Free Space Laser Communication Cubesat Payload Development MIDN 1/C Colston Polly Primary Advisor: Assoc. Prof. Tae Lim Off-site Advisors: Drs. Rita Mahon and Chris Moore at the U.S. Naval Research Laboratory

Background Significant benefits in optical communication Security Data rates Error minimization Previous success LADEE OPALS Change examples (maybe), and put full names

Challenges with Optical Communication Beam divergence Availability of ground stations Earth’s atmosphere Weather

What was accomplished in Spring/Summer 2015 MIDN 1/C Dods, Blanchard, and A. Kelly Proof-of-concept demo for optically communicating 6U cubesat Laboratory tabletop test (~ 6 ft) Desired data rate Data rates prediction Experimental determination and comparison Link Margin Established working link margin Solidworks Model Lay foundation for future years’ work Collaboration with NRL advisors at the Chesapeake Bay Detachment (CBD) Summer internship of MIDN 1/C Polly at NRL-CBD

Physical setup

Transmit Computer Connected through Ethernet to MiniMc MiniMc (Media Converter) Signal modulator Single mode fibers Laser diode Collimator Transmits signal across free space

Receive Copies transmit, but in reverse. Collimator acts as light bucket MiniMc demodulates signal Multimode fibers

Inefficiency losses mW dBmW Produced 0.55 -2.60 Loss_Tx 0.01 0.08 Tx 0.54 -2.68 Loss_Space 0.03 0.25 Rx 0.51 -2.92 Loss_Rx 0.33 4.52 Computed 0.18 -7.45

Link margin Difference potentially due to short distance (quantum saturation)

Future work This academic year and next (AY2015-2016) Longer range tests 50 meter - Kilometer scale (Rickover Hallway to Across the Severn) Signal acquisition Auto alignment system: position sensing detector and fast steering mirror Tracking system Keeping the free-space comm link between moving objects: two axis gimbals Future academic years (AY2016-2017) Optical comm payload (3U) design for 6U cubesat Component design, integration, testing Pointing, acquisition, and tracking system design Developing concept of mission operations

Who are we looking for? Two (2) midshipmen who are interested in: Optical design for laser communication Link budget analysis Alignment system design and testing Tracking system design and testing Mission concept of operations and systems engineering for cubesat payload development

Back-Up Slides

Link Budget test goals Component Inefficiencies Determined Actual beamwidth Needs further test distance to be determined. Detector Sensitivity Needs further test distance/greater attenuation (likely around 10 dBmW more). Adequate predictive capability Predicted -6.74 dBmW at media converter Got -7.45 dBmW at media converter

SNR-to-Data Rate Relationship Our system uses On-Off Keying (OOK) To find data rate Large ping between two computers Use WireShark, a network-analyzing program, to determine time delay Attenuate signal over several trials On-Off Keying – explain.

SNR-to-Data Rate Relationship   Computed Power [mW] Computed Power [dBmW] Data Rate [MBps] Ethernet n/a 45.02 Trial 1 0.180  -7.45 1.45 Trial 2 0.110  -9.59 1.44 Trial 3 0.053 -12.76 Trial 4 0.011 -19.59 Trial 5 0.001 -30.00

SNR-to-data rate relationship “Waterfall” ~ approx. -40 dBmW Max Data Rate (1.45 MBps) Data Rate [MBps] Sensitivity Limit (-42 dBmW) SNR [dBmW]

Solidworks

Sponsors/help NRL optical communications team Chris Moore and Rita Mahon Working on optical communication aboard naval platforms