Laser Communication with CubeSats. K. Cahoy, MIT Space Telecommunications, Astronomy and Radiation (STAR) Laboratory

Transcription

1 Laser Communication with CubeSats K. Cahoy, MIT Space Telecommunications, Astronomy and Radiation (STAR) Laboratory

2 Overview Motivation Radio Frequency for CubeSats RF and Free Space Optical (FSO, lasercom) pros and cons Enabling CubeSat technologies for FSO Current and developing CubeSat FSO New technologies for CubeSat FSO MIT PorTeL Ground Station: Portable Telescope for Lasercom 2

3 What s a CubeSat? Invented in 1999 Jordi Puig-Suari (Cal Poly SLO) Bob Twiggs (Stanford) OPAL Orbiting Picosatellite Automatic Launcher Launch integration, deployment complicated Spacecraft size: Beanie babies vs. Klondike bars 1 standard CubeSat unit (1U) Volume: 10 cm x 10 cm x 10 cm Mass: < 1.33 kg Common sizes: 1U, 1.5U, 2U, 3U Now 6U, 12U Low cost and short development time Increased accessibility to space atellite-missions/o/opal, credit SSDL 3

4 Poly-Picosatellite Orbital Deployer Spring-loaded box, bolt to rocket interface plate 3U CubeSat goes inside 4

5 Launch integration on Rocket CubeSat deployment pods on top of the Bion-M1 spacecraft: BeeSat-2, BeeSat-3 and SOMP in front; OSSI-1 (1U) in a 3U-Pod back left; DOVE-2 (3U) in back right. 5

6 SmallSat vs. CubeSat Small Satellites have total (wet) mass less than 180 kg About the size of a small refrigerator Minisatellite, kilograms Microsatellite, kilograms Nanosatellite, 1-10 kilograms Picosatellite, kilograms Femtosatellite, kilograms Dnepr fairing 2013 cluster launch SkySat-1, 83 kg DubaiSat-2, 300 kg 6

7 Can launch many CubeSats easily 7

8 Animation courtesy Bill Litant Images courtesy NASA/NanoRacks 8

9 Small Satellite Challenge: Resources 30 Orbital power usage [Wh] Payload Power 3 Mbps UHF Consumed Power [12] 5 Mbps S Band Consumed Power [13] 100 Mbps X Band Consumed Power [14] 50 Mbps Lasercom Consumed Power (NODE with 1m ground station) ~ 26 Wh/orbit generated by 6U CubeSat with deployable solar panels ~ 13 Wh/orbit generated by 3U CubeSat with deployable solar panels [11] MB/orbit Magnetometer [6] 200 MB/orbit 3Mp camera [8] 7500 MB/orbit Hyperspectral [9] Clements ,000 MB/orbit Low-resolution video [4,10] Clements, et al., Optical Engineering,

10 CubeSat Lasercom Motivation Commercial CubeSat companies have invested tens of millions of dollars to address the data downlink bottleneck from CubeSats Currently have satisfactory RF solutions >200 Mbps But the commercial systems are not available to scientific and defense research programs IP and security concerns, limited commercial resources (usually skilled employee time) Others have not yet invested tens of millions of dollars to make a data downlink system for research CubeSats operational, fast, reliable, cost effective, and available Budget-constrained scientific and technology demonstrations on CubeSats still have limited communications capability, which prevents emergent functions Planet: 22 global ~5-m X-band dishes 10

11 Lasercom Downlink Motivation What if there were a low cost way for a CubeSat to downlink 100 Gb/day? Most CubeSats downlink << 10 Gb/day (UHF or S-band systems) Radio frequency (RF) downlinks challenged by resource constraints Limited by ground station size, transmitter power, or spectrum Lasercom is more power-efficient for given size, weight, and power (SWaP) & has no spectrum constraints UHF, 18.3 m S band, 11 m Wallops UHF dish used by MiRaTA CubeSat lasercom could scale to Gbps, but tech development still required Many groups working on it: MIT, The Aerospace Corporation, Sinclair Interplanetary, UF, DLR, JAXA, Space Micro, Fibertek, ATA, compact UAV lasercom from Google and Facebook MiRaTA CubeSat 11

12 Lasercom Crosslink Motivation Credit: Kit Kennedy, Patrick Kage 12

13 Swarm Crosslink Applications Spectrum access and agility Anti-jam GPS augmentation/resiliency Precision timing and ranging George Lordos (MIT) 13

14 Overview Motivation Radio Frequency for CubeSats RF and Free Space Optical (FSO, lasercom) pros and cons Enabling CubeSat technologies for FSO Current and developing CubeSat FSO New technologies for CubeSat FSO Integrated Solar Array and Reflectarray Antenna (ISARA) JPL, The Aerospace Corporation, Pumpkin, Inc. 30 cm x 70 cm, ~35 db gain at 32 GHz (Ka-band) Launched Nov. 10,

15 Radio Frequency for CubeSats Research CubeSats typically use: Beacons, VHF or UHF Low-rate ( baud) command and control, UHF Mid-rate (1-3 Mbps) data downlink, UHF, L- band, or S-band Commercial CubeSats use: Low-rate ( baud) command and control, UHF Mid-rate (> 1 Mbps) data downlink, S-band High rate (>200 Mbps) data downlink, X-band or Ka-band LEO comm constellations, e.g., Globalstar, offer: Continuous operation at low rate, 9600 baud; too expensive for data downlink Software defined radios for CubeSats: Allow agility in frequency (within constraints of RF front end), modulation, and coding Cal Poly Friis UHF ground station 15

16 Overview Motivation Radio Frequency for CubeSats RF and Free Space Optical (FSO, lasercom) pros and cons Enabling CubeSat technologies for FSO Current and developing CubeSat FSO New technologies for CubeSat FSO 16

17 RF vs. Free Space Optical (Lasercom) Lasercom wavelengths: λ = 0.4 um to 2 um RF: 1 cm to 10 m Lasercom Gain increases by several tens of db æ G = p D ö ç è l ø 2 Lasercom Advantages High gain (narrow beam width) Few spectrum regulations Lasercom Limitations Requires high-accuracy pointing Clouds Radio Waves Visible/NIR 1 cm - 2 m 0.4 μm - 2 μm Laser (red line) and radio (yellow cone) communication beam width comparison NASA.gov LLCD Fact Sheet 17

18 Free Space Optical vs. RF Radio Optical Lasercom Space Segment Spectrum / License Ground Segment Radio modem, patch antenna MHz Heavily regulated 5 m to 18 m Large dish and facility > $1M each Laser transmitter, steering system MIT NODE $15k THz available Unregulated 30 cm amateur astronomy telescope MIT PorTeL $40k Lasercom offers superior link efficiency (less power per bit) due to its ability to better direct signal to receiver 18

19 Comparison of RF and Optical TX aperture is 30 cm RX aperture is 30 cm Link range is 700 km (LEO) Receiver sensitivities typical for 1 Gbps link Optical λ = 1000 nm RF (10 GHz) λ = 3 cm Units TX Power (P t ) 0 0 dbw TX Losses (L t ) -2 0 db TX Aperture (G t ) db Path Loss (L path ) db RX Aperture (G r ) db RX Power (P r ) dbw RX Sensitivity dbw Margin 74 5 db Adapted from: Caplan, D. Free-Space Laser Communications, 2008 All system parameters are matched, except wavelength Optical system has a 70 db advantage 19

20 Overview Motivation Radio Frequency for CubeSats RF and Free Space Optical (FSO, lasercom) pros and cons Enabling CubeSat technologies for FSO Current and developing CubeSat FSO New technologies for CubeSat FSO 20

21 Enabling CubeSat tech for FSO Pointing control needs to be 1/10 the laser beamwidth Star trackers Reaction wheel assemblies Fine pointing actuators Compact amplifiers High speed, power-efficient interfaces and sampling Components/electronics for high rate mod/demod Precision timing for clock recovery; also ranging Chip scale atomic clocks (CSAC) Propulsion for constellation and swarm applications to control range Electrospray, green monopropellant 21

22 Small Lasercom Missions Lunar Laser Communications Demonstration (MIT LL) Optical Payload for Lasercom Science (JPL) Optical Communication and Sensor Demonstration (The Aerospace Corporation) Nanosatellite Optical Downlink Experiment (MIT) Data Rate 622 Mbps 50 Mbps 40 Mbps /300 Mbps 10 Mbps / 100 Mbps Tx Power 0.5 W 2.5 W 6 W 200 mw Orbit Lunar LEO (ISS) LEO LEO Payload mass 30 kg 180 kg 2 kg 1 kg Beamwidth 2.5 urad ~0.01 deg 0.30 deg 1.3 mrad Ground station White Sands OCTL 1-m MOCAM / MAFIOT PorTeL / OCTL 22

23 Overview Motivation Radio Frequency for CubeSats RF and Free Space Optical (FSO, lasercom) pros and cons Enabling CubeSat technologies for FSO Current and developing CubeSat FSO New technologies for CubeSat FSO 23

24 Accessible CubeSat Lasercom MIT-affiliated examples (others exist*) Downlink Nanosatellite Optical Downlink Experiment (NODE) Ground Station Portable Telescope for Lasercom (PorTeL) Beaver Signal NODE EM space terminal at vibe on Nov. 27, 2017 Crosslink CubeSat Lasercom Infrared CrosslinK (CLICK) *e.g., OCSD, NASA/MIT LL DTE, Fibertek, SA photonics, SPAWAR MRR, Sinclair, SpaceMicro, Analytical Space PorTeL on MIT 37 Roof 24

25 NODE Architecture LEO satellite Downlink beam (1550 nm) Communication channel Uplink beacon (976 nm) Ground station tracking Optical ground station 25

26 Pointing, Acquisition & Tracking Satellite autonomously slews from mission-defined attitude Acquisition on satellite sensor stares for beacon signal from ground Centroid algorithm estimates boresight offset ADCS closes loop using beacon offset Integrated fine-steering mechanism (if you have one) rejects residual error Fast mirror steers downlink If you don t then your beam has to match body pointing ability 26

27 Lasercom Space Segment 27

28 NODE Space Terminal Application Approach Size Beamwidth Downlink Data Rates Power Interface Attitude Control Low-cost (<$15k in COTS hardware) compact lasercom transmitter Direct detection master oscillator power amplifier (MOPA) with downlink at 1550 nm. Uses uplink beacon at 976 nm. < 1.0 kg, < 1.2 U NODE: 1.3 mrad half power (first generation, initial demo). 10 Mbps, initial demo to COTS 30 cm diameter amateur telescope, MIT PoRTeL 100 Mbps (1 m diameter, JPL OCTL) 0.2 W (average transmit power), < 15 W (consumed power). Needs 5V (3A, 25 mvpp ripple) and 3.3V (3A, 25 mvpp ripple) from bus. Desired Bus coarse pointing: accuracy: +/ deg (3-sigma), stability +/ deg/s (3-sigma). Allows open loop operation with Bus. NODE in 3U host Mirrorcle MEMS fine steering mirror Can support coarse pointing < Beacon FOV but would require closed loop ADCS with Bus. NODE FSM fine pointing capability (experimentally verified in lab): Pointing accuracy: +/ mrad (3-sigma). Beacon receiver for pointing knowledge (0.01 mrad). Beacon Camera Signal FOV: +/- 5.4 degrees (10.8 degrees full angle) Detector: mvbluefox-mlc205wg, Aptina MT9P, 2592 x 1944 pixels PPM, RS(255,239), 8 bits per symbol Flight electronics boards 28

29 PorTeL Ground Terminal Downlink with PorTeL amateur telescope: Data rate GS Parameters Detector Receiver electronics Coarse Pointing Fine Pointing Mbps 30 cm, 50 kg, < 120 W consumed Direct detection w/ Voxtel APD NODE electronics (APD & custom electronics) < 60 arcsec, IR camera and star tracker < 5 arcsec, FSM to keep spot on APD (no AO) Uplink beacon OCTL beacon (976 nm, 10 W tx power, 1 mrad beam) Current Status Downlink with JPL OCTL telescope: Data rate Satellite tracking, over the air testing Mbps FSM APD Beam splitter Receiver Diameter Receiver electronics Uplink beacon 1 m NODE electronics (APD & custom electronics) 976 nm, 10 W tx power, 1 mrad beam IR camera Yoon, Hyosang, Kathleen Riesing, and Kerri Cahoy. "Satellite Tracking System using Amateur Telescope and Star Camera for Portable Optical Ground Station." (2016). Image credits: Clements (above), Riesing (below) 29

30 PorTeL Ground Terminal Observed closed-loop tracking errors when tracking the International Space Station on January 24 th, Portable telescopes (here in FL in January) are graduate-studentapproved The red line shows the area of the receiver. The signal stayed within the area 95% of the time. (K. Riesing, PhD thesis work in progress) 30

31 LED Uplink Beacon 80 W transmit from Wallace Astrophysical Observatory successfully detected and centroided by on-orbit CubeSat (more info not releasable publicly yet) A. Bosh, J. Figura, and K. Cahoy 31

32 Next Generations of NODE Initial Demonstration (NODE) NODE Generation 2 NODE Generation 3 10 Mbps downlink to 28 cm diameter telescope PPM at 1550 nm 1.3 mrad half power 0.2 W transmitter 400 Mbps downlink to 1 m diameter telescope PPM at 1550 nm 0.2 mrad beamwidth 0.5 W transmitter > 1 Gbps downlink to 1 m diameter telescope (some electronics redesign) Possible OOK at 1064 nm with different amplifier < 0.2 mrad beamwidth 3 W transmitter 32

33 CLICK: CubeSat Lasercom Crosslink D. Barnes and K. Cahoy 33

34 CLICK Concept of Operations Launch Vehicle Separation and Ejection CubeSat Launcher: TBD Deployment Attached Pre-Operations Spacecraft Separation Deploy Solar Panels System Diagnostic Initiate Drift G PS Pre-Link Operations Update internal propagators from GPS Exchange orbit determination info 450 MHz RF crosslink G PS Typical Separation times after checkout (for reference orbit as defined in MRD): 5 km: 2.3 days 25 km: 11.4 days 100 km: 44.7 days 500 km: days 1000 km: days LaserCom Operations 5-minute lasercom crosslink tests ~1550 nm Lasercom crosslink Launch Operations Launch Vehicle: TBD Launch Site: TBD Orbit: km TBR Inclination: TBD Launch Date(s): TBD Degraded and Failure Mode Operations Sun-Safe Mode Survival Mode UHF 401 MHz (downlink) 450 MHz (uplink) ~1550 nm Lasercom downlink De-orbit Ground Station Location: MIT Receiver Assets: TBD Transmitter Assets: TBD Transmit divergence: 0.07 mrad (FWHM) Beacon divergence: mrad (FWHM) 34

35 CLICK Payload Overview Use Cases: Optical crosslink >20 Mbps at >580 km with BER <10-4 Optical downlink >10 Mbps to a 30 cm ground aperture from a 400 km to 600 km LEO orbit Development Status: Optical design and analysis complete Prototype Miniature Optical Communications Transceiver (MOCT) and Pointing, Acquisition, and Tracking (PAT) testing complete All boards in design and testing, some from NODE Mechanical design for 1.5U payload is complete. 3D printed model complete. Engineering model fab is planned. Optical Table Telescope Beacon Beacon Camera Courtesy M. LaRocca 110 mm 1.5U Board Stack FSM Tx/Rx Optics 96 mm 35

36 CLICK Link Budget - Crosslink Inter-satellite Crosslink Budget Range (km) PPM Order Transmit Power (dbw) Full Width Half Maximum (mrad) 0.07 Beam Solid Angle (steradians) 3.96E-09 Transmitter Gain (dbi) Transmitter Loss (db) Receiver Gain (dbi) Receiver Loss (db) Path Loss (db) Atmospheric Loss (db) 0.00 Pointing Loss (db) Photons Per Bit Power Received (dbw) Power Required (dbw) Margin

37 CLICK Link Budget Beacon/Quadcell Link Range (km) Beacon Optical Power (dbw) Beacon Wavelength (m) 9.76E E E E E E-07 Pointing Loss (db) Half Power Beamwidth (rad) FSO Path Loss (db) Tx Optical Loss (db) Rx Optical Loss (db) Receiver Aperture Diameter (mm) Sensor Responsivity (A/W) SNR (db)

38 Overview Motivation Radio Frequency for CubeSats RF and Free Space Optical (FSO, lasercom) pros and cons Enabling CubeSat technologies for FSO Current and developing CubeSat FSO New technologies for CubeSat FSO 38

39 New Tech for CubeSat FSO Photonic integrated circuits (PIC) High performance detectors Optical preamplification (AO) Multiple-access systems Phase modulated systems for CubeSats Digital coherent combining Compact, power-efficient ADCs and demodulators 39

40 Photonic Integrated Circuits Example from OpSIS foundry: 48 channel WDM in 1 mm x 2.5 mm, including Ge highspeed photodetectors (>10 GHz) for receiver. Input grating couplers and amplitude and phase modulation Also Acacia, others: single chip transceivers OpSIS: Optoelectronics Systems Integration in Silicon 40

41 High performance detectors Example, Superconducting Nanowire Photodetectors (SNPDs) 41

42 Optical Preamplification Couple to single mode fiber for additional gain MIT DeMi to test MEMS DMs on orbit 42

43 Multiple Access Systems Terminals to support multiple users Not an actual lasercom terminal but imagine each color was an independent beam (with FSM or gimbal) 43

44 Coherent CubeSat Lasercom Leveraging commercial coherent lasercom technology, e.g. Acacia networks 44

45 Digital Coherent Combining Ground terminals with large collection areas are costly Instead, many small apertures are coherently combined while maintaining excellent receiver sensitivity Coherent detection behind each aperture followed by digitization The digitized signals are then combined Yarnall et al., 2015, /ICSOS

46 Compact, high speed ADC or TDC Need minimum 2x and typically 4-8x sampling for high speed signals Evaluating performance of TDC vs. ADC (time to digital vs. analog to digital) conversion Power consumption, cost, complexity are challenges at high sampling rates DRS4 based example, used up to 5 GSPS 46

47 Summary CubeSats successfully use RF communication systems But higher data rates would be enabling Research CubeSats cannot cost-effectively access higher rate solutions (space and ground terminals) Lasercom may be a solution Many research applications can tolerate occasional weather outages, or can afford to field multiple lowcost ground stations Free space optical (FSO) technologies are good candidates for CubeSat demonstrations 47

48 Coherent Detection Hamid Hemmati NELC, Ch4 Use intensity and phase information LO oscillator laser mixes received & local light waves Current depends on the amplitude, phase, and polarization for both tx and LO lasers 48