Columbia subject headings:
Harvard subject headings:
Aerospace planes--Technological innovations--United States--Finance.
Hypersonic planes--Research--United States--Finance.
United States. National Aeronautics and Space Administration--Appropriations and expenditures.
Princeton subject headings:
Aerospace planes--United States--Technological innovations--Finance.
Hypersonic planes--Research--United States--Finance.
United States. National Aeronautics and Space Administration--Appropriations and expenditures.