Imperial Earth

Duncan Makenzie is the latest generation of the 'first family' of Titan, a colonised moon of Saturn. Originally settled by his grandfather Malcolm Makenzie in the early 23rd century, Titan's economy has flourished based on the harvest and sale of hydrogen mined from the atmosphere, which is used to fuel the fusion engines of interplanetary spacecraft.

As the plot opens in 2276, a number of factors are combining to make a diplomatic visit to the 'mother world' of Earth a necessity. Firstly, the forthcoming 500th anniversary of US Independence, which is bringing in colonists from the entire Solar System, obviously needs a suitable representative from Titan. Secondly, the Makenzie family carry a fatal damaged gene that means any normal continuation of the family line is impossible—so both Duncan and his "father" Colin are clones of his "grandfather" Malcolm. Human cloning is a mature technology but is even at this time ethically controversial.

Synopsis from Open Library.