# Apollo 13 (1995)

## 1 correction since 6 Sep '22, 06:24

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

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.

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.

Peter Harrison

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&deg; 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&deg; 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&deg;. The answer is not much.

Peter Harrison

### Mistakes

When the cabin temperature drops, an astronaut's breath is visible. His visible breath rises as he exhales. This is an effect of gravity - on earth the water vapor in breath, which is the component that becomes visible in the cold, rises because it is lighter than the surrounding air. Since the astronaut was in a "weightless" environment, his breath should have travelled in a straight path from his mouth into the surrounding atmosphere, rather than rising.

### Quotes

Gene Kranz: I don't care about what anything was *designed* to do. I care about what it *can* do.

### Trivia

The Apollo 13 mission set a record for the greatest distance from Earth ever achieved by mankind. This occurred because unlike the other Apollos, Apollo 13 did not make a burn behind the moon to drop into lunar orbit. The free-return trajectory the mission followed took the spacecraft farther behind the moon than any other mission.

### Questions

When Aquarius is descending during re-entry, why is the Navy preparing Search & Rescue instead of the Coast Guard?

Cubs Fan

Chosen answer: Aquarius was most likely going to splashdown in international waters; since the U.S. Coast Guard only has jurisdiction within American waters, the Navy would have to rescue them.

Xofer

Answer: Because the Navy was assigned the Search, Rescue and Recovery task for all of NASA's space program. Imagine how long it would take the Coast Guard to get to the other side of the world.

stiiggy

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