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

2. AAE450 Spring 2009 2 Problem  Minimize mass and cost of attitude control during lunar descent burn –3-axis stabilized with current configuration 26 kg of hydrogen peroxide propellant for attitude control Additional mass for tanking, thrusters, etc.  Spin spacecraft around its axis of symmetry –Counteracts 100 Nm torque caused by 1% thrust misalignment  Need to know required spin rate and mass of propulsion system needed for spin up Christine Troy Attitude

3. AAE450 Spring 2009 3 Spin Stabilization  Faster rotation results in greater stability –1.0 Hz spin gives 7˚ nutation error –1.5 Hz spin gives 3˚ nutation error  Relatively small impulse needed for spin up –7˚ nutation error requires 1200 Ns –3˚ nutation error requires 1800 Ns  Solid motors ideal, potentially model rocket motors –7˚ nutation error – 11 G78 motors (<1.5 kg, <$290) –3˚ nutation error – 16 G78 motors (2.0 kg, <$420) –1˚ nutation error – 27 G78 motors (<3.5 kg, <$700)  Forward work – analysis of mass and cost changes in other systems due to spinning lander Christine Troy Attitude

4. AAE450 Spring 2009 4 Backup Slides Christine Troy Attitude

5. AAE450 Spring 2009 5 Descent Module Model Christine Troy Attitude From Structures Group: Radius = 2.8 m Height = 2 m Mass = 272 kg From Propulsion Group: Descent Engine Thrust = 7600 N From Operations Group: Length of Descent = 12 min = 720 sec Assume SC is uniform circular cylinder and thrust misalignment of 1% of radius (1.4 cm) Rotate SC around axis Thrust misalignment torque

6. AAE450 Spring 2009 6 Model Rocket and Spin Stabilization Information Christine Troy Attitude

7. AAE450 Spring 2009 7 Spin Frequency and Allowable Error Christine Troy Attitude

8. AAE450 Spring 2009 8 References  Rauschenbakh, Boris, Michael Ovchinnikov, and Susan McKenna-Lawlor. Essential Spaceflight Dynamics and Magnetospherics. Dordrecht, The Netherlands: Kluwer Academic Publishers, 2003.  Wiesel, William. Spaceflight Dynamics. New York: McGraw-Hill, 1997.  Howell, Kathleen. Notes from A&AE 440. Spring 2008.  Model Rocket Specifications. Apogee Components. http://www.apogeerockets.com/ 4 FEB 2009. Christine Troy Attitude