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

2. 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

3. 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 3 11.20.0012 55.90.0059 1011.80.0117

4. AAE450 Spring 2009 Backup Slides Christine Troy Attitude

5. 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

6. 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

7. AAE450 Spring 2009 Excel Table for Prop Calculation Christine Troy Attitude

8. AAE450 Spring 2009 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 http://www.tsgc.utexas.edu/spacecraft/apollo17/timeline.html  APSAT Propulsion Historical Reference  Rauschenbakh, Boris, Michael Ovchinnikov, and Susan McKenna-Lawlor.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