A SpaceX Falcon 9 stands on the launch pad on Dec. 8, 2021, the night before launching NASA’s Imaging X-ray Polarimetry Explorer (IXPE). The Falcon 9 Block 5 was the most-used vehicle of 2021 with 31 launches – and 30 successful first-stage landings. Credit: NASA/Joel Kowsky

Introduction | Succes...