COMMS FOR WAY, WAY OUT THERE

摘要

THEY'RE THE STUFF OF DREAMS, legend, maritime lore: the Northwest Passage, the Drake Passage, Greenland, South Georgia Island, Cape Horn. Cruising these fabled waters requires a capable and prepared yacht, a seasoned and adventurous crew, the right communications and safety tools, and a pinch of luck. In this sense, the ancient Roman philosopher Seneca was right: Luck is what happens when preparation meets opportunity. Satellite connectivity isn't new. The first very-small-aperture terminal (VSAT) satcom systems rolled out in the late 1970s, giving mariners the ability to send and receive information at sea. Contemporary VSAT systems typically operate on the Ka-frequency or Ku-frequency bands to offer high-speed performance and bandwidth. The problem, however, is that VSAT networks typically concentrate their coverage beams on populated areas and commonly cruised waters. Moreover, these systems utilize high frequencies that often suffer from rain and snowfade when the weather sours.Iridium's Certus network doesn't deliver the kinds of data-transfer speeds that enable video or social media streaming, but it does provide global connectivity that isn't affected by weather. The largest Certus terminals are built with multi-element patched antennas that can simultaneously listen to-and evaluate the signal strength of-multiple satellites for trustworthy connectivity. Certus terminals also can be paired with a VSAT terminal, and long-range cellular and Wi-Fi antennas, to provide out-of-band management and lowest-cost routing. For adventurous cruisers, Certus' connectivity improves the farther north (or south) from the equator one cruises. Iridium began work on its Certus network in 2015. Today, the system is composed of 66 cross-linked low-Earth-orbit (LEO) satellites that circle the globe in near-polar orbits that are each roughly perpendicular to the equator. (Imagine the segments of a peeled orange coming together at either end.) At any given time, there are more LEO satellites concentrated at the north and south poles than at the equator. And Iridium's LEO satellites operate on the L band (1 to 2 GHz), which is a much lower frequency than the Ka and Ku bands, and which isn't frazzled by rain or snow.