Sensors for orientation and control of satellites and space probes Ing. Ondrej Závodský GOSPACE s.r.o. ESA Contract No. 4000117400/16NL/NDe Specialized lectures
Content 1) How to determine the orientation of the satellite? Sensors Calibration Sensor fusion 2) How to control the orientation of the satellite? Passive systems Magnetorquers B-dot algorithm Testing with 3D helmholtz coils system Reaction wheel
Gyroscope Measure angular velocity Types MEMS vibrating structure Optical gyroscopes Sensors
MEMS vibrating gyroscope Uses Coriolis force Hurricanes Toilets Sensors
MEMS vibrating gyroscope Uses Coriolis force Sensors
Optical gyroscope Sensors Developed soon after the discovery of laser technology Operate under the principle of the Sagnac effect 6
Optical gyroscope Polarised light interference Sensors 7
Gyroscope main parameters Sensitivity [deg/s] Noise [deg/s] Bandwidth [Hz] Full-scale [deg/s] Zero drift and temperature drift [deg/s] Sensitivity drift Cross-axis Sensors 8
Magnetometer Measure three-axis magnetic field Possible detect position relative to the Earth IGRF or WMM2015 model Types Fluxgate AMR Hall-effect Sensors
Fluxgate magnetometer Uses saturation of high permeable core Very high sensitivity (up to 1nT) Sensors 10
Fluxgate magnetometer Sensors 11
Fluxgate magnetometer Sensors 12
Sensors 13
AMR (Anisotropic Magnetoresistance) Sensors Changes the value of its electrical resistance in an externally-applied magnetic field. 14
AMR (Anisotropic Magnetoresistance) Sensors 15
AMR (Anisotropic Magnetoresistance) Null-field offsets Sensors 16
AMR (Anisotropic Magnetoresistance) Temperature drift Sensors 17
AMR (Anisotropic Magnetoresistance) Set/reset procedure Sensors Reduces null-field offset and temperature drift offset 18
Magnetometer main parameters Sensitivity [ut or Gauss] (1gauss = 100uT) Noise [ut] Bandwidth [Hz] Full-scale [ut] Zero drift [ut] Temperature drift [ut/ C] Sensitivity drift [%/ C] Cross-axis [%] Sensors 19
Earth sensor 16x4 px thermopile Sensors Detects earth-space horizon based on the temperature difference
Sun sensor Detects position of the Sun Types: PSD detector QUAD detector Sensors
PSD detector measure a position of a light spot in one or two-dimensions on a sensor surface High precision Sensors
Quad photodiode detector Incoming light is focused on the detector as a spot Comparing of the output currents received from each of the four quadrants = position of light source 23
Calibration 24
VÝSTUP SNÍMAČA 1) Attitude Determination Sun-sensors orthogonality Calibration Sun-sensors 100 80 60 40 20 0-40 -30-20 -10 0 10 20 30 40-20 -40-60 -80 y = -2.437x - 0.7143-100 UHOL VZHĽADOM K ZDROJU SVETLA [ ] X- X+ Y+ Y- X- polo X+ polo Y+ polo Y- polo Linear (Y-) 25
Star tracker Sensors Optical device that measures the position(s) of star(s) using photocell(s) or a camera. 26
Sensors 27
Sensor fusion Gyroscope Drift Low-pass noise Poor response Magnetometer Noisy low-drift Sensor fusion 28
2) Attitude control Passive systems Magnetic stabilization B-dot algorithm Testing with 3D helmholtz coils system Reaction wheel 29
2) Attitude control Passive magnetic stabilization Uses permanent magnet 2-axis stabilization Passive systems 30
2) Attitude control Gravitation Gradient Stabilization Passive systems Different distance of the two masses m1 and m2 to the center of gravity -> F1 > F2 Centrifugal forces Fz1 and Fz2 also different 31
2) Attitude control Gravitation Gradient Stabilization Example of a Gravitational Stabilized Satellite (UoSat-12) Passive systems 32
2) Attitude control Spin-Stabilization Rotating mass has an inherent stability (just like a spintop) Long duration stability around the spinning axis Antenna and instruments are rotating Solar arrays must be body mounted Examples: INTELSAT I, II und III, METEOSAT, MSG Passive systems 33
2) Attitude control Reaction wheels Implemented as special electric motors Reaction wheels rotation speed is changed - counter-rotate proportionately through conservation of angular momentum 34
2) Attitude control Reaction wheels 35
2) Attitude control Active magnetic stabilization Complexity (Actuators, Sensors, Software) Magnetic stabilization Not for interplanetary missions (require external magnetic field)
2) Attitude control Magnetorquer Small coercivity is required Higher permeability = lower energy Magnetic stabilization
2) Attitude control Magnetic stabilization 38
2) Attitude control B-dotequation m = k B Magnetic stabilization Commanded magnetic dipole moment Proportional gain Derivation of the magnetic field 39
2) Attitude control B-dot algorithm Magnetic stabilization Magnetorquers 40
2) Attitude control Testing of ADCS 3D hemholtz coils system Generates an external magnetic field Air bearing Creates conditions of microgravity Testing
2) Attitude control Magnetic stabilization 42
2) Attitude control Magnetic stabilization 43
ANGULAR VELOCITY [ /SEC] 2) Attitude control Magnetic stabilization B-dot axis Y-Z 35 30 25 20 15 y = 29.838e -0.019x y = 30.506e -0.029x 10 5 0 0 5 10 15 20 25 30 35 ČAS bez b-dot z b-dot z-os Expon. (bez b-dot z) Expon. (b-dot z-os) 44
Thank you for your attention 45