 One of the main causes of trepidation as Riduk prepares to enter the garden is
When nobody aboard ship remembers where it's going, how can they tell when it has arrived? But ever since the engines somewhere in the rear of the world had changed their tone, from the steady whining Rikud had heard all twenty-five years of his life, to the sullen roar that came to his ears now, the feelings had grown. Rikud knew that something which he could not explain had entered the elder man's head for a moment, but it had departed almost before Chuls knew of its existence. The people had decided that they did not know where they were going, or why, and that it was unfair that the elders alone had this authority.
 is its vast endlessness.
 nothing.  Riduk is ready to go.  is its vast endlessness.  Riduk is fearful that his shipmates will want to go with him, and he wants the garden and its beauty for himself.  that Riduk is fearful he will get caught and punished for attempting to leave.