Approaching its 40th birthday, the National Air and Space Museum is in need of a facelift.  

Renovation of the building systems at the Smithsonian’s most popular attraction had long been part of the institution’s plan, acting Secretary Albert G. Horvath told lawmakers on the House Administration Committee during a Wednesday morning hearing on the state of the world’s largest museum and research complex. But engineers discovered a major problem with the limestone facade of the National Mall mainstay during the early phase of planning. The “Tennessee pink marble” looked “thinner than it should be,” Horvath testified. “Unfortunately, after 40 years of wear and tear, it is starting to crack and bow.”  

The Smithsonian’s budget request for fiscal 2016 includes nearly $35 million to start addressing these issues at the National Air and Space Museum, plus pre-construction activities required for collections care during the full renovation. The full renovation, expected to start in 2017, will cost around $500 million.  

“Wow, that is a huge price tag,” said Chairwoman Candice S. Miller, R-Mich.  

“It sure is,” Horvath replied.  

It’s a big request for the institution that in 2013 worried congressional budget-cutting might force some of the District’s most beloved museums to furlough workers or close their doors. However, some projects have since benefited from large private donations.  

For context, the Smithsonian asked for a total of $200 million in fiscal 2016 for major renovation projects at its 19 museums and galleries, plus the National Zoo. Installations of a smoke evacuation system is underway in the zoo’s animal facilities, plus other improvements to increase traffic and pedestrian safety.  

Much interior work remains at the Arts and Industries Building , which was closed in 2006 due to its deteriorating condition and has been named one of America’s Most Endangered Places by the National Trust for Historic Preservation. Upgrades are underway at the Freer Gallery of Art’s humidification system, which is unreliable and frequently fails, putting collections at risk for loss or damage. At the National Air and Space Museum, generally known as the most-visited museum at the Smithsonian — “neck and neck” with the Natural History Museum for annual visitors, according to Horvath — renovations will be a major, but critical, undertaking.  

Nearly 7 million people visit it each year, more than double the amount planners envisioned when it opened in 1976. Sustainability studies found that the higher-than-expected traffic, combined with thinning, bowing, cracking of its “exterior envelope,” plus the age and condition of its heating and cooling systems, all contribute to the building’s energy inefficiency. Those conditions create “unacceptable interior environmental risks for the public, staff and collections,” according to Horvath’s testimony. Horvath said the National Air and Space Museum would try to keep portions of building opened to the public during the five-year, multiphase project, though he did not provide specific details on which exhibits.  

Prior to the exterior renovation, the museum is overhauling its central exhibit space with the help of a $30 million donation from Boeing. In appreciation for the gift, “Milestones of Flight” gallery will become the “Boeing Milestones of Flight Hall” when it opens in 2016.  

Housing important pieces from aviation and spaceflight history, such as the Wright Brothers’ 1903 plane, Charles Lindbergh’s “Spirit of St. Louis” and former Sen. John Glenn’s Mercury “Friendship 7,” the classic gallery’s renovation will be completed just in time for the museum’s 40th anniversary celebration. Some icons, including the huge Apollo Lunar Module, the Telstar satellite and a model of Star Trek’s “Starship Enterprise” will be surprise additions.