# James Potter

James Potter, helped engineer navigation systems for the Apollo missions. Potter was a graduate student in mathematics at MIT at the time, working part time at the Instrumentation Laboratory on the Apollo Project.

Potter was known both for his brilliant problem-solving and his compassion for his students, said John Deyst, professor of aeronautics and astronautics. "I always found him to be just the most kind and understanding person with his students you could imagine," said Deyst, who had Potter as one of his thesis advisors.

In 1962, Potter came up with what became known as the "Potter square root method," which solved a problem that had baffled everyone working on the guidance systems for the Apollo spacecraft. Potter was aware of the limited word-length of the Apollo Guidance Computer (AGC), and thus proposed using the square root filter in the AGC. From his deep mathematical background, Potter knew that the square root of a matrix contains all the information in the matrix itself, and the square root also preserves the same scaling and accuracy as the original variables (whose squares appear in a covariance matrix).

He took the problem home with him one Friday afternoon and arrived back on Monday with a solution. The approach came to be called *square-root filtering*, and alternative implementations of square-root filters with better numerical stability were soon discovered. Potter's implementation of the Kalman filter was programmed into the Apollo Guidance Computer, designed by an MIT team led by Eldon Hall, and executed in 15-bit arithmetic to navigate to the Moon and back. "Everyone was stumped by the problem," Deyst said. "He went home over the weekend and came back with the solution and just kind of blew everybody away."

Potter joined the faculty at MIT in 1965, three years after earning his doctorate from MIT in mathematics. He left MIT in 1974 and worked at several private companies before returning to work at Draper Laboratory. In 1993 he launched a consulting firm, Potter Engineering, where he worked on classified intelligence research.

Born in Iowa City, he earned his bachelor's degree at Caltech in 1959. Potter passed away in 2005.