Her gravity-defying score arrives Nov. 4.

Sarah Schachner is no stranger to exploration and combat. Growing up in suburban Philadelphia, local kids took up shields and swords to play on the full-sized Viking ship in her backyard (the result of a letter-writing campaign to the Leif Erikson Society). Now 31, Schachner is exploring the deep recesses of space in a much higher-stakes game, the Nov. 4 release of Activision's Call of Duty: Infinite Warfare, which features her gravity-defying score.

Much has been made of the fact that Infinite Warfare is the first Call of Duty game to go interstellar, a somewhat risky move for a franchise whose fans have come to expect a first-person experience of earthly battle. That formula has made Call of Duty one of the most lucrative game properties on this or any planet -- one that for seven years running has with each new iteration been North America's No. 1 selling game of the year, generating $15 billion on 250 million units since the series debut in 2003, according to consumer research firm NPD.

That the title many expect to be the console blockbuster of the season is the first on which Schachner has sole composer credit is nothing short of astonishing, but like a soldier taking to the field, she kept her cool: "If you feel zero pressure knowing that your music will be heard by millions of fans, you must be a cyborg," she observed. "But you have to thrive under pressure, to some degree. I find finishing music with no constraints or deadlines more daunting than working on a multibillion-dollar franchise."

Previously, Schachner was best known for her work on Ubisoft's Assassin's Creed: Unity, a 2014 title on which she shared credit with two others. Prior to that, working alongside her mentor, composer Brian Tyler (Thor: Dark World, Fast & Furious), Schachner contributed additional music and arrangements to films such as Iron Man 3, The Expendables 2 and Now You See Me, and on games including Assassin's Creed IV: Black Flag and, in 2011, Call of Duty 3: Modern Warfare. This is her first foray into space.

"Scoring a sci-fi project has always been a dream of mine," she confessed. "Space can be as suffocating and isolating as it is seemingly infinite, a fascinating challenge from a musical standpoint. The goal of the score was to capture the loneliness felt in space, the emotional burdens of leadership and the gritty combat of war." Mysterious, but not at the expense of the martial themes expected of war games, Schachner's music ebbs and flows, managing to sound both organic and mechanized.

"Sarah was on our short list of composers for Infinite Warfare," said Stephen Miller, audio director for Activision's Infinity Ward studio, which produces Call of Duty. "We had done big orchestral pieces for past games, but we wanted something more intimate for this -- a sound that captured the essence of the fragileness of human life."

Schachner's audition track, drawn from early story information, was so well-received it evolved into the main theme for the game. Titled "Anthropic Universe," it plays on the main menu and recurs throughout (and to particular effect on "Operation Black Flag"). "Sarah took each instrument and gave it beautifully nuanced, highly emotive parts that were haunting and deep," Miller said. "She really captured something, blending the organic strings with incredibly crafted synthetic elements. It blew us away."

For inspiration, Schachner turned to "bands like Tool and Meshuggah who use a lot of crazy polyrhythms and odd time signatures. And Stravinsky -- I've always loved the way he combines complete chaos with beautiful melodies."

The score was recorded at Ocean Way in Nashville, with about 30 musicians. "We did an unusual orchestral layout in the live sessions, which was really fun," Schachner explained. "The low strings -- violas and cellos -- were all close mic'd up front, while the violins were way in the back, split up in the left and right corners for ambient effects. Some of the strings had pickups on their instruments and were later put through amps. The Nashville musicians had a great attitude -- even when asked to hit their instruments with pencils."

The brass also underwent some processing, with the low brass ensemble -- horns, trombones and bass trombones -- "usually playing as one unit that we treated as a low, growly synth with distortion." Schachner said her aim was to blur the lines between orchestra and synth. "The dynamic is constantly shifting, but they work together to create this sound."

In addition to doing her own synth programming and performance, Schachner's own violin, viola and cello work can be heard on the final recording. "A lot of the playing I did as I was writing was mixed in with the live orchestra," she said, noting that that many of the percussion sounds were found metallic objects recorded in her home studio. "Pretty much every metal object in my house ended up being used at some point."

The music was mixed, mastered and edited into the game at Sony Interactive Entertainment's Bridgepointe Studios in San Mateo, California, where Schachner's 120 minutes of original score was transformed into 360 minutes "including alternate edits, internal demos and other materials," Miller explained. Since games can involve hundreds of hours of play, music inevitably repeats, ideally in a subtle way.

The 70-minute soundtrack will be available for download on iTunes, Spotify, Amazon and the PlayStation Network on Nov. 4, with a $35 vinyl release scheduled for the fourth quarter through Iam8bit.

Track list for Call of Duty: Infinite Warfare, original score by Sarah Schachner (listen to five of the songs below):

1. Anthropic Universe

2. Home

3. Rising Threat

4. Olympus Mons

5. Black Sky

6. Operation Black Flag

7. Rally Point

8. Terrible Resolve

9. Infinite Warfare

10. Adrift

11. All or Nothing

12. Endure

13. Peace to the Fallen

14. Sentient Mechanism

15. Europa

16. Reyes

17. Taken Dagger

18. Titan

19. Pyrrhic Victory

20. Faulty Wiring

21. Safe Harbor

22. Fair Winds

23. Phoenix

24. Blood Storm

25. The Retribution

26. Fight or Flight (Bonus Track)

27. Afterlife (Bonus Track)

28. Rogue Astroid (Bonus Track)

29. Dark Quarry (Bonus Track)