Power on the Moon

All the power required by the LM for the duration of its separate mission came from batteries. There were four mounted in the descent stage, two in the ascent stage and a fifth battery was added in the descent stage for the J-missions solely to extend the crew’s stay Lime on the surface. Known as the ’lunar battery, it was not used in flight. For the duration of the powered descent, all six major batteries were linked in parallel to power the spacecraft. The batteries for the ascent stage were included in order to power the LM in the event of an abort. Now. on the surface, fewer systems required power so the crew took the ascent batteries offline and reduced the number of online descent batteries. This was when the lunar battery, if present, was brought into use to share the load with combinations of the other four.

Many of the LM’s electronics were designed to run on AC power so a couple of inverters were provided. These electronic devices convert direct current to alternating current but unlike the 50-Н/ or 60-Н/ supplies that most people arc aware of in their homes, these ran at 400 Hz. Control of all these power systems was via two electrical control assemblies (fCAs), one each on the commander’s and LMP’s side of the cabin. Little talkback indicators showed the status of the ECAs to confirm that their switch settings had worked. For the next few’ minutes, the crew w’orked their w’ay through a checklist that set their systems either to a mode suitable for the surface, or pow’ered dowm altogether.

Other tasks at this time included dealing with the multitude of items, large and small, that had to be unstowed and prepared for the first EVA. From back packs to cameras and film magazines, even a brush to keep their lenses clean, they had to be placed in bags that would be taken to the surface or readied for when suiting up would begin.