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Telecommand Decoder Shell

The Telecommand Decoder Shell package is a commercial off-the-shelf software component which implements the space based parts of a telecommand system, including the TC Space Data Link Protocol, the Communications Operation Procedure (COP-1) and the channel coding (BCH code).

It is highly portable so that it is easy to use for building into different software systems, such as spacecraft simulators and on-board telecommand decoders.  It is also ideal for building demonstration systems.  To demonstrate ground system telecommand elements to users or customers, there is no need for spacecraft hardware: the Shell can be used to build a software-based simulation of the spacecraft behaviour.

The Shell has an API (Application Programming Interface) which provides access to the telecommand facilities. The API uses calls in ANSI-C.

TC Decoder Shell on-board application

The Telecommand Decoder Shell accepts the incoming telecommand data. The data can be supplied as Communications Link Transmission Units (CLTUs) each containing a telecommand transfer frame, or as the candidate BCH codeblocks of a CLTU. The Shell delivers packets and the other SDUs (service data units) defined for the TC Space Data Link Protocol. It also delivers Communications Link Control Words (CLCWs) for the spacecraft telemetry.

The facilities and interfaces of the Telecommand Decoder Shell package are described further in the detailed description.

Security options for the Telecommand Decoder Shell

There are currently three versions of the Shell package:

The Shell can provide support for ESA Telecommand Authentication as an optional extra.  When this option is selected, the Shell provides the receiving-end processing for the ESA AU, including the validation of the authentication tail on telecommand segments.

The Shell can provide an interface for external implementation of security features such as authentication.  The Segment Level Security Interface (SLSI) is an optional extra.  When this option is selected, the Shell passes each segment to the interface for processing.

Addition of Space Data Link Security (SDLS):  The September 2015 issue of the TC Space Data Link Protocol standard (CCSDS 232.0-B-3) includes the specification of the interfaces between the TC protocol and the Space Data Link Security Protocol (SDLS). We are currently updating the Telecommand Decoder Shell to include optional interfaces to the SDLS protocol.

Optional feature: Failure simulation for test systems

The Telecommand Decoder Shell package has a unique feature: Built-In-Failures (BIFs).  The BIFs can be switched on and off for testing the response of the ground system to spacecraft exceptions.  This controlled generation of spacecraft errors is an advantage of our software-based telecommand decoder.  However, the capability could create a risk in operational applications, so the BIF interface is not in a standard release.  A modified release of the Telecommand Decoder Shell which includes the BIF interface is available on request.
 

Please contact us for further information on technical questions or licensing conditions for the Telecommand Decoder Shell package.


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