operation of a spacecraft is controlled with an uploaded command script containing SCET markers to ensure a certain timeline of events. Because of the delay between the sending of instructions from Earth and their receipt and execution by the spacecraft, real-time commanding of robotic spacecraft is done rarely: usually only in response to an emergency event, when changes in spacecraft operations must be made as soon as possible. For example, a spacecraft could be instructed to go into
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be defined as equal to the ERT (Earth-Received Time) minus the OWLT (One-Way Light Time). For events transmitted from Earth to the spacecraft, the calculation is TRM (transmission time) plus OWLT. For example, if a signal were received on Earth at exactly 11:00 UTC from a spacecraft showing that it had just completed a maneuvering thrust, but the spacecraft was four light-hours away from Earth (the distance of the
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a delay between when instructions are sent from Earth and when the spacecraft receives the instructions. The length of delay is related to the distance between the sending and receiving points. Failure to take this delay into account could result in inaccurate data or mistakes in spacecraft control.
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Since signals between the spacecraft and Earth are limited to the speed of light, there is a delay between the time an event happens on the spacecraft (such as the transmission of data taken from an instrument reading) and the time that a signal reporting the event reaches Earth. Similarly, there is
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Determining the
Spacecraft Event Time involves taking the time at Earth and adding or subtracting the signal travel time, depending on whether the signal is being sent to or received from the spacecraft. For events transmitted from the spacecraft to Earth, the SCET of an event on the spacecraft can
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Spacecraft event times stored in relation to instrument data from spacecraft events (e.g. images) are generally presented in
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Since it takes time for a radio transmission to reach a spacecraft from
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However, the trailing Z (which indicates that the time is given in
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Spacecraft-local time for events that happen at the spacecraft
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127:CCYY-MM-DDTHH:MM:SS.sssZ (preferred format)
198:Basics of Space Flight Glossary, JPL/NASA
157:Basics of Space Flight Glossary; JPL/NASA
59:spacecraft at one point as it approaches
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123:using one of the following formats:
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168:"Synonyms for Transmission Time"
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203:Data Standards, PDS/NASA
184:Data Standards, PDS/NASA
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41:SCET versus Earth time
67:Spacecraft Event Time
31:Spacecraft Event Time
234:Spaceflight concepts
218:Space flight portal
109:Presentation format
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239:Time scales
75:Orbiter UTC
228:Categories
192:References
79:Ground UTC
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121:ISO 8601
115:ISO 8601
145:Notes
91:Earth
61:Pluto
35:SCET
136:UTC
103:Sun
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69:in
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