In Scott Manley's video Why Lunar Landers Had Jumper Cables For Emergencies he describes the "LOSS OF ED [Explosive Device] SUB-SYSTEM" procedure, which includes the use of a jumper cable called the "ED Adapter Cable" that draws power from the Descent Stage.

He poses the question; if required, could the Lunar Roving Vehicle have been used instead?

Note you can find the "LOSS OF ED SUB-SYSTEM" procedure in the Apollo Operations Handbook; Lunar Module; Volume II, it's the last procedure, on PDF Page 929

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    $\begingroup$ Do we have some information about what this jumper cable actually did? I find it a bit unlikely that it is just for power - why would they need such a complicated procedure if just one subsystem was not powered? Why not take the power from some local source? I guess they also switched the control circuits in this case. $\endgroup$ – asdfex Jun 15 '19 at 9:39
  • $\begingroup$ If the information in the video and texts presented is accurate, it doesn't sound like a "jump start", but about bypassing all control circuits and applying a voltage directly to the ED to force the valves to open. That would imply that you can't use the LRV and leave the Moon yourself. $\endgroup$ – asdfex Jun 15 '19 at 13:08
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    $\begingroup$ That's a very interesting procedure, thanks for this intriguing question. It seems to me that if the LRV battery could have been used, they would have done that after step 13 in the procedure instead of just using the LRV as a ladder to access the power supply in the descent stage. Fascinating how they fire the stage separation system with the hatch open and a cable running through it! $\endgroup$ – Organic Marble Jun 15 '19 at 14:14
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    $\begingroup$ FYI, there's a good writeup on the ED subystem in section 2.8 of this document: hq.nasa.gov/alsj/LM10HandbookVol1.pdf $\endgroup$ – Organic Marble Jun 15 '19 at 14:35

I don't think that cable is for power. Before launching from the moon, the explosive device (ED) subsystem performs three tasks:

  1. The ascent stage propellants are pressurized. Like all other LM propellant tanks, they are filled but unpressurized at the start of the mission. Explosives open valves to supercritical helium tanks, which pressurize the propellants.
  2. The bolts holding the descent and ascent stages together are blown ("staging").
  3. An umbilical between the descent and ascent stages is cut.

(source: Apollo LM Operations Handbook, section 2.8.3)

The problem is that if something accidentally severs the umbilical first, you might not be able to perform #2 and lift off. That's why they included the emergency cable. The procedure you cite connects the controls in the cabin with the ED relay box on the descent stage. Then you blow the bolts, disconnect the cable and toss it out the hatch, close the hatch, and take off.

LM explosives subsystem

Taking the question literally, could the rover batteries replace an ED battery? Perhaps:

  • The ED batteries are rated to provide "75 amperes for 36 seconds at more than 20 volts at 60°F to 143°F or for 15 seconds at more than 20 volts at 50°$\pm$3°F." (source: Apollo Experience Report: Battery Subsystem, TN D-6976, p. 6 and p. 13)
  • The rover has two batteries. Each battery is nominally 36 V, 33-41 V fully charged, 47 A max but peak to 90 A. (source: Lunar Roving Vehicle System Handbook, p. 6-2) Expect this situation to happen after they've been used for driving around, so they won't be at full capacity.
  • The rover battery is over-voltage, but that's not a problem. The only loads in the ED system are pyrotechnics; those batteries do not power sensitive electronics.
  • You will either need to hot-wire a rover battery, or use the auxillary power port on the rover. The latter was used to power the TV camera used to record the LM's liftoff. It goes through a 7.5 A circuit breaker (which has a bypass switch) and a 70 A main bus breaker.
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    $\begingroup$ @OrganicMarble: Okay, so I'll change "return to the cabin" to "and throw it out the hatch, then close the hatch". As far "apply power", the relay box on the descent stage is literally a box of relays. Each relay has a coil side which is powered by the main LM electrical buses, and a contacts side which is electrically isolated and powered by the ED battery. The ED cable is powering the coil side because its connections are severed on the umbilical. $\endgroup$ – DrSheldon Jun 16 '19 at 16:45
  • $\begingroup$ I am thinking the power is flowing out of the ascent stage to the ED relay box. There are good schematics of the ED relay box in the Vol1 document, but sadly they don't show where the GSE connector fits in. $\endgroup$ – Organic Marble Jun 16 '19 at 16:49

Yes, but it would have been really tense to do so. A good summary of the document that describes the procedure in detail is here. That page also links to a lunar module operations manual that it summarizes. Here's the way it was supposed to go down:

On the assumption that, for some reason, the ascent stage engine and explosive bolts etc. couldn't be activated by the ascent stage, the astronauts had no choice but to do things on EVA.

Problem with that was they would have jettisoned their life support systems by that time. They had a backup oxygen supply that lasted for 30 minutes, so the entire thing would have to have been done within that time. Also, without the life support system, they would have had no cooling in their pressure suits.

There were then two procedures that had to be followed, with the first procedure being deemed safer and easier.

The first procedure would be to attempt to use the LM's descent stage batteries and a jumper to do what could be described as absurd: rush out the LM (remember, you only have thirty minutes and, if this procedure failed, you have to use the rover) and attach the jumper to one of the descent stage batteries. Leave the cabin unpressurized. Launch, and when you're done the burn collect the cables that are now dangling out of the LM and finally close the hatch.

The second procedure would be followed if the first failed. This involved going to find the rover (rapidly), and then using it as a jump starter just like the descent stage battery.

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    $\begingroup$ The narrative in that link does not agree with the procedure as posted in the question. The stage separation is fired in step 29, the cable is demated and the hatch is closed in step 30. Step 29 does not launch the ascent module. The link may be describing a different procedure, but it does not describe the one in the question. The procedure in the question does not power the engine valves. $\endgroup$ – Organic Marble Jun 16 '19 at 1:46

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