On her official Facebook page, Brightman writes, "Ms. Brightman said that for personal family reasons her intentions have had to change and she is postponing her cosmonaut training and flight plans at this time."
Brightman, who was to be part of a three-person crew, reportedly paid $52 million for the chance to travel in space, according to Reuters.
Because of an investigation following a Soyuz rocket accident, Russia had postponed the next launch; it is unknown whether the delay affected Brightman's decision.
"[Others who have traveled in space] have all said it is indescribable," Brightman previously said at a press conference, according to the BBC. "You feel a mixture of laughter and tears. You feel humble but you can see the bigger picture. It's been an unusual path that has taken me to this point and it hasn't been an easy journey. I've found out a lot about myself."
The 54-year-old Brightman would have been the first professional singer to visit the orbital outpost. Sarah Brightman, who had a '70s dance hit on the British pop charts, caught the public's attention in Andrew Lloyd Webber's megahit The Phantom of the Opera when she created the role of opera singer Christine Daae. She also appeared in Lloyd Webber's Aspects of Love before launching an internationally successful concert and recording career. Her duet with tenor Andrea Boccelli, "Time to Say Goodbye," was certified gold in the U.S., was number one on the Billboard charts for more than 30 weeks and sold more than 12 million copies worldwide. Her other solo recordings include, among others, "Symphony," "Encore," "Classics," "Fly," "La Luna," "Timeless," "Eden," "Fly 2," "Dive," "As I Came of Age," "Songs That Got Away" and "Sarah Brightman Sings the Music of Andrew Lloyd Webber."