Atmospheric Impacts on Approach Operations and EDL Targeting for the InSight Mission

Early in operational testing for the InSight mission to Mars, it was discovered that the final maneuver to target the entry-interface point was unexpectedly sensitive to planned atmosphere updates that would be based on real-time measurements of the Martian atmosphere by Mars Reconnaissance Orbiter. Upon investigation, the team realized the Phoenix mission also discovered this sensitivity during operational testing. Further investigation identified that the sensitivity was a result of the fact that both the entry flight path angle and ground target were being held fixed in the maneuver design process, constraining the maneuver in a way that forced the entry time to change to compensate for changes to the nominal trajectory from updating the atmosphere model. The final maneuver was planned for 22 hours prior to entry, at which point it is very expensive to change entry time. The study also revealed that any unguided Mars entry, descent, and landing mission would be impacted by this sensitivity if it used real-time atmosphere observations to model the nominal expected atmosphere used for maneuver targeting of the entry-interface point. This paper discusses the results of that investigation and presents a number of mitigations as well as the consequences of ignoring the sensitivity.