Astrionics is the science and technology of the development and application of electronic systems, sub-systems, and components used in spacecraft. The electronic systems on board a spacecraft include attitude determination and control, communications, command and telemetry, and computer systems. Sensors refers to the electronic components on board a spacecraft. For engineers one of the most important considerations that must be made in the design process is the environment in which the spacecraft systems and components must operate and endure. The challenges of designing systems and components for the space environment include more than the fact that space is a vacuum.