sensors for orientation and control of satellites and ... · sensors for orientation and control of...

Sensors for orientation and control of satellites and space probes Space for Education, Education for Space

Space for Education, Education for Space ESA Contract No. 4000117400/16NL/NDe

Specialized lectures

Sensors for orientation and control of satellites and space probes

Ing. Ondrej Závodský

GOSPACE s.r.o.


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

Content


1) Attitude Determination

• 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

– Developed soon after the discovery of laser technology

– Operate under the principle of the Sagnac effect

Sensors

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

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• Fluxgate magnetometer Sensors

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• Fluxgate magnetometer Sensors

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1) Attitude Determination Sensors

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• AMR (Anisotropic Magnetoresistance)

– Changes the value of its electrical resistance in an externally-applied magnetic field.

Sensors

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• AMR (Anisotropic Magnetoresistance) Sensors

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– Null-field offsets

Sensors

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– Temperature drift

Sensors

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– Set/reset procedure

• Reduces null-field offset and temperature drift offset

Sensors

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• 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

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• Earth sensor

– 16x4 px thermopile

– Detects earth-space horizon based on the temperature difference

Sensors



• 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

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1) Attitude Determination Calibration

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• Sun-sensors orthogonality Calibration

25

y = -2.437x - 0.7143

-100

-80

-60

-40

-20

0

20

40

60

80

100

-40 -30 -20 -10 0 10 20 30 40

VÝ

STU

P S

NÍM

AČ

A

UHOL VZHĽADOM K ZDROJU SVETLA [°]

Sun-sensors

X- X+ Y+ Y- X- polo

X+ polo Y+ polo Y- polo Linear (Y-)



• Star tracker

– Optical device that measures the position(s) of star(s) using photocell(s) or a camera.

Sensors

26


1) Attitude Determination Sensors

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• Sensor fusion

– Gyroscope

• Drift

• Low-pass noise

• Poor response

– Magnetometer

• Noisy

• low-drift

Sensor fusion

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• Passive systems

• Magnetic stabilization

– B-dot algorithm

– Testing with 3D helmholtz coils system

• Reaction wheel

2) Attitude control

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2) Attitude control

• Passive magnetic stabilization

– Uses permanent magnet

– 2-axis stabilization

Passive systems

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2) Attitude control

• Gravitation Gradient Stabilization

– Different distance of the two masses m1

and m2 to the center of gravity -> F1 > F2

– Centrifugal forces Fz1 and Fz2 also different

Passive systems

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

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2) Attitude control Reaction wheels

34

• Reaction wheels

– Implemented as special electric motors

– rotation speed is changed - counter-rotate proportionately through conservation of angular momentum


2) Attitude control Reaction wheels

35


2) Attitude control

• Active magnetic stabilization

– Complexity (Actuators, Sensors, Software)

– Not for interplanetary missions (require external magnetic field)

Magnetic stabilization


2) Attitude control

• Magnetorquer

– Small coercivity is required

– Higher permeability = lower energy



2) Attitude control Magnetic stabilization

38


2) Attitude control

• B-dotequation 𝑚 = −𝑘 𝐵


39

Derivation of the magnetic field Proportional gain Commanded magnetic dipole moment


2) Attitude control

• B-dot algorithm

• Magnetorquers


40


2) Attitude control

• Testing of ADCS

– 3D hemholtz coils system

• Generates an external magnetic field

– Air bearing

• Creates conditions of microgravity

Testing



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43



44

y = 29.838e-0.019x

y = 30.506e-0.029x

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

AN

GU

LAR

VEL

OC

ITY

[°/

SEC

]

ČAS

B-dot axis Y-Z

bez b-dot z b-dot z-os Expon. (bez b-dot z) Expon. (b-dot z-os)


• Thank you for your attention

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