On-Board Program-Timing Apparatus

an electronic device mounted on board a spacecraft that provides the distribution of commands for the control of on-board systems at prescribed moments. The program of command distribution (the sequence of commands and time intervals between them) can be specified beforehand (for example, during flight training) or in flight (by a command radio link from earth); in the latter case apparatus for storage of the input program is necessary. An on-board program-timing apparatus permits control of the spacecraft in the absence of radio visibility and in the intervals between periods of radio communication with earth. The on-board program-timing apparatus is a complex electronic system, usually with semiconductor elements.