Presentación Tesis

Autor: Agustín García Sáez

Director: José Manuel Quero Reboul

1. Introduction

2. State of the art

3. Objectives and motivation

4. Theoretical study of the sensor

5. Prototype manufacturing

6. Evaluation

7. Conclusions

Table of contents

Collaboration between MEMS research

group and Instituto Nacional de Técnica

Aeroespacial (INTA) for development of

payloads

Idea of studying of an Earth sensor for

integration into the Microsat mission

Financial support by group own funds

1. Introduction

Earth’s

magnetic field

North

magnetic pole

South

magnetic pole

Sun

Magnetic

vector

Solar

vectorNadir

vector

Vast progress in the space industry and development of small satellites

Need for more integration of attitude control instruments with high accuracy

New concept of Earth sensor based in Earth thermal emission

1. Introduction

2. State of the art 2.1. Attitude control sensors

2.2. Earth sensors

2.3. Simulation tools

2.4. State of art conclusions




6. Evaluation

7. Conclusions

Table of contents

2.1. Atittude control sensors

Many technologies related to attitude controlling:

Sun sensors: High accuracy but need of the Sun in fov.

Star trackers: High accuracy but complex and expensive devices.

Magnetometers: Difficulty to sense Earth‟s magnetic field with high accuracy.

Earth sensors: Can reach good accuracy. Simple electronics and processing

software. Main technologies: quantum, pyroelectric and thermopile detectors.

MAG-30 magnetometer

by Satrec Initiative

NanoSSOC-D60 Sun

sensor by Solar MEMS

TDP 6 Star Tracker of

Alphasat mission

Jain, Y.K.; Alex, T.K.; Kalakrishnan, B. “Ultimate IR Horizon Sensor”,

IEEE transactions on Aerospace and Electronics System, 1980, Vol.

AES-16, Issue 2, pp. 233-238.

3σ error: 0.022 º

Weight: 4 kg

W.G. Krigbaum, Shu-Jone Lee, A.Y. Okamoto, G.T Sakoda,

“Microbolometer earth sensor assembly”, U.S. Patent 6026337 A, Feb. 15,

2000.

3σ error: 0.137 º

Weight: no data

C. Hersom, Z. Afik, A. Hollinger, P.J. Thomas, “Satellite attitude sensor

using thermal imaging”, U.S. Patent 6066850 A, May. 23, 2000.

3σ error: 0.05 º

Weight: no data

Based on radiant balance on the device

Output signal very small and overshadowed

by noise generated internally → cooling

problem

2.1. Earth sensors: Quantum detectors

Crystalline material: electric charge moving when temperature gradient

Based on Earth – background space transition detection → generation of a

negative/positive voltage pulse

Scanning → moving parts

2.2. Earth sensors: Pyroelectric detectors

𝑑𝑇

𝑑𝑡> 0

2.2. Earth sensors: Pyroelectric detectors

Sensor Mass Power

consumption

Accuracy

(3σ error)

MiDES Servo

Corporation

of America

1.5 kg 0.8 W ±0.04°

Earth

sensor

by SSBV

0.5 kg

plus optics &

mounting feet

1.5 W ±0.2°

IRES

SELEX

Galileo

2.5 kg 4 W ±0.05°

STD16

EADS

SODERN

3.5 kg 7.5 W ±0.06°

Based on radiant balance on the device.

Seebeck effect : p-n union with different

temperature junctions produces a voltage

Dependence of temperature. Must be

taken into account.

V = S · ( Thot - Tcold )

V : Output voltage

S : Seebeck coefficient

Thot , Tcold : Temperature of the junctions

2.2. Earth sensors: Thermopile detectors

2.2. Earth sensors: Thermopile detectors

Sensor Mass Power

consumption

Accuracy

(3σ error)

MAI-SES Maryland

Aerospace

66 g

plus enclosure 0.264 W

±0.25°

(resolution)

IRES-C SELEX

Galileo

1.5 kg 3.3 W ±1° (LEO)

±0.36° (GEO)

PSSCT-2

pico-satellite /

STS-135

mission

No data No data ±0.5°

Siegfried W. Janson, Brian S. Hardy, Andrew Y. Chin, Daniel L. Rumsey, Daniel A. Ehrlich and

David A. Hinkley, “Attitude Control on the Pico Satellite Solar Cell Testbed-2 ”, The Aerospace

Corporation.

N. Scheidegger, R. Krpoun, H. Shea, C. Niclass and E. Charbon, “A new Concept for a Low-Cost

Earth Sensor: Imaging Oxygen Airglow with Arrays of Single Photon Detectors”, 30th annual AAS

guidance and control conference. February 3-7, 2007.

Ghose, K. ; Shea, H. , “A micromachined Earth sensor based on measuring the gravity gradient

torque”, ASME 2009 International Mechanical Engineering Congress & Exposition, Lake Buena

Vista, Florida, USA. November 13-19, 2009.

2.2. Earth sensors: Other technologies

Sensor Mass Power

consumption

Accuracy

(3σ error)

Earth Sensor

based on imaging

oxygen airglow

(CMOS camera)

No data No data LEO: ±7.5°

GEO: ±0.9°

Inertial MEMS

Earth sensor 0.5 kg 5 W ±5°

None simulation model useful to the

proposed sensor

Need to develop our own modeling

2.3. Modeling and simulation tools

Simulation of the

airglow

measurement by

the pixel array of

the CMOS sensor

N. Scheidegger, R. Krpoun, H. Shea, C. Niclass and E.

Charbon, “A new Concept for a Low-Cost Earth Sensor:

Imaging Oxygen Airglow with Arrays of Single Photon

Detectors”, 30th annual AAS guidance and control conference.

February 3-7, 2007.

Jain, Y.K.; Alex, T.K.; Kalakrishnan, B. “Ultimate IR Horizon

Sensor”, IEEE transactions on Aerospace and Electronics

System, 1980, Vol. AES-16, Issue 2, pp. 233-238.

J. Rogers, M. Costello, “Low Cost Orientation Estimator Smart

Projectiles using Magnetometers and Thermopiles”, Journal of

the Institute of Navigation, Vol. 59, pp. 9-24, Issue 1, 2012. Thermopile geometry simulation

and electrical behavior

Many technologies used for Earth sensors, most of them based

in Earth thermal emission

Different kinds of thermal detectors:

Scanning (moving parts): Pyroelectric

Static: Quantum and Thermopile

Simulation model needed for studying and adjusting of the

sensor parameters

None simulation model useful to the new concept of Earth

sensor proposed

2.4. State of art conclusions

1. Introduction

2. State of the art




6. Evaluation

7. Conclusions

Table of contents


Earth sensor for integration in

nano and pico-satellites

Good integration, high accuracy

and low power consumption

Study and modeling of a new

concept of Earth sensor consisting

on thermopile detectors with

integrated optics

Microsat mission requirements:

LEO: 700 km

3σ error <0.2°

Nominal temperature range: 15 - 50°C

Detector model

Validation tests

Optics

model

Electronics

model

Radiant balance

model on sensor

Detector-optics model

Validation tests

Detector-optics behavior

model in flight conditions

Adjusting electronics

Detector-optics-electronics behavior model

Sensor behavior model in flight conditions

Sensor manufacturing

Evaluation and environmental tests

1. Introduction

2. State of the art


4. Theoretical study of the sensor 4.1. Sensor general description

4.2. Behavior models and validation

4.3 Thermal analysis

4.4 Pointing error simulations

4.5 Theoretical study conclusions


6. Evaluation

7. Conclusions

Table of contents


Earth sensor consisting on thermopile detectors with integrated optics

Four thermal detectors orthogonally distributed

Nadir pointing: each detector around 50% of Earth / background space

Cells work in pairs (differential scheme) to achieve dual-axes pointing

Cell 3

FOV

Earth

Cell 1

FOV

Cell 4

FOV

Cell 2

FOV

β (pitch)

α (roll)

Thermal

targetOptics

Signal

conditioning

Thermopile

Thermopile

output (V)

Thermistor

output (Ω)

Thermistor

Detector

Output

signal (V)

Radiant

balance

(W/m2)

Radiant

balance

(W/m2)

IR sensor ZTP-135SR by GE Sensing (integrated thermistor )

Focusing system composed of germanium lenses

Optics optimized in the 14–16 µm range (no cloud thermal effects )

Electronic design to get 0-5 V output signals

4.1. Sensor general description

Radiation balance thermopile - thermal target (parallel flat surfaces):

Thermopile output voltage:

Theoretical/experimental thermopile behavior

4.2. Behavior models and validation: Thermopile

, , · · , ,max

mínNet Target Target Tp Target Target Tpq T T Tr E T E T d

· ·Tp Active Thermopile NetV A S q

Positive meniscus geometry: low focal length

Uncoated surface: avoid transmission changes due to aging by

irradiation

Employment optics provides a more narrow

fov in comparison with a no-lens design

Germanium lens:

Good transmission in 14-16 µm band (40% – 45% )

Greater rejection of unwanted wavelengths

Good properties of toughness and strength

As a semiconductor, it provides some electrical

and irradiation shielding to the detector Optical system representation

4.2. Behavior models and validation: Optics

Goal: calculation of the response of

optics-detector set

Minimum spot size determined by

spherical aberration and diffraction

effects

Third-order aberration theory

concludes that aberration effects

prevail → minimum spot on the

focusing plane

Effect of spherical

aberration

Airy disc due to

diffraction effects

Minimum spot on the focusing plane as

function of wavelength


Proportion of the spot within the

active area → Ratio

Optimized for 14 -16 µm band

Spectral sensitivity given by:

Experimental fov of ±2.5°

Geometrical analysis as

function of the spot on the

active area of the thermopile

Proportion of the spot on the

thermopile as function of wavelength


· ·Tp GeSens Tr Ratio Tr

Thermal sources involved in the balance:

Sensor: 𝜀~1 (Kirchhoff's law of thermal radiation)

Background space: 𝜀=1 / 𝑇𝑆𝑝𝑎𝑐𝑒= 3 K

Earth: 𝜀=0.612 / 𝑇𝐸𝑎𝑟𝑡ℎ= 288.15 K / Spherical surface

Earth thermal emission: surface discretization + divergence theorem

Detail of the Earth surface discretization Detail of the fov of a cell

4.2. Behavior models and validation: Radiant balance model

2D representation of the fov of a cell in

case of 𝛼 = 𝛽 = 0° obtained with MATLAB


max

min

max

1 min

2

, , , · · , ,

, , · · · · , ,n

Net Sensor Sensor Space Space Sensor

AEarth

Sensor Earth Earth Earth SensorA

Earth

q T F Sens E T E T d

RF A Sens E T E T d dA

R d A

Geometrical study: background space and

Earth view factor as function of 𝛼 and 𝛽.

Thermal study: radiant balance modeling

as function of 𝑇𝑆𝑒𝑛𝑠𝑜𝑟.

Equation as function of 𝛼, 𝛽 and 𝑇𝑆𝑒𝑛𝑠𝑜𝑟:

1st term: sensor – background space balance

2nd term: sensor – Earth balance

Balance at 𝑇𝑆𝑒𝑛𝑠𝑜𝑟=25ºC as function of 𝛼 and 𝛽 Balance as function of 𝛽 and 𝑇𝑆𝑒𝑛𝑠𝑜𝑟

Results of radiant balance equation:

Negligible 𝛼 dependence

Great temperature dependence

Goal: minimize temperature dependence


First gain

stage (G1)

+

-

Sensor package

VTp

+

-+

Second

gain stage

(G2)

Thermal

compensation

network

VCell

RThermistorVComp

Thermopile output voltage

Electronics output voltage

Signal amplification and thermal

compensation

Worst Case Circuit Analysis (WCCA)

Microcontroller COTS (calibration

tables, SPI communication) and

thermistor for temperature monitoring Structure of one cell adaptation

4.2. Behavior models and validation: Signal conditioning

Mathematical tool for 𝛼, 𝛽 calculation

Physical meaning: comparison of the area of the Earth within the FOV in complementary cells

Normalized functions

Monotonically increase → inverse functions F can be calculated

3 4

2

3 4

, , , ,,

, , , , 2·

Cell Cell Cell Cell

Cell Cell Cell Cell off Cell

V T V Tf

V T V T V T

1 2

1

1 2

, , , ,,

, , , , 2·

Cell Cell Cell Cell

Cell Cell Cell Cell off Cell

V T V Tf

V T V T V T

Simulated 𝑓1 and 𝑓2 functions

4.2. Behavior models and validation: f functions

F functions allow obtain the pointing

angles from the cell measurements

Needed a microcontroller to storage the

F functions and to do the calculations

Extraction flow of the pointing angles:

Simulated 𝐹1 and 𝐹2 functions

1

2 1 exp 1Real

Real 3 2 exp 2

4

Cell

Cell erimental calibration Out

Cell erimental calibration Out

Cell

V

V f F

V f F

V

4.2. Behavior models and validation: f functions

Considerations:

Thermal control with an imposed base

temperature of 25°C

Low emissivity surface treatment (𝜀=0.1):

lower heat transfer to the environment

Heat flux and temperature distribution

with/without Sun radiation

Simulation results:

Maximum difference in complementary cells with Sun radiation: 1°C

Maximum difference in complementary cells in darkness: 0.2°C

Thermal simulation carried out with Comsol

4.3. Behavior models and validation: Thermal analysis

Earth thermal parameters homogeneous:

Thermal gradients in the cells + WCCA → nadir: ±0.006° / FOV limits: ±0.07°

Variation of Earth thermal parameters:

Emissivity variations of the Earth (0.612±0.05) → nadir: ±0.049° max

Thermal variations of the Earth (15±5°C) → nadir: ±0.042° max

Pointing error analysis for geostationary orbit (thermal gradients in

the cells and WCCA) → nadir: ±0.01° / FOV limits: ±0.2°

ADC influence (quantization error) → ±0.003° @ 12 bits, 𝑇𝑆𝑒𝑛𝑠𝑜𝑟=25°C

4.4. Behavior models and validation: Pointing error simulations

Differential scheme: canceling out common mode effects

Complete behavioral model developed → Adjusting of optics and

electronics for best results

Flexible model adaptable to different geometrical and thermal

conditions

Optics provided by germanium lens:

Fine FOV → Higher sensitivity/accuracy: nadir: ±0.006° / FOV limits: ±0.07°

Lower probability of interference with Sun/Moon (𝑃=0.004).

Thermal study: Heat flux and temperature gradients in the box

Pointing error characterization under non-ideal conditions

4.5. Theoretical study conclusions

1. Introduction

2. State of the art



5. Prototype manufacturing 5.1. Electrical interface

5.2. Sensor integration

5.3. Prototype manufacturing conclusions

6. Evaluation

7. Conclusions

Table of contents


Mechanical design carried out with Catia V5

Constraints: PCB size, lenses diameter and focal length

#Pin Reference Description

1 CLK SPI CLK

2 TERM- Thermistor negative pin

3 SENS4 Telemetry – Thermopile 4



6 RX SPI Rx

7 TX SPI Tx

8 TERM+ Thermistor positive pin


10 GND Telemetry GND

11 SEL SPI selection signal

12 GND Digital GND

13 VPP Microcontroller programming

14 GND Power GND

15 VCC 5V Power supply

Female D-SUB HD 15-way

connector

Group of signals:

Power supply

Internal thermistor measurement

Cell telemetries

Microcontroller programming

and SPI communication

5.1. Electrical interface

The optical detector block

includes:

Thermopile detector

Teflon cap

Focuser tube

Germanium lens

Toric gasket

Top of focuser tube

Section view of the optics

5.2. Sensor integration: Optics

Thermopile detector, Teflon cap and

focuser tube bonded with EPO-TEK

353ND epoxy adhesive

Focuser tube coiled and bonded on

the main body with epoxy adhesive

5.2. Sensor integration: Optics

Signal conditioning electronics

COTS Microcontroller (calibration tables, SPI communication)

Integrated thermistor

Female D-SUB HD 15-way connector integrated into the PCB

5.2. Sensor integration: Electronics

Germanium lens, toric gasket

and top of focuser tube

mounted on the focuser tube

PCB wired to the thermopile

detectors

Vent-holes to provide a way to

decompress the sensor cavities

5.2. Sensor integration: Final assembly

Final assembly of the Earth sensor

Manufacturing of the Earth sensor prototype based on the

optimization algorithms and simulation results

Taken into account ECSS normative

Employment of space compatible materials (teflon, silicone,

aluminum 7075 compliant and adhesive for space applications)

Low mass (246 g) and power consumption (125 mW)

5.2. Prototype manufacturing conclusions

1. Introduction

2. State of the art




6. Evaluation 6.1 Evaluation

6.2. Environmental tests

6.3. In-flight calibration procedure

6.4. Evaluation conclusions

7. Conclusions

Table of contents

Test bench includes:

Stepper motor positioner

Hot and cold thermal sources to emulate the Earth and background space

Thermal gradient: 25°C versus 285°C in-flight conditions

3σ error 0.176° (expected improvement in-flight thermal conditions)

Test bench for sensor characterization

6.1. Evaluation

Calibration

f functions

Calibration

F functions

and random

evaluation

points

6.1. Evaluation

Thermal compensation test:

Discrepancy of 1.03% between

theoretical model and test

Taken into account in the theoretical

error calculation.

Correction through characterization

Vacuum test at 10−5 mbar carried

out in climatic chambers of INTA →

No behavior change


Sensor compensation test with thermal

target at 25°C and 𝜀=0.9

Irradiation:

High energy protons (10 MeV)

Reference value test of space solar cells

Predominant radiation in LEO

Results:

Lost of thermopile sensitivity

Voltage offset in thermopile

Integrated thermistor out of nominal

values at temperatures below to -10°C

TID [krad] 6 32 65 650

Offset [µV] 0 40 160 190

Sensitivity

factor 0.95 0.9 0.85 0.8

Degradation of the f function by irradiation

Cyclotron (Centro Nacional de Aceleradores)


Recommended in commissioning phase to compensate for any

deviation of the environmental parameters

Consist on measure the signal generated by cells with 100%

background space in its FOV

Mitigate deviation effects such as aging by irradiation

Limitation: calculation of angles not possible when saturated areas

6.3. Evaluation: In-flight recalibration procedure

Environmental tests:

Thermal compensation

Vacuum

Aging by irradiation

Apt results for space qualification

Pending tests:

Thermal shock

Vibration

6.3. Evaluation: conclusions

1. Introduction

2. State of the art




6. Evaluation

7. Conclusions 7.1. Contributions

7.2. Comparison with other sensors

7.3. Future work

Table of contents

Study, design and manufacturing of a new concept of Earth sensor

with thermopile and integrated optics

Optics provides lower FOV:

Higher sensitivity and accuracy

Interference reduction with the Earth and Moon

Developing of a model behaviour of the sensor

Structure that allows the integration in nano and pico-satellites

Technology transfer to the company Solar MEMS

Pending embarking:

Microsat mission (Insituto Nacional de Técnica Aeroespacial - INTA)

Recent negotiations with Instituto de Microgravedad “Ignacio Da Riva”

7.1. Contributions

7.2. Comparison between sensors

Parameters taken into account: accuracy, mass and power consumption

Mobile parts sensors („o‟), Static sensors („*‟)

Sensor Accuracy

[3σ]

Mass

[kg]

Power

[W]

MIDES 0.04 1.5 0.8

SSBV 0.2 1 0.5

STD16 0.06 3.5 7.5

IRES 0.05 2.5 4.5

IRES-C 0.36 1.3 3

MAI-SES 0.25 0.066 0.264

mES 0.07 0.246 0.125

Deeper study of the optics to get a tighter bandwidth centered in the

14 -16 µm band

Mechanical study for the integration in nano and pico-satellites

Improvement of the test bench:

Greater thermal gradient between hot and cold surfaces

Calibration with the four cells

Final validation in Microsat mission (INTA)

Use in industrial applications for tracking and distance measurement

7.3. Future work

A. G. Sáez, J. M. Quero, M. Angulo, “Earth Sensor Based on

Thermopile Detectors for Satellite Attitude Determination”, Sensors

Journal, IEEE, Dec. 2015, Vol. 16, Issue 8, pp. 2260-2271.

A. G. Sáez, J. M. Quero, M. Angulo. “Earth thermal modeling for

infrared optical instruments of horizon sensors”, 9th IAA

Symposium on Small Satellites for Earth Observation, April 8-12

2013. Berlin, Germany.

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