January 1987 figure 2 4 telecommand data structures

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Unformatted text preview: and Data Structures CB#1 CB#2 ST SEQ CLTU 2 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE Issue 6 TC PACKET CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE 2 . 2 . 3 COMMUNICATIONS SECURITY/DATA PROTECTION CONCEPT For many missions there is a requirement to prevent any intentional or accidental attempts to manipulate or control the spacecraft by an unauthorized party, including efforts to deny access to authorized users. Some missions may also have requirements to render the contents of telecommand messages unintelligible to unauthorized users. The CCSDS has developed a telecommand data protection concept, which is described in Annex C of this report, that permits authentication and encryption measures to be implemented when required by a particular mission. 2 . 2 . 4 TELECOMMAND SYSTEM PERFORMANCE Performance considerations associated with the CCSDS TC System are discussed in Annex D of this report. Issue 6 Page 2-11 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE 3 TELECOMMAND SERVICES This section summarizes the services, functions, inputs, and outputs characterizing each layer of the Telecommand System. The component layers are discussed for both the sending end (where the user resides) and the receiving end (where the control actions are effected). 3 . 1 TC DATA MANAGEMENT SERVICE The Data Management Service, Reference [2], provides the primary user interface with the TC System. This service enables user requests for command activity to be generated, integrated, aggregated, translated, and scheduled for delivery to a spacecraft. 3 . 1 . 1 TC APPLICATION PROCESS LAYER The basic service of the Application Process layer is to provide users with a method by which they can formulate instructions to control a remote device in space, and to interface those instructions with the systems which provide the physical delivery of telecommands. Figure 3-1 depicts the activities and interfaces of the Application Process layer. Inputs to the sending end of the layer take the form of user requests for specific command actions, plus associated requests concerning any desired overall delivery and execution conditions. The user command requests are translated into corresponding machine interpretable "command directives" which are passed to the layer below, along with control instructions to lower layers that specify the overall configuration of the TC System required for their delivery. Control instructions are also sent ACROSS the layer (to the peer application process in space) to define the overall conditions which must exist within that process at the time of execution of the command directives. At the receiving end of the Application Process layer, named sets of command directives, and their associated delivery status information, are received from the System Management layer. The receiving application process executes the command directives when specified operational conditions are satisfied: the resulting executed command actions cause changes in the state of spacecraft instruments or subsystems, which may be observed and confirmed by the user via telemetered measurements. Issue 6 Page 3-1 January 1987 CCSDS REPORT...
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This document was uploaded on 03/06/2014.

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