4.3.4 -  Apollo 11: Day 4, Final Approach

LM inspection complete, the crew settle in for a rest period and the small matter of Lunar Orbit Insertion for which they need to prepare. There is, therefore, quite a gap before the next photograph. AS11-36-5402 is shown below in figure 4.3.4.1, and analysed in figure 4.3.4.2. There aren’t any high resolution NIMBUS images available for the image, but there is a low resolution one from the recovered data that covers Africa, so we’ll use that.

Figure 4.3.4.1: AS11-36-5402. Source

Figure 4.3.4.2: ESSA-9 image dated 19/0/69 (above left) and 18/07/69 (centreright), low resolution NIMBUS HRIR image (left) compared with AS11-36-5402 and SkySafari time estimate. Below those are 3D reconstructions from digitally restored ESSA (left) and NIMBUS (centre) Satellite data.

SkySafari puts the terminator here at around 13:15, which would be around 71:45 MET, a few hours after the crew resumed their post=rest break communications. The crew are engaged in photographing the solar corona, getting news reports from home (including the progress of the Soviet Luna 15 probe), and preparing for LOI.

As usual with African views there is the split between ESSA's orbital day, running up the East coast of Africa. In this case, there is relatively little difference between the weather patterns either side of that divide, as indicated by the purple and cyan arrows. What the low resolution NIMBUS data lack in quality is made up by the supporting evidence it provides, particularly covering the cloud systems off West Africa. The only ATS image available shows poor definition of the western hemisphere only, with the African part of the globe in darkness.

The most obvious weather systems are those showing around southern Africa, which don't occur in that formation on any other day. The best fit orbit for the terminator is track 10 (number 1786), the penultimate on the image dated the 18th, which was commenced on the 19th at 08:02.

The next photograph examined is the first to feature the Earth with Apollo equipment in shot, and turns out to be the last one taken before images of the lunar surface appear. After this point we start to get images shown of the Earth from two perspectives: one from the crew bound for the lunar surface, and the other from Collins as he orbits in the CSM. AS11-36-5404 (shown in figure 4.3.4.3 and analysed in figure 4.3.4.4) occurs after the initial LM inspection, but the LM & CSM are obviously still attached, so it must have been taken (at the very least) before 17:44 on the 20th.

Figure 4.3.4.3: AS11-36-5404. Source

Figure 4.3.4.4: ESSA-9 image (above left) and low resolution NIMBUS-3 HRIR image (left) compared with AS11-36-5404 and SkySafari time estimate. Below those are 3D reconstructions from digitally restored ESSA (left) and NIMBUS (centre) Satellite data.

SkySafari suggests that the terminator is at roughly 16:00. If this was 16:00 on the 20th, the crew would have separated into the two craft and be performing system checks, unlikely to be taking photographs, so it seems a reasonable starting point to assume this image was taken on the 19th. The NIMBUS data, despite the reduction in quality, again shows a useful corroboration.

The cloud patterns in the north and south Atlantic are distinctive, and easy to pick out on the ESSA images, despite them being fainter. As for timing, the terminator portion of the ESSA image was taken on orbit 1788 (Track 12), which was commenced on July 19th at 12:05, progressing over the Atlantic later that afternoon, coinciding very nicely with the time SkySafari says the Apollo image was taken.

The next images of Earth come at the business end of the mission, with Armstrong and Aldrin preparing for their trip to the surface by testing out the cameras, and that happens on Day 5. Click the link below