Corrected entry: In the television interview, when the expert is describing the tolerance requirements for re-entry angle, he asks the reader to imagine that the earth is a basketball and the moon is a softball, and that the two balls are 14 feet apart, which is about 16.8 times the diameter of a basketball. The distance from the earth to the moon is about 30.14 times the diameter of the earth. This means that the 14 feet should really have been about 25 feet. Finally, the expert says that the re-entry angle has to be accurate to within 2.5 degrees, which he says is like aiming for a target the thickness of a sheet of paper. 2.5 degrees at 30 feet is actually about 13.14 inches thick (even at 14 feet, 2.5 degrees is about 7.34 inches).
qwer5r
1st Mar 2011
Apollo 13 (1995)
Correction: The correction to the correction is wrong and makes the same mistake as the original entry. The expert isn't talking about a 2.5 degree error in the trajectory from the moon to the earth. He is talking about a 2.5 degree error in the angle of re-entry. A 2.5 degree error in the trajectory would give a much bigger error in the angle of re-entry.
Correction: I noted the same thing and it bothered me. It doesn't matter if the angle is with respect to to the moon or the earth. The expert's opinion was 2.5° based on 14 feet. That is 7." A far cry from the thickness of paper. Either the writers took extreme literary license for drama or the 'expert', (if actual testimony), was incorrect. It's simple math, not rocket science.
Correction: Yes, if you are out by 2.5° at the moon, you are going to be 13.14 inches out at the earth if the distance is 30 feet. But that is not what we are talking about. If you are 2.5° out at the moon, you will miss the earth completely. The question is, from the point where we leave moon orbit, how much tolerance is there to get a re-entry angle into the earth's atmosphere within 2.5°. The answer is not much.
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Correction: Re-entry angle refers to the angle at which the spacecraft will re-enter the atmosphere, presumably with respect to the earth's surface. That angle would have to be correct within 2.5°. This post seems to refer to an angle of trajectory between the moon and earth, which would not have been the concern in preparing for re-entry.