Power Management, Attitude Determination and Control Systems for small satellites

1. Power Management, Attitude Determination and Control Systems for small satellites Anwar Ali Tutor: Prof. Leonardo M. Reyneri

2. Problem Statment (1) Integration of EPS & ADCS on a single module of CubeSat standard • Reduce the overall cost, weight and power consumption • EPS should meet the power requirement of AraMiS-C1 • ADCS should meet orientation and stabilization requirement of AraMiS-C1 • COTS • Selected on the basis of power loss analysis • Small dimensions, compact, Low price and easily available • Techniques for miniturization • Embedded maqnetorquer coil in internal layers of the CubePMT (II) Thermal Modeling of CubeSat and different tiles • Universities & SMEs have a great emphasis on nanosatellites • Low cost, small size, short development time • Challenges with these satellites, they have • Small surface area for heat dissipation • Not enough space for mounting radiators • Required thermal modeling to know • Thermal resistance, power absorption and temperature difference

3. Outline • AraMiS-C1 • CubePMT • EPS • ADCS • Thermal Modeling • CubeSat & Panels • CubePMT • AraMiS-C1 • Conclusion

4. Spacecraft Configurations • Physical Module Based Configuration • Reusable design configuration • Satellite on demand Configuration • CubePMT • AraMiS-C1

5. AraMiS-C1 • CubeSat standard nano-satellites • Size 10x10x10 cm3 • Mass < 1.3kg • Based on tiles • Four Power Management Tiles (CubePMT) • Two Communication Tiles (CubeTCT) • Room for batteries and payload boards

6. CubePMT • CubePMT is CubeSat standard Power Management Tile • Dimensions 98 x 82.5 mm2 & 1.6 mm thickness • It is an 8-layers PCB • On top layer : Solar panel and sun sensor • Bottom layer : electronic of EPS and ADCS subsystems • Magnetorquer coil embedded in four internal layers • Goals • Implement all the subsystems on a single Module • Increase efficiency of EPS • Reduce the overall cost, weight, size and power consumption • COTS

7. CubePMT: Block Diagram

8. CubePMT: Solar Panel Side

9. CubePMT: Component Side 5 pins I2C Connector Magnetometer 3.3V Switching Regulator 5V Switching Regulator Magnetorquer Driver J-Tag 15 pins analog connector Tile Processor Module CalibrationMemory 15 pins digital connector 4 pins power connector 3V Linear Regulator 3.3V Linear Regulator Temperature Sensor Boost Converter Bidirectional Load Switch Gyroscope Current Sensor

10. CubePMT internal Layers

11. CubePMT • CubePMT Subsystems • EPS (Electric Power Supply) • Housekeeping Sensors • ADCS (Attitude Determination and Control System ) • Tile Processor

12. EPS • To generate, distribute and convert power to different levels • Solar panel, boost converter with MPPT, over voltage protection, switching & linear regulators and different load switches. • Boost converter steps up the solar panel voltage (4.2V) to PDB • Over voltage protection circuit keeps the PDB voltage within the limits. • Switching and linear regulators step down the PDB voltage • Load switches : input of each subsystem • Bidirectional load switch • Latch up protection

13. EPS: Solar Panel • Composed of two triple junction GaAs solar cells • Efficiency of 26% • Each cell generates 2.14V • Connected in series • Output voltage 4.28V • Single solar cell P-V characteristics at two different temperatures (25˚C & 45˚C) • As the temperature increase performance degrades in terms of • Output voltage • Power

14. Boost Converter: Simulations • Converts the Solar Panel voltage to PDB level • Solar panel MPP is not constant varies with environment conditions • To operate solar panel at MPP, MPPT is needed • MPPT extracts maximum power from solar panel • Different components were analyzed in PSpice simulations • Best selected on basis of minimum losses and small dimensions

15. Boost Converter: Simulations

16. Implemented Boost Converter • After good simulation results with the selected components, the converter was implemented • Operation of the MPPT • Input capacitor is charged from solar cells • When voltage on (IN+) of OPAM • is greater than ref (IN-) terminal

17. Boost Converter: Testing 16V 4V

18. Regulators • PDB voltage to low levels(3V, 3.3V, 5V) • Linear regulator (small area & less auxiliary components but low efficiency) • 3V Reference: 5V input to 3V • 3.3V Processor Supply: PDB voltage to 3.3V • Switching regulator (high efficiency, large dimensions & more auxiliary components) • PDB voltage level to 3.3V (all the subsystem components) • PDB voltage level to 5V (all the subsystem components)

19. AraMiS-C1: Power Budget • To evaluate designed EPS: Power budget analysis of AraMiS-C1 • Power Sources • One panel • Solar power 7.63W • Solar cell efficiency is 26% which gives 1.98W • Two panels • 45o from sunlight, solar power is10.678W • 26% solar cell efficiency gives 2.8W • Energy Storage • Single pack of10 NiCd rechargeable batteries each 1.2 V: total12V • Battery capacity 0.9Ah • Max. available energy is 10.8Wh (38.9kJ) • Average power to recharge batteries is (1.98x0.93) 1.84W • Worst case efficiency of battery 80% • Average power available (10.8x0.8) 8.64W

20. AraMiS-C1 Power Budget • Power consumption of AraMiS-C1 subsystems

21. AraMiS-C1 Power Budget • Magnetorquer system Power consumption • Power Budget • Any Satellite designed EPS should always meet the criteria • Ppeak-consumed< Pmax_bat • Pavg-consumed< Psolar_avg • Enight< Estore

22. Housekeeping Sensors • Housekeeping and monitoring purposes • Mounted at different points on the module

23. ADCS • Attitude Determination Sensors (ADS) • Attitude Control System (ACS)

24. Attitude Determination Sensors (ADS) • Fundamental element for successful mission • Provide satellite orientation information • References: sun, center of the earth, known star or earth magnetic field • Design constraints: • Budget, size and power consumption • Type of Attitude Snesors used on CubePMT (COTS components ) • Sun directional sensor • Two-axis Magnetometer Sensor • Gyroscope

25. ADS: Magnetometer Sensor • In LEO satellites, for sensing orientation earth magnetic field • Magnetometer are extensively used • low-price, lightweight and low power consumption • Types of magnetic sensor technologies available • FG (Fluxgates): Good magnetic properties but heavier (500mg), consume high power (2W), expensive • GMR (Giant Magneto Resistance): Good sensing properties and repeatability but high hysteresis (up to 10%) and low magnetic field sensing is not trivial • TMR (Tunnel Magneto Resistance): Good sensitivities, high magnetic field range and good resolution. But TMR is immature technology, COTS are not very widely spread • AMR (Anisotropic Magneto Resistance): High dynamic ranges (hundred of µT), high resolution (1nT), higher sensitivities (10mV/mT/Vbridge ) and Set/Reset pulses • CubePMT: COTS Honeywell HMC1002 • AMR technology • Two-axis sensors • Measurement range: -2~2 G • Maximum earth magnetic field -0.625~0.625 G

26. ADS: Magnetometer Sensor • Set/reset pulses • Refresh the sensor • Maintain sensitivity • Eliminate memory effects of the magnetic elements • Magnetometer • Conditional circuit • Output voltage in range of tile processor (0V~2.5V).

27. ADS • Sun Sensor • COTS component: CPC1822 • Monolithic photovoltaic string of solar cells • Tested at AM0 • Open circuit voltage of 4.75V and • Short circuit current of 75uA • Output voltage in range of tile processor (0V~2.5V). • Gyroscope • Measure angular velocity • COTS component: Yaw rate digital gyroscope ADIS16080 • Dynamic range ±80˚/sec • Operating range ±2rpm and occasionally up to ±6rpm • Filter bandwidth is software programmed • Lower bandwidth (more accuracy) • Higher bandwidth (fast maneuvers) • Software filter of 1Hz • RMS noise value is 0.0025rpm

28. Attitude Control System (ACS) • Manages satellite orientation, in order to point its antenna toward ground station or solar panels toward sun. • Choices • Permanent magnets • Cheap, simple, light and consuming no power • Problem pointing accuracy and pointing direction • Reaction wheels • better pointing accuracy and can orientate satellite in any direction • Price, weight and size make them incompatible with CubePMT • Magnetic rods • better pointing accuracy and can orientate satellite in any direction • Price, weight and size make them incompatible with CubePMT • Magnetorquer system • Magnetorquer Coil Driver • Magnetorquer Coil

29. ACS: Magnetorquer Coil Driver • COTS IC A3953 • Controls • Amount of current • Direction through the coil • Current decides • Torque generated • Direction of satellite spin

30. ACS: Magnetorquer Coil • Design requirements • Small dimensions • Low weight • Low heat dissipation • Reconfigurable • Occupying no excess space • Can generate different amount of magnetic moment and torque

31. ACS: Magnetorquer Coil • Working Principle • When current flows through a solenoid, magnetic moment is generated • Current carrying coil is placed in a magnetic field, it generates a torque • In case of LEO, at an altitude of 800 km and inclination angle of 89°, varies between 0.15G and 0.45G

32. ACS: Magnetorquer Coil • Design parameters • Embedded in four internal layers • 50 turns in each layer • 200 turns total • Trace width 0.3mm and thickness of 18µm • Space between adjacent traces is 0.2mm

33. ACS: Magnetorquer Coil • Reconfigurable design: To achieve reconfigurabality • Coil is divided into four subcoils (L1, L2, L3 and L4) • Attached/detached through zero ohm resistors • Changing the arrangements of these resistors • Up to four coils connected in series • Up to four coils connected in parallel • Hybrid combination of series and parallel connected coils

34. ACS: Magnetorquer Coil • PDB Voltage= 18V and Single coil resistance=64Ω • Torque Generated • Current is related with Power Consumption and Temperature increase

35. Time to rotate AraMiS-C1 by 90̊

36. ACS: Magnetorquer Coil • Thermal Modeling • Stefan-Boltzmann’s law : At steady state, Pd=0

37. Magnetorquer Coil: Thermal Modeling • Emissivity Measurement at Infra Red Wavelength • Ability of a surface to emit energy by radiation • Surfaces with different colors have different emissivity values • Voltage, current, temperature are captured

38. Magnetorquer Coil: Emissivity • The resulting emissivity (α) • value 0.9.

39. ACS: Magnetorquer Coil

40. ACS: Magnetorquer Coil

41. ACS: Magnetorquer Coil

42. Tile Processor • MSP430F5438 • Mainly responsible for; • Power management and scheduling • Decoding and executing commands • Executing attitude control algorithm • Storing housekeeping data

43. Thermal Modeling

44. Outline • Thermal models • CubeSat solar panel • Detailed model • Simplified model • Two models applied to AraMiS-C1 tiles (CubePMT & CubeTCT) • Thermal model of CubeSat • Thermal resistance of AraMiS-C1 • CubeSat model • Test

45. Thermal Resistace • Heat sources • Generated by the satellite subsystems • Absorbed from the surrounding • Some portion of heat is • Lost to the surrounding • Trapped inside the satellite • Trapped heat energy • Increases temperature of the satellite • Depends on the thermal resistance • Suppose two materials • Fourier’s law of heat conduction

46. Thermal Modeling • Thermal resistor representation • θ denotes the resistor • F represents FR4 • Cu represents copper • Alphabets (a, b, c, d, e) represent the respective subsection and • Numbers (1, 2, 3, 4) represent the relevant layer • For example θF-a2-3 represents the thermal resistor of FR4 material in subsection a of layers 2 and 3

47. Top to bottom thermal model of CubeSat panel (Detailed) • Suppose four layers panel • Solar cells, Resin, FR4, Copper traces, Ground plane • Each material have an associated thermal resistance • Mathematical form

48. Top to bottom thermal model of the CubeSat panel (Simplified) • Layers with similar material combined together • Assigned a single resistor • Mathematical form

49. Top to bottom Resistance of CubePMT (AraMiS-C1) • CubePMT thermal resistance • Simplified Model • Detailed Model • Applying the Detailed Model, • Applying the Simplified Model,

50. Centre to edge thermal model (Detailed)