Challenges and Solutions for Early Morning Terrain Relative Navigation on Mars

Launching the Mars Sample Return Lander (SRL) in 2031 or 2033 would necessitate a landing in the early morning. This is outside the operational envelope of the successful Mars 2020 Terrain Relative Navigation that would be required by SRL for accurate landing at pre-determined safe zones. This paper first uses terrestrial field test and orbital Mars imagery to quantify the sensitivity of landmark matching to sun illumination differences between the reference map and descent images. It then proposes two novel methods for predicting the appearance of an early morning reference map from the available afternoon orbital imagery. The predicted reference maps boost the number of correct landmark matches by a factor of four to show that early morning landing is feasible for SRL without dramatic changes to the on-board algorithms.