Saturday Night Live is known for bittersweet Star Trek skits. William Shatner’s “Get a life!” bit is infamous, and the other standout is “The Last Voyage of the Starship Enterprise” from season one in 1976.
John Belushi was an early star of the show and Michael O’Donoghue was SNL’s first head writer. They were also Star Trek fans. The 12-minute Last Voyage sketch they wrote tells the story of a network executive (Elliot Gould) chasing down the Enterprise in a Chrysler Imperial. He boards the ship, announces that Star Trek has been cancelled and orders the set dismantled. Spock, played by Chevy Chase, and Dan Akroyd’s McCoy slowly acknowledge the reality and break character, walking off the bridge with the rest of the crew. Only Belushi’s Kirk sticks it out, closing out the scene by recording his last captain’s log.

The only way to watch that skit now is on an old VHS or DVD copy of The Best of John Belushi or this bootleg version. (Online at time of writing.)
The 1977 book Saturday Night Live collects scripts and notes from many of the best early SNL skits. It has a $7.95 price tag printed on the cover. I bought my copy secondhand for $4. You can get one today for about $6 at Thriftbooks and elsewhere.

I scanned the Star Trek section, which contains the script plus some photos and a set sketch, and created a PDF.
The book also includes a letter Gene Roddenberry wrote to express his appreciation of the bit. Strangely, he addressed the letter to Gould, that episode’s host, rather than to Lorne Michaels or another member of the production staff. Perhaps this was because, as Roddenberry wrote, he had been “something of an Elliot Gould fan for years.” Still, sending the praise to O’Donoghue or Belushi would have been better choices.

The approval he expressed makes sense, however, as Belushi and O’Donoghue clearly knew their Trek and respected the source material, even as they parodied it. Belushi’s Kirk says twice that there are 430 crewmembers aboard the Enterprise and accurately cites the captain’s serial number — SC937-0176CEC — as heard in Court Martial. There are also two references to the Promise Margarine commercial Shatner made in 1974.
Postscript
The tunics worn in the sketch were purchased from the Federation Trading Post in NYC.