The starship Enterprise began its mission to explore strange new worlds in 1966, and for the past 50 years Star Trek has inspired countless fans with stories of adventurers boldly going where no one has gone before.

Although the original series ended in 1969, creator Gene Roddenberry's vision went on to live long and prosper, inspiring five other television series and 13 movies. The latest film, Star Trek Beyond, debuted in July. Moreover, a sixth TV series helmed by Bryan Fuller—who began his career writing on two previous Star Trek series—promises to seek out new life and new civilizations when it premieres in 2017.

To help the curious peer behind the scenes of the Star Trek legend, Edward Gross and Mark Altman collected an oral history of the Star Trek franchise, interviewing hundreds of television and film cast members, executives, writers, creators and fans. The first book in the two-volume set—The Fifty-Year Mission: The First 25 Years—was released on June 28. The Next 25 Years came out August 30.

Scientific American spoke with Gross and Altman to learn more about the never-before-told and often shocking tales they heard.

[An edited transcript of the interview follows.]

Your books reveal that Star Trek could have explored some very interesting territory if different casting decisions were made, such as casting Eddie Murphy as a college professor who believed in aliens and listened to whale songs on Star Trek IV: The Voyage Home, or Wesley Snipes as Geordi on Star Trek: The Next Generation. What were your most and least favorite of these decisions?
Gross: I think Toshiro Mifune (an actor who starred in The Seven Samurai, Yojimbo and many other films) would've probably been the most formidable Klingon ever seen. (The unproduced film Star Trek: Planet of the Titans, which reached the script and design phases of production, would have thrown the crew of the Enterprise back in time to become the Titans of Greek myth, fighting a Klingon captain played by Mifune along the way.)

Altman: My favorite casting choice that never happened was Lindsay Wagner (star of The Bionic Woman) as Capt. Janeway (of Star Trek: Voyager).

One of the exclusive discoveries your book excerpts is the secret memo Roddenberry sent to William Shatner (who played the role of Captain Kirk), Leonard Nimoy (Mr. Spock) and DeForest Kelley (Dr. McCoy) lambasting them for their “childish antics” behind the scenes. Could you talk about how we should view Star Trek in light of this discovery?
Gross: What the classic Roddenberry memo says to me is that we have human beings behind these things, and that TV shows can really get derailed by egos. We can look back at Star Trek now that it's the 50th anniversary and say how wonderful it is—but boy oh boy, did it fight for its life in the beginning, and there was fighting behind the scenes, too.

Gene Roddenberry's optimistic vision of the future and the perfectibility of humanity is what many found most enchanting about Star Trek. However, there were many times when Roddenberry seemed to actively hamstring the show, such as how he drove away writer and producer Gene L. Coon, who invented the Klingons and the Prime Directive of the original series—and when Roddenberry's utopian views of the future could stifle drama in the early seasons of Star Trek: The Next Generation. What might fans want to think of Roddenberry, on balance?
Gross: Roddenberry came up with the concept, and knew there was something special about a future where lots of different kinds of people worked alongside each other. It gave hope in a time of hopelessness. And now in 2016 it can still seem hopeless out there, and Star Trek can still present a vision where we can aspire to be better than we are. But his actual writing on Star Trek didn't often live up to his vision. He was smart enough to bring people in. He was a great concept man.

Altman: There's no denying that Gene Roddenberry's contribution to Star Trek was unparalleled. He was a visionary. And if you look at his work on [the TV series] Have Gun Will Travel or The Lieutenant, you can see what a talented writer he was. However, like all of us, he was a flawed human being.

Your books discuss some lurid details such as sexual predilections and drug use. Is this something you feel fans want to read?
Altman: My feeling is if you're not interested in a warts-and-all story of the behind the scenes making of these series, or any series, don't read the book. The book is not gossipy, but it is honest. We weren't interested in telling another whitewashed or legacy-perpetuating chronicle of the series. What I often say is the true story of Star Trek has more drama, betrayal and skulduggery than any episode of Game of Thrones, which is why it's a story that's likely to appeal to nonfans as well as Trekkers.

On Star Trek, what showed up on screen sometimes fell far short of what everyone wanted. Still, in your oral history, David Gerrold—writer of the original series episode “The Trouble with Tribbles”—noted that what's great about Star Trek isn't what it shows, but what is suggests.
Altman: There's a great line in Futurama's homage to Star Trek: “79 episodes, 30 good ones.” I would argue 30 great ones, but they're not wrong.

But even an episode like “Spock's Brain,” which is misguided in so many ways, can be wonderfully enjoyable, particularly when looked at as a reflection of the time where heart transplantation was first becoming a viable medical procedure. And even episodes like “Specter of the Gun,” which at face value is absurd—aliens pit Kirk, Spock, McCoy, Scotty and Chekov against the Earps in Tombstone, Ariz.—is so beautifully photographed, surreally designed and beautifully scored by Jerry Fielding, who later did The Wild Bunch, that you can't help but appreciate its sublime genius.

What do you think the future holds for Star Trek? What do you think about the fact that the franchise even has a future on its 50th anniversary?
Gross: It’s amazing to me that this thing is still going. But the concept of exploring ourselves through the prism of the future, commenting on where we are and where we’re going, that doesn't ever have to go away.

Altman: I am so hopeful and optimistic about the future of Star Trek. Bryan Fuller is not only a huge fan but a visionary writer with an incredible visual and aesthetic sense, and I for one can't wait to see what he brings to the screen in January. If he does his job well, as I suspect he and his team of super-scribes will, we'll still be talking and writing abut Star Trek in another 50 years.