From the Background: "NSS [National Security Space] is a Major Force Program (MFP) of the Department of Defense (DOD). An MFP is an aggregation of resources necessary to achieve DOD objectives or plans. Of the dozen MFPs, six are combat force programs and six are support programs. The MFP for National Security Space, MFP-12, is the newest. Congress directed its establishment in the FY2016 National Defense Authorization Act (P.L. 114-92). MFP-12, a support program, includes funding for some classified programs. It generally excludes funding for National Geospatial-Intelligence Agency (NGA) and National Reconnaissance Office (NRO) programs."
CRS In Focus, IF11244
Congressional Research Service: https://crsreports.congress.gov/