Satellite Construction Attitude Control and Determination System Attitude Control and Determination System Jan Hales, Martin Pedersen & Klaus Krogsgaard

2 ACDS Concept Magnetometer and magnetotorquers Sun sensor for unambiguous determination B-dot control Optional: full three-axis control Magnetometer and magnetotorquers Sun sensor for unambiguous determination B-dot control Optional: full three-axis control

3 Sun Sensor Linear analog slit sensor (MOEMS) –FOV:  70° (Required: 54.75°) –Theoretical resolution:0.07° (Required: 1°) –Chip size:8100µm  6900µm –Expected mass: 2.5-3g –Expected size (PCB):25mm  35mm Linear analog slit sensor (MOEMS) –FOV:  70° (Required: 54.75°) –Theoretical resolution:0.07° (Required: 1°) –Chip size:8100µm  6900µm –Expected mass: 2.5-3g –Expected size (PCB):25mm  35mm

4 Sun Sensor – Reflection

5 Sun Sensor – Linear, how? Independent of: –Degradation –Temperature –Dark currents –Cosine dependence –Sun power fluctuations –Albedo intensity contributions Independent of: –Degradation –Temperature –Dark currents –Cosine dependence –Sun power fluctuations –Albedo intensity contributions Division implemented using Vref of an ADC Reference area used to cancel out various dependencies

6 I t1 I t2 Sun Sensor – Linear It It  I t

7  I t /I ref I ref It It Sun Sensor – Linear  I t /I ref

8 Sun Sensor – Circuit

9 Sun Sensor Chip Conservative mask design Digital sensor chip with  70° FOV and 0.6° resolution Process sequence compatible with MIC’s cleanroom

10 Magnetometer Specification: –Range: |B|  [18200nT;49800nT] –Accuracy: < 1º  sin(1º)·18200nT=300nT –Resolution:> 8.4-bit effective Design goals: –Range:± 64000nT –Accuracy:< 50nT –Sample time:< 2ms per axis Specification: –Range: |B|  [18200nT;49800nT] –Accuracy: < 1º  sin(1º)·18200nT=300nT –Resolution:> 8.4-bit effective Design goals: –Range:± 64000nT –Accuracy:< 50nT –Sample time:< 2ms per axis

11 Magnetoresistive sensor Sensor –Honeywell HMC1021: Wheatstone bridge with intergrated offset and reset coils Sensor –Honeywell HMC1021: Wheatstone bridge with intergrated offset and reset coils Compensation –Constant field, linearity error reduced to noise –Temperature drift: sensor, amplifier, A/D converter, and voltager reference Compensation –Constant field, linearity error reduced to noise –Temperature drift: sensor, amplifier, A/D converter, and voltager reference

12 Magnetotorquers Torque 0.6 – 1.5  Nm H-brige configuration as driver circuit. Switch frequency: f = 32kHz Switch frequency: f = 32kHz

13 Environment Modeling Environment models: –Orbit (SGP) –Geomagnetic (IGRF2000) Environment models: –Orbit (SGP) –Geomagnetic (IGRF2000) – Sun positioning – Gravity Gradient