Optical Inter-Satellite Links for CubeSat Satellites

II SCIENTIFIC FORUM OF TELECOMMUNICATIONS: THEORY AND TECHNOLOGY TTT-2017 (Kazan, November 20 - 24, 2017)

Transcript

1. Optical Inter-Satellite Links for CubeSat Satellites 12.03.2019 Page 1 Zlata Gibalina, Vladimir Fadeev II SCIENTIFIC FORUM TELECOMMUNICATIONS: THEORY AND TECHNOLOGY TTT-2017 Kazan, November 20 - 24, 2017
2. Structure of the presentation oIntroduction oCubsat format oInter-Satellite Link (ISL) oRadio Frequency ISL oOptical ISL o Link budget o Pointing, Acquisition and Tracking (PAT) system oComparison optical and RF ISL oConclusion Page 2
3. INTRODUCTION: Cubesat format • a type of miniaturized satellite for space research, Earth observation, amateur radio on the Low Earth Orbit Page 3 Pic. from http://www.space.aau.dk/cubesat/ Cubesat format Dimensions, cm Mass, kg 1 U 10 x 10 x 10 1.33 1.5 U 15 x 10 x 10 2 2 U 20 x 10 x 10 2.66 3 U 30 x 10 x 10 4 6 U 30 x 20 x 10 12
4. INTRODUCTION: Inter-Satellite Link • is a link between satellites, which provides: • Communication and exchanging information directly between satellites • Can be a data relay to ground Page 4 Pic. from www.slideshare.net/ajal4u/design-of-the-satellite-link
5. INTRODUCTION: Existing projects • QB50 • RF ISL between Cubesat (90 km) • 50 cubesats (2U, 3U) • Thermospheric research • Launch in 2017 • Bitrate 0.5 – 10 kbps Page 5 • OCDN (Optical Communication and Sensor Demonstration Program) – the optical downlink/uplink communication (RF communication if optical link cant not be established; optical ISL – 2 km) – Two 1.5U Cubesat – 30 cm diameter telescope located on Mt. Wilson in southern California – Bitrate 5-50 Mbps – Pointing accuracy of 0.1  Tam Nguyen, Kerri Cahoy, ’Laser Beacon Tracking for Free-space Optical Communication on Small-Satellite Platforms in Low-Earth Orbit’, 2015
6. RF ISL: Link budget Page 6 Required power in dBm assuming thermal noise:
7. OPTICAL ISL: Block diagram Page 7 Communication processing electronics Laser diode Optical transmitter Optical receiver Optical detector Communication processing electronics PAT system PAT system FREE SPACE CHANNEL
8. OPTICAL ISL: Link budget Page 8 is path loss; is transmit power; is receive power; = 4 2 is receive area, is aperture of receiver; R is distance between satellites; is transmit beam divergence angle
9. OPTICAL ISL: Required received power Noise variance calculation: • PIN receiver • APD receiver Page 9 T – temperature, k – Planck constant, - photodiode resistance, - bit rate, q – electron charge, 2 - Personick integral, - dark current, - base-emitter current, M – gain, F – noise factor
10. OPTICAL ISL: Required transmit power Page 10
11. OPTICAL ISL: Block diagram Page 11 Communication processing electronics Laser diode Optical transmitter Optical receiver Optical detector Communication processing electronics PAT system PAT system FREE SPACE CHANNEL
12. OPTICAL ISL: PAT system There are three modes: 1.Acquisition: compensation initial beam pointing error due to spatial acquisition errors from spacecraft location prediction errors. 2.Tracking: it track out local angular disturbances transmitted from the host platform and the dynamic elements of the payload with submicroradian accuracy. 3.Pointing: wherein the terminal‘s optical head is pointed towards the opposite satellite after compensation for reactive platform motions and finite transmit time of light. Page 12 PAT system is developed for the NASA OCDN project: • pointing accuracy of 0.1. Possible laser beam divergence: • 2.1 mrad (0.12). Tam Nguyen, Kerri Cahoy, ’Laser Beacon Tracking for Free-space Optical Communication on Small-Satellite Platforms in Low-Earth Orbit’, 2015
13. COMPARISON: RF vs Optical ISL Page 13 Optical ISL RF ISL Transmit power, W 1 1 Distance, km 100 100 Received power, dBm a) -40.1 b) -48 a) -88.2 b) -75.5 c) -67.9 Required receiver sensitivity, dBm PIN: -52.9 APD: -65.5 -102 a) = 0.2 b) = 0.5 a) = 5.8 b) = 25 c) = 60
14. CONCLUSION In optical case we have lower required received power and lower power consumption (in APD case). However, RF case has greater margin and does not require too much precise pointing, acquisition and tracking and can be implemented more easily. RF can be better solution for cubesat ISL, than optical. Page 14