AAE450 Spring 2009 Preliminary Lunar Descent Attitude Control Analysis Christine Troy Assistant Project Manager Webmaster Lunar Descent Attitude Control Analysis Christine Troy Attitude

AAE450 Spring 2009 Problem  Attitude control during descent burn –Thrust direction –Communication  Many sources of perturbation –Thrust not through CG –~7 Nm for 1 mm thrust offset  Need to know prop mass and volume Christine Troy Attitude Thrust CG

AAE450 Spring 2009 Prop Mass Estimate  Subject to a constant Torque –From Rauschenbakh, Ovchinnikov, and McKenna-Lawlor  Forward work – refine thrust misalignment value, update burn length and vehicle size based on numbers from other groups Christine Troy Attitude Thrust Misalignment, mmProp Mass, kgProp Volume, m

AAE450 Spring 2009 Backup Slides Christine Troy Attitude

AAE450 Spring 2009 Control Phase Diagrams  Based on Rauschenbakh, Ovchinnikov, and McKenna-Lawlor θ. θ +θ1+θ1 -θ1-θ1 No External Torque θ +θ1+θ1 -θ1-θ1 “Large” External Torque θ. Christine Troy Attitude

AAE450 Spring 2009 Source of Values Used  Powered Descent Burn Time – 12 min (Apollo)  Descent Engine Thrust – linear ratio from Apollo descent thrust and mass  Distance from CG to control thrusters – approximate dimensions of Surveyor (similar mass lunar lander, roughly pyramidal in shape)  Exit velocity of thrusters – based on approximate Isp of existing hydrazine thrusters Christine Troy Attitude

AAE450 Spring 2009 Excel Table for Prop Calculation Christine Troy Attitude

AAE450 Spring 2009 References  Fowler, Wallace. Lunar Mission Characteristics. Texas Space Grant Consortium. 21 Jan  APSAT Propulsion Historical Reference  Rauschenbakh, Boris, Michael Ovchinnikov, and Susan McKenna-Lawlor. Essential Spaceflight Dynamics and Magnetospherics. Dordrecht, The Netherlands: Kluwer Academic Publishers,  Ball, Andrew et al. Planetary Landers and Entry Probes. Cambridge: University Press,  Surveyor Lunar Lander. Smithsonian Collections Database. 21 Jan &quicksearch=A  Monopropellant Hydrazine Thrusters. Astrium Space Propulsion. 21 Jan  Apollo Lunar Module. Wikipedia. 21 Jan  Hydrazine. Astronautix. 21 Jan Christine Troy Attitude