This happened Thursday, although the source, a SpaceX Tweet, doesn't say exactly when. It simply says:
Last night’s storm in Florida produced hail, tornadoes, and lightning. Following this strike on the tower at 39A, teams performed additional checkouts of Falcon Heavy, the payloads, and ground support equipment.
The Tweet with picture is time tagged 9:53AM on Friday, April 28.
SpaceX photo; I reduced it in size somewhat to fit in this template.
Obligatory side story. In the later part of the 1980s, I helped the local ham club teaching classes to help guys get their first ham license as well as upgrade classes. In one Novice (entry level license) class, I had a student who had worked on that system. He said it was man-rated, meaning no person working on the launch tower under the protection could touch two points that would allow a high enough voltage to injure them.
The essence of how that's accomplished is that they specify resistance across
a given distance on the tower. I don't recall the distance, but think of
a person's wing span; fingertip to fingertip distance with arms
outstretched. It's close to their height, so they'd probably add some
margin and specify that any two points can't have more than some number of
milliohms of resistance. Ohm's law says that the voltage difference
across the points is the current from the lightning flowing through the points
multiplied by the resistance between the points, so by using some measured
data for lightning strike currents, they can set the resistance to produce less than the desired voltage at that current.
I asked the guy if he'd be willing to teach the session on lightning that's included in the Novice class and he gladly accepted. It's the only time I ever had a student teach a session for me.
As for the Falcon Heavy mission, it's currently scheduled for Sunday night, 4/30 at 7:29 PM ET.
ALL of the equipment in a Minuteman silo, manned or unmanned, had to be bonded together. The EMP resistance meant that surfaces had to be bonded with LESS than .001 ohms - a difficult (but not impossible, only expensive) target to hit. you wouldn't believe the trouble we had to go through to test the bonding every time we opened a shielded box!
ReplyDeleteThe machine we used was called a "megger", it put out 100KV across the test leads to measure the resistance. Quite a ball-breaker to use and mis-use.
'Nuff said.
I've seen the lightning protection system, but it's neat to see it in action. So cool.
ReplyDeleteAlso seen this happen to sailboats in the Banana River, not so cool.
It's not just current flowing across a resistance - the voltage includes a reactive component Vr = L (dI/dt). That often is bigger than the resistive part.
ReplyDeleteIn the RF world I've spent my life in, large, essentially ribbon conductors have inductance, but it's not dominant. Can you bound that a little? I don't want anything confidential, of course, just are you saying the I-beams and structural members of the tower would contribute microhenries? Tens of them? Nanohenries?
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