ABSTRACT
Timing information may also appear in the system as an explicit datum that the system collects or displays. The payload data system may use timing information as a parameter in the telemetry data stream to time tag the data transmitted to the user. The user's data processing computers may archive the received data with a reception time stamp. Operator displays typically show the current time as local time or universal time, or perhaps, the elapsed time since the experiment began. This chapter first examines the definitions of time and how the different definitions are related. This includes discussions of absolute and relative time measurement. It investigates the ways in which timing information is encoded. Several standards have been set by the International Organization for Standardization (ISO), Inter-Range Instrumentation Group (IRIG), National Institute of Standards and Technology (NIST), and the Consultative Committee for Space Data Systems (CCSDS).
