PredGuid entry guidance for orion return from low earth orbit

When returning from low Earth orbit, Orion will perform a lifting atmospheric entry with precision landing using the PredGuid entry guidance algorithm.¹² The PredGuid algorithm is designed to guide Orion to the desired landing site while accounting for vehicle and environment uncertainties and day of flight dispersions during atmospheric entry. The low Earth orbit mode of the PredGuid entry guidance algorithm consists of three phases: the Initial Roll Phase which maintains proper entry attitude and steers the vehicle to proper transition conditions for the Final Phase; the Final Phase, a terminal point guidance algorithm that uses a stored reference trajectory to steer out range error and achieve precision landing; and the Terminal Phase, which seeks to null the remaining crossrange error through a simple proportional steering law. Simulation results indicate that the PredGuid algorithm provides precision landing capability to Orion as well as significant robustness to day-of-flight uncertainties and dispersions.