Alpha-Beta Steering for Mars Entries

All guided entries of blunt-body entry vehicles have utilized bank-angle steering for hypersonic trajectory control. While bank-angle steering has been successful on Mars entry missions so far, such as the Mars Science Laboratory [1] and Mars 2020 missions [2], control over the longitudinal and lateral motion are highly coupled for this steering option. An alternative hypersonic steering scheme involves modulating the vehicle's angle of attack (𝛼) and sideslip angle (𝛽) to steer the vehicle, i.e. 𝛼-𝛽 steering. Also called direct force
control (DFC), 𝛼-𝛽 steering has been recently studied in the literature for both entry and aerocapture missions at several planetary bodies, including Mars [3], Venus [4], Titan [5], and the ice giants [6]. 𝛼-𝛽 steering provides more decoupled control over the trajectory than bank-angle steering by primarily using 𝛼 to control the longitudinal motion 𝛽 to control the lateral motion [6]. Studies have shown that 𝛼-𝛽steering may provide increased robustness to atmospheric dispersions [7], higher precision in landed accuracy, a lower propellant usage for powered descent, and a larger payload mass, relative to bank-angle steering [3], but the magnitude of flight performance differences are not fully explored. This study further investigates 𝛼-𝛽 steering and flapbased implementations [8] and compares performance to bank-angle steering.