When Katherine Johnson began working at the National Advisory Committee for Aeronautics in 1953, she was classified as “subprofessional,” not far outranking a secretary or janitor.

Hers was a labor not of scheduling or cleaning but rather of mathematics: using a slide rule or mechanical calculator in complex calculations to check the work of her superiors — engineers who, unlike her, were white and male.

Her title, poached by the technology that would soon make the services of many of her colleagues obsolete, was “computer.”

Mrs. Johnson, who died Feb. 24 at 101, went on to develop equations that helped the NACA and its successor, NASA, send astronauts into orbit and, later, to the moon. In 26 signed reports for the space agency, and in many more papers that bore others’ signatures on her work, she codified mathematical principles that remain at the core of human space travel.