Nanosatellite Lasercom System

Transcription

1 Nanosatellite Lasercom System Rachel Morgan Space Telecommunications, Astronomy, and Radiation Lab Massachusetts Institute of Technology August 9,

2 Outline Introduction Design Approach Link Budget Results Benchtop Prototyping Results Conclusions 2

3 Laser Communications: Motivation for CubeSats Laser communications offers faster data rates with smaller, lower power systems and with fewer regulatory hurdles 3

4 CLICK- CubeSat Lasercom Infrared CrosslinK 1.5U CubeSat payload to demonstrate lasercom crosslinks between two 3U LEO CubeSats Designed, analyzed, and prototyped transceiver capable of 20 Mbps data rate crosslinks at ranges of over 500 km Low-cost, scalable system could enable new classes of small satellite missions: Swarms for remote sensing Global constellations for communications 4

5 Outline Introduction Design Approach Concept of Operations Optical Design Link Budget Results Benchtop Prototyping Results Conclusions 5

6 Concept of Operations 6

7 Optical Design Overview 4 optical signals: Beacon Transmit Receive Calibration of MEMS FSM COTS-based design Wavelength division for full duplex operations Credit: Michael Long 7

8 Outline Introduction Design Overview Link Budget Results Communications link Beacon to camera link Beacon to quadrant cell detector link Benchtop Prototyping Conclusions 8

9 Laser Communications Link Range 25 km 100 km Optical signal power (W) km Wavelength (nm) 1550* 1550* 1550* Pointing loss (db) Half power beam width (mrad) Free space path loss (db) Optical loss (db) Data rate (Mbps) Sensor responsivity (A/W at 1550 nm) Margin (db) *wavelengths approximated here, will actually be 1535 and 1565 nm Design meets recommended 3dB margin for all mission distances 9

10 Beacon to Camera Link (ACDS) Range 25 km 100 km Optical signal power (W) km Wavelength (nm) Pointing loss (db) Half power beam width (rad) Free space path loss (db) Optical loss (db) Sensor responsivity (A/W at 976 nm) Signal to noise ratio (db) e- count Simulated point spread function image received by camera at 20 km range 10

11 Beacon to Quadcell Link (FSM feedback) Range 25 km 100 km Optical signal power (W) km Wavelength (nm) Pointing loss (db) Half power beam width (rad) Free space path loss (db) Optical loss (db) Sensor responsivity (A/W at 976 nm) Signal to noise ratio (db)

12 20 Mbps with 3 db margin out to 500+ km Meets recommended 3dB margin out to 500+ km 12

13 5 Mbps with 3 db margin out to km Meets recommended 3dB margin out to km 13

14 Outline Introduction Design Approach Link Budget Results Benchtop Prototyping Results Conclusions 14

15 Transmitter Prototype 2-inch collimating assembly simulates far-range transmitter Interchangeable fibercoupled lasers at representative wavelengths 15

16 Transceiver Prototype 16

17 Results Measured communications signal received on APD with oscilloscope Detected beacon signal on target (placeholder for quadcell detector) 17

18 Conclusions CLICK is a technology demonstration payload expanding capabilities of CubeSats Transceiver design has been Designed Analyzed Prototyped Next steps: Implement pointing capabilities, modulation More realistic prototypes Testing for flight demonstration 18

19 Acknowledgements- Thank You! Prof. Kerri Cahoy Grad student Mike Long Rest of FLARE/CLICK team SmallSat Judges and Organizers MIT SuperUROP Program Northrop Grumman Corporation Questions? 19

20 References 1. Clements, E. and R. Aniceto et al., Nanosatellite Optical Downlink Experiment: Design, Simulation, and Prototyping, Optical Engineering, vol. 55, No. 1, November Janson, S. and R. Welle, The NASA Optical Communication and Sensor Demonstration Program, Proceedings of the 27 th Annnual AIAA/USU Conference on Small Satellites, Logan, UT, August Gregory, M. and F. Heine et al., TESAT Laser Communication Terminal Performance Results on 5.6 Gbit Coherent Inter Satellite and Satellite to Ground Links, Proceedings of the International Conference on Space Optics ISCO, Nag, S., Design and Analysis of Distributed Nano-Satellite Systems for Multi-Angular, Multi- Spectral Earth Observation, Proceedings of the 64 th International Astronautical Congress, Shuber, P. and A. Cline et al., System Design of Low SWaP Optical Terminals for Free Space Optical Communications, Proceedings of SPIE, vol , Kingsbury, R., Optical Communications for Small Satellites, PhD Dissertation, Massachusetts Institute of Technology, Cambridge, MA, Nyugen, T., Laser Beacon Tracking for Free-Space Optical Communication on Small-Satellite Platforms in Low-Earth Orbit, Master s thesis, Massachusetts Institute of Technology, Cambridge, MA, Ramsey, P. C., Spectral Irradiance from Stars and Planets, Above the Atmosphere, from.1 to Microns, Applied Optics, vol. 1, issue 4,

21 Figures Slide 3: Emily Clements (MIT) Slides 1, 4, 6: Derek Barnes (MIT) Slide 7: Michael Long (MIT) Slides 10, 12-13, 15-17: Rachel Morgan (MIT) 21

22 BACKUP- Quadcell Overview Source: 22

23 BACKUP- Pointing Budget Parameters (1/2) Courtesy of Chris Roll 23

24 BACKUP- Pointing Budget Parameters (2/2) Parameter Beacon Divergence FWHM Beacon Camera FOV Body pointing (with beacon on camera feedback) Quad cell FOV Quad Cell angular sensitivity APD FOV (with lens) Demonstrated accuracy of FSM (tested with disturbances) Value 1.2º or 4320 arcsec ~45,000 arcsec ~400 arcsec ~440 arcsec ~3 arcsec ~115 arcsec <12 arcsec Conclusion: body pointing and FSM feedback will be good enough to close link Note: numbers based on 25 km lowest link distance, ConOps subject to change 24

25 BACKUP- Pointing Demonstration Sinusoidal Disturbance, 100 arcsec, 1 Hz FSM Feedback on Demonstrated better than 12 arcsec pointing control 25 Image credit: Dr. Hyosang Yoon

26 BACKUP- Pointing Demonstration Have used this setup to simulate ( mean, σ) arcseconds error which is realistic for a star tracker-only CubeSat system. Once the fine pointing control is activated, we have shown in hardware ( mean, σ) arcseconds error. Credit: Emily Clements and Hyosang Yoon 26

27 BACKUP- Optical Components Courtesy of Chris Roll 27

28 BACKUP- Communications Link Budget Specifications Parameter Value Justification Laser power (W) Optic Diameter (m) Pointing loss (db) Wavelength (nm) Half Power Beam Width (mrad) PPM Transmit loss (db) Receiver Loss (db) 0.2 Design choice 0.02 design 3 Pointing within HPBW 1550 Analyzing 1550 assuming real performance at 1535/1565 will be similar From Chris Roll Zemax analysis 128 Changed according to data rate (128 maps to ~5 Mbps) *2 (lenses, thorlabs c coating)+1.5 (TBD dichroic BS) +.22 (dichroic) *3 (lenses, thorlabs c coating)+1.5 (TBD dichroic) +.22 (dichroic) APD responsivity 0.99 From Laser Components IAG200T6 spec sheet, M=10 Transmitter extinction ratio Noise Equivalent Power (W/Hz^.5) APD gain Optical filter width (nm) APD Sensitive Diameter (mm) Bit error rate 38 From ryan kingsbury s thesis 3.20E-11 From APD spec sheet 10 Baseline in spec sheet, factory setting 20 Filter spec.2 APD Spec Sheet 1e-4 Can be handled with coding 28

29 BACKUP- Beacon to Camera Link Budget Specifications Parameter Value Justification Input power (W) Wavelength (nm) HPBW (rad) Detector Quantum Efficiency Receive Aperture diameter (m) 0.5 Current design 976 To keep same as NODE and use existing quadcell circuit Current design 0.02 Aptina MT9P Schneider lens (same as NODE) Filter bandwidth (nm) 10 Current design This is minimum assumption from Tam cloud cover analysis, meant to Background Spectral be conservative estimate before refining this value to reflect expected Radiance (W/m^2/sr/um) stellar noise and stray light 29

30 BACKUP- Beacon to quadcell link specifications Parameter Value Justification Quadcell Input power (W) Wavelength (nm) HPBW (rad) Transmit Optics Loss (db) Pointing Loss (db) Receive Optic diameter (m) Receive optics loss (db) Responsivity Dark current (A) Fitler width (nm) Integration time (s) Background star radiance (W/m^2/um) Hamamatsu S Current design 976 To keep same as NODE and use existing quadcell circuit Current design 1 Assumed, conservative estimate 3 Assuming pointing within HPBW 0.02 Current design 6 Assumption, will fix with updated optics 0.7 Hamamatsu S Detector spec sheet 10 Need to fill in selected filter 6.00E-04 Assuming constant int time Derived from worst case stellar radiance at beacon wavelength, 1.00E-07 conservative estimate for background noise 30

31 BACKUP- NODE Status Credit: Raichelle Aniceto 31

32 BACKUP- Why 2 FSMs? For fine pointing/steerin g control For calibration to account for launch-induced misalignments 32