TIME FOR THE STARS

Relativistic exploration story, with the added wrinkle that mental communications between twins is instantaneous, regardless of distance. Later adjustments to this are less scientific, and the ending is a disappointment.

The majority of the novel is a shipboard life story. The main character's twin is manipulative, to the point of manipulating which twin would go on a likely doomed voyage of exploration. The coming-of-age aspects of the book involve him growing to understand this, as additionally demonstrated by an irritating shipmate. In this respect, a good fit with other Heinlein juveniles.

I was willing to accept the ESP FTL connection, but allowing a non-related connection, along with later connections to descendants, was a bit much. The characters were pretty basic, and some of the conflict seemed artificial. I can't complain much about the ending without spoilers, but the marriage? Just no.