Passive Magnetic Attitude Control for CubeSat Spacecraft

Transcription

1 Passive Magnetic Attitude Control for CubeSat Spacecraft David Gerhardt Advisor: Dr. Scott Palo University of Colorado at Boulder Department of Aerospace Engineering Sciences August 11, 2010

2 Motivation Low cost & performance, simple, robust High cost & performance, complex Bar Magnet & Hysteresis Rods Magnetic Torque Coils Momentum Wheels Difficulties: Design, Modeling & Testing 2

3 Application: CSSWE Colorado Student Space Weather Experiment B Charged particle detection / classification Mag. field alignment benefit km, 55 deg. inclination ADCS requirements: 10 day settling time Settle to B ±15 3

4 PMAC Description Hardware Bar magnet - restoring torque Hysteresis rods - dampening torque Performance Alignment within ±10 deg. of B Settling time 1-2 weeks (varies with ω 0 ) Hyst. rods Bar magnet 4

5 PMAC Design Torque Expected Magnitude (N m) Major Contributor Aerodynamic 4.5E-8 CoM offset Gravity Gradient 2.5E-8 MoI difference Radiometric 6.0E-9 Solar Residual mag. field 1.3E-8 Materials / electronics Sum Minor inertia axis B 8.9E-8 T m magnet m Bsin β magnet B earth max 15 Tenv 5

6 PMAC Design Slow convergence Offset error high Hyst. Rod Vol. System volume limitations low Bar Magnet Strength high Does not overcome other torques Slow convergence Oscillatory error low 6

7 PMAC Simulation MATLAB ode45 integrator Euler rotational EoM + Euler Parameter kinematic diff EQ I I I xx yy zz x y z I I zz xx External torque inputs Dipole model (earth mag.) Parallelogram model (hyst.) Aerodynamic Gravity gradient Residual magnetic field I I yy zz I yy I xx x y Lz y z z x L L x y 7

8 PMAC Simulation Nominal Results Error tolerance Hysteresis rods / axis Initial angular velocity Residual magnetism Bar magnet strength Hysteresis parameters Hysteresis volume Center of mass CUBESIM comparison Moment of inertia / axis Orbit altitude / inclination Initial orientation m ω 0 Rods/ axis 8

9 Nominal Results B β 9

10 Error Tolerance 10

11 Nominal Results X Z Y 11

12 Hysteresis Rods / Axis 12

13 Initial Angular Velocity X ω 0 Z Y 13

14 Residual Magnetism B m 14

15 Residual Magnetism B m 15

16 Conclusion PMAC: inexpensive, coarse (10 deg) pointing Use model to guide design Performance factors Bar magnet strength (0.30 Am 2 ) Hysteresis rod volume (3 rods) Residual magnetic moment (<0.05 Am 2 ) Future Work Lagrangian integrator 16

17 Acknowledgements CSSWE team LASP + CU advisors 17

18 Acknowledgements CSSWE team LASP + CU advisors dgerhard@colorado.edu 18

19 Acknowledgements CSSWE team LASP + CU advisors dgerhard@colorado.edu QUESTIONS? 19

20 Recent Heritage Munin, 6kg, 2000 Unisat-4, 12kg, 2006 (launch failure) GeneSat-1, 4.5kg,

21 PMAC Design: Hyst. Rod Hysteresis loop size = dampening Loop characterized by Coercive force Hc Remanence Br Saturation Bs material apparent Material vs. apparent parameters Each rod unique F. Santoni, M. Zelli, Passive Magnetic Attitude Stabilization of the UNISAT-4 microsatellite 21

22 Nominal Input Input Value Unit End Time 10 Days Error tolerance 5E-8 Initial ang. vel. 10 deg. / s Bar Magnet Strength 0.3 Am 2 Hyst rods 3 per axis Hyst rod length 9.5 cm Hyst rod diameter 1 mm C D 2.4 CoM offset 0.75 cm Residual dipole 0.01 Am 2 22

23 Beta Zoom B β 23

24 Angular Velocity Zoom X Z Y 24

25 CUBESIM comparison material apparent 25

26 Error Tolerance Zoom B β 26

27 Initial Angular Velocity Zoom B β 27

28 Center of Mass X Z Y 28

29 Center of Mass X Z Y 29

30 Center of Mass X Z Y 30

31 Center of Mass Zoom X Z Y 31