Software for Sequencing Spacecraft Actions

SEQ_GEN is a component of the Sequence Subsystem computer program, which assists in generating a sequence of commands to be executed by a control computer aboard a spacecraft to perform scientific observations and supporting engineering actions in response to requests by numerous users. SEQ_GEN assists a designer in devising a final, valid sequence. Using SEQ_GEN, the designer prepares a file of requested spacecraft actions. SEQ_GEN then processes this file plus a file of spacecraft- and mission-specific information prepared by another Sequence Subsystem software component to (1) generate the sequence of commands, (2) predict what the commands will cause to happen on the spacecraft, and (3) give warnings when the sequence violates rules or causes misuse of spacecraft systems. SEQ_GEN generates an interactive graphical time-line display of the predictions and warnings. The user can change the sequence by keyboard entry in a text file, or by use of a mouse to add or delete an item or move an item to a new position on the display. SEQ_GEN then processes the revised input data, starting from a time earlier than the earliest time affected by the change(s). The process is repeated, if necessary, until a valid sequence is produced.