One thing against widespread use of semaphore stations in Roman times is a lack of optics. If you rely on a legionnaires eyesight to read the flags then the stations have to be quite close together. For decent spacing and throughput you need to have a telescope fixed on the station either side of you in the line.
]]>Back when they had the inflight RUD with a cargo Dragon shortly after launch, the NASA component of the investigation team came in to the first meeting expecting to be going over paper listings of a limited number of telemetry sensors and data points for many weeks trying to find the cause. They were astounded when the SpaceX side told them what had happened complete with supporting evidence. There are multiple microphones in each propellant tank, and the ones in the 2nd stage LOX tank had recorded a snapping sound. The slight delay between the different microphones enabled SpaceX to work out the location of the sound and testing the batch of support rods remaining in Hawthorne showed the manufacturer had been skimping on testing as several failed with the same snapping noise.
SpaceX are very good at telemetry, their rockets are instrumented up the wazoo and they collect far more data from each flight than any other rocket manufacturer.
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