21st Century Aerospace Infrastructure Act of 202 1 This bill directs the Department of Transportation (DOT) to establish a pilot program, through FY2023, to issue grants to operators of space launch and reentry sites for projects to construct, repair, maintain, or improve transportation infrastructure and facilities at such sites. Launch site is defined as the location on Earth from which a launch takes place and necessary facilities at that location, and reentry site is defined as the location on Earth to which a reentry vehicle (i.e., spacecraft) is intended to return. Grants issued to an operator may not exceed $2.5 million for a fiscal year. DOT may issue supplemental grants to operators in support of state, local, or private matching under specified conditions.