4.9.10 - Apollo 17 Day 10 - Orbital Science

The crew continue to orbit the Moon for some time after re-uniting, and it is another 4 orbits before the Earthrise image they want to capture is taken, using magazine 152. This magazine starts with that Earthrise sequence which covers images AS17-152-23271 to 23277, and the last one in that sequence is used to compare with satellite images.

AS17-152-23277 is shown below in figure 4.9.10.1, and analysed in figure 4.9.10.2.

The crescent Earth is an early indicator that some time has passed since the last photographed examined here. The timeline tells us that the LM & CSM were re-united at 01:10 on the 15th, and that TEI was carried out at 23:35 on the 16th, so the last possible Earthrise would be shortly after that. We also have a couple of clues from the Photo Index, and the mission transcript.

At the risk of carrying out exactly the sort of pre-judgement warned against only a few paragraphs ago, the Photo Index tells us that this image was taken on orbit number 66. At AOS on this orbit, which occurred at 04:13, Evans says:

217:20:23 Evans . ... We've been taking its picture just as we came up.

Can we therefore find weather patterns on the crescent Earth that we would expect to find at that time and date?

Before going on to answer this question, it is first necessary to point out that only the IR spectrum image was available covering this time. No original data were available for the 15th in the visible spectrum, but which is the mosaic that would have been required to cover the early hours of the 16th. The time of the orbital pass at the terminator would be around 06:00 on the 16th.The most obvious feature to be seen is the large arc of cloud just on the terminator, and this can easily be made out on the IR mosaic. That cloud is in the mid-Pacific of the Southern Hemisphere, with Australia just beyond the western limb. Once this is correctly picked out, all other weather features are easy to match up, and the we therefore have an an Apollo photograph taken 2 hours before the first part of the infra-red mosaic was taken that matches exactly with it.

One of the best clues to look for here is the return of Storm Violet into the frame - conveniently identified by the magenta arrow. This document looks at DMSP images and their use in examining tropical storms, and features an image that it times at 01:25 GMT, and gives a precise location of 8.9 degrees North, 167.6 degrees West. If we zoom in on the Apollo image above we can compare it with the DMSP photo in figure 4.9.10.3.

Figure 4.9.10.2: AS17-152-23275 compared with NOAA IR mosaic  and and SkySafari estimate of terminator using mission transcript data. Left is digitally restored NOAA data dated the 16th, with 3D reconstruction centre.

 Figure 4.9.10.1: AS17-152-23275

If you care to check the location of the storm in the Apollo image and compare it with the coordinates given, you’ll find they match, just as the storm itself does perfectly.

The next image presents us with something of a dilemma, for reasons that will become apparent. It is a return to magazine 148, the final Earth image in the magazine, and is shown in figure 4.9.10.4. It is analysed in figure 4.9.10.5.

Figure 4.9.10.3: DMSP image of Tropical Storm Violet compared with a section of AS17-152-23275

Now we come to the tricky part - proving that this image was taken when we think it was taken.

Initial studies focused on South America as the land mass on the eastern limb. This is because the mission photo index records it as being taken between two lunar surface features - a crater called Sulpicius Gallus and crater on the edge of Mare Smythii, recorded as being taken on revolutions 73 and 74 respectively. There’s just one small problem - if this were true then the image would have been taken at somewhere between 17:30 and 19:15 on the 16th, but close examination of the image revealed Australia, which could not have been photographed between those two times. For Australia to be visible where it is, and with such a gap between it and the terminator, we have to be looking at a time nearer 08:00 GMT on the 16th.

What we need to do is trace through the records to see when these images were taken. We have this exchange during rev 66:

217:29:40 Evans And, I took a picture of that one in Smythii - is frame 160 on mag November November, and the reason I took the picture is really because on the western edge of the big basin it looks like there's a small impact crater, but it's only been dished out in the more recent flat dark-gray mare material. {Music in background) And looks like when it comes to the edge of the original basin ring, that part is not ejected out at all. So, essentially, you have a cone-type depression with an impact crater. The material's only been excavated in the - in the newer mare material.

That image is AS17-148-22766, and the time in the transcript equates to around 04:22 am on the 16th.

A few hours later, recorded at 07:20 GMT, we have Schmitt stating that:

220:27:36 Schmitt Bob, that's the most beautiful crescent Earth I've ever seen.

and then (captured by the CM tape recorder but lost in the transmission):

“That bright spot. See it - how bright it is? Right in the center of the crescent? Yes, yes, but it's never been that bright. Usually you just get the zero phase. It's getting so it's glancing off now and giving you a ... It used to be - I guess that's what the term ...reflection.”

If you look at the photograph you can see that there is indeed a bright solar reflection in the centre of the Earth crescent, and it seems likely that Schmitt was impressed enough at the time to photograph it. Shortly after this they then enter a rest period and there is no communication recorded with the ground. By way of confirmation that he photographed Earth, we have this remark from the Command Module transcript as he continues to discuss Earth’s crescent at 07:26:

220:33:55 "Oh, darn. There's the picture. Oh gosh. Never even thought about it. Oh well. Remember it, gang."

To be fair it’s not an absolute confirmation that he took the photograph, but he was certainly indicating that he wanted to.

So where has the confusion come from? It would appear that it comes from the crew relating back details of photographs taken during the preceding hours during their rest period.

For example at 18:22 and 18:37 GMT we have Evans saying:

231:29:17 Evans Okay, Houston, frame 163 and 164 and 165 were taken of the mud craters in Smythii. And 166, I guess, was taken of the great slopings - side of the crater in Crisium. That's just south of Yerkes.

231:44:42 Evans And, Houston; 166 and 167 were taken of a crater that looks like it's got a reddish dike in it and it's on - in the - again in the Haemus Mountains to the west of Sulpicius Gallus.

Those image numbers are actually  AS17-148-22766 and 22767 the ‘mud craters and Smythii’, 22769 for the one near Yerkes Recorded correctly as rev 66), and then AS17-148-22771 and 21772. The Earth photo must have been taken either as they set, or as they reappeared on the next orbit. The photograph after the one in question, AS17-148-22774, is of Kiess crater in Mare Smythii, so must be from the next orbit: rev 67.

Rev 67 was commenced at 218:33:45, or 05:26 GMT, with communications resumed at around 219:16, or 06:09 GMT. We do have this at 218:53, recorded in the CM transcript:

218:53 SC Take a picture of Earth, Ron.

CMP Yes.

Which converts to a time of 05:46 GMT. It isn’t clear whether that’s an instruction to do it there and then, or at the next opportunity, but again, the configuration of Australia isn’t quite right for that time. The one that matches best is the description of the beautiful crescent Earth at 07:10, so we’ve gone with that.

To cut a long story short, the obvious conclusion is that the image of Earth was not taken during rev 73 but several orbits earlier, and the way the information has been given by the crew in discussions held later on has led to them being mis-recorded in the photography index. The appearance of Australia is an obvious match.

Having decided when we are seeing the image, we can look at what’s in it. Again we are restricted to an infra-red view, with an estimated satellite image time at the terminator of 10:40 GMT. We have a distinctive curl of cloud extending from the Northern Territories to the east coast (yellow arrow). The band of cloud north of Papua New Guinea (green arrow) is also easy to make out. The Pacific has many thin east-west trending bands of light cloud that are also matched in the IR view. All of these (and the other ones identified) serve to confirm that we are definitely looking at Australia in this photograph, and consequently the Photography Index is wrong.

We also have a Landsat pass over Australia on this date, and we can see this in figure 4.9.10.6.

Figure 4.9.10.4: AS17-148-22773

Figure 4.9.10.5: AS17-148-22773 compared with NOAA IR  mosaic, and SkySafari time depiction

Figure 4.9.10.6 Landsat image paths shown on AS17-148-22773 (top left), Google Earth (bottom left), and close ups over Australia (centre) and Indonesia (above)

It would hardly be reasonable to draw any solid conclusions from these images, but there we are - largely cloud free areas in the Apollo image largely cloud free in the Landsat ones! It also doesn’t help us when we learn that the Indonesian images were done at around 01:00 on the 16th, whereas Australia was imaged at nearly 23:35 - both passes many hours either side of the Apollo photograph.

Moving on from the confusion over image timings after the Earthrise sequence in magazine 152 shown earlier, there is an Earthset, comprising AS17-152-23278 to 23282 (figure 4.9.10.7). The first in this sequence will be used here.

Figure 4.9.10.7: Earthset - AS17-152-23278 to 23282

In addition to photographs from magazine 152, we also have a contribution from 139, this time in black and white. Magazine 139 was taken to the lunar surface, and the first half of the photographs on it are those from an EVA. AS17-139-21300 and 2301 also show an Earthset, and these are also shown as being from orbit 71 in the Photo Index. As the 2nd of these shows an Earth almost totally hidden behind the lunar horizon, 20300 will be used.

Again, we can use the Photo Index and mission transcript to act as a guide as to what part of the Earth's surface is appropriate to start looking, and we find that the photos are recorded as being taken on orbit 71.

The mission transcript has this to say towards the end of orbit 71 at 15:!3 GMT,

228:19:59 Cernan Beautiful, Bob. We're going to get your picture as you set this time. Right out number ...

LOS on orbit 71 is recorded as 225:45 MET, or 15:25 on the 16th.

Both these images are shown  in figure 4.9.10.7, and they are analysed together in figure 4.9.10.8.

Figure 4.9.10.7:  AS17-152-23278 and AS17-139-21300

If the colour version of the image is examined carefully, it is possibly to make out the coast of South Africa, and the fog shrouding that coast is marked by the red arrow. Land continues north of that fog almost all the way up the image, so we can be confident that our prediction for what should be visible is correct, and the images do show Africa.

As far as the NOAA images are concerned, the visible spectrum image (now available again) has the usual problem of half of Africa being commenced at the start of the day in question, and the other half 24 hours later. The IR spectrum however has no such problems. The times for these mosaics at the terminator are roughly 19:00 GMT for the IR image, and 07:00 for the visible spectrum. For the visible spectrum, most of Africa was started on the 16th, but the terminator area would actually have been imaged on the 17th. SkySafari image confirms that Africa should be visible at the time of the photographs.

We can also conclude that the clouds shown in the central part of the image are the same ITCZ clouds, and the long strips of cloud in the top half of the image are over the Sahara in the mosaics.

We also have a good pass over Southern Africa by Landsat, and the details are shown in figure 4.9.10.9

Figure 4.9.10.8: AS17-139-21300 (centre right) and AS17-152-23278 (right) compared with NOAA visible spectrum (centre left) and IR (left) mosaics, and Sky Safari time depiction.

Figure 4.9.10.9: Landsat passes recorded over southern and central Africa as shown on Google Earth (bottom left) and AS17-152-23278, with close ups of southern Africa (centre) and central Africa (above).

As before the angles are oblique, and several hours have elapsed between the Landsat images and Apollo (South Africa was photographed at 08:05), but again we have a broad consistency between the two. We have clear air over most of the areas covered with some coastal cloud. The pass over the middle east is hidden in darkness for the Apollo photograph.

That’s the last of the images from lunar orbit - we now move onto the final phase of the mission, the last voyage home from the moon by Apollo. See tomorrow’s link for that.