A LATERAL SENSOR FOR THE ALIGNMENT OF TWO FORMATION-FLYING SATELLITES · · 2013-06-12ALIGNMENT...

Centre Spatial de Liège

A LATERAL SENSOR FOR THE ALIGNMENT OF TWO

FORMATION-FLYING SATELLITES

slide 1

S. Roose(1), Y. Stockman (1), Z. Sodnik(2)

(1) Centre Spatial de Liège, Belgium(2) European Space Agency - ESA/ESTEC

5th International Conference on Spacecraft Formation Flying Missions and TechnologiesMunich City, Germany, May 29 – 31, 2013

Centre Spatial de LiègeOutline

Concept and Design

Introduction

slide 2

The instrument

Conclusions

Performance and qualification tests



Introduction

Goal of the projectTo develop an EQM of a coarse lateral sensor for flight formation as PROBA III.

Requirements– Lateral displacement measurement– 5 arcsec resolution in a measurement volume of +/- 5 arcdeg and depth of

25 m to 250 m– Sun in the FOV

Large OP temperature range ( 40°C + 60°C)

slide 3

– Large OP temperature range (-40 C + 60 C)– Only lateral displacement “d” shall be measured (ambiguity with tilt “t” is

taken up by S/C: t<<d)

d

t

Satellite 1

Satellite 2



CSL solution The concept •

Barrel

Cube

Filter

BS

LD

Detector unitSTAR1000Detector

Lens

EGSE Corner cube

TTL

RS422 Link

Concept and design

slide 4slide 4

LDLaser diode driver

Optical fiber

The H/W is based on detection head with single camera derived from earlier

heritage of scientific camera developments (Integral-OMC (optics, lenses),

Proba II-SWAP (camera, electronics)).



CLS general design

Cube

Fiber collimator

Barel

Corner cube

Source unit

Camera head

Concept and design

slide 5slide 5

• A corner cube (50 mm - diameter) on the Occulter S/C.

• A CLS telescope unit containing a barrel, lens(es), filter, cube.

• A CLS camera head unit Cypress HAS 2 CMOS APS detector.

• The centroid data is downloaded via an RS422 link to an EGSE.

• The laser diode driver is controlled via the detector unit.

• The laser diode itself is a fiber laser diode.

• A source unit powering the laser diode and detector voltages

• EGSE to manage the system

EGSE

Power Cable RS422 link

Optical fibre



What is critical in the system design

High SNR for high centroidisation accuracy

Dynamic range of 80 in the measurement volumeSmall integration time (camera, electronics noise reduction: 1ms)Telecentric optics (nearly absolute angle sensor)CLS signal needs to be high wrt. Sun signal level

Concept and design

slide 6

Choice of sourceNeed of 17 W optical power to have a sun/signal ratio of 1Spectral choice where detector has high sensitivity and wherepowerful lasers are available.+ rejection filter of the sun lightBUT only 8 W available from the S/C

Fiber coupled DIODE of 18W in CW, 980 nm; NA 0.22



CLS DU Algorithm Design

Acquisition algorithm– Sun in FoV– Occulter & sun in motion

Background pixels removal by differentiation– [Spot on] – [spot off]

Small exposure time (1 ms)

slide 7

p ( )– Sensor readout min 100 ms– Processing in Horizontal stripes

Overlapping conditions– Blooming on occulter edges– Motion creates artifacts on edges



Optical designAngle to position converterTelecentric design

Concept and design

slide 8

• In front NDF OD=2 (also heat filter)• IF filter 10 nm width @980 nm (-50°C to 70°C) 0.03 nm/K temperature slope • All substrates BK7 with RadHard equivalent• Nominal Distortion in FOV (@ 293 K) < 0.05% Detector Size• Calibration needed to bring it in 0.01% Detector Size• (nearly absolute detector)• 0.01% Detector Size for 50% of FOV


D.U. Operating principles – DU controls Laser diode on/off– Reflected spot image captured on HAS2 sensor

• 1024x1024 pixels (18 µm pitch)– Operating states :

• Acquisition :

CLS Detector Unit

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– DU searches full array for valid spot– Sun in FoV => sensor blooming issue– Motion : 1 mm/s at detector level– Exposure time : 1 msec

• Tracking : – DU acquires small window “centered” on spot– DU computes CoG (=> 0,1 pixel accuracy)– CoG Readout through TM/TC


Centre Spatial de LiègeLaser Diode Driver



Performance and qualification tests

Assembly

Telescope WFE

Detector Spot

Integration

Range and resolution

Straylight test

Verification

slide 11

Distance test

Interruption/recovery testQualification tests

Thermal vac test

Vibration

Performance tests


Centre Spatial de LiègeSystem performance test

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CLS X-Calibration y = 102.36x + 493.08R2 = 1.00

0

256

512

768

1024

-5 -4 -3 -2 -1 0 1 2 3 4 5

Angle (Arcdegree)

Cen

troi

d po

sitio

n (P

ixel

)


Centre Spatial de LiègeStray light test

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0

200

400

600

800

1000

0 40 80 120 160 200 240 280

Time (s)

Cen

troi

d po

sitio

n(D

etec

tor p

ixel

)


Centre Spatial de LiègeThermal test

Operating mode Non-operating mode Switch-on Equipment

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T min T max T min T max

CLS optics: -40°C +55°C -60°C +70°C -40°C

CLS electronics: -20°C +50°C -30°C +60°C -20°C

In full temperature range for an object

located at 13.2 m.

• Accuracy 0.1 pixels centroidisation

• Focal length stability of 0.4%

• Repeatability of the optical axis of 0.3 pixels580

581

582

583

12:00:00 12:36:00 13:12:00 13:48:00 14:24:00


Centre Spatial de LiègeVibration test

Test Objectives Verify the survival to a vibration test. Test parameters Range and resolution test (at CSL)

CSL Functional test in situ with test corner cube Random vibration test 3-axis

• Low level sine test • Random test (25 grms) • Low level sine test

CSL Functional test in situ with test corner cube Sine vibration test 3-axis

• Low level sine test • Random test (25 grms) • Low level sine test

CSL Functional test in situ with test corner cube Range and resolution test (at CSL)

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Range and resolution test (at CSL) Success criteria Range and resolution curve shall be the same before and after

vibration test.

0

50

100

150

200

250

300

0 500 1000 1500 2000

Acce

lera

tion

(m/s

2)

Frequency (Hz)

Low level Y-sine after Y-shock test

CAM_Y

TEL_Y

REAR_Y

The camera and telescope have survived the high level

sinus, random and shock test in the 3–axis.

Stable Eigen frequencies at 239 Hz (which are above

140 Hz) as predicted in the FE model


Centre Spatial de LiègeSummary table

Technical requirements

Operational measurement distance: Designed for 25 to 250 mVerified in ambient conditions to 84 mIn thermal vacuum tested @13.2 m

Lateral displacement range (in two

dimensions):

±5arcdeg

In thermal vacuum tested @ 0.5 arcdeg

Lateral displacement accuracy (3 Sigma): Centroidisation accuracy < 3.6 arcsec (13.2 m to84 m, ±5arcdeg)Absolute calibration 0.3% in the interval of±5arcdeg

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±5arcdeg

Maximum lateral range rate: 0.5 arcdeg/s

Measurement bandwidth: 980 nm

Total radiation dose (5 mm aluminium

shielding)

Compliant for FM with Rad-Hard components

Total mass 1.6 kg DU + 1.6 kg SU cables excluded

Total power consumption 7.85W average

Operational pressure range Bar to 1e-6 mbar

Data interface RS422

Operational Temperature range -40 °C to +60°C

Thermal environment and test requirements Cold start up of the detector head demonstrated

Centre Spatial de LiègeConclusion

The functional, performance and stray light tests on the CLS

have demonstrated that the CLS head is conform (@1 bar,

@293 K) in terms of:

• Position resolution of 3.6 arcsec within the FOV (with

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the sun in the FOV)

• Acquisition and tracking speed of 0.5 arcdeg/s (with

the sun in the FOV)

A CLS is ready to be used for PROBA III


Centre Spatial de LiègeConclusion

Thank you for your attention

Any question

slide 18

y q


A LATERAL SENSOR FOR THE ALIGNMENT OF TWO FORMATION-FLYING SATELLITES · · 2013-06-12ALIGNMENT...

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Transcript of A LATERAL SENSOR FOR THE ALIGNMENT OF TWO FORMATION-FLYING SATELLITES · · 2013-06-12ALIGNMENT...