It takes 29 years for Saturn to orbit the sun and only slightly longer than that for Pat Flaherty to close a loop on his coaching career.

Flaherty, 67, is the Rutgers offensive line coach, which is unusual only because it is the same job that he held from 1984-91. That was long before any of his current players were born and even longer before he won two Super Bowl rings as one of Tom Coughlin’s most trusted assistants over 12 seasons with the Giants (2004-15).

“I did a complete circle in my life, which is great,” Flaherty told The Post after a training camp practice in Piscataway, N.J. “People ask me if I fell on my head.”

Flaherty laughs and tells them no. He says he is back because of the relationship he made in 1989 with a graduate assistant coach under his watch who went on to bigger things, like leading Rutgers football out of the doldrums once before, becoming head coach of the NFL’s Tampa Bay Buccaneers and returning to the helm at Rutgers in December 2019 for his own Act II.

“The reason I’m coaching at Rutgers is because of Greg Schiano,” Flaherty said. “The biggest reason I coach is to teach players and get them out on the field to coach other players. When I have to do something else, then I have to work again.”

In the eight years since he left the Giants when Coughlin was forced out, Flaherty’s career has become transient. This is his seventh stop — including working for the NFL office in 2020, returning to the Giants as an advisor under head coach Joe Judge in 2021 and consulting for Schiano at Rutgers last season.

“When I worked for the league office, I did it all from my man cave. I golfed three times a week and I didn’t get any better, so my wife said, ‘You ought to go back to coaching,’” quipped Flaherty, whose last college coaching gig was at Iowa in 1999.

“I had opportunities to go back to the NFL as a consultant. But when Greg asked me to do this I said, ‘I think those guys can be really good Big Ten competitors.’ I’ve known him for years, so I knew the culture was going to be a fit.”

Because of his resume — and maybe more so because of his area of expertise — Flaherty is one of the most important people in the program, which opens the season at noon Sunday against Northwestern in Piscataway.

The offensive line has only one starter returning to the same spot (two are changing positions) after allowing pressure on 35.5 percent of dropbacks, according to Pro Football Focus, and surrendering 21 sacks in nine Big Ten games last season. Schiano said it was the most barren position in the program when he returned.

One of Flaherty’s pupils this season is senior offensive guard Mike Ciaffoni, who, unbeknownst to him, has been training to play for Flaherty all his life. His father, Joe, was a Rutgers offensive lineman in the early 1990s.

“The crazy thing about Coach Flats coaching my dad is that I didn’t even realize until we started doing drills, but every single drill that I’ve worked on with my dad since I was a little kid has been the same exact drills that Coach Flats does,” Ciaffoni said. “Three-step starts, perfect stance, from the top down to the basics, everything I’ve ever learned in my entire life is what Coach Flats taught.”

In a landscape that is trending toward hiring younger coaches whose lifestyle lends itself to never leaving the office and are more likely to share pop-culture interests with high school recruits, Schiano went against the grain. He urged offensive coordinator Kirk Ciarrocca to consider Flaherty for the staff but wasn’t going to force a marriage.

“Flats has an incredible capacity to work — hours is never an issue — and he connects with the players in his way,” Schiano said. “To me, the coaches who get in trouble are the ones who try to be what they are not. I don’t care how old you are: If you are authentic and you are a good man and you are making them better, they are going to connect. Flats does that every day.”

Things change over 30-plus years, however. Almost everything has on campus except the name on the helmet. Actually, even the logo on the helmets is different.

“I tell the guys and they don’t believe it: We’d come off the field in training camp and in between meetings we would go watch a high school practice and drive back,” Flaherty said. “When we had tape, it took longer to get the tape together.

“I help in recruiting now. I call kids, and if they need me to go see someone, I don’t mind.”

Here’s what he does mind: Negative recruiting — or the practice of one school boosting its standing with a player by trash-talking another.

“The biggest connection with kids is they want to play in the NFL and the NFL experience I have,” Flaherty said. “What bothers me is if we are close to a kid and they say, ‘Well, [Flaherty] is an old guy and he isn’t going to be there.’

“I tell them, ‘I’ll be here as long as you are, as long as Greg Schiano is, as long as I’m healthy. I have no vision of retirement because I found when I slow down, that doesn’t motivate me. What motivates me is teaching the guys when they are locked in and interjecting thoughts to Kirk Ciarocca, who is a great listener.”

Further emphasizing his point, Flaherty signed a two-year, $750,000 contract, per public records.

There are rewards in listening to Flaherty, who still is scheming things the way he used to ask the Giants’ David Diehl to block Hall of Famer DeMarcus Ware. It’s the only way he knows, passed down from former Rutgers head coach Dick Anderson, whom Flaherty credited as “the guy who taught me to coach.”

“Pat can tell them, ‘This is exactly what I told So-and-So when he was getting ready to block So-and-So, so I trust it will work,’” Schiano said. “His credibility isn’t just based on his history. His credibility is based on his problem-solving — and he helps our kids figure it out.”

The Giants once built one of the NFL’s best blue-collar lines under Flaherty. Diehl, Rich Seubert, Shaun O’Hara, Chris Snee and Kareem McKenzie played together for 44 of 48 regular-season games from 2007-09 and Diehl, Snee and McKenzie still were starters when the Giants won a second title in five years in 2011.

“That’s definitely something that sits in the back of our mind,” Ciaffoni said. “Coach Flats is such a humble guy, so in love with the sport, that you don’t even realize he’s a legend. He’s already probably one of the best offensive line coaches of all-time and he has the humility that it’s his first season.”

If he truly was a rookie, he wouldn’t have the two Super Bowl rings. The second one even makes it into the office sometimes.

“I hung in there and was very fortunate to coach good players,” Flaherty said. “Once you do that and you have success, everybody thinks you invented the game, which I did not. I’m very proud of that ring. It took a lot of hard work from a lot of people. I don’t wear it just to flash it. If we have little kids visiting, I’ll let them hold it and take pictures with it because that is going to be an experience in their life.”

Flaherty sees potential in his current position group.

“I believe that they really have the desire to be good,” he said.

And on the plays that they are not? Payback has a long memory. Schiano probably does, too.

“There were times I chewed his ass out,” Flaherty said, referring to the days when he was Schiano’s superior. “So — and I’m hoping this doesn’t come — when we get sacked, he’ll be chewing my ass out, which is fine. If I deserve it, he’ll let me hear it.”

Then they will put their heads together again to continue problem-solving.