A Low Power Optical Communication Instrument for Deep-Space CubeSats Paul Serra, Nathan Barnwell, John W. Conklin Paul Serra, CubeSat Developers Workshop, 2015 v1.5
Motivation and Objectives Objectives: Demonstrate optical communication with small volume, low power. 2U, ~5 W, 10s kbps to 10s Mbps Proof of Concept (TRL 1 to TRL 3) Initial studies and feasibility in 2014. Prototype realization started in February 2015. LLST Model on LADEE Virtex 5 QV on M-Cubed/COVE2 Paul Serra, CubeSat Developers Workshop, 2015 2/13
M-slot Differential Pulse Position Modulation Example for M = 4 0 1 2 3 0 1 2 3 M slots Paul Serra, CubeSat Developers Workshop, 2015 3/13
Optimal Number of Slots, M M M An optimal M is chosen from required pulse energy and channel noise: Requirements: Pulse energy Channel Noise Guard Time Slot size Optimal M Data rate Paul Serra, CubeSat Developers Workshop, 2015 4/13
Structure Two subsystems: Software Defined Pulse Modulator (SDPM) Generate electric pulses according to the modulation scheme. Master Oscillator Power Fiber Amplifier (MOPFA) Transform electric pulses into amplified light pulses. data Time Standard Modulator Pulsed Laser Cesium Clock FPGA Laser Diode Amplifier Pump Laser & Erbium fiber Laser pulses SDPM Software Defined Pulse Modulator MOPFA Master Oscillator Power Fiber Amplifier Paul Serra, CubeSat Developers Workshop, 2015 5/13
Hardware: Time Standard Characteristic Standard Allan Deviation (time error) Power Mass Size (LxWxH) Chip Scale Atomic Clock (CSAC) Cesium 3.3x10-12 @ 6000 sec (20 nsec) 0.12 W 35 g 40.64 x 35.31 x 11.42 mm CSAC in a CubeSat packaging Paul Serra, CubeSat Developers Workshop, 2015 6/13
Hardware: FPGA Timing performance in FPGAs are very dependent of the platform: FPGA selection must be done early. Complete revalidation of timing section required if FPGA changes. Flash-based FPGA: Reprogrammable: Allows part-to-part calibration. Flash storage: No configuration upsets; No external programing. Rad Tolerant version with same production process and structure. Paul Serra, CubeSat Developers Workshop, 2015 7/13
Timing Digital Modulator Data Flow Data Input Raw data Encoded data Timestamp Raw Time Vector Env. information Next slide Compensated Time Vector Input bus decoder Communication Error Correction code M-DPPM Modulation Pulse Encoder Counter Value Delay chain setting Environmental Compensation Counter Value Delay chain setting SPI, Ethernet, Spacewire Turbo codes or other code correction codes, interleaver, Framing Variable M and time slot size. Clock input Counter Delay Chain Laser trigger output to laser pulse driver Paul Serra, CubeSat Developers Workshop, 2015 8/13
Environmental Compensation Temperature, voltage, radiation, aging chain delay variations. Delay Locked Loop (DLL) measures delay variations. Environmental Compensation Feedback Law Counter Launcher D Flip- Flop Delay Chain Arbiter D Flip-Flop Counter Clock Controlled Oscillator (2 PLLs) Variable period Paul Serra, CubeSat Developers Workshop, 2015 9/13
Modulator Initial Results Consistent with 100 ps slot width Result from DLL circuit with 65280 samples per time (3 10 6 samples in 40 ms) Resolution of DLL oscillator: 1 ps typical, 2.3 ps worst case; Range: 4 to 24 ns. Paul Serra, CubeSat Developers Workshop, 2015 10/13
Master Oscillator Power Fiber Amplifier Erbium doped Fiber Laser High gain with low average power Maintains good beam quality Solid-state Compact Trig. 1550 nm Seed Laser Pulsed Coupler Faraday Isolator Axicon Lens Telescope 980 nm Pump Laser CW Erbium doped fiber Paul Serra, CubeSat Developers Workshop, 2015 11/13
Power Budget 1 m telescope Diffracted beam 10 cm telescope At least 10,000 photons at target 1 W optical power, at 400,000,000 km 1 mj pulses T g = 1 ms M 10 5 20 kbps (10 kbps with error correction) 1 W optical power, at 50,000,000 km 10 µj pulses T g = 10 µs M 10 3 2 Mbps (1 Mbps with error correction) Paul Serra, CubeSat Developers Workshop, 2015 12/13
Conclusion Completed: Automated modulator test bed Delay chain design Optical components selection and purchase Future work: Low resolution data loopback with optics by August Timing characterization in rad tolerant parts Highland T165-2 Driver Seed Laser Collimator Axicon Lens Gold-coated 5 in Telescope Paul Serra, CubeSat Developers Workshop, 2015 13/13