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I noticed four(?) towers around the SpaceX launch pad during yesterday's aborted launch

enter image description here

Image credit NBC News

What are the towers used for? Tracking? Radio communications?

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They are used to redirect lightning in the immediate area. This essentially creates a faraday cage, shielding the rocket from being fried by lightning. You can see how high the towers reach, high enough to ensure there is no risk of lightning hitting the craft.

Update by @highonrope: The rectangle which the rocket launches through is huge...from the ground to the bottom of the "candle stick" is 250 feet tall. The candle stick is the big white thing at the top. It is about another 150 feet tall. They look a lot smaller in a picture, but it takes several minutes for an experienced tower climber to go from ground to the top. They say that inside the lightning suppression system there, you are 100% safe from lightning. The towers are all interconnected with stainless steel cables which form a rectangle through which the rockets are launched from the rectangle, the cables run to the ground and are fully grounded. @highonrope was part of a team of people who were tasked with cleaning and repainting the top of the tower and testing the "ground" of each cable where it attached at the top and at the ground, when SpaceX first started at Kennedy, before the first launch there. We got to see first hand how huge the SpaceX rocket was and what it does to the pavement in the "exhaust" tube, where the rocket exhaust is redirected at ground level. It's an awesome complex. It was designed for the Saturn rockets and is one of the oldest launch pads at Kennedy.

TL;DR: They're lightning rods.

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    $\begingroup$ There seems to be some confusion about SpaceX launch pads in the answer. SpaceX's first pad at Kennedy Space Center (KSC) is 39A. The only signed the lease for it in Apr 2014, and have not yet launched from it. 39A was originally designed for Saturn V rockets. Currently, they launch from SLC-40, which is in Cape Canaveral Air Force Station (CCAFS). It's right next door to KSC, but you need special clearance to go to CCAFS, since it is an active military base. SLC-40 was used for launching Titan rockets before SpaceX took over. They were big, but not nearly as big as Saturn V's $\endgroup$
    – Nickolai
    Mar 8, 2015 at 3:57
  • $\begingroup$ @Nickolai: Feel free to edit the answer. $\endgroup$
    – Mark Adler
    Mar 8, 2015 at 6:55
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    $\begingroup$ Hi @MarkAdler, could you clarify something for me? What is the purpose of installing any insulator (the candle sticks) at the top of each tower at all? With or without an insulator, it seems like the main current from a lightning strike would still go down the grounding cable. It seems important to insulate the top of the tower from the spot where the lightning hits; can you clarify the reasoning? $\endgroup$
    – John Walthour
    Feb 16, 2016 at 18:38
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The big top rods are insulators. Such cages are grounded through wires sloping out to ground points several tens of meters away. Also the ground points are connected to each other by a potential equalization loop. The metal lattices of the towers are grounded too, and also connected to the loop - but they are insulated from the tips, so in a strike they do not act as conductors. There was one such insulator on the top of the Shuttle launch tower. It was a spun fiber in polymer matrix structure, ad the time the biggest such cylinder in the world. The tip was connected to three ground points.

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    $\begingroup$ Welcome to Space Exploration Stack Exchange! It is clear from your answer that you are knowledgeable about the subject, but for the benefit of others we have a standard here that we try to include the source of our information in our posts. The source does not have to be physical text or a web link, but even if you are an expert in the field and this is from off the top of your head a little bit of an explanation helps the rest of us understand the context of your information and accurately judge its worth. Thanks! Feel free to join us in chat when you reach 20 reputation points for more help. $\endgroup$
    – called2voyage ♦
    Dec 2, 2013 at 16:40
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    $\begingroup$ @called2voyage: I didn't realize that is the same Mark Adler from zip! In fact, it has been nagging me that the name seemed familiar. Thanks for mentioning that! $\endgroup$
    – dotancohen
    Dec 6, 2013 at 9:37
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    $\begingroup$ Saying they're insulators doesn't really answer what they're used for so I'm surprised this answer has so many upvotes. $\endgroup$
    – NickG
    Feb 10, 2015 at 10:29
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    $\begingroup$ @raptortech97 I'll talk with the other mods. I don't know if it would be appropriate to call out a specific user in the help pages, but in this case that would be helpful. $\endgroup$
    – called2voyage ♦
    Jun 5, 2015 at 13:43
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    $\begingroup$ @AndrewMedico Is this better? mars.jpl.nasa.gov/MPF/bios/team/adler.html $\endgroup$
    – called2voyage ♦
    Jun 22, 2015 at 14:39
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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.

(Source for quote/images: collectSPACE)

Construction of three lightning towers continues at Kennedy Space Center's Launch Pad 39B in January 2009

(Source: NASA)

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The fiberglass (FRP) tubes on the top of the launch platforms are a part of a lightning protection system and are insulators with cables that form a cone of protection for the launch tower. They were designed by my former company CH2M HILL, (Gainesville,FL)an engineering firm, and were manufactured by Starline Fabricators, Astatula, FL. I brought this design project in for the company from a contact I made with the fabricator during a business development trip to Lake County in the late 70s.

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    $\begingroup$ As an engineer involved in designing these towers, maybe you can clarify @johnwalthour's question to another answer - why would you install insulators on the top of a lightning rod? $\endgroup$
    – craq
    Sep 8, 2018 at 19:20
  • $\begingroup$ Answered here: space.stackexchange.com/questions/32927/… $\endgroup$
    – Organic Marble
    May 7, 2019 at 15:47
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This is a complement to the already given answers, namely that these are supports for a lightning protection system.

Below is a picture of an ULA launch that shows that besides the spires themselves, there are wires stretched over the launch pad to redirect any lightning that would want to strike the rocket. It makes the role of the towers much clearer.

Rocket launch with cables visible over and around the rocket.

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