The Apollo Program, A Personal Journal: High-G Roller Coaster

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  1. Thanks, Jack. I LOVE these articles. I thought I knew a lot about the Apollo program, but every time I read one of your articles, I learn something new. For example: I didn’t know that the Command Module had off-center weight, so it would tilt properly on re-entry. Question: in the image, the astronauts are re-entering upside-down and butt-first. The butt-first, I get, as their backs are up against the heat shield (how many inches between their skin and the actual burning hot surface of metal?). But upside-down? In most (all?) of the Mercury re-entry images I’ve seen, the astronauts returned right-side-up. for example. Were the Apollo astronauts upside-down the whole time? Or did it change during re-entry? I suppose, of course, that they’d feel the effects of traveling 30X the speed of sound more than being upside down, though.

    1. Thank you, Frank! Your enthusiasm makes writing these blogs fun for me. Your question is a good one (again) and the answer has everything to do with reentry from Earth orbit vs. coming back from the Moon. About the butt-forward position, first, they faced away from the heat shield because that kept their seats as a cushion for the g-forces. In other words, they were pressed back into their seats during reentry rather than thrown forward. That was the same as Mercury and Gemini. (Think of a rear-end car collision vs. head-on). But during the early stages of an Apollo reentry, visibility through the CM windows (also opposite the heat shield) was important.
      As I mentioned in an earlier blog, the guidance software and onboard computer were new, and NASA took no chances with it going wrong at a critical moment. One thing that was reliable was the location of the Earth’s horizon when viewed from the Apollo cockpit. And to see that, they had to start the reentry heads down, since heads-up would put it mostly out of view. There were even lines etched on the window that showed them where the horizon should line up if everything was ok. Cool, eh?
      The big thing they were worried about was coming in too fast and too shallow and skipping back out of the atmosphere again. On Mercury and Gemini that wasn’t an issue because they were already in Earth orbit and only had to slow down to reenter. And yes, after reentry started the astronauts rolled heads up, heads down and heads sideways as the computer or backup system navigated its way between keeping the g-force at acceptable levels and working its way cross-range and down-range to get to the recovery ship. Like I said – it was quite a ride!

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