Apollo 13 math formula used in the movie and a slide rule question

[GIGObuster]

From this movie error site:

http://www.moviemistakes.com/film75/...ns?viewall=yes

As the Apollo 13 crew is readying to "slingshot" around the back of the moon, burn calculations are being made by Houston which are relayed to the crew. Tom Hanks is calculating total fuel amounts in the various fuel tanks by mathematical addition using a slide rule. You don't add and subtract with a slide rule. You multiply and divide.
[Wrong - the only time a slide rule is seen is when the crew are transferring from the Command Module to the Lunar Module and they need to convert the gimbal angles. Lovell (Hanks) is attempting to work out the conversions using pencil and paper. He asks for confirmation that he has got the figures right. At this point we see one of the flight controllers using a slide rule to check the calculations, which DO involve multiplication and division].
[Wrong again - the slide rule is being used when transferring the gimbal angles from the CM to the LM. (The offsets between the two would have been measured earlier in the flight.) The LM angles are the three CM angles with the offsets added or taken away. No multiplication or division are involved]

Well, who is right over there regarding the slide rule use?

Also, I had a hard time finding the formula and the math used in the movie, I need it to possibly show students in my class how math can save one's skin in an emergency.

[Lazlo]

Hmm. I'm a slide rule collector and and an Apollo 13 fan, so I know the scene of which you speak.

First of all, addition and subtraction are not performed on a slide rule. Simple multiplication and division is usually easier without the rule as well. Eg. you won't use a slide rule for 12/4 or 9*7 (but you could!). Depending on the complexity of the slide rule, you can use them to calculate trigonometric functions, squares, cubes, and their respective roots. There were also special slide rules for electronics that did those imaginary calculations for AC power and whatnot.

Now as far as the scene on Apollo 13 is concerned, I distinctly remember thinking, "Why would mission control use a slide rule for addition and subtraction?" The worksheet that Lovell was shown scribbling on had definite + and - operators on it, and from what I understand, the gimbal conversions were indeed simple addition and subtraction. I chalked it up to that whole artistic-license thing. There was no need for a slide rule in that scene.

Unfortunately, I'm visiting my folks so I don't have access to my Apollo 13 DVD to double check.

Now, just because I'm rambling on about stuff I like, you might be interested to know that the entire crew of Apollo 13 carried a Pickett N600-ES pocket slide rule on every mission. The really neat thing about these is that there are still hundreds of new-old stock available and it's a cheap piece of Apollo history (Yep! I have one!).

Here are a couple of very informative links about slide rules and how to use them:

http://sliderulemuseum.com/SR_Course.htm

http://www.sliderule.ca/intro.htm

Anyhow, I'm sorry I don't have the exact formula for gimbal conversion available for you, but I'm 99% sure it's just an offset you'd add or subtract.

[timbicile]

Gigo, I always try to interact with you but you make it difficult.
Lazlo, I have never heard of a nerdier hobby. ::bows::

[Lazlo]

I try!

Even though my grammar is so bad that I use the wrong tense sometimes.

[GIGObuster]

Originally Posted by Lazlo

I try!

Even though my grammar is so bad that I use the wrong tense sometimes.

Oh don't worry about that!

There is a reason why I told my principal that I could teach almost anything, except teaching English. Besides being my second language, even I can see that my English grammar is a crime against nature.

In any case, thank you for your reply. As it is a high school class, I think it will be OK if it is a simple formula (it will be a throw away exercise when talking about the moon and the exploration of it), but I have still not found what formula and values they used.

[Lazlo]

I think I found a similar checklist page from Apollo 15. Check page 55 of this huge PDF.

I don't know if those are for the gimbal conversions or if it's for something else. There are a lot of acronyms I'm not familar with.

There are links to many more PDFs here. I'm going to peruse through the LM Operations Handbook. That sucker is 37 megs!

[Tuckerfan]

The subject has come up on The Bad Astronomer's forum in the past, but their search engine is so wonky that finding it is probably going to be difficult. I'm sure, however, that if you post your question over there, you'll not only get an answer as to what they were doing in the film, but also what they were really doing on the Apollo 13 mission (and the innumerable debates as to which type of slide rule is superior).

[Lazlo]

Good call on that, Tuckerfan. I'm searching their forums right now and I even ran into a few of your posts so far.

[wring]

Originally Posted by Lazlo

Good call on that, Tuckerfan. I'm searching their forums right now and I even ran into a few of your posts so far.

I think Snookie used to post there, too. He stopped for the most part 'cause he found it difficult to cull his humor to "appropriate for the family and children" all the time. PM me if you want to know his screenname. (I'm the only one who really calls him Snookie - oh, and folks I work w/'cause that's how I refer to him all the time)

[BJMoose]

I'm looking at Lost Moon, p. 130 to see what Lovell had to say about this. I'm not sure. The text suggests that he had to deal with more than roll-pitch-yaw angle conversions (wouldn't the roll angle be the same when the vehicles were docked?). One could look at the com transcript to see what sort of numbers Lovell passed down to Mission Control. I had a copy, but the hard drive on the other computer ate it a few days back. . . .

Regarding Lovell's sudden math skills paranoia, it says: "Could he perform the calculations properly? Would his ciphering be correct? 3 times 5 is 15, isn't it? 175 minus 82 is 93, isn't it? With the clock ticking down, Lovell all at once found himself doubting his ability to add and subtract." So maybe multiplication was involved. Or maybe this is just loose language indicating that he didn't trust himself with even basic math skills.

In any case, I'm sure Ron Howard saw this scene as an opportunity to put a little "obsolete technology" on display, even if it wasn't appropiate to that particular scene. Maybe they didn't use a slide rule on this occasion, but the trajectory guys in the Trench certainly gave their slide rules a good workout over the course of a flight.

[Lazlo]

Originally Posted by wring

I think Snookie used to post there, too. He stopped for the most part 'cause he found it difficult to cull his humor to "appropriate for the family and children" all the time. PM me if you want to know his screenname. (I'm the only one who really calls him Snookie - oh, and folks I work w/'cause that's how I refer to him all the time)

Will do if I start posting there! I'm done with the site for now, though. I've skimmed through enough Apollo threads to get weary of the subject. GIGO, if you want to find (or ask) your question there, you're on your own, buddy.

Originally Posted by BJMoose

Maybe they didn't use a slide rule on this occasion, but the trajectory guys in the Trench certainly gave their slide rules a good workout over the course of a flight.

I have no doubt about that! You know, now I'm starting to wonder if there wouldn't be some trigonometry involved in making those angle conversions. Gah, this is going to be in my head for a while.