second. For weight, fiber-optic glass strand is four times lighter than copper wire of the same diameter. For size, the diameter of a single glass fiber is 125 microns, with cores as small as nine microns with a jacketed diameter under one millimeter. Compare that to ultra-thin Category 6a Ethernet cable where four 200 micron (32 American wire gauge [AWG]) copper wires are contained within a 2.8 mm thick jacket. The result: optic fiber cable is nearly 78% lighter for the same length. The need for speed differs between satellites and eVTOL aircraft. Individual LEO satellites may transmit up to about 25 Gb/s with total constellation bandwidth measured in multiple terabytes per second. In eVTOL aircraft, CAN bus control-signal data rates operate up to 8 Mb/s; in-flight entertainment (IFE) systems, assuming their use in future six-passenger vehicles, might require around 1 Gb/s. While the speed requirements differ between the two applications, the desire for weight and space savings is the same. Each extra kilogram in modern LEO satellite missions can potentially add up to $10,000 per launch. In eVTOL aircraft, fuel is not burned off and discharged, but spent batteries literally become dead weight. Each pound and cubic inch saved extends flight time and payload/passenger capacity.
Robustness is also an advantage, but it may seem a surprising one. The installation parameters of optical fiber — including bend-radius and cable-stress requirements — are well known in industrial and commercial applications. In aerospace applications, fiber optics offer three critical contributions:
1. COMPLETE ELECTROMAGNETIC INTERFERENCE (EMI) IMMUNITY
Optical fibers are made of dielectric materials that neither emit nor receive EMI, making them an ideal choice for avoiding this common cause of avionics system failure. Cable shielding is not required. Available optical inserts support ceramic ferrules, expanded beam termini, and multimode MT ferrules for PC connectors — all compliant with ARINC, MIL- Spec, and EN standards. 2. SPECIFIC TO SPACE Outgassing, the release of gas or vapor by materials in a vacuum environment, is a concern for components used in space applications. NASA has identified space-qualified materials for fiber optic assemblies. The degrading effects of ionizing radiation is another concern that is minimized by employing radiation- hardened fiber with adapted glass compositions.
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