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# Lunar Descent Attitude Control Analysis

Lunar Descent Attitude Control Analysis. Christine Troy Assistant Project Manager Webmaster Lunar Descent Attitude Control Analysis. Problem. Minimize mass and cost of attitude control during lunar descent burn 3-axis stabilized with current configuration

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## Lunar Descent Attitude Control Analysis

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

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. 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. Backup Slides Christine Troy Attitude

5. Descent Module Model 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 Christine Troy Attitude

6. Model Rocket and Spin Stabilization Information Christine Troy Attitude

7. Spin Frequency and Allowable Error Christine Troy Attitude

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

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