Renominated by Trump in November, Isaacman, age 42, has twice flown to space via the company SpaceX, including in a 2024 mission that saw him perform the first-ever commercial space walk. The billionaire entrepreneur’s provisional “Project Athena” plan for NASA, leaked in November, called for smaller, more numerous science missions, a reorganization of the agency’s research centers and a hard push for nuclear-electric rockets for future human voyages to Mars.