[Intro]   If you’ve been following the news recently, you know that getting into space is a tricky business, even with half a century of experience and plenty of advanced technology helping us out.   But in the early days of spaceflight, it was a lot harder -- in fact, the paths of many of those first missions were calculated entirely by hand, by people like Katherine Johnson, a mathematician who helped plan the missions that sent the first Americans into space and then into orbit, and finally to the Moon.   Johnson was born in White Sulphur Springs, West Virginia in 1918. An excellent student who was especially good at math, she was ready for high school at the age of ten.    But in White Sulphur Springs, African American students couldn’t attend high school, so the family moved to another part of the state, to a town called Institute. There, she and her siblings continued their education -- though her father remained in their original hometown to work.   When Johnson started college at 15, one of her professors recognized her math skills, and encouraged her to pursue the subject. The professor created a course in analytic geometry -- the study of shapes using coordinates -- just for her.    She became known for asking lots of questions in class -- not because she didn’t understand, but because she could tell other people didn’t even understand enough of what was going on to ask what they needed to know.   At 18, Johnson graduated college with degrees in French and Mathematics.    She’d originally planned to earn a graduate degree, too, but when her husband was diagnosed with cancer, she took up teaching to support her family.   Later, at a family gathering, a relative mentioned that the National Advisory Committee for Aeronautics, or NACA -- the organization that would later become NASA -- was looking specifically for African-American women to act as “computers.” NACA needed these skills to check engineers’ calculations in the Guidance and Navigation Department.    Her work at NACA started in 1953 as one of these so-called “computers in skirts,” reading data from the black boxes of airplanes and making calculations based on that data, to learn how the flight went.   But she still had a lot of questions -- how did these calculations work, and why were they so important?   She started going to the researchers’ meetings to find some answers. Some people protested at first, since women weren’t usually invited, but Johnson pointed out that there was no rule against it, and was allowed to stay.    When the all-male Flight Mechanics Branch -- which studied how airplanes fly -- needed extra help, Johnson was selected because of her knowledge of analytic geometry.    At first, it was meant to be a temporary transfer, but her skills proved valuable, and she remained on the team until she moved to the Spacecraft Control Branch, which was responsible for designing space missions and calculating trajectories.    One of those missions was Freedom 7, Alan Shepard’s flight that made him the first American in space.   The goal was just to get him to space and back -- a simple-looking parabolic arc -- but there were lots of factors to consider.   NASA told Johnson where they wanted Shepard to land, and she worked backward from there. She had to take into account things like how high they wanted the capsule to go and the burnout conditions -- that is, the velocity and position of the rocket when the fuel ran out and it entered free fall back to Earth.   Shepard’s space flight lasted 15 minutes and 22 seconds and traveled 486 kilometers from its launch point.    And thanks to Johnson’s calculations, he splashed down right on target in the Atlantic Ocean, where NASA had a helicopter ready to fish him out.   By the time NASA was ready to send John Glenn into orbit, they were using digital computers to do the calculations.    But even then, they asked Johnson to confirm the computer’s results, planning how Glenn would go from launch to three elliptical orbits, then fire rockets to slow himself down and land in the ocean.   Johnson went on to contribute to NASA’s famous Apollo 11 mission, but this time, the planned end point wasn’t the ocean. You guessed it, the end point was the Moon.    This presented a whole new set of challenges for calculating the trajectory, because the Moon is a moving target, the kind you really didn’t want to miss.   NASA also needed Apollo 11 to land smoothly on the Moon, away from cliffs and craters.    So the rocket had to leave Earth during a specific launch window, a time when the Moon would be orbiting Earth right in the rocket’s path.   And the trajectory wasn’t just a straight shot from the Earth to the Moon, either. NASA’s computers -- and again, Johnson -- had to factor in the Moon’s gravitation and plan for the rocket’s path to be skewed by it.    With Johnson’s calculations to back them up, the mission was launched, and on July 20th, 1969, Neil Armstrong took those first steps on the Moon.    Johnson retired from NASA in 1986, and while she no longer calculates altitudes, burnout velocities, or launch windows, she hasn’t stopped counting -- August 26th is her 97th birthday!   Thanks for watching this episode of SciShow Space, and especially to our patrons on Patreon who help make this show possible. If you want to help support this content, and receive rewards like Google Hangouts with the hosts and crew, go to patreon.com/scishow to learn more. And don’t forget to go to youtube.com/scishowspace and subscribe!