NEW YORK—How long can Billie Jean King play air guitar to “Beautiful Day” by U2? This was the question that some in the audience inside Arthur Ashe Stadium may have been asking themselves on Tuesday morning. Like the rest of us, King had been listening to—and playing along with—that song for the last 20 minutes. It was meant to be the soundtrack to the first official opening of the new, $150-million, 6,500-ton, decade-in-the-making, retractable roof over Ashe. Except that the roof wouldn’t retract.

On Tuesday morning the USTA held its unveiling ceremony for the roof, and also offered a peek inside the new and impressive, 8,125-seat Grandstand court that will make its debut in three weeks. Everything went according to plan for the first 10 minutes or so. Arthur Ashe’s widow, Jeanne Moutoussamy-Ashe, pushed a button on court that signaled the roof to close for the first time. After six quick minutes, the structure’s two sides had slid together seamlessly and blocked out the bright sun and blue sky above. At that speed, players should be able to remain on court as it closes.

Apparently, though, that which comes together doesn’t easily break apart again. To signal the roof to re-open, King pushed the same button. Eyes went up, U2 blared from the dozens of new speakers that dangle from the stadium’s ceiling, and then...nothing happened. After a few awkward minutes, BJK got the thumb’s up from the technicians and tried again, but with the same result. Finally, on the third attempt, the two sides split and the sky reappeared.

Danny Zausner, the National Tennis Center’s Chief Operating Officer, and the man in charge of this 10-year project, said the glitch had been caused by a “racking” problem; one of the sensors that guide the two sides along their tracks had malfunctioned.

It hadn’t happened before, Zausner said, “But it could happen during the Open, there’s no doubt about it.” He also said that they would be testing it for this issue every chance they get until the first matches are played on Ashe on August 29.

We’ll have to wait until then to see how it goes; the only thing we know is that there will be a lot of tightly crossed fingers at Flushing Meadows if and when the first drops of rain begin to fall during the tournament. For now, though, there’s no doubt that the USTA’s architects and builders have pulled off a titanically dazzling piece of engineering.

“The complexity is mind-boggling,” said Matt Rossetti, president of the Rossetti architectural firm, which designed both Ashe Stadium and its roof. “Because frankly, as you watch the roof in action, it’s what you don’t see which is fascinating.”

The numbers do boggle. Each of the roof’s two, teflon-coated retractable panels weighs one million pounds and moves 25 feet per minute. The roof’s total size is the equivalent of 17 Olympic swimming pools. More than 13 million pounds of steel were used to create it, and 48 computers are used to make it open and close. The top of the stadium is now 55 feet higher than the Statue of Liberty. And, just in case you were wondering, 2.6 billion tennis balls can fit inside the stadium with the roof closed. That’s nine times more than can fit inside Centre Court. Take that, Wimbledon!

The most important number, though, may be 175; that’s how many feet the 22 support piles around the stadium were drilled into the earth three years ago. The Tennis Center is built on landfill, a fact that had long seemed to rule out a roof. But by using lighter materials, building the roof as a free-standing structure—it doesn’t sit directly on the stadium—and digging deep enough for support, that problem has finally been solved.

Unfortunately, according to one long-term forecast, this is supposed to be a dry Open. But even if the roof never has to close, it should be popular with fans. At noon on Tuesday, the entire upper deck, as well as large parts of the mezzanine, were shaded from the sun. And when it is closed, natural light still breaks through, but the arena is cooler. Massive ducts pump in air from a “chiller” building, which was built separately from the stadium.

U.S. Open officials may be tempted to close their new toy on a brutally hot or windy day, but they say they won’t do that. This is an outdoor tournament, according to them, and it’s going to stay that way as much as possible. I guess now we just have to pray for rain.