Having scored “Zootopia,” “Star Trek Beyond,” “Doctor Strange” and the still unreleased “Book of Henry” in 2016, composer Michael Giacchino was ready for a nice long vacation. Flights were set, hotels booked.

Then, as he was finishing “Doctor Strange” in mid-September, the phone rang. Alexandre Desplat had dropped out of “Rogue One: A Star Wars Story” due to scheduling issues. Would he consider taking it on?

Vacation cancelled.

He flew home from the final “Strange” sessions in London on a Friday and started writing “Rogue One” on Monday. He would have just four and a half weeks to compose more than two hours of music for the first standalone “Star Wars” film, a prequel to the original 1977 adventure.

It wasn’t an easy decision to make. But, Giacchino confesses, “When I was 9, I saw ‘Star Wars’ and it set me on a path to where I am today. There was this need inside of me to make sure that this film felt like what I loved as a kid, as a fan, somebody who grew up playing with the action figures.”

In fact, he still has those action figures and brought them with him to the recording sessions at Sony that first week of November. It was only then, when his 110-piece orchestra launched into John Williams’ original “Star Wars” theme, that he began to have second thoughts: “Why did I say yes to this? What was I thinking?”

Yet, while he acknowledges that no one can top Williams, Giacchino felt up to the task. “There were all these new characters, so they needed new themes. But I wanted it to feel like ‘Star Wars.’ It’s a very specific style of orchestration and composing, grounded in Ravel, Prokofiev, Holst – in the same way that George (Lucas), when he was making ‘Star Wars,’ looked to ‘Flash Gordon’ and all those serials that inspired him when he was growing up.”

Despite fleeting references to original Williams themes, “98 percent of the score is all new,” Giacchino says, including themes for Jyn (Felicity Jones), Krennic (Ben Mendelsohn), the Guardians of the Whills (Donnie Yen, Jiang Wen) and, especially, a “hope” theme for the Rebel Alliance – whose final appearance includes a 80-voice choir.

It’s a war movie, Giacchino points out. A veteran of war music for video games like “Medal of Honor” and “Call of Duty,” he says, “I’ve always wanted to do a World War II film, and I feel like I just had my chance.”

Unlike those previous projects, however, this score didn’t need to be filled with bravado, he adds. There is a heartrending moment near the end of the film that needed “a sense of hope and a sense of loss. I wanted it to feel like a church hymn. It’s about sacrifice, and I didn’t want it to be completely maudlin; I wanted it to feel balanced, for what (the rebels) accomplished.”

It’s a little-known fact that Giacchino played a storm trooper in the previous “Star Wars” movie, “The Force Awakens.” Director J.J. Abrams is an old friend (dating back to their work on “Alias” and “Lost”), so he flew to London, suited up as FN-3181, “got to have the fun part of the gig, and I thought that was the end of it.”

Prior to “Rogue One,” Giacchino created a mystical mood for Marvel’s “Doctor Strange,” spiced with the unusual colors of harpsichord and electric sitar; Disney’s animated “Zootopia,” for which he again reached back into his childhood, writing a ’70s-style TV-cop-show theme for the rabbit and fox detective partners; and “Star Trek Beyond,” his third trip into outer space with the Enterprise crew.

So is it time for that vacation? “Nope,” Giacchino says ruefully. As soon as his Christmas break is over, he dives into two more huge projects: “Spider-Man: Homecoming,” his second visit to the Marvel Universe; and “War for the Planet of the Apes,” his second score for Fox’s ongoing Apes saga.