The SPACEPORT Act modifies the federal grant program that funds spaceport and space launch infrastructure projects. The bill increases the maximum federal funding share from a current unspecified amount to 80 percent of project costs, though the Secretary of Transportation can waive this limit if deemed in the national interest. The legislation expands eligible grant recipients to include state agencies and public corporations, and broadens the types of space transportation needs the program addresses to encompass civil, national security, and commercial space activities, rather than focusing solely on government space transportation. The bill authorizes $10 million annually in congressional appropriations for these grants and requires the Transportation Department to report to Congress within two years on space transportation demand, funding options, and international competitiveness, with updates every four years thereafter.