Mars Science Laboratory Entry, Descent, and Landing Triggers

In 2010, plans call for the Mars Science Laboratory (MSL) mission to pioneer the next generation of robotic entry, descent, and landing (EDL) systems by delivering the largest and most capable rover to date to the surface of Mars. Improved altitude performance, coupled with latitude limits as large as 45 degrees off the equator and a precise delivery to within 10 km of a surface target, will allow the science community to select the MSL landing site from thousands of scientifically interesting and previously inaccessible locations. Realizing these impressive performance metrics requires proper execution of a complex sequence of time-critical flight system reconfiguration events. This sequence, which begins approximately 15 minutes prior to touchdown, includes cruise stage separation, cruise balance mass jettison, entry balance mass jettison, parachute deployment, heatshield separation, backshell separation, rover separation, and flyaway start. Each of these events must occur within a narrow operational envelope and must be triggered autonomously based on estimates of the spacecraft state. Triggers are either 'timed', whereby the spacecraft state estimate is reliant upon pre-flight predictions, or 'sensed', whereby the spacecraft state estimates are constructed in real-time using data from the on-board sensor suite. Regardless of method, all triggers must execute properly in the presence of potentially significant variability in Martian winds, atmospheric properties, and surface topography. Careful budgeting is necessary to manage uncertainties and impacts on EDL performance. This paper discusses the design of trigger algorithms that control event execution during the EDL sequence and highlights some of the related challenges faced by the MSL design team.