Since it was erected 50 years ago, the Space Needle has become the most prominent symbol of Seattle, piercing the sky with its uniquely sleek vision of the future.

The tower has been altered a handful of times, but now the company that operates it has plans for a bold new addition: three all-glass viewing platforms that jut out from the observation deck and look down on the city 520 feet below.

Space Needle CEO Ron Sevart said the goal is to install the 10-foot by 10-foot platforms by year's end to celebrate the structure's 50th anniversary, but first the project needs approval from the city's Landmarks Preservation Board later this month.

"We have a history of reinvesting in the Space Needle and always trying to improve the viewing experience," Sevart said. "This is a legacy project for us."

The company added a new pavilion to the base of the tower in 2000 and interactive viewing kiosks in 2006, but has left the upper part of the tower untouched since 1982, when banquet space was constructed 100 feet off the ground.

That addition to the privately owned tower upset some preservationists and sparked a long court battle with the city before it could be built.

This time around, local preservation groups have decided to go along with the new additions, which the company says will not be visible from afar.

"This is about as far as you can go without jeopardizing the integrity of the building," said Michael Herschensohn, president of the Queen Anne Historical Society. Although some people on the board had reservations about further modifications, no one formally opposed the new platforms.

Other prominent structures have installed similar glass structures, including the former Sears Tower in Chicago and the CN Tower in Toronto, which built a glass-floored elevator.

The Space Needle's three platforms would align with — and look down on — the legs of the tower and extend toward the "halo," offering breathtaking views of Seattle Center and the new Chihuly Garden and Glass exhibit, designed by artist Dale Chihuly.

Laminated glass forming the boxes would contain a clear structural interlayer, which is not supposed to yellow over time.

After meeting with the Space Needle company over the past year, Eugenia Woo, director of preservation services at Historic Seattle, said the board also decided to go along with the changes. The alterations, she said, are not big enough to raise concerns.

"They are trying to attract new generations of visitors and make sure it is kept relevant," Woo said. "This is very special and very beloved, and we want to make sure the integrity of the Needle is maintained."

But not all are in agreement.

Peter Steinbrueck, an architect and a former City Council member whose father, Victor, helped design the Space Needle, said he would be surprised if the landmarks board approves the glass platforms.

"Whether this is seen as a minor alteration or not, I think it calls for more scrutiny," he said after viewing renderings of the proposed addition. "It is just too important an icon ... a symbol, for Seattle to mess with."

Kimo Griggs, an associate professor of architecture of at the University of Washington who specializes in materials and digital fabrication, said the tower could probably handle the architectural change.

"It's hard to change that tower. It was such a pure expression of that period and of that style," he said. "But it is also a pretty good scaffolding for new ideas."

Javier Panzar: 206-464-2204 or jpanzar@seattletimes.com