Low Power Magnetic Attitude Control System for a...
Transcript of Low Power Magnetic Attitude Control System for a...
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Low Power Magnetic Attitude Control System for a CubeSat
Jesse Frey, Donald Mentch, Michael Polites, Joseph Hawkins, Denise Thorsen
University of Alaska Fairbanks Alaska Space Grant program
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Concept
Nadir Pointing CubeSat with low power magnetic control
Low Power Magnetic Torquers • Hard magnetic material reduces power consumption • Allows bias with no power penalty
Bias algorithm • No required attitude knowledge • Three axis magnetic control
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Bias Algorithm
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Motivation Ac
tive
Mag
netic
• Moderate power usage
• More control of attitude
• More complex algorithm
LPM
T • Low power usage
• Simple algorithm
• Allows for nadir pointing
Pass
ive
Mag
netic
• No electric power usage
• Attitude relative to local magnetic field
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Low-power Magnetic Torquer
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History
Initial Concept • Originally conceived to
dump momentum from reaction wheels on larger spacecraft
• Used remendur for torquer cores
CubeSat Adaptation • Primary Torquers with
Alnico 1 for detumble. • Vernier Torquers with inert
core coated with magnetic material for alignment
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Algorithm Overview
• 3 modes – 1 for detumble – 2 for alignment
• dual axis bias for three-axis attitude alignment
• No direct attitude knowledge necessary
• Latitude information required for alignment
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Mode 1 (Detumble) Algorithm
• Detumble is the only use of the ALNICO1 torquers
• The detumble algorithm can arrest a maximum rate of 5°/s
• For a 64° inclination the detumble procedure will take 2 orbits 0
2
4
6
8
10
12
0 2 4 6 8 10 12 14
Max
Pul
se L
engt
h (s
ec)
Starting RPM
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Bias Windows
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Alignment Window Offsets
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Alignment Modes
• Apply bias in equatorial and north polar windows • Outside windows coast • Run for 10 orbits
Mode 2
• Apply bias in north polar window • Outside window run detumble algorithm with small
torquers
Mode 3
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CubeSat System Overview
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Torquer Driver Schematic (Simplified)
• Core driven to saturation by a 7A current pulse
• Capacitor stores charge for current pulse to smooth current spikes and prevent supply overdraw
• Resistor charges capacitor from supply rail
2.7k
680u
Vbatt(7.4V nominal)
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Torquer Placement
• X and Y torquers are mounted on the ADCS board
• Z axis torquers are mounted in standoffs
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Simulation Results : Detumble
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Simulation Results : Mode 2 Establish Alignment
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Simulation Results : Mode 3 Maintain Alignment
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Joules of Energy Consumption
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Future Work
• Need to balance magnetic dipole moments
• Correct magnetometer data for locally generated magnetic fields
• Validate Control Algorithm
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Conclusion
Low power for nadir pointing CubeSat applications
Designed for high inclination orbits
Alignment accuracy depends on balance of torque rods