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https://xkcd.com/2107/

Why are the lightning towers around launch pads topped with big hollow tubes with spiral windings? Why not conventional lightning rods - big metal rods with pointy things at the top?

Possibly related: https://electronics.stackexchange.com/q/410152/102305

Cropped and recklessly sharpened from NASA Spaceflight

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Screenshot from this video

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From this answer and Source

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Above: The first piece of Pad 39B to be removed, the 80-foot lightning mast that topped the fixed service structure (FSS), was lowered on March 3, 2009. NASA's first launch pad lightning protection mast, it was used for the 1975 Apollo-Soyuz Test Project (ASTP) before being adapted for the space shuttle program. Photo: NASA/Amanda Diller

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Because those tubes are not lightning rods!

They are insulators. Their function is to hold up the conducting wires that actually soak up the lightning strikes. The big hollow tubes are made of fibreglass. There is a (relatively) small lightning rod on the top of the insulator.

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It's more obvious on the old Shuttle pad. Why would you have a giant lightning rod connected directly to the metal structure you are trying to protect?

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Lightning protection at the Space Shuttle launch pads is provided primarily by a 70-foot insulating fiberglass mast 5 feet in diameter located on the Fixed Service Structure with a lightning rod at the top of the mast, as shown in Figure 1. A catenary wire running from the top of the mast to grounding points 1000 feet to the north and south of the tower is used to direct the current away from the pad structure.

(PDF) LIGHTNING PROTECTION AT THE KENNEDY SPACE CENTER AND CAPE CANAVERAL AIR FORCE STATION. Available from: https://www.researchgate.net/publication/237605413_LIGHTNING_PROTECTION_AT_THE_KENNEDY_SPACE_CENTER_AND_CAPE_CANAVERAL_AIR_FORCE_STATION [accessed Dec 19 2018].

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  • $\begingroup$ The metrology discussed in the article is pretty impressive as well! 1.network of magnetic direction finder antennas; Lightning Detection and Ranging (LDAR) (VHF ~ 66 MHz) 2.Video cameras 3.Sonic Lightning Location (SOLLO) system based on both electric field and thunder measurements can achieve 5-meter accuracy for strikes within pad perimeter 4.The Lightning Induced Voltage Instrumentation System (LIVIS) connected to selected power and communication cables 5.Catenary Wire Lightning Instrumentation System (CWLIS) measures current on catenary wire following a direct lightning strike $\endgroup$ – uhoh Dec 20 '18 at 0:18
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    $\begingroup$ Thank you for clearing this up! slightly related: Are there websites where I can get “lightning frequency maps” in near-real time (worldwide)? $\endgroup$ – uhoh Dec 20 '18 at 0:21
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    $\begingroup$ The paper is a bit dated, by the end of the program there was an extensive network of "field mills" measuring the electric potential and new rules about launching into clouds - nasa.gov/centers/kennedy/news/releases/2003/… I remember being in meetings where a guy was pushing a new way of calculating the hazards but I don't know if it was accepted. $\endgroup$ – Organic Marble Dec 20 '18 at 0:30
  • $\begingroup$ "This field mill criteria becomes -1.5 or + 1.5 kilovolts per meter if there are no clouds within 10 nautical miles of the flight path except those which are transparent. "I'm thinking about asking "what is a transparent cloud" in Earth Science SE. Am I understanding this correctly that it's transparent clouds that are excepted here? $\endgroup$ – uhoh Dec 20 '18 at 0:34
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    $\begingroup$ Are there “transparent” clouds? $\endgroup$ – uhoh Dec 20 '18 at 0:48

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