Seedship Series
Background
The first stories are near-future, the first seedships are sent out to colonize other planets. Most are sent by large coalations (UN, Nato) some are sent out by individual governments (China, Russia) and a few are sent out by idealogical faction. A protocol is established for how the seed planets will communicate and interact.
Ship Design
The ships are fusion powered, I'm picturing something like General Fusion. The reactor takes in ??? and produces energy and waste (lithium?). The energy is used to electromagnetically accelerate the waste as propulsion. The ship accelerates at 1G for 16 hours then while the crew is asleep, accelerates at 1.25G. The ship doesn't carry fuel on board, the fuel is "shot" at it by solar-orbiting launcher (fuel drive). The fuel drive has two linear accelerators point in opposite directions, so that launching the fuel doesn't change it's own orbit. The fuel pellets orbit the sun, up to one full orbit, then leave on an escape trajectory. Before they do, they pass through one of two 'primary collators' that alters the trajectory enough that it will travel straight. There are secondary collators that help keep the 'fuel train' focused over the several light year journey. The act of collating the pellets is enough for them to pick up some acceleration. Their energy source is a laser that is also passed and collated between them.
The ship itself is relatively small and simple. It is kept as light as possible to maximize acceleration.
Book 1: Journey
Told from the perspective of a small child (Alec) on one of the first seed ships. The ship is populated with 20 families. Much of the story revolves around a friendship between Alec and Stan, who is staying on Earth. While the ship is relatively close, and moving and relatively slow speeds. High bandwidth communication is possible. They can video chat, play games, and there is no noticeable difference. After a few years, relativity starts to catch up. Video chat is no longer possible, nor realtime games, and even audio becomes strained because a conversation for Stan is taking 10% longer. Eventually they reach a point where only asynchronous communication is possible, recorded audio or email and they are playing turn based games.
At this point the relationship is starting to change because Alec is now a few years younger than Stan. As their ship continues to accelerate, the situation worsens. Stan seems to be aging even faster. From Alec's perspective, they talk every day, but from Stans perspective, it's growing longer and longer until he's only receiving a message every few weeks.
In the end, Stan grows old and dies and the conversations take on a very different tone, an old man talking back in time to his teenage friend. Alec is of course very saddened. But he finds that Stan had worked on the Seedship project as he aged, researching biology and how the terraforming process would work. Alec, as he approaches 'college' picks up the work his friend left off and in the epilogue, we're shown that he leads the first human terraforming project.
I want to use the story to lay out some of the operations of the ship. Alec, particularly when he is young, won't understand them. But he'll catch bits and pieces of the conversations.
It may make sense to start the story at the point where Alec and Stan have to switch to email, the story can be a log of their emails. It could also be a memoir compiled by Alec.