A man who helped design a top-secret, Cold War spy satellite dubbed "Big Bird" will give a presentation on the project on Saturday at the Fairfield Senior Center.

The talk by former Perkin-Elmer Corp. engineer Marty Yellin is planned at 10 a.m. at the center, 100 Mona Terrace. The program is free, but registration is required.

For 40 years, Yellin and his Cold War-era coworkers at Perkin-Elmer's optics lab in Danbury had been forbidden from talking about the KH-9 Hexagon, a satellite equipped with cameras that could take reconnaissance photos at previously unheard of speeds.

But "Big Bird" was declassified in 2011 -- 25 years after it was retired -- and Westport resident Yellin now is free to talk about it. He is one of the few development team members still alive.

One NASA official told Yellin the satellite "helped prevent World War III," the senior center said in a news release.

Yellin and about 30 colleagues in 1966 were brought together for a secret briefing on plans for a 60-foot-long, 15-ton satellite that would carry 60 miles of film and supply 200 inches of images per second. According to the release, Yellin looked around the room and thought, "How on Earth is this going to be possible?" The precision and complexity went beyond his imagination.

Once launched, "Big Bird orbited the earth snapping vast, panoramic photographs of the Soviet Union, China and other potential foes. A total of 20 KH-9 Hexagons were launched by the National Reconnaissance Office between 1971 and 1986, according to the website www.space.com.

Hexagon is credited with providing crucial information for the Strategic Arms Limitation Talks between the United States and the Soviet Union in the 1970s, according to the release.

After numerous launches, Yellin one day was shown a clear image of his car in his parking space at work photographed by a Hexagon satellite.

Tours of the 2,800-square-foot Senior Center also will be available following Yellin's talk.

To register to hear the spy-satellite presentation, call the Fairfield Senior Center at 203-256-3166. Registration is required by Tuesday.