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Satellite Construction

Satellite Construction. Attitude Control and Determination System. Jan Hales, Martin Pedersen & Klaus Krogsgaard. ACDS Concept. Magnetometer and magnetotorquers Sun sensor for unambiguous determination B-dot control Optional: full three-axis control. Sun Sensor.

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Satellite Construction

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  1. Satellite Construction 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

  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

  4. Sun Sensor – Reflection

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

  6. It2 It1 It It Sun Sensor – Linear

  7. It/Iref Iref It It/Iref Sun Sensor – Linear

  8. Sun Sensor – Circuit

  9. Conservative mask design • Digital sensor chip with 70° FOV and 0.6° resolution Sun Sensor Chip • 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

  11. Magnetoresistive sensor • 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

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

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

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