Final preparations

Over the final few hours before they entered lunar orbit, the Apollo crews worked through an exhaustive series of checks and adjustments, interrogating the spacecraft’s systems about their ability to sustain life while in the Moon’s clutches, and on the engine’s readiness to do its job properly.

Another important task in the build-up to LOI was to change the spacecraft’s knowledge of which way was ‘up’. During the five or six minutes of the burn, the crew’ would want to avoid any appreciable errors in the direction of the engine’s thrust. Additionally, they needed to ensure that the guidance system could measure the effect of the burn on their velocity. As was usual before a burn, the CMP performed a P52 to check the alignment of the guidance platform, but this time special procedures were applied. Up to this point, the platform had been aligned with an orientation that suited the coast to the Moon and made the barbecue rotation easier to set up and maintain. Now the platform would be realigned to match a new

REFSMMAT[3] that suited the LOI burn, and so obviously it was known as the LOI RHFSMM AT.

First, the CMP carried out a realignment to refine the platform’s orientation in terms of the REFSMMAT they had been using. This yielded a measure of its inherent drift, a parameter that was always carefully monitored and no opportunity was missed to gain another data point. Once the amount of drift had been measured, the platform’s orientation was torqued around align with the new RFFSMMAT. This one had been chosen to match the attitude in which the spacecraft would make the upcoming burn. By lining up the coordinate systems of the platform and the spacecraft, the crew’s job of monitoring attitude during the burn became a lot easier. Their 8-ball attitude indicators would now read zero on all three axes w’hich made them much simpler to interpret, к is wise to be certain that your ship is pointing in the correct direction when you make major engine burns near planets (especially ones without atmospheres) as a mistake can lead to a crash.

Next, they put the entry monitor system (FMS) through a test to demonstrate that it could still accurately measure the change in speed brought about by the burn. This feature of the FMS, its ‘Dclla-v‘ display, w-as one of the redundant methods by which the engine could be commanded to shut down once it had achieved its task.

The spacecraft’s cooling circuits w’ere next to be checked. At first glance this may appear to be one of the less exotic systems, but if any flaw were to be found in cither the main or the backup circuit – especially if any leaks had formed in the radiator pipes due to micromcLcoroid damage – the crew would return directly to Earth.

More checks followed w’hich covered the caution and warning system, the tanks and valves associated w’ith the manoeuvring thrusters on both the service module and the command module, and the spacecraft’s supplies of oxygen, water and power. Once these essential tasks had been completed, the crew could begin to implement the burn itself.