posted 11-23-2013 05:40 PM               

The 12-foot-tall Apollo spacecraft command module contains almost 15 miles of wire, enough to wire 50 two-bedroom homes.

posted 05-14-2020 09:20 AM            

As each spacecraft was an individual vehicle, I'm sure no two spacecraft had exactly the same length of wiring, and I can't imagine anyone could ever have measured the precise length of the wiring, but if we take the example of Apollo 1, there are widely-differing estimates. I have seen 12 miles, 20 miles and 30 miles, which actually makes it look like guesswork.

posted 05-14-2020 09:29 AM               

quote:

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Originally posted by Blackarrow:
I'm sure no two spacecraft had exactly the same length of wiring...

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posted 05-15-2020 02:24 AM               

Later on in the report: "I think the problem that we have here is that we have got to recognize with 20 miles of wire, and the amount of work that goes on during fabrication."

My take from this report is that there is either around 30 miles of wiring in an Apollo Saturn V rocket, 20 miles of which is in the command and service modules, or that a consolidated total of wire lengths is difficult to come by. The figure will exist within the NAA build data somewhere.

posted 05-15-2020 09:05 AM               

quote:

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Originally posted by Blackarrow:
...but it implies that it should be easy to state the precise length of electrical wiring in a Block 2 command module.

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posted 05-15-2020 10:13 AM               

Electrical components have multiple pinouts, some used as power supply, others for signal transfer, and other to complete circuits. Many wires have multiple cores and a shield sleeve and they may pass through couplings (plugs) at frames or bulkheads. The components receive wires from multiple sources and feed wires back to instruments, other components, or complete the circuit via frame or switch.

Loom manufacture is not simply a case of make one and install, consider each switch and circuit breaker having multiple wire connections and many systems have redundancy that is fed from alternate power sources located in different areas, including onboard batteries and external sources fed umbilically.

Large wires are made as short as possible to save weight and space, with electrical relays activated by smaller gauge wire. Some of these have feedback circuits for system indications annunciation or verification.

The majority of looms would be manufactured with the plugs or connectors installed at one end, the wires would be run along specified pathways and several looms would be integrated together into bundles, with specific wires branching off where required. Once installed and secured, the second end of the wire would be prepared by stripping the insulation material, and depending upon the type of termination required, soldered or terminated using crimped pins designed to fit into the desired plug or socket, switch or terminal board.

The process would allow for additional length during manufacture to avoid making a loom too short, the act of removing a short wire and replacing from a large bundle that snakes around a structure is huge, and any excess wire is cut away during the termination process. How much wire is cut away may not be huge lengths, but with the stated 13,000 wires, the length and weight would add up. (another advantage using this method versus pre-making the complete loom as a single unit).

Each wire termination was hermetically sealed on Block B vehicles using various methods. Places where wiring was to pass from inside the vehicle cabin to outside, specialist connections are used, which makes additional joints. The requirement to reduce the number of pressure vessel pass through points means that it is not always feasible to simply run wires from point A to point B.

Finally, during access and maintenance it is possible that wires get damaged or need to be re-terminated for fault finding or component replacement, meaning some additional length of wire should be left during installation just in case. Failing to do this results in the subject wire needing replacement, making the gaining access to the installed looms difficult on completed vehicles.

It is well known that the lunar module wiring looms were a target of the weight saving program, with several iterations being made using lighter gauge wire and light weight insulations. These light gauge wires became problematic for maintenance engineering staff.

posted 05-16-2020 09:50 AM            

Jim Behling suggests that an accurate answer would require someone "...to go through the actual effort to add it all up." One would like to think that someone paid by NASA (or one of its contractors) went to some effort to arrive at the figure of 15 miles* contained in the Apollo Spacecraft News Reference. Unless, of course, it was just a "best guess" to satisfy the needs of the press for "gee whizz figures."

It seems odd that the figure of 15 miles stated by NASA contradicts the already contradictory figures quoted from the Apollo 1 congressional hearings. I assume those figures of 30 miles and 20 miles quoted from the Apollo 1 hearings were given on oath by people doing their best to give accurate information.

Based on all of the above contributions, I am not persuaded that anyone knows, or will ever know, the "correct" answer, but it remains puzzling that the estimates cover such a wide range (based on the above, between 14 miles and 30 miles). I can appreciate NavyPilot's scepticism about "data." I think the only safe answer is "many miles of wiring."

posted 05-16-2020 10:06 AM            

quote:

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Originally posted by Blackarrow:
Unless, of course, it was just a "best guess" to satisfy the needs of the press for "gee whizz figures."

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posted 05-16-2020 11:32 AM            

I've always considered that, from a quality/safety perspective, number of terminations is more relevant than length of runs. The industry concerns itself a lot with bend radii, riding conditions, suspension support, and electromagnetic interference too.

Wiring is a real art form, especially in cramped vehicles like spacecraft and small tactical aircraft. I get impressed regularly by how elegantly and gracefully design engineers allocate and package wiring bundles.