How Margaret Hamilton Wrote the Computer Code That Helped Save the Apollo Moon Landing Mission

From a dis­tance of half a cen­tu­ry, we look back on the moon land­ing as a thor­ough­ly ana­log affair, an old-school engi­neer­ing project of the kind sel­dom even pro­posed any­more in this dig­i­tal age. But the Apol­lo 11 mis­sion could nev­er have hap­pened with­out com­put­ers and the peo­ple who pro­gram them, a fact that has become bet­ter-known in recent years thanks to pub­lic inter­est in the work of Mar­garet Hamil­ton, direc­tor of the Soft­ware Engi­neer­ing Divi­sion of MIT’s Instru­men­ta­tion Lab­o­ra­to­ry when it devel­oped on-board flight soft­ware for NASA’s Apol­lo space pro­gram. You can learn more about Hamil­ton, whom we’ve pre­vi­ous­ly fea­tured here on Open Cul­ture, from the short MAKERS pro­file video above.

Today we con­sid­er soft­ware engi­neer­ing a per­fect­ly viable field, but back in the mid-1960s, when Hamil­ton first joined the Apol­lo project, it did­n’t even have a name. “I came up with the term ‘soft­ware engi­neer­ing,’ and it was con­sid­ered a joke,” says Hamil­ton, who remem­bers her col­leagues mak­ing remarks like, “What, soft­ware is engi­neer­ing?”

But her own expe­ri­ence went some way toward prov­ing that work­ing in code had become as impor­tant as work­ing in steel. Only by watch­ing her young daugh­ter play at the same con­trols the astro­nauts would lat­er use did she real­ize that just one human error could poten­tial­ly bring the mis­sion into ruin — and that she could min­i­mize the pos­si­bil­i­ty by tak­ing it into account when design­ing its soft­ware. Hamil­ton’s pro­pos­al met with resis­tance, NASA’s offi­cial line at the time being that “astro­nauts are trained nev­er to make a mis­take.”

But Hamil­ton per­sist­ed, pre­vailed, and was vin­di­cat­ed dur­ing the moon land­ing itself, when an astro­naut did make a mis­take, one that caused an over­load­ing of the flight com­put­er. The whole land­ing might have been abort­ed if not for Hamil­ton’s fore­sight in imple­ment­ing an “asyn­chro­nous exec­u­tive” func­tion capa­ble, in the event of an over­load, of set­ting less impor­tant tasks aside and pri­or­i­tiz­ing more impor­tant ones. “The soft­ware worked just the way it should have,” Hamil­ton says in the Christie’s video on the inci­dent above, describ­ing what she felt after­ward as “a com­bi­na­tion of excite­ment and relief.” Engi­neers of soft­ware, hard­ware, and every­thing else know that feel­ing when they see a com­pli­cat­ed project work — but sure­ly few know it as well as Hamil­ton and her Apol­lo col­lab­o­ra­tors do.

Relat­ed Con­tent:

Mar­garet Hamil­ton, Lead Soft­ware Engi­neer of the Apol­lo Project, Stands Next to Her Code That Took Us to the Moon (1969)

How 1940s Film Star Hedy Lamarr Helped Invent the Tech­nol­o­gy Behind Wi-Fi & Blue­tooth Dur­ing WWII

Meet Grace Hop­per, the Pio­neer­ing Com­put­er Sci­en­tist Who Helped Invent COBOL and Build the His­toric Mark I Com­put­er (1906–1992)

How Ada Lovelace, Daugh­ter of Lord Byron, Wrote the First Com­put­er Pro­gram in 1842–a Cen­tu­ry Before the First Com­put­er

Based in Seoul, Col­in Mar­shall writes and broad­casts on cities, lan­guage, and cul­ture. His projects include the book The State­less City: a Walk through 21st-Cen­tu­ry Los Ange­les and the video series The City in Cin­e­ma. Fol­low him on Twit­ter at @colinmarshall, on Face­book, or on Insta­gram.

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