This inspiring picture book tells the story of four black women mathematicians who overcame barriers of both race and gender to make vital contributions to the development of space travel. Dorothy Vaughan is the earliest of these pioneers, working as a 'computer' for the American government aeronautical agency, joined in the 1950's by Mary Jackson and Katherine Johnson. We learn how their working lives are constrained by both by prejudice against women, and the effects of racial segregation - at work, as well as in the outside world. Nonetheless, their mathematical skills and determination to contribute at the highest level win recognition: John Glenn the first American in space wanted Katherine Johnson to personally check the machine computer's trajectory calculations. When Christine Darden joined NASA in 1967 some barriers have been weakened, and, as an accomplished engineer for supersonic travel, her first job was to help with the mission to the moon. The bold illustrations succeed admirably in showing the four individuals engaged in important work, measuring, quantifying, using computers, or teaching others. A timeline and brief biographies complete the account.