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I'm thinking, specifically, of the Falcon 9, where I read from their specs that the entire structure is coated with an ESD-conductive paint.

I was also under the impression that the launch vehicle's (LV) electrical reference was its chassis. Again, according to their specs, the paint surface is grounded to the vehicle's structure.

What happens, then, if surface current is induced on the vehicle's skin due to (indirect) lightning? The chassis of the vehicle is closer to the internal electrical links than is the skin. Why would you risk return current through your system's grounding?

geoffc
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dalarev
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  • What do you mean by chassis? In rockets, the skin is generally a load-bearing part – Hobbes Apr 17 '15 at 12:49
  • From what I've read, the skin of the launch vehicle is made of aluminum (Al Li alloy), so I assumed that the architecture of the vehicle was either:
    1. Multiple layers of Al Li alloy;
    2. Multiple layers of Al Li, with an embedded skeleton chassis, perhaps made of reinforced steel or something typical of chassis.
     – dalarev Apr 17 '15 at 16:21
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    No. The tank sections are usually just an aluminium pipe with bulkheads at each end. Sometimes stringers are placed lengthwise against the skin (on the inside or outside), or corrugated panels are used. Steel is rarely used in rockets (the Shuttle SRBs were an exception, IIRC). Rockets are fragile. Some have such a light construction you can only transport them if the tanks are pressurized to provide extra rigidity. – Hobbes Apr 18 '15 at 06:58

1 Answers1

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Yes, the skin is usually (part of) the ground plane.

Here are some examples of the construction of the Falcon 9.

This is the interstage:
Falcon 9 interstage

This is a section of the fuel tank:
F9 tank

In both cases the skin is a major structural element. There are some stringers in the tank, but these are shorter than the tank section, so they don't form a continuous path from the top to the bottom of the tank.

Boeing has an informative page on lightning protection for aircraft (which use similar construction methods).

But the main strategy for lightning protection in spacecraft is avoidance: a launch will be postponed if thunderstorms are anywhere near the launch site. And the launch site has massive lightning towers to protect the rocket before takeoff.

This document describes NASA's best practices for electrical grounding in rockets.

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Hobbes
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  • Excellent images, and very helpful links as well. Thank you for that. Those links contain very relevant info to what I'm looking for. – dalarev Apr 23 '15 at 18:24