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Preliminary Lunar Descent Attitude Control Analysis. Christine Troy Assistant Project Manager Webmaster Lunar Descent Attitude Control Analysis. Problem. Attitude control during descent burn Thrust direction Communication Many sources of perturbation Thrust not through CG

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## Preliminary Lunar Descent Attitude Control Analysis

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**Preliminary Lunar Descent Attitude Control Analysis**Christine Troy Assistant Project Manager Webmaster Lunar Descent Attitude Control Analysis Christine Troy Attitude**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 Thrust CG Christine Troy Attitude**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**Backup Slides**Christine Troy Attitude**Control Phase Diagrams**Based on Rauschenbakh, Ovchinnikov, and McKenna-Lawlor . . θ θ +θ1 +θ1 θ θ -θ1 -θ1 No External Torque “Large” External Torque Christine Troy Attitude**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**Excel Table for Prop Calculation**Christine Troy Attitude**References**Fowler, Wallace. Lunar Mission Characteristics. Texas Space Grant Consortium. 21 Jan 2009. http://www.tsgc.utexas.edu/spacecraft/apollo17/timeline.html APSAT Propulsion Historical Reference Rauschenbakh, Boris, Michael Ovchinnikov, and Susan McKenna-Lawlor. Essential Spaceflight Dynamics and Magnetospherics. Dordrecht, The Netherlands: Kluwer Academic Publishers, 2003. Ball, Andrew et al. Planetary Landers and Entry Probes. Cambridge: University Press, 2007. Surveyor Lunar Lander. Smithsonian Collections Database. 21 Jan 2009. http://collections.nasm.si.edu/code/emuseum.asp?profile=objects&newstyle=single&quicksearch=A19700294000 Monopropellant Hydrazine Thrusters. Astrium Space Propulsion. 21 Jan 2009. http://cs.astrium.eads.net/sp/SpacecraftPropulsion/MonopropellantThrusters.html Apollo Lunar Module. Wikipedia. 21 Jan 2009. http://en.wikipedia.org/wiki/Apollo_Lunar_Module Hydrazine. Astronautix. 21 Jan 2009. http://www.astronautix.com/props/hydazine.htm Christine Troy Attitude

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