The cause was breast cancer, said her sister, Suzanne Alexander. I never dreamed that one day I’d become a grumpy old Librarian but here I am killing it shirt  nearly three decades at  Jet Propulsion Laboratory in La Cañada Flintridge, Alexander was known for her research on subjects including solar wind, Jupiter and its moons, and the evolution and inner workings of comets. She was the last project manager of Galileo, one of the most successful missions for exploring the distant reaches of the solar system. Alexander was leading the mission when scientists orchestrated its death dive into Jupiter’s dense atmosphere in 2003, when the spacecraft finally ran out of fuel after eight years orbiting the giant planet. Most recently, she was Rosetta’s U.S. project manager, coordinating with the European Space Agency on the orbiter’s journey to rendezvous with the 67P/Churyumov Gerasimenko comet as it circles the sun. Colleagues said Alexander was particularly keen on engaging the public in space science.