The purpose of a telemetry system is to reliably and transparently convey measurement information from a remotely located data-generating source to users located in space or on Earth. Typically, data generators are scientific sensors, science housekeeping sensors, engineering sensors, and other subsystems aboard a spacecraft.
In the past, most of the telemetry resources used by a science mission have been wholly contained within a project office and are completely dedicated to that mission. The lack of effective standardization among various missions forces the multimission tracking network to implement the lowest level of telemetry transport service, i.e., bit transport. Higher-level data delivery services, oriented more toward computer-to-computer transfers and typical of modern commercial and military networks, had to be custom designed and implemented on a mission-to-mission basis.
The CCSDS telemetry system is recommended to ease the transition toward greater automation within individual space agencies and to ensure harmony among the agencies, thereby resulting in greater cross-support opportunities and services. The layering technique is introduced to the CCSDS telemetry system to allow the telemetering of spacecraft data to the users to be decomposed into sets of peer functions residing in common architectural strata. There are three layers in the CCSDS telemetry system:
1. Packetization layer,
2. Transfer frame layer, and
3. Channel coding layer.
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