Blue Marble: My theory (and what it is, too)

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[edit] Who's on First


The detailed timeline shows that the "Blue Marble" photo was taken between 5:00 and 5:08 after launch. The Apollo spacecraft was facing back towards the Earth, and the astronauts were still in their space suits.

The time of Apollo 17's launch, 12:33 a.m. EST, meant that Africa was in daylight, and with the December solstice approaching, Antarctica was also illuminated. The photograph was taken at a distance of about 45,000 kilometers, about 1 hour 48 minutes after the spacecraft left Earth orbit on its way to the Moon, and about 5 hours 6 minutes after launch. The spacecraft's trajectory aligned it with the Earth and Sun, providing a view of an almost completely full Earth.

Image:CMWindowsA.gif

Command Module Pilot (CMP) Ronald Evans was in the left-hand seat. After docking with the Lunar Module (LM) and extracting it from the S-IVB, Evans initiated a separation maneuver, then pitched the CSM/LM stack down so that the S-IVB was clearly visible through the center, hatch window.

Commander (CDR) Eugene Cernan was in the center seat. After the Command and Service Module (CSM) docked with the LM, Cernan went down into the short tunnel leading to the lander, opened the hatch cover, and verified the latches holding the two spacecraft together. He connected electrical umbilical cables, reinstalled the hatch, then returned to his seat to observe the S-IVB.

Lunar Module Pilot (LMP) Jack Schmitt was in the right-hand seat, observing, photographing, then monitoring the LM. During this part of the flight Schmitt managed communications and the flight plan checklist and updates.

The astronauts were waiting to watch the S-IVB as it fired its engines to send it into a controlled crash on the Moon.

The spacecraft was facing back towards the Earth, pitched down so that the S-IVB was clearly visible through the Command Module's hatch window.

I've determined the actual orientation of the S-IVB/LM relative to the Earth by pasting together the 16 mm movie frames from the pitch maneuver. Since the pitch maneuver was performed at a constant rate, it's possible to measure the angles directly from the combined image. The center of the Earth was 70° down from the CSM/S-IVB/LM axis.

All three astronauts took photos during this period.

The Earth was visible through the side windows, 1 and 5, but probably blocked by the LM through the other windows. This narrows the possibilities down to Evans or Schmitt ... or, possibly Cernan. D'Oh!

[edit] You said it

There are critical disagreements between the PAO Mission Commentary Transcript and the Technical Air-to-Ground Voice Transcription, while the Onboard Voice Transcription is missing the entire period from 1:27 to 35:30.

Nevertheless, here's my reconstruction of the actual events:

004:47 Evans?
Cernan?		 Okay. POWER's OFF. Hey, Jack. Hand me the Hasselblad. I think we're bowing the right direction. Yes, the Moon is there. The Earth is - that's the Earth. ... The Earth just fills up window 5. Okay, f infinity, about a 250th.
  Cernan? Let's get a picture or two here yet, and we'll give you a GO...
  Cernan: Okay, you have a GO.
004:56 Cernan?
Schmitt? 		And for your reference, at frame 105 I started a few 250-millimeter pictures of the S-IVB
  Capcom: Roger, Gene (according to PAO transcript)
Roger, Jack (according to Technical transcript)

After separation and pitch down, (probably) Evans took some photos of the Earth. He then passed the camera to Cernan (or Schmitt), who photographed the S-IVB.

  • Murphy's law steps in with a disagreement between the two existing transcripts. One of the astronauts says, "And for your reference, at frame 105 I started a few 250-millimeter pictures of the S-IVB," then Mission Control identifies the photographer as Cernan (PAO) or Schmitt (Technical).
    • According to the mission plan, Cernan's task was to photograph the S-IVB.
    • The PAO (Public Affairs Office) transcript, based on the public feed of the mission audio, was transacribed by stenographers in a hurry for use by journalists, and is prone to errors.
    • The Technical Air-to-Ground transcription, based on the internal feed, was transcribed more carefully and is usually more accurate. In this case, it suggests that Schmitt was the photographer instead of Cernan.

Both Evans and Schmitt were looking at the Earth through their side windows.

004:59 Cernan: I know we're not the first to discover this - but we'd like to confirm, from the crew of America, that the world is round.
CapCom: Roger. That's a good data point.
CapCom: Have you gotten a good look at any of that weather down there on the Antarctic?
Cernan: Well, Ron's at window number 1 - maybe he can tell you a little about it.
Evans: You know, it's real funny there in Antarctica the - You can see the snow, but there isn't any weather at all in it. All of the weather's around it in the water.
Schmitt: That's where the moisture is.
Schmitt?
Evans?		 I don't know what to take a picture of.

[edit] Photographing the Earth

22717.jpg
#110 AS17-148-22717 		22718.jpg
#111 AS17-148-22718
22719.jpg
#112 AS17-148-22719 		22720.jpg
#113 AS17-148-22720
22721.jpg
#114 AS17-148-22721 		22722.jpg
#115 AS17-148-22722
22723.jpg
#116 AS17-148-22723 		22724.jpg
#117 AS17-148-22724
22725.jpg
#118 AS17-148-22725 		22726.jpg
#119 AS17-148-22726
22727.jpg
#120 AS17-148-22727 		22728.jpg
#121 AS17-148-22728

Schmitt took a series of Earth photos (#110 AS17-148-22717 through #115 AS17-148-22722) with varying exposures, using the telephoto lens.

005:02: Cernan?
Schmitt?		 No, I'll change lens now.
  Cernan?
Evans?		 Okay. Here Jack, can you see it good?
  Schmitt?
Evans?
Cernan? 		Check the lens[settings] now. I took an F-22 stop.

They changed the lens from 250mm telephoto to 80mm normal in preparation for the S-IVB burn. While changing the lens, they bumped the shutter causing the blank frame (#118, AS17-148-22724). Cernan (probably) took the photo of the S-IVB (#118, AS17-148-22724) through the hatch window.

The transcripts disagree on who said what. Here are two interpretations:

  1. Cernan: Okay. Here Jack, can you see it good?
    Schmitt: Check the lens[settings] now. I took an F-22 stop.
    1. Cernan passed the camera to Schmitt so he could photograph the whole Earth with the normal lens.
    2. Schmitt took the first picture (frame #119, AS17-148-22725) then remembered to [BlueMarbleOverview.htm#f-stop change the f-stop] to compensate for the brightness of the Earth.
    3. Schmitt then took three more photos, with slightly different aim because there's no viewfinder and he wanted to make sure to get the whole planet in the picture. These photos are the famous "Blue Marble".
    4. Schmitt passed the camera back to Cernan for pictures of the S-IVB burn through the hatch window. Schmitt reminded Cernan that he had changed the lens setting.
       
  2. Cernan: Okay. Here Jack, can you see it good?
    Cernam: Check the lens[settings] now. I took an F-22 stop.
    1. Cernan passed the camera to Schmitt so he could photograph the whole Earth with the normal lens.
    2. Schmitt took the first picture (frame #119, AS17-148-22725) then Cernan reminded him to change the f-stop to compensate for the brightness of the Earth.
    3. Schmitt then took three more photos, with slightly different aim because there's no viewfinder and he wanted to make sure to get the whole planet in the picture. These photos are the 4 shots of the famous "Blue Marble".
  Cernan: There it goes, Bob.
  Schmitt? There it goes, finally.
  Schmitt?
Evans? 		It's going to be gone, I think, before we -
  Evans?
Schmitt? 		Houston, Magazine, November, November is on about 123 right now.

There is no photo of the S-IVB after the evasive burn started. "It's going to be gone, I think, before we -" Then Evans (apparently) reported the frame count.

How did Evans get the camera? Here's one possible interpretation:
  • Cernan didn't get a photo of the S-IVB through the hatch window, so he passed the camera to Evans (or Schmitt) for a parting shot through window 1, but it's too late.
  • Evans (or Schmitt) reported the frame count. (Note: The actual frame count is ±1 due to the analog frame counter.)

[edit] Testing the Theory

Of course, all this is speculation based on contradictory, circumstantial evidence. NASA's policy is to credit photos to the entire crew unless there's only one person who could have possibly taken it. The astronauts were very busy at the time the picture was taken, observing the S-IVB and the Earth, and passing the camera back and forth, so it could have been any of them.

There are a number of things we can do to refine or disprove this theory:

  • Get a copy of the original audio tape to verify the transcript, identify the speakers, and narrow down the actual times
    March update: Waiting on NASA archives
  • See if there's movie footage that can help narrow the timeline
    March 2006 update: The 16mm film of the S-IVB firing doesn't add much. It appears the camera was handheld, and after the burn, the camera was turned on again for a few frames of the "Blue Marble".
  • Try to run an accurate simulation of Apollo 17's TD&E using Orbiter to establish the actual fields of view from windows 3 and 5.
    March update: Orbiter is a serious simulator, and I'm still learning how to use it.
  • Ask Cernan and Schmitt to comment
  • Ask other commanders and LM pilots to comment

[edit] Sources

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