The IA, or "shooters" are 1km long tunnels made of elements such as concrete, with pipes containing super-heavy Z particles being formed by particle acceleration. The Z particles attract large amounts of Higgs Bosons, and anything passing through the accelerator are not affected by the bosons and are allowed to pass through with no mass, accelerating them to FTL speeds.
Cargo ships and personnel shuttles which do not have Interstellar (electroplasmic) drives,cannot travel between star systems without a lot of difficulty and time. So they pass through the shooter and the ships on board computer calculates the distance and adjusts its bearing to hit the Acceleration buffer.
The Acceleration Buffer is a force field designed to stop matter passing through without damaging it or causing it to have large inertial problems, it works by first, stopping the object with a field that will slow the object to a halt over a few hundred meters, and will then be secured in place using magnets.