The voyage
A seed delivers the machinery; later residents arrive as data over a laser link.
The Vigil began as a seed. It weighed 1,000 kg and left the Solar System on a thin sail, pushed by a laser array on the Moon to a tenth of the speed of light. It crossed 28 light-years in 297 years and stopped on a fusion engine at Vesper, a black hole, and Ember, the small orange star that circles with it. The fuel for that stop left the Moon on the same beam, so the laser pushed 23 times the seed's mass.
These pages cover launch, braking and the later transmission of software minds.
Where should I start?
Start with pushed by light. The rocket equation explains the fuel requirements for this journey. A laser array on the Moon accelerates a thin sail, so no fuel is burned to leave.
Next, Stopping from 0.1c shows why the free brakes fail. The seed arrived with 4.5 × 1017 joules of motion. A magnetic sail dragging on the thin gas between the stars would need a 77-tonne loop to slow it in 30 years, and Ember's light can stop even a bare graphene sheet only from 0.02 of light speed. So the seed carried a deuterium and helium-3 fusion stage with 17,206 kg of propellant and burned it for the last 50 years of the trip. The last leg, from the end of that burn to Kindling, Ember's close planet, with Vesper's pull included, was integrated: it needs 79.2 km/s, which the stage's 14 kg reserve covers.
The third page covers later arrivals. Bits travel, atoms do not explains why the minds of the Vigil came as a signal. A whole mind, represented here by 1 × 1017 bits, crosses the same distance for 9.5 seconds of link time, against the seed's 297 years. It still takes 28 years for the light to arrive, because nothing outruns light.
Where does it lead?
The seed's landing is the start of the Vigil's energy story, and the minds that followed are the subject of the ideas strand. The mass-energy sums that make the voyage cheap are on the page a gram is a fortune.