What is necessary for the operation of any launch site according to U.S. regulation?

FAA approval is essential for the operation of any launch site as it ensures compliance with safety and environmental regulations within the United States. The Federal Aviation Administration (FAA) is tasked with regulating all aspects of civil aviation, including commercial space launch operations. Before a launch site can be utilized, operators must acquire a license from the FAA, which involves a review process that assesses the proposed site for its safety measures, potential environmental impacts, and adherence to operational guidelines.

In contrast, other options like NTSB certification, ICAO endorsement, and NASA clearance pertain to different regulatory frameworks or agencies that may be involved in aviation and space operations, but they do not specifically govern the operational authority of launch sites within the U.S. NTSB primarily focuses on accident investigations, ICAO deals with international aviation standards and practices, and NASA's role is more focused on aerospace research and development rather than the regulation of commercial launch sites. Thus, FAA approval is clearly the key requirement to ensure that a launch site operates legally and safely according to U.S. regulations.