; and purchase, lease, charter, maintenance, and operation of mission and administrative aircraft, $2,953,400,000, to remain available until September 30, 2022: Provided , That if available balances in the Science, Space, and Technology Education Trust Fund are not sufficient to provide for the grant disbursements required under the third and fourth provisos under such heading in the Department of Housing and Urban Development-Independent Agencies Appropriations Act, 1989, ( Public Law 100–404 ), as amended by the Departments of Veterans Affairs and Housing and Urban Development, and Independent Agencies Appropriations Act, 1995, ( Public Law 103–327 ), up to $1,000,000 shall be available from amounts made available under this heading to make such grant disbursements. Construction and environmental compliance and restoration For necessary expenses for construction of facilities including repair, rehabilitation, revitalization, and modification of facilities, construction of new facilities and additions to existing facilities, facility planning and design, and restoration, and acquisition or condemnation of real property, as authorized by law, and environmental compliance and restoration, $419,100,000, to remain available until September 30, 2026: Provided , That proceeds from leases deposited into this account shall be available for a period of 5 years to the extent and in amounts as provided in annual appropriations Acts: Provided further , That such proceeds referred to in the preceding proviso shall be available for obligation for fiscal year 2021 in an amount not to exceed $18,700,000: Provided further , That each annual budget request shall include an annual estimate of gross receipts and collections and proposed use of all funds collected pursuant to section 20145 of title 51, United States Code. Office of inspector general For necessary expenses of the Office of Inspector General in carrying out the Inspector General Act of 1978, $44,200,000, of which $500,000 shall remain available until September 30,