Tau Zero - Poul Anderson
I have selected songs from various genres that support space travel and the story. Most also include the theme of loss, and travel to the end of space and end of time. The sole exception to the theme is the song "Rise, King Valdemar" by Jens Peter Jacobsen, which is directly quoted in the novel.
The Highwayman - The Highwaymen
This would be played during the launch to the Leonora Christine. The song speaks of a highwayman, a sailor, a dam builder, and a starship captain. The crew of the starship is composed of outcasts and scientists, willing to spend the rest of their life on a new world. Men and women similar to the highwaymen and builders would become starship pilots and star mariners, on a path to a new world.
Cygnus X-1 Book I (v2) - Rush
The launch of the ship sends the crew to a faraway world. However, the mission soon experiences trouble when the ship impacts a nebula and its deceleration drive is damaged. The verse about the ship flying into the future fits the Leonora Chirstine's new mission, soon after the encounter with the nebula, as it turns away on a course to leave the galaxy forever.
Rise, King Valdemar (2nd and 3rd verses sung by Valdemar's Men)- Songs of Gurre - Jens Peter Jacobsen - sung in character by actress who plays Ingrid Lindgren
This song was sung in the novel by the character Ingrid Lindgren, who accompanied the song on a lute. This scene occurs soon after the Leonora Christine finally left the galaxy. She used this song to describe the ship's voyage as the Wild Hunt, a legend where a group of supernatural hunters ride past an observer. The ship is on its own Wild Hunt to the end of time, looking for a place where it can repair its deceleration drive and come to rest.
'39 - Queen
As the movie would finally end, the starship comes to rest on a new world. This song would play as the credits roll. The song could have been based off the novel, for the crew had left humanity, the galaxy, and finally the entire universe behind. As the song states, they had written "letters in the sand" to the family and world they had left behind. Even as they come to rest, they will never be able to forget what what was left behind, as relativistic time sends them forever on.