The U.N.S. Slayton is named after Deke Slayton, who was one of the original NASA Mercury Seven astronauts, while the U.N.S. Gagarin was named after Yuri Gagarin, a Soviet cosmonaut who became the first human in space on April 12, 1961.
This is the first episode to be set in the future.
Per the title, dark matter is an astronomical term referring to matter that cannot be detected by electromagnetic (EM) means, only by gravitational means since it does not emit EM waves.
Although his character Paul Stein is 37 years old, John Heard was 49 when this episode was produced. Furthermore, David Cubitt plays his elder brother Kevin Stein but is 19 years Heard's junior in real life. Even taking into account that Kevin has been dead for ten years and appears to Paul as a ghost, there is still a nine year age gap.