Star Trek fans have been waiting for Sunday night for years. That’s when CBS will air the premiere of Star Trek: Discovery, the first Star Trek TV series since Enterprise signed off 12 years ago.

But Sunday will be an even bigger moment for CBS All Access; it’s the streaming service’s single most important day since its launch three years ago. CBS Corp. has set lofty goals for CBS All Access and its direct-to-consumer Showtime streaming service—like 8 million combined subscribers by 2020. Star Trek: Discovery, which will be available exclusively on All Access after the premiere on CBS, represents its best chance to reach that number and convince millions more to shell out $5.99 a month for the service. (CBS said in August that it expects the two services to have 4 million combined subscribers by December.)

Speaking last week at New York’s Goldman Sachs Communacopia Conference, CBS Corp. chairman and CEO Leslie Moonves called Star Trek: Discovery “the main event” for his streaming service. Earlier this year, All Access’ first original scripted series, The Good Wife spinoff The Good Fight “did fine,” Moonves said, “but this is the big kahuna.”

Discovery was originally supposed to debut in January, but producers said in August that Moonves agreed to delay the show eight months so it would be “huge” enough to satisfy fans.

Replicating its premiere strategy for The Good Fight, CBS All Access will launch the show with a linear premiere on CBS Sunday night, and then the network will direct viewers to watch the second episode on CBS All Access, where it will be available to stream immediately following the premiere.

“We hope it’s a watershed [moment] for the service,” said Marc DeBevoise, president and COO of CBS Interactive.

To drive viewers to CBS and then All Access on Sunday, CBS Marketing Group president George Schweitzer said he created a campaign with the same objective as the series itself: “Don’t disappoint the fans, but appeal to the widest audience possible.”

That meant playing up the sci-fi elements for Trek fans, while making it clear to other audiences that “this is a human story.” And most importantly, Schweitzer made sure to “create an event on that Sunday night. That’s the key. We scheduled it Sunday night, on CBS, after the premiere of 60 Minutes, and an [NFL] doubleheader night. You can’t miss this.”

While All Access won’t have linear premieres for every original show—its next series, the comedy No Activity, won’t debut on CBS—but for Star Trek: Discovery, “using our most powerful asset, that No. 1 network, makes a lot of sense. It’s the best promotion we could ever give something,” DeBevoise said.

Discovery’s first two episodes offer an “an awesome, movielike experience to kick off the show,” he said, which leads into “a really interesting, deep and slightly more serialized Star Trek series.”

The CBS episode ends on a major cliffhanger, which DeBevoise hopes will prompt people to immediately watch the second episode on All Access.

CBS All Access is also rolling out a Star Trek: Discovery aftershow, which is a first for a streaming service and will be streamed live each Sunday night.

As another part of its marketing campaign, the company opted to embargo reviews from TV critics until after Discovery’s debut, which is unprecedented for a new series. That is usually a surefire sign of a troubled production, but DeBevoise said CBS simply wanted to prevent spoilers and maintain the veil of secrecy they’ve kept around the production.

“We think it’s a tremendous show,” he said. “It’s really more about this franchise having such a big, deep fan focus, that we really wanted them to have the chance not to have it leak and have too much out there before they’re able to see it.” (Indeed, the first episodes screened for the media late this week are far more ambitious than any new broadcast show rolling out this fall, including Fox’s own attempt at a freshman sci-fi series, The Orville.)