Wikipedia:Reference desk/Archives/Science/2025 August 5

Science desk
< August 4	<< Jul | August | Sep >>	August 6 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 5

Electricity in rockets

How is electricity normally stored/generated and distributed in rockets? How about when it needs to cross a stage boundary - does it use something similar to a slip ring, and how are arcs prevented on separation?

I'm also interested to know how this was done in early historical rockets, such as the Mercury, R-7, Saturn etc. What methods did they employ to provide electricity to various control systems? DXPower (talk) 11:48, 5 August 2025 (UTC)[reply]

It's a bit tricky to generate an arc in a vacuum. -- Verbarson  ^talk_edits 18:06, 5 August 2025 (UTC)[reply]

Not all electrostatic or electrical discharges are arcs (one of the several types of discharge). It's pretty easy to have an electrical discharge through a vacuum, especially when it's a short path length and there's hot organic material nearby, such as overheating insulation. You might note that high power switchgear doesn't use vacuums, but rather a non-arcing fluid or even an air blast to extinguish any arcs. Andy Dingley (talk) 23:22, 5 August 2025 (UTC)[reply]

I think they used batteries. Later on electricity was generated with fuel cells and sometimes Radioisotope thermoelectric generator in unmanned probes. Bubba73 ^{You talkin' to me?} 19:06, 5 August 2025 (UTC)[reply]

• NASA Battery Power for Space Vehicles
• Fuel Cell, Apollo.

Alansplodge (talk) 22:20, 5 August 2025 (UTC)[reply]

• Every possible way. It all depends on the type of rocket, also the power required and total energy (how long the power is delivered). Particular questions are how long the rocket (nuclear weapons have the same issues, BTW) is stored before initiation, and how long its flight time is. The military are obsessed with the concept of 'the wooden bomb'; something that can be stored as long as possible without servicing, isn't fussy about its storage conditions, and then works reliably when needed.

For batteries, many used silver zinc batteries. These (before lithium batteries) had high energy density and high discharge currents for high power. Their downside was that they were expensive and had a limited number of discharge cycles compared to other chemistries. So rare otherwise, but not an issue for rocketry.

Fast reaction man-portable missiles, such as Stinger use thermal batteries in the launcher. These have a long inert storage time, then when triggered they produce a high current for a short time. These are used to power the Stinger seeker and IFF system before launch. The missile is supplied with 3 batteries in the field, because they only run for a short time. If the launcher is triggered to track a target, but not fired, then a new battery is needed for the next shot.

For long duration flights, fuel cells were useful. Apollo's Service Module carried such a system - which led to the problems with Apollo 13. It also produced water as a waste product, which supplied the crew.

For larger rapid-response missiles, they might use a flux switching alternator as a generator on-board, powered by either a gas generator (which can fire before launch, to spin up the guidance gyros) or the rocket motor exhaust.

Very large multi-stage launchers generally use rechargeable batteries, especially now with lithium technology. A separate supply is provided for each stage and each stage is as independent of the others as possible. For Apollo, look at the details of the Saturn V instrument unit. This was placed at the top of the third stage (the black ring visible externally), so that it could be used during the flight of all three stages. It weighed two tons, and although computers were big and heavy in those days, much of this bulk was for the inertial measuring unit and also the environmental control and high pressure gas supplies needed to keep it happy. The power supply was silver zinc batteries.

Slip rings aren't used as power connectors. The handful of them employed for rotary motion where needed are much smaller. Generally an umbilical cable connection is preferred with a positively-latched plug and socket connection. To disconnect these some of the launch umbilicals were mechanically separated but in flight NASA have their traditional preference for the reliability of a pyrotechnic (or pyrotechnically-released spring) guillotine to sever the cable. Andy Dingley (talk) 23:21, 5 August 2025 (UTC)[reply]

The Lunar Roving Vehicle had an interesting power supply: silver-zinc rechargeable batteries, but without any chance to recharge them (the Apollo Lander itself ran on batteries). Apart from the regular careful husbanding of remaining capacity, they also had a thermal management problem, to limit heat buildup in the batteries.

https://www.nasa.gov/wp-content/uploads/static/history/alsj/a17/A17_LunarRover2.pdf (page 16)

Andy Dingley (talk) 23:28, 5 August 2025 (UTC)[reply]

I can't find the right article at the moment, but one of the Apollo(?) missions failed because someone used the wrong length cable to connect the rocket to the launchpad. Going from memory, in lieu of link, part of the rocket's launch-sequence system was that when the rocket lifted off a certain distance, the cable would pull out, which would trigger a status indication to the controller. The cable unplugged at the wrong time relative to the actual height the rocket had risen, so the engine shut down and the re-entry parachute deployed before the rocket actually got more than a few inches/feet off the launchpad. Then because the whole rocket was still self-powered, nobody could do much until the batteries ran down. DMacks (talk) 13:24, 10 August 2025 (UTC)[reply]

Found it: Mercury-Redstone 1. DMacks (talk) 19:09, 10 August 2025 (UTC)[reply]