Cryogenic Testbed for Passive Optical Data Links on Planetary Surface

As aerospace missions extend to smaller, powerconstrained spacecraft operating in low-temperatureenvironments, especially on deep space planetary surfaces,traditional radio communication can become insufficient. Freespace optical (FSO) data links using Modulating Retroreflectors(MRRs) offer a passive, high-bandwidth alternative bymodulating externally supplied laser light, eliminating the needfor onboard transmitters and significantly reducing size, weight,and power demands. While MRRs have demonstrated longdistance optical links at room temperature, their performanceunder cryogenic conditions remains largely untested. This workpresents the development of a cryogenic optical communicationstestbed designed to evaluate MRR-based systems attemperatures representative of the lunar night. The setupconsists of a 1550 nm continuous-wave laser routed through afiber collimator and acousto-optic modulator (AOM) into avacuum cryogenic chamber with a planar retroreflectingmirror. Thermal regulation was implemented using resistiveheaters and isolation blocks to maintain the AOM electronicsnear 280 K while cooling the optical stage to lunar nighttemperatures (110 K). Limited by the bulky AOM, the testbedexhibited a narrow field-of-view of ~0.5°, requiring precisealignment. Modulation experiments were performed from 260K down to 135 K and across frequencies from 1–50 kHz. Resultsshowed modulation depths of ~10% at 1 kHz and 260 K,decreasing to ~3% at 135 K, with further reductions at higherfrequencies. Despite this decline, modulated signals remaineddetectable at all tested conditions. These results validated thetestbed for future MRR-based communication under cryogenicconditions. The testbed provides a foundation for developingand testing low-power optical links for lunar, Martian, anddeep-space exploration missions.