Electron Losses and Fields Investigation - UCLA IGPP

1

Electron Losses and Fields Investigation

Subsystem PDRAttitude Determination and Control

Ryan Baker, Oliver Wang

Los Angeles, CaliforniaDecember 5, 2014

ELFIN ADCS Peer PDR – December 5, 2014

2

REVIEW BOARD MEMBERS

Name Organization

Marcin Pilinski Atmospheric & Space Technology Research Associates

Rick Schnurr NASA Goddard Space Flight Center

Hannes Leinweber UCLA IGPP


Primary objective: To ensure that the design meets requirements

Objectives for ADCS design team: Clearly define the subsystem scope and responsibilities Clearly ensure personnel roles and responsibilities Expose design to experts in an open and relaxed

environment where technical discussions can take place Identify potential engineering and implementation flaws to

increase probability of success Provide feedback on the detailed design of the subsystem

3

OBJECTIVE AND SCOPE OF PDR


Scope: The peer PDR chair will coordinate review

team minutes as follows: Request for action (RFAs), to be acted upon by a lead

actionee and closed with concurrence of initiator Recommendations, to be considered by the team without

need for closure by initiator Observations, points of information to be noted in the

review report for the team

4

OBJECTIVE AND SCOPE OF PDR


5

TABLE OF CONTENTS


Mission Objectives and Science ADCS Team Overview

Personnel and Internal Teams

Top-Level System Design System Requirements Timeline and Operations

ADCS System Hardware and Data Architecture

ADCS Control Law Detumble and Spin Control Precession Control

Simulation and Testing Software and Hardware-in-

the-Loop Simulations Sensor Tests

6

ADCS Team Overview


7

ADCS TEAM OVERVIEW

Name ResponsibilityRyan Baker ADCS Lead (Outgoing)

Oliver Wang ADCS Lead (Incoming)

Camilla Harris Control Law

Erik Lamb Control Law

Zach Yee Control Law

Jake Romanas Hardware Testbed

Markus Notti Hardware Testbed

Elizabeth Harmeier Sensors

Kyle Gronich Sensors

Alice Tang Sensors

Stanway Liau Embedded (CDH)

Aamoy Gupta Magnetic Analysis GSE

Alekhya Dalta Magnetic Analysis GSE


8

ADCS TEAM OVERVIEW


Top-Level System Design

• Subsystem Requirements• Overview• Mission Timeline• ADCS Operations

9ELFIN ADCS Peer PDR – December 5, 2014

10

SUBSYSTEM REQUIREMENTS


REQ ID Requirement 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

• Demonstrated in simulation• Microcontroller implementation

completed• Hardware tests in progress

ADCS-02 The ADC subsystem shall be capable of ±5 degrees of attitude control


being developed

ADCS-03 The ADC subsystem shall be capable of ±3 degrees of attitude knowledge

• Attitude determination algorithms still in development

• Simulation has not yet been modified to include attitude determination

ADCS-04 The ADC system shall be capable of detumbling and spinning up ELFIN after deployment from the P-POD


completed• Hardware tests in progress

ADCS-05 The integration time of all ADCS sensors shall be sufficiently low so that they are capable of operating while the spacecraft is spinning at rate of up to 30 rpm

• Sensor selection driven by requirement

• Sensor tests currently in progress

11

SUBSYSTEM REQUIREMENTS


REQ ID Requirement Status

ADCS-06 The ADC subsystem shall have at least two separate sensors capable of being processed onboard for maneuvers

• System design satisfies requirement

• Magnetometer CDH software developed

• Testing of both magnetometers yet to be completed

ADCS-07 The ADC subsystem shall be capable of running a deperm cycle after maneuvers to ensure the magnetic moment of the spacecraft at 75 cm as measured by the magnetometer is less than 1 nT

• Operational concept developed• H-bridge driver controller is

complete, but no hardware demo has been developed yet

ADCS-10 The ADC subsystem shall not exceed the mass allocated by Systems

• System design driven by requirement

• Some components have been weighed

• Conservative estimates for CBE

ADCS-11 The ADC subsystem shall not exceed the power allocated in the ELFIN system power budget

• System design driven by requirement

• Verification via hardware testing yet to be completed

12

MASS REQUIREMENT - ADCSREQ ID Requirement Parent(s) Verification Verification Document

ADCS‐10 The ADC subsystem shall not exceed the mass allocated by Systems SYS‐14 T: Components will

be weighedSystem

Mass Budget

Mass allocated for ADCS: 204 gCurrent best estimate (CBE): 175 gMargin: 15 % (26.25 g)CBE + Margin: 201.25 gContingency: 2.75 g

ADCSComponent Maturity Qty Unit mass CBE Margin CBE+MarginADCS Pointing board P 1 26.62 26.6 15% 30.6Magnetorquers P 2 74.12 148.2 15% 170.5


13

POWER REQUIREMENT - ADCSREQ ID Requirement Parent(s) Verification Method Verification Procedure

ADCS‐11

The ADC subsystem shall not exceed the power allocated in the ELFIN system power budget

SYS‐22T: Measured power consumption data during component tests;

System Power Budget


Componenets Current [mA]

Voltage [V] Efficiency Power

[mW]ADCS Board 43.16 3.3 0.66 215.8Precession Coil 81 5 1 405Spin Coil 71 5 1 355

Components CBE [W] Power Margin

CBE + Margin

Time On per orbit (min)

OAP [W/orbit] Allocated OAP [W/orbit]

ADCS Board 0.216 13.52% 0.245 1.000 0.003 0.005

Torquers 0.760 25.00% 0.950 1.333 0.013 0.040

14

ELFIN EXPLODED VIEW


ELFIN MOIs (kg m2) xx yy zz Stability Ratio

Stowed Configuration 0.006 0.030 0.034 1.13

Deployed Configuration 0.080 0.030 0.114 1.41

FGE

Achieve spin stabilization about Z-axis Spin axis is antiparallel to orbit normal Detumble and spin-up the spacecraft using magnetorquers

Provide attitude control accurate to 5 degrees Precess spin axis to be orbit normal during science observations Target location for science measurements near poles Periodic (daily/weekly) scheduled maneuvers with magnetorquers

Provide attitude knowledge accurate to 3 degrees using magnetometers, sun sensors, and geomagnetic reference

15

ADCS OBJECTIVES


16

ADCS OVERVIEW:SUBSYSTEM COMPONENTS


17

ADCS OVERVIEW:CLOSED-LOOP CONTROL


2 weeks

6 weeks

3 months

End ofMission

18

MISSION TIMELINE

Phase 1: Early Orbit Deployment of antennas and stacer System checkouts ADCS responsibility:

Commanded detumble

Phase 2: Science Preparation Instrument checkouts and recalibration ADCS responsibility:

Commanded spin-up/precession

Phase 3: Science Operations 1-4 possible science operations per orbit Several communication passes per day ADCS responsibility: Commanded spin

maintenance and spin plane adjustments

Phase 4: Extended Science Ops Science of opportunity, if possible

Phase 5: End of Life Disable ADCS maneuvers

Spin ~0 RPM


Spin ~20 RPM

1. Deploy the stacer and fluxgate magnetometer

2. Perform detumble maneuver

3. Minimal spin-up (~3 RPM) Provides 3-axis control authority Allows for later precession to correct attitude Prevents getting “stuck” in gravity-gradient attitude No target pointing direction

4. Preliminary phase shift calibration of FGM

5. Precess to predicted target attitude for the start of the science phase

19

ADCS ORDER OF OPERATIONS


7. Spin up to nominal (20 RPM) science rate Energy intensive Requires 30+ orbits Torque only during efficient orientations

8. Re-adjustment of spin plane Determine attitude based on re-calibrated FGM Precess to counter prediction errors, preliminary calibration errors, and

disturbances due to spin-up operation

9. Begin science phase, with daily ADCS functions Attitude determination; evaluate drifts from environmental torques Schedule precession maneuvers to counter drifts, based on operational

requirements Check for de-spin effects due to eddy currents throughout the spacecraft

structure Schedule re-spin maneuvers along with precession maneuvers

20

ADCS ORDER OF OPERATIONS

Day 160


ADCS Components• Magnetorquers• Magnetometers• Fine Sun Sensors• Coarse Sun Sensors• Data Architecture


22

Magnetorquers


Torquer coils (and rods) commonly used as actuators on CubeSats

ELFIN Torquer Coil System: Two coils spanning long faces of chassis

A third coil on end face would be area-constrained and weaker

Open-air to reduce residual dipole High efficiency coils (1.15 A m2 W-1)

Torque output : Power input Dipole moments:

Y: 0.453 A m2

Z: 0.414 A m2

Conductor wrapped on PEEK spool Developed in-house

23

MAGNETORQUERS


System Trade: Coil Conductor Material Copper

Higher conductivity, greater magnetic moment Higher mass

Aluminum Lower mass Longer delta T to impart impulse Similar efficiency (within 5% of copper) Lower moment ADCS maneuvers take longer

Selection: Aluminum Copper remains late upscope option Concerns:

Thermal fatigue susceptibility (lower tensile strength) Electrical contact reliability

24

MAGNETORQUERS


Structural Interface Secured to the chassis with standard countersunk brass 4-

40 fasteners Spin Coil: Negative Y side of chassis, 10 fasteners Precession Coil: Negative Z frame of chassis, 8 fasteners


MAGNETORQUERS

26

MAGNETORQUERS Spin Coil (Y-normal) Precession Coil (Z-normal)

Position Plane normal to spacecraft Y-axis Mounted on interior -Y face

Plane normal to spacecraft Z-axis Mounted on interior -Z face

Voltage 5 V 5 V

Current 81 mA 71 mA

Mass 39 g 45 g

Wire Type 28 AWG aluminum 28 AWG aluminum

Number of Turns 275 323

Length of Wire 176 m 202 m

Perimeter 0.640 m 0.625 m

Area 0.0203 m^2 0.0181 m^2

Circular Dipole Moment

0.453 A m^2 0.414 A m^2

Performance 1.117 A m^2 / W 1.172 A m^2 / W


27

ADCS Magnetometers


Magnetoresistive magnetometers (MRM) Enable low-field magnetic sensing Primary sensor to determine orientation

relative to Earth’s magnetic field Only sensor type within closed-loop controller

Honeywell HMC5883L 3-Axis Digital Compass 1 unit on ADCS control board and 1 unit on

IDPU board Low power consumption Self-test and temperature compensation

capability Digital interface to ADCS peripheral controller

28

ADCS MAGNETOMETERS


Operational Plan: Output at TBD frequency Internal sample averaging Regular temperature compensation Powered down when not in use Powered on for ADCS maneuvers and ADCS data collection Secondary MRM on IDPU board

Orthogonal to ADCS MRM Sensor XY in spacecraft spin plane Increased distance from batteries and power supplies Prevent against single-point ADCS magnetometer loss

Only to be used as backup MRM Must route pointing board harness to IDPU

29

ADCS MAGNETOMETERS


MRM Interface Integrated into the avionics stack

ADCS pointing board: 55.88 x 55.88 mm Secured with four 4-40 threaded rods

One MRM surface mounted on to the ADCS pointing board

MRM sends and receives data to/from ADCS Peripheral Controller through an I2C connection with TBD pins

Second MRM surface mounted on IDPU MRM 2 data sent to LETC 1 board via

I2C Data then sent to ADCS board through

I2C Flexi Cable 1

30

ADCS MAGNETOMETERS


mm

mm

mm


ADCS MAGNETOMETERS

REQ ID Requirement




ADCS-04 The ADC system shall be capable of detumbling and spinning upELFIN after deployment from the P-POD


REQ ID Requirement

ADCS-06 The ADC subsystem shall have at least two separate sensorscapable of being processed onboard for maneuvers

ADCS-07 The ADC subsystem shall be capable of running a depermcycle after maneuvers to ensure the magnetic moment of the spacecraft at 75 cm as measured by the magnetometer is less than 1 nT

ADCS-10 The ADC subsystem shall not exceed the mass allocated by Systems

ADCS-11 The ADC subsystem shall not exceed the power allocated in the ELFIN system power budget

32

ADCS MAGNETOMETERS


33

Fine Sun Sensor (FSS)


Sensor: SD085 Quadphotodiode Primary purpose is to detect sun to

prevent oversaturation of EPD-I Not part of closed-loop ADCS

controller Aids in determining spacecraft

attitude during ground-side analysis

34

FINE SUN SENSOR (FSS)


35

FINE SUN SENSOR (FSS) Requirements:

Field of view greater than 56° (field of view of EPD-I)

Support 30 RPM operation Operational Concept

Sunlight on four electrically isolated quadrants of the detector

Intensity in each quadrant used to determine the azimuth and elevation angles to the incident light source

Aluminum aperture to limit field of view (86° 60°) and limit size of light spot to prevent saturation


Interface Quadphotodiode (SD085) with ADC (ADS1115) Custom aluminum aperture Mounted to positive X face w/ 2 standard 2-56 brass screws Connects directly to IDPU via a 10 contact card edge (uses 6

edges)

36

FINE SUN SENSOR (FSS)


37

Coarse Sun Sensors


Operational Concept: Simple photodiodes to provide additional attitude

information (not used in closed-loop controller) Redundancy for information about illumination of solar

panels Much lower resolution than FSS, but higher coverage

Simple photodiode vs. 4-quadrant sensor 2 photodiodes on +Z, 2 photodiodes on –Z 1 photodiode on +Y, 1 photodiode on –Y (in spin plane)

Interface: Surface mounted to interior surface of each exterior panel Mounted along with ADCs (ADS1115S) Connected to ADCS board with Kapton flexi cable

38

COARSE SUN SENSORS


ADCS Data Architecture


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)

40

ADCS DATA ARCHITECTURE


41



42



ADCS Control Logic

• Detumble and Spin-Up• Precession Control• Control Analyses• Closed-Loop Controller


Detumble and Spin-Up


B-Dot Controller: Extensive flight history ADCS magnetometer data as primary indicator of rotation of

satellite B vector is magnetic field in spacecraft body frame B-Dot vector indicates angular velocity vector direction in

spacecraft body Rotating satellite causes magnetic field measurements in

each component body frame of reference to vary sinusoidally

Control Law: M = ± C * dB/dt T = M x B

45

DETUMBLE AND SPIN-UP


Detumble M = - C * dB/dt T = M x B Control brings the rate of change of B in the spacecraft

body frame to zero Energy is removed from the system Initial detumble and spin maintenance (dampening of

incurred rates in X and Y)

Image source: B. Young, Design and Specification of an Attitude Control System for the DANDE Mission

46



Spin-Up M = + C * dB/dt T = M x B Control increases the rate of change of B in the spacecraft

body frame Energy is added to the system Initial spin-up to nominal rate and spin maintenance

(restoring Z rate after gradual dampening)

47


Image source: B. Young, Design and Specification of an Attitude Control System for the DANDE Mission


Precession Control


Control of Spin Axis Physical torque:

T = M x B Desired torque to adjust spin

plane: T = L x Q x L L: Spacecraft angular

momentum vector Q: Target spacecraft angular

momentum vector Spin axis, determined by science

requirements Unit vectors (bang-bang control) Based on physics of spinning

object precession

49

PRECESSION CONTROL

L∆L

Q

T


Control of Spin Axis Operational concept:

Ground-based calculation of phase offset to torque Dogleg maneuver if necessary Push complexity to the ground

Attitude determination Spin axis control

Analytical and simulation methods to calculate offsets Transmit phase offsets relative to zero crossing to

spacecraft during comm pass Decrease complexity of on-board software

Control logic remains simple and general Same fundamental zero-crossing detection code as B-Dot

Timing parameters utilized to generalize control law Time delay from zero crossing to torque Torque time

50

PRECESSION CONTROL


Control Analyses


Control Trade Study: Bang-Bang vs. Proportional Proportional

Moment produced proportional to B-dot Not viable given hardware (electrical) constraints

Bang-Bang Driven at full voltage, switching between on/off, pos/neg Simpler to implement on the microcontroller Demonstrated to have a faster spin rate decay

Design choice: Bang-Bang

52

CONTROL ANALYSES


Control Trade Study: Three-Axis vs. Two-Axis Three-Axis

One additional dimension in the space of possible dipole moments produced by magnetorquers (simpler control)

Third coil would be inefficient due to the geometry limitations of the 3U CubeSat

Volume constraints in ELFIN spacecraft limit feasibility of third coil

Two-Axis Control mechanism is still viable

Can use dogleg maneuver to re-orient Both coils are power efficient Space efficient

Design choice: Two-Axis

53

CONTROL ANALYSES


Viability of Two-Axis Control T = M x B Each coil can produce a torque in its

plane Between the two coils, the torque-

space is all 3 dimensions (dependent on B geometry)

B geometry changes over an orbit B geometry within s/c reference

frame constantly changes with spin A torque can always be produced

If B is parallel with one axis, it is perpendicular to another

If B is parallel to X-axis, either coil can be used to effectively torque

54

CONTROL ANALYSES


ADCS Simulations

• MATLAB & Simulink Simulation• Hardware LabVIEW Simuation• Sensor Testing


MATLAB & Simulink Simulation


Software Simulation Development of in-house orbit and attitude propagator

Build off of library by B. Young for DANDE

57

MATLAB SIMULATION


Orbit Propagation Propagate R and V vectors dR/dt = V dV/dt is a result of various effects

Gravitational motion (two body problem) Oblateness of earth (non-spherically symmetric field) Atmospheric drag

58

MATLAB SIMULATION


Attitude Propagation Propagated state vector:

Attitude quaternion Characterizes rotation from ECI to

body frame Angular velocity

Quaternion mathematics: Scalar element coupled with a

3D vector Convenient computationally Excellent representation of

rotations in 3D space Model: Euler’s equations of motion

for a rigid body Solved numerically with ode45

Runge-Kutta solver, variable time step

59

MATLAB SIMULATION


Geomagnetic Model IGRF – International Geomagnetic Reference Field (1995 Edition) Tabulated by NASA Langley Research Center Spacecraft and

Sensors Branch Ported to MATLAB Code by M. Pilinski and B. Young of DANDE

mission Serves as a lookup table

Function of position Table in inertial frame of

reference Use quaternion rotation to

obtain B in body-fixedframe (as seen byspacecraft)

Can be used for attitudedetermination testing

60

MATLAB SIMULATION


Control Block Processing of sensor data & control law logic Implements B-Dot Control and Precession Control

Continuous time: transfer function w/ low-pass filter Discretized for controller implementation

Additional features: “Half duplex” cycle, noise, discretization of signal Latitude threshold: torque only near the equator Constant dipole moment amplitude from coils

61

MATLAB SIMULATION


62

MATLAB SIMULATION:ORBIT PROPAGATION


Orbit Propagation Simulation (98 degree inclination)

63

MATLAB SIMULATION:MAGNETOMETER READINGS


Magnetic Field

B-Dot Reading

B-Dot Estimate

Coordinate system: spacecraft body frame

Magnetometer Reading Simulation, Noiseless

MATLAB SIMULATION: DETUMBLE

64

REQ ID Requirement



MATLAB SIMULATION:SPIN-UP


REQ ID Requirement


REQ ID Requirement


MATLAB SIMULATION:SPIN RATE MAINTENANCE


REQ ID Requirement



MATLAB SIMULATION:PRECESSION CONTROL (MAINTENANCE)

REQ ID Requirement


L-Actual Spin∆L

Q-Desired Spin

T-Torque

MATLAB SIMULATION:PRECESSION CONTROL (LARGE ANGLE)

68

L-Actual Spin∆L

Q-Desired Spin

T-Torque


REQ ID Requirement



MATLAB SIMULATION:PRECESSION CONTROL (LARGE ANGLE)

REQ ID Requirement


L-Actual Spin∆L

Q-Desired Spin

T-Torque

Hardware-in-the-Loop Simulations


Hardware-in-the-Loop Testing Basic version of ADCS control law implemented on

microcontroller Low-pass filter Numerical differentiation Zero crossing detection algorithm Modeled on-board interrupts:

Telemetry interrupt Torque interrupt

71

HARDWARE SIMULATION


Hardware-in-the-Loop Testing Control law modeled as state diagram with timing parameters

72

HARDWARE SIMULATION


Hardware-in-the-Loop Testing LabVIEW Real-Time Engine Compact NI-Rio 9073

Signals generated by NI 9263 module 3 voltage signals (arbitrary X, Y, Z) simulate MRM readings Microcontroller ADC (data processing & control logic) Output back to test bed & LabVIEW Real-Time Engine

73

HARDWARE SIMULATION


ADCS MAIN SOFTWARE TESTS

Used a waveform generator to supply a faux B-field reading to a PIC24 microcontroller

PIC24 sent resulting data to a PC for plotting and analyzing

Tested filter for data smoothing

Tested calculations of the B-field derivative, B-dot

ELFIN ADCS Peer PDR – December 5, 2014 74

75

ZERO CROSSING DETECTION


Time (s)

Amplitude (V)

Time (s)

Example Torque Periods as a Result of Above SimulationWaitTime = 50 ms, TorqueTime = 500 ms, ZeroTolerance = 0.15 V

Simulation of B-Dot Zero Detection TriggeringWaveform Amplitude = 4 V, Period = 3 sec

PRELIMINARY B-DOT TEST

0 500 1000 1500 2000 2500 30000

100

200

300

400

500

600

700

800

Time (ms)

B-Dot Test - 1/3 Hz Sine Wave (20 RPM Spin)Faux B-field reading (smoothed) B-dot (scaked)B-Field Signal (from signal generator)

B-Dot Computed Signal (scaled)

ELFIN ADCS Peer PDR – December 5, 2014 76

Sensor Testing


Two-Axis Rotary Table Azimuth angle ± 72° determined by servo motor controlled by

Arduino Elevation set by swinging arm that can rest at a selected elevation

using a pin (+/- 40 degrees) Rotation rate of 20 RPM Reflections can act as

secondary light sources Test bed placed inside

dark, non-reflectivehousing

78

FINE SUN SENSOR TESTING


REQ ID Requirement


REQ ID Requirement


79

FINE SUN SENSOR: 2D


80

FINE SUN SENSOR: AZ ERROR


81

FINE SUN SENSOR: AZ ERROR


82

FINE SUN SENSOR: EL ERROR


83

FINE SUN SENSOR: EL ERROR


84

ADCS Schedule andFuture Testing


85

ADCS FUTURE WORK

Day 160

Additional hardware-in-the-loop testing Quantitative analysis of microcontroller implementation of

control algorithms using testbed Implement closed-loop feedback in testbed

Stim testing including use of Helmholtz coil, adding ADCS magnetometer to the test loop

Continue developing sensor test platform to investigate ability of hardware to handle 30 RPM case

Sun sensor testing with full automation FCR Demo NASA Marshall Brain in a Jar Testing EyasSat Hamster Ball Testing


86

ADCS FUTURE WORK

FCR Demo:


87

ADCS FUTURE WORK

Day 160

NASA Marshall Brain in a Jar Testing: LabVIEW and STK package (physical box) Attitude and orbit propagator built in Visualizations and fault conditions incorporated Output is IMU data

Extract magnetometer data Plug in via I2C to ADCS pointing board

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


88

ADCS FUTURE WORK

Day 160

EyasSat Hamster Ball Testing:

Transparent ball holds a 3U CubeSat

3 degrees of freedom, low friction via air bearings

Potential issues: 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


Image source: EyasSat, LLC

89

ADCS SCHEDULE

Day 160


90

ADCS SCHEDULE

Day 160


Thank you to all of our sponsors, stakeholders,and contributors

Shaun Murphy @ Northrop GrummanKatharine Gamble @ UT Austin

Jim White WD0E @ Colorado Satellite ServicesMark Spencer WA8SME @ ARRL

Tony Monteiro AA2TX & Bob Davis KF4KSS @ AMSAT-NA

91

ACKNOWLEDGEMENTS


Electron Losses and Fields Investigation - UCLA IGPP

Documents

Transcript of Electron Losses and Fields Investigation - UCLA IGPP