"Statement of William H. Gerstenmaier Associate Administrator for Space Operations before the Committee on Science, Space and Technology Subcommittee on Space and Aeronautics U.S. House of Representatives" (PDF).
Truy cập ngày 24 tháng 6 năm 2017.  ^ “Statement of William H. Gerstenmaier Associate Administrator for Space Operations before the Committee on Science, Space and Technology Subcommittee on Space and Aeronautics U.S. House of Representatives” (PDF).