Design of a Novel Discrete Command Generation and Distribution Scheme for Spacecrafts

Spacecraft telecommand system plays a critical role in receiving commands from ground station and distributing them to various subsystems. Command Execution Units (CEUs) and Command Distribution Units (CDUs) are the critical building blocks of a spacecraft telecommand system that perform the major functions of generation and distribution of discrete commands (pulse, level and serial data). The number of discrete commands required to support operation of subsystems varies from spacecraft to spacecraft and hence has impact on the design of hardware modules used in the telecommand system. In this article, a novel scheme for generation and distribution of discrete commands is presented that provides the feature of reprogramming the command outputs for supporting different types of discrete commands. This feature helps in minimizing the types of Very Large Scale Integration (VLSI) devices and number of hardware modules used in generation and distribution of discrete commands. It also supports the development of reusable hardware designs for use across different spacecraft missions and aids in reducing the turn around time for realization of mission specific telecommand hardware. At the core of the scheme is the design of a VLSI device with reconfigurable outputs that support the four basic discrete command interfaces - pulse, level, serial data and switch matrix. Suitable mitigation techniques have been incorporated in the design for overcoming single event upsets caused due to space radiation. This design has been realized as an Application Specific Integrated Circuit (ASIC) and planned to be used in the development of reconfigurable hardware module for CDU.