A LATERAL SENSOR FOR THE ALIGNMENT OF TWO FORMATION-FLYING SATELLITES

Transcription

1 A LATERAL SENSOR FOR THE ALIGNMENT OF TWO FORMATION-FLYING SATELLITES S. Roose (1), Y. Stockman (1), Z. Sodnik (2) (1) Centre Spatial de Liège, Belgium (2) European Space Agency - ESA/ESTEC slide 1

2 Outline Introduction Concept and Design The instrument Performance and qualification tests Conclusions slide 2

3 Introduction Goal of the project To 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) Only lateral displacement d shall be measured (ambiguity with tilt t is taken up by S/C: t<<d) Satellite 1 t Satellite 2 d slide 3

4 Concept and design CSL solution The concept EGSE RS422 Link TTL Detector unit STAR1000 Detector Barrel BS Lens Filter Cube Corner cube LD Laser 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)). slide 4

5 Concept and design CLS general design Corner cube Fiber collimator Camera head Cube Barel Source unit Optical fibre 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 Power Cable EGSE RS422 link slide 5

6 Concept and design What is critical in the system design High SNR for high centroidisation accuracy Dynamic range of 80 in the measurement volume Small integration time (camera, electronics noise reduction: 1ms) Telecentric optics (nearly absolute angle sensor) CLS signal needs to be high wrt. Sun signal level Choice of source Need of 17 W optical power to have a sun/signal ratio of 1 Spectral choice where detector has high sensitivity and where powerful lasers are available. + rejection filter of the sun light BUT only 8 W available from the S/C Fiber coupled DIODE of 18W in CW, 980 nm; NA 0.22 slide 6

7 CLS DU Algorithm Design Centre Spatial de Liège Acquisition algorithm Sun in FoV Occulter & sun in motion Background pixels removal by differentiation [Spot on] [spot off] Small exposure time (1 ms) Sensor readout min 100 ms Processing in Horizontal stripes Overlapping conditions Blooming on occulter edges Motion creates artifacts on edges slide 7

8 Concept and design Optical design Angle to position converter Telecentric design In front NDF OD=2 (also heat filter) IF filter 10 nm 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 slide 8

9 CLS Detector Unit 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 : 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 slide 9

10 Laser Diode Driver

11 Performance and qualification tests Assembly Telescope WFE Detector Spot Integration Verification Range and resolution Straylight test Distance test Qualification tests Interruption/recovery test Thermal vac test Vibration Performance tests slide 11

12 System performance test CLS X-Calibration y = x R 2 = 1.00 Centroid position (Pixel) Angle (Arcdegree) slide 12

13 Stray light test 1000 Centroid position (Detector pixel) Time (s) slide 13

14 Thermal test Equipment Operating mode Non-operating mode Switch-on 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 583 located at 13.2 m. Accuracy 0.1 pixels centroidisation Focal length stability of 0.4% Repeatability of the optical axis of 0.3 pixels :00:00 12:36:00 13:12:00 13:48:00 14:24:00 slide 14

15 Vibration test Test Objectives Test parameters Success criteria Verify the survival to a vibration test. 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) Range and resolution curve shall be the same before and after vibration test. Acceleration (m/s2) Low level Y-sine after Y-shock test 300 CAM_Y 250 TEL_Y 200 REAR_Y Frequency (Hz) 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 slide 15

16 Summary table Technical requirements Operational measurement distance: Lateral displacement range (in two dimensions): Lateral displacement accuracy (3 Sigma): Maximum lateral range rate: Measurement bandwidth: Total radiation dose (5 mm aluminium shielding) Total mass Total power consumption Operational pressure range Data interface Operational Temperature range Thermal environment and test requirements Designed for 25 to 250 m Verified in ambient conditions to 84 m In thermal vacuum m ±5arcdeg In thermal vacuum 0.5 arcdeg Centroidisation accuracy < 3.6 arcsec (13.2 m to 84 m, ±5arcdeg) Absolute calibration 0.3% in the interval of ±5arcdeg 0.5 arcdeg/s 980 nm Compliant for FM with Rad-Hard components 1.6 kg DU kg SU cables excluded 7.85W average Bar to 1e-6 mbar RS C to +60 C slide 16 Cold start up of the detector head demonstrated

17 Conclusion The functional, performance and stray light tests on the CLS have demonstrated that the CLS head is conform K) in terms of: Position resolution of 3.6 arcsec within the FOV (with 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 slide 17

18 Conclusion Thank you for your attention Any question slide 18