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Thank Goodness for Computers!

Space Roundup - around 1970

The Public Affairs Office recently received an inquiry on the number of man-years it would require to manually calculate the trajectory that was necessary for a safe return of the Apollo 13 crew in April 1970. The Mission Planning and Analysis Division came up with the answer. The figuring was based in part on an IBM study several years ago of the equivalency of IBM-7094 computer time to man-years of manual calculations.

Are you ready? Here we go!

Using the IBM-360 computer in the Mission Control Center Real Time Computer Complex, twelve six-minute computer runs were made toward determining the proper return trajectory for Apollo 13. Nine of these were transferred to the Return-To-Earth console for examination. From these, three were selected for return-to-earth candidates, and two additional computer runs of two minutes each were made on these three before the final return to-earth trajectory was chosen.

From the initial computer runs to the six two-minute runs on the final return-to-earth candidates, a total of 84 minutes of IBM-360 computer time was required to determine the initial return trajectory for Apollo 13. Previous calculations had determined that five seconds of IBM-7094 computer time was the equivalent of 86 man-years of manual calculations.

Projecting further, the UNIVAC-1108 is three times faster in computing than the IBM-7094, and the IBM-360 on which the computations were made for the Apollo 13 return trajectory is four times faster than the UNIVAC-1108. Based on these calculations, 84 minutes of IBM-360 computer time is equal to 336 minutes of UNIVAC-1108 time. This is equivalent to 1,008 minutes of IBM-7094 computer time. Each minute of IBM-7094 time is the equivalent of 1,032 man-years of manual calculations. Then, multiplying 1,008 minutes by 1,032 man-years per minute brings the total man-years of manual calculation to 1,040,256. This is how long it would have taken one man to calculate the correct trajectory for the burn of the Lunar Module Descent Propulsion System engine, to place the Apollo 13 crew on a free return trajectory.

Had a desk calculator been used, the time to figure the correct trajectory would have been shortened to a mere 60,480 man years. Had all the people in the Mission Planning and Analysis Division at that time (a total of 220) been assigned the task, it could have been manually computed in just under 4,730 years or by the year 6700.

As we said to begin with, thank goodness for computers!

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