Fans of the National Air and Space Museum have two months to visit favorite attractions before a massive renovation closes portions of the building.

Beginning Dec. 3, two galleries of the Smithsonian museum — one of the most visited museums in the world — will be closed for the start of a seven-year, $1 billion renovation. The entire building — with all new exhibitions and gallery displays — won’t reopen until 2025.

The 42-year-old facility will remain partially open as work begins on the costliest project the Smithsonian has ever undertaken. Mechanical systems will be upgraded, the stone exterior replaced, the entrance on the Mall improved and 23 galleries and presentation spaces will be updated.

Many of the most popular attractions, such as the Spirit of St. Louis and the 1903 Wright Flyer, will remain on view for the first part of the project.

“We are a well-loved museum, and that’s part of the reason we’re falling apart,” museum director Ellen Stofan said about the project. “We’re updating everything. It’s going to look a lot different inside.”

Six years in the planning, the renovation will be funded by about $700 million in federal aid, including $50 million for new storage space, and $250 million in private donations for new exhibitions. The museum has raised about $70 million toward its goal, Stofan said.

The museum initially will close “Apollo to the Moon” and “Looking at Earth,” two galleries on the eastern side of the building that stretches along Independence Avenue from Fourth to Seventh streets. In January, seven more galleries — representing most of the western side of the building — will shutter, including exhibitions focused on the golden age of flight, World War I, World War II and jet aviation and sea-air operations.

The Spirit of St. Louis is the aircraft that Charles A. Lindbergh used for the first non-stop solo trans-Atlantic flight from New York to Paris on May 20, 1927 (Smithsonian National Air and Space Museum)

The public will be invited to watch as officials remove the artifacts from the seven galleries, Stofan said. “We want people to be looking over our shoulder,” she said.

Among the items being removed will be the Douglas DC-3, Boeing 747 nose, and the Supermarine Spitfire Mk. VIII. The virtual reality and flight simulators will be closed temporarily as they are relocated to the eastern side of the building.

The galleries will reopen in 2022 with Destination Moon, a redesigned exhibition of the popular Apollo missions, and other exhibits. Stofan said she hopes the displays will bring back some of the museum’s original wow factor.

“When it opened, it was a place of the future,” she said. “Over the years we’ve been more of a history museum. We’ve lost a little bit of that science and technology center.”

While the western portion of the building will close first, upcoming phases will include the closing of the entrance on the Mall, the Imax theater and the planetarium.

The museum expects most of the eastern galleries will remain open until 2022, when the first refurbished exhibits come on view. The entire project is expected to be completed in 2025.