David J. Skorton, the 13th secretary of the Smithsonian, outside the Smithsonian Castle. (Photo by Kate Patterson for The Washington Post)

Appearing at his first Congressional budget hearing, Smithsonian Secretary David J. Skorton said the National Air and Space Museum will need $600 million over five years to repair its faulty facade and mechanical systems.

Skorton appeared before a House subcommittee to ask for $922.2 million for the Smithsonian’s 2017 budget, an increase of almost 10 percent. Chairman Ken Calvert (R-Calif) told him that such an increase was “not realistic.” The Smithsonian annually receives about two-thirds of its budget from Congress. This year’s funding is $840 million.

The Smithsonian will announce next month if it will work with developers in London to open its first museum outside the United States, Skorton said. Rep. Betty McCollum (D-Minnesota) chastised Skorton for not consulting fully with Congress about the project and questioned the costs associated with it.

The repairs to the 40-year-old Air and Space Museum, which Skorton repeatedly noted is one of the most visited museums in the world, will cost more than the construction of the National Museum of African American History and Culture, a $540 million structure set to open Sept. 24. While Congress paid for half of the new museum (with private donations making up the balance), Skorton told the panel he wants the federal government to pay for the entire cost of repairing Air and Space.

“It is difficult to raise philanthropic funds for repairs and renovations,” Skorton said, adding that the institution will seek $250 million in private donations to fund improvements to programs and exhibitions.

Calvert described the project’s costs as “extraordinary” and wondered if it wouldn’t be more efficient to tear it down and replace it. Skorton said doing so would cost more than $2 billion. The building’s stone cladding can’t be reused because it is too thin, he said. The Smithsonian wants to keep the popular destination open during the renovation, he said, which increases the costs. The Smithsonian expects work to begin in 2018 and take five years to complete.

During an hour of testimony, the 13th Secretary of the Smithsonian said the quasi-governmental agency is also focused on rebuilding its ranks of curators, which have decreased significantly in recent years. A new program, “The Smithsonian Secretarial Scholars,” will hire 40 curators for five-year positions to be paid with private donations.