ADCS. Electron Losses and Fields Investigation. Mission PDR Attitude Determination and Control. Oliver Wang. Los Angeles, California

Transcription

1 ADCS Electron Losses and Fields Investigation Mission PDR Attitude Determination and Control Oliver Wang Los Angeles, California ADCS-1 MPDR, 2/12/2015

2 Team Organization Subsystem Requirement Overview & Operations ADCS Subsystem Logic Control Law Actuators Magnetorquers Sensors Magnetometers Sensors Sun Sensors Interface ADCS Testing & Simulation Control Law Sensors Magnetometer Sensors Sun Sensors GSE Magnetic Scanner Integration RFAs TABLE OF CONTENTS ADCS-2 MPDR, 2/12/2015

3 TEAM ORGANIZATION Name Class Responsibility Ryan Baker Senior ADCS Lead (Outgoing) Oliver Wang Sophomore ADCS Lead (Incoming) Camilla Harris Senior Control Law Erik Lamb Junior Control Law Liya Oster Freshmen Control Law Jake Romanas Sophomore Hardware Testbed Markus Notti Sophomore Hardware Testbed Elizabeth Harmeier Junior Sensors Kyle Gronich Junior Sensors Alice Tang Freshmen Sensors Stanway Liau Junior Embedded Software (CDH) Aamoy Gupta Senior Magnetic Analysis GSE Alekhya Dalta Junior Magnetic Analysis GSE ADCS-3 MPDR, 2/12/2015

4 OVERVIEW & OPERATIONS Overview ELFIN ADCS use torquer coils as actuators and magnetometers as sensors controlled by our control laws to achieve three primary objectives: Spin Stabilization about Z-axis (0 30 RPM) Attitude Knowledge to within 5 degrees. Attitude Control with spin axis to be orbit anti-normal within 3 degrees. ADCS use fine and coarse sun sensors to provide additional attitude information for ground analysis Mission Timeline & ADCS Operations Phase 1: Early Orbit Commanded* Detumble Phase 2: Science Preparation Commanded spin-up/precession Minimal Spin up (about 3 RPM) for control authority Calibrate FGM. Precess to predicted target attitude Spin up to nominal (20 RPM) science rate Phase 3: Science Operations Commanded spin maintenance and spin plane adjustments Precess to counter errors from prediction, preliminary calibration, spin-up caused disturbances Phase 4: Extended Science Ops Phase 5: End of Life Disable ADCS maneuvers ADCS-4 MPDR, 2/12/2015

5 REQUIREMENT REQ ID Requirement Rationale Verification Method Status ADCS-01 The ADC subsystem shall be capable of producing and maintaining a spin rate between 10 and 30 rpm to within ±2 rpm. Science mission requires certain spin rate to collect sufficient amount of data for science. A: Software simulation of initial conditions and defined orbit Demonstrated in simulation. Implemented and tested in ADCS dev board. More test in progress ADCS-02 The ADC subsystem shall be capable of ±5 degrees of attitude control Science mission require specific orientation to collect data. A: Software simulation of initial conditions and defined orbit Demonstrated in simulation Implementation and testing in progress ADCS-03 The ADC subsystem shall be capable of ±3 degrees of attitude knowledge Science mission need to match its collected data with orientation informaiton. A: Software simulation of initial conditions and defined orbit Algorithms close to completion Not yet included in simulation ADCS-04 The ADC system shall be capable of automatically detumbling ELFIN after deployment from the P-POD. ADCS need automatic detumble capabilities in case it it couldn't communicate with the ground. A/T: Software Simulation and spin testing Demonstrated in simulation Microcontroller implementation completed Hardware test in progress ADCS-05 The integration time of all ADCS sensors shall be sufficiently short so that they are capable of operating while the spacecraft is spinning at rate of up to 30 rpm Low integration time ensure manuevering efficiency at high spin rate. T: Spin sensors testing Sensor selection driven by requirement Sensor tests currently in progress ADCS-06 The ADC subsystem shall have at least two separate sensors capable of being processed onboard for maneuvers. Two sensors provide fail safe capability. I/T: Inspection of Development Model and hardware testing System design satisfies requirement Magnetometer CDH software close to completion Testing of both magnetometers in progress ADCS-07 The ADC subsystem shall be capable of running a deperm cycle after maneuvers to ensure the magnetic moment of the spacecraft is less than 1 nt as measured at the fluxgate magnetometer Deperm cycle is needed to clean the build up of magnetic field by torqueing, especially on battery. T: Testing in UCLA in house magnetic testing facility. Operational concept developed H-bridge driver controller is completed Hardware demo built and presented ADCS-10 The ADC subsystem shall not exceed the mass allocated by Systems T: Instruments will be weighed Met system mass budget ADCS-11 SYS-22The ADC subsystem shall not exceed the power allocated in the ELFIN system power budget T/A: Measured power consumption data during component tests Met system power budget ADCS-5 MPDR, 2/12/2015

6 CONTROL LAW Detumble & Spin Up Controller: B-Dot. Extensive flight history. ADCS magnetometer is the primary indicator of rotation, and the only sensor within the control loop. Computationally efficient. B-Dot Control Law: B vector is magnetic field in spacecraft body frame. B-Dot vector indicate angular velocity vector direction in spacecraft body. Detumble: M = -C * db/dt Spin Up: M = +C * db/dt Attitude (Spin axis) Control Desired torque to adjust spin plane: T = L x Q x L L: Spacecraft angular momentum vector Q: Target spacecraft momentum vector (determined by science requirement Operational Concept: Ground based calculation of phase offset to torque Push complexity to the ground. Simple onboard software (control logic remain simple, same fundamental zero-crossing detection code as B-Dot). Analytical and simulation methods to calculate offsets. Transmit phase offsets relative to zero crossing to spacecraft during COMM pass Trade: Phase offset vs. Bar Magnet method Bar magnet mode: consume more power, less efficient. Simpler to implement. Phase offset: use less power, efficient. Need to calculate phase offset, increased complexity. L L Q T ADCS-6 MPDR, 2/12/2015

7 Attitude Knowledge CONTROL LAW Ground based analysis to determine the spin axis Same method as in FAST CubeSat mission, with comparable spin rate and orbit Use only spacecraft s position and magnetic field s reading to determine spin axis in ECI frame. Require spin rate on non-spin axis to be low. Progress Concept adapted and tested Running simulation to determine model s accuracy ADCS-7 MPDR, 2/12/2015

8 MAGNETORQUERS Magnetorquers Two coils system Magnetorquers: Magnetic cleanliness Two coils system: efficient. Conductor wrapped on PEEK spool Trade: Copper vs. Aluminum vs. Copper-clad-Aluminum Copper: High conductivity, greater magnetic moment, higher mass Aluminum: Lower mass, similar efficiency, lower moment, maneuvers take longer, oxidization problem. Copper-clad-Alunimum: Similar to Aluminum, reduce risk caused by oxidization, increase electrical contact reliability Open trade. Looking into copper-cladaluminum with copper remain upscope option. Concerns: Thermal fatigue susceptibility, electrical contact reliability, oxidization. Testing: Accelerated thermal chamber Circular Dipole Moment Y-Coil Z-Coil A^ A*m^2 Performance A*m^2/W A*m^2/W ADCS-8 MPDR, 2/12/2015

9 MAGNETOMETERS ADCS Magnetometers Honeywell HMC5883L 3-Axis Digital Compass. Magnetoresistive magnetometers (MRM) Usage: Primary sensor to determine orientation, only sensor within closed-loop controller Additional capability: Internal sample averaging. Temperature compensation. Placement: 1 unit on ADCS control board, and 1 unit on IDPU board Secondary MRM: Orthogonal to ADCS MRM, further from batteries and power, only used as backup MRM Max Dynamic Range Digital Resolution Min Max +- 1 gauss +- 8 gauss 0.73 milli-gauss 4.35 milli-gauss Output Rate 0.75 Hz 75 Hz Noise Floor 2 milli-gauss (Typical Value) ADCS-9 MPDR, 2/12/2015

10 SUN SENSORS Fine Sun Sensor (FSS) SD085 Quadphotodiode Operation: Determine azimuth and elevation angle to the light source Primary purpose: Detect sun to prevent EPD-I oversaturation Secondary purpose: Help determine attitude during ground side analysis Field of view: Aluminum aperture to limit field of view from to degree, greater than that of EPD-I s degrees. Coarse Sun Sensor (CSS) VBPW34SR Simple Photodiode and ADS1115 ADC. Usage: Provide additional attitude information. Redundancy for information about illumination of solar panels Feature: Much lower resolution than FSS, higher coverage Placement: 2 on +Z, 2 on Z, 1 on +Y, 1 on Y. Surface mounted to interior surface of each panel, looking through the board. ADCS-10 MPDR, 2/12/2015

11 INTERFACE ADCS subsystem interfaces with the flight computer and watchdog UART connections on ADCS Main (PIC24) Connection has interrupt capabilities ADCS board connects to boards in the avionics stack ADCS Main (PIC24) connects to: ADCS Peripheral Controller (PIC18) Connected by UART with interrupt capabilities Two sets of flash memory (AT45) via SPI Two torquer coils H-Bridges to allow the current flow to be reversed Torquer current sensor Analog connection to ADCS Main ADCS Peripheral Controller connects to sensors (I2C) MRMs, CSSs ADCS-11 MPDR, 2/12/2015

12 CONTROL LAW SIMULATION ADCS Simulation is built in house running on MatLab & Simulink. It is built off of library by B. Young for DANDE. Shown above is the black diagram. Magnetometer reading simulation. Orbit propagation based on gravitational motion, oblateness of earth, and atmospheric drag. ADCS-12 MPDR, 2/12/2015

13 CONTROL LAW SIMULATION Detumble from 10 RPM, takes about 4.5 orbits. Precess from 5 degree pointing error at 20 RPM, takes about 6.5 orbits. Spin up to 20 RPM, takes about 50 orbits. Precess from 45 degree pointing error at 20 RPM, takes about 40 orbits. Maintain spin rate of Z axis while dampen out spin rate of X and Y axis. Precess from 45 degree pointing error at 4 RPM, takes about 20 orbits. ADCS-13 MPDR, 2/12/2015

14 MAGNETOMETER TESTING Objective Determine the precision of the magnetometer readings Help correct magnetometer readings on the ground Confirm pointing error budget. Testing plan Use modified testing platform to change the orientation of the magnetometer. Attach the magnetometer to a long aluminum rail so servo won t interfere with its reading. Make repeated measurement while rotating the servo, match magnetometer s reading with servo s position feedback. Change the axis on the magnetometer that is normal to the attaching surface, to test all three axis. ADCS-14 MPDR, 2/12/2015

15 SUN SENSORS TESTING Objective: Fine sun sensor: Test its azimuth and elevation error with light coming from different angles, preferably model them with plane functions. Use for ground side analysis correction. Coarse sun sensor: Test its reading with light source coming from different angles. Use for ground side analysis correction. Test plan: Drive servo motors to simulate light source coming from different angles. Calculate angles from sensors reading, compare with encoder s truth value. Model the data for future ground side analysis correction. Azimuth Error FSS Readings Elevation Error ADCS-15 MPDR, 2/12/2015

16 Objective: GSE MAGNETIC SCANNER Scan parts for magnetic cleanliness. Obtain ambient magnetic measurement of the object Design: Spin table driven by servo motor and timing belt to able to spin the object (change theta angle). Magnetometer is positioned on a vertical rail, which is placed on a horizontal rail passing through the center of the spin table to be able to move up/down, further/closer to the spin table (R and Z axis). ADCS-16 MPDR, 2/12/2015

17 INTEGRATION Hardware-in-the-Loop Testing w/ni-rio Procedure: LabVIEW Real-Time Engine drive Compact NI-Rio 9073 to generate 3 voltage signals (arbitrary X, Y, Z) simulate MRM readings to send to the ADCS computer. ADCS computer process the signal, run control law and send command back to the LabView Real-Time Engine Features: Capable to simulate magnetic field at different orbital position by change sinusoidal wave parameters. Capable to simulate magnetometer reading noises Hardware-in-the-Loop Testing w/magnetometer Procedure: Spin a power source and all the components in ADCS closed control loop, including the ADCS computer, magnetometer, and magnetoquers on a spin table. Run different mode of control law on ADCS computer Send data back via Bluetooth for analysis Usage: Error analysis. Simulate ground-side data analysis. ADCS FCR Demo ADCS demo for FCR. Utilized all components in closed loop control. Demonstrated software & hardware integration. ADCS-17 MPDR, 2/12/2015

18 INTEGRATION NASA Marshall Brain in a Jar Test Package: LabVIEW and STK package (physical box) Attitude and orbit propagator built in Visualizations and fault conditions incorporated Output from ADCS pointing board, Input to package to incorporate torquer coil feedback Free, but on loan Would have to schedule with NASA Marshall and adapt to their system EyasSat Hamster Ball Test Platform: Transparent ball holds a 3U CubeSat 3 degrees of freedom, low friction via air bearings Friction levels with air bearings. Product designed to be used typically with reaction wheels. Increase coil voltage/use Helmholtz coil (built-in) Commercial product; would likely have to purchase Still in development by EyasSat ADCS-18 MPDR, 2/12/2015

19 RFAS RFA Status Comment Ensure coil is off when making measurement. Closed Checked time constant. Obtain FAST high fidelity simulation toolbox. Verify simulation with FAST simulation toolbox. Open Open Model Aerodynamic drag. In progress. Defined equation. Wait for simulation integration. Model gravity gradient. In progress. Defined equation. Wait for simulation integration. Model eddy current. In progress. Researching model. Investigate nutation effect and damping. Open Attitude knowledge. In progress. Running simulation to determine accuracy. Attitude control: consider bar magnet mode as an alternative. In progress. Open trade. Working on both phase offset mode and bar magnet mode. Pointing error budget. In progress Testing MRM accuracy. Investigate copper clad aluminum wire to replace aluminum wire. In progress Open Trade. Will conduct accelerated thermal testing. ADCS-19 MPDR, 2/12/2015

20 QUESTIONS QUESTIONS? ADCS-20 MPDR, 2/12/2015