The Apollo Program, A Personal Journal: Hand-Held Calculators (Circa 1968)

The first manned landing on the Moon occurred in 1969. The first hand-held calculator didn’t come on the market until 1972. So we got men to the Moon using pencil and paper and a slide rule. Really!

This post has been removed because its content may be incorporated into a forthcoming book by the author. To find more articles by Jack Clemons, go here.

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Copyright 2013 Dandelion Beach LLC   Images: NASA except where noted

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  1. Thanks, Jack. So… you guys were responsible for making sure that the command module splashed down at or near its target?

    Also, in case you’re not planning on writing about this later, could I ask about Apollo 13. In the movie, the re-entry path is off because they’re not carrying the hundred (?) pounds of moon rocks that they had intended to. Is this accurate? Any fun details you can add to that story? (Or, again, if you’re planning on writing about this in the future, I can wait until your article comes out!)

    1. Frank – yes, we had responsibility for the reentry into Earth’s atmosphere and then “flying” the Command Module to the recovery ship. As for the movie, while it’s true that the lighter weight (no moon rocks) had to be accommodated, the real problem with the reentry path being off (and ontinuing to change as Apollo 13 traveled back from the moon) had to do with some unexpected consequences of the explosion on the way out – and that caused me some serious agida at the time (though we didn’t use that term in those days). I’ll talk about all of this in later posts – these blogs will cover all of my time on Apollo – but I certainly don’t mind answering your questions now. Thanks for asking, and for being interested!

  2. Thanks, Frank. Yeah, we did use slide rules a lot. In fact very much the way we use handhelds today. We also had some heavy-duty computers (for the day) in the form of several IBM mainframes located at NASA, but these were only available for 1-2 day turnaround (so-called “batch”) runs unless we were doing live support for a mission. All of the parameters you mention were being re-worked by someone, but since my team was responsible for reentry, I mostly did return from the moon trajectory recalculations on the fly. We’d get updates from the spacecraft of their current position, velocity and time of arrival and if that was different than was predicted on the last update (which happened repeatedly on Apollo 13) we’d rerun all our entry projections again. There’ll be more on that in later postings.

  3. There’s a scene in Apollo 13 wherein the astronauts and Mission Control double-check each others’ calculations with slide rulers. I assume that sort of thing happened a lot?

    I was wondering if there was a particular example or two you could give us of some calculations you had to do on the fly – were they things like fuel consumption? Predicted carbon dioxide levels? Trajectories? What sorts of things did you have to calculate or re-calculate mid-mission?

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