Space Detection Network

Long range detection has always relied heavily on burn detection, but naturally that has never been the sole method. Normally ships coming in to a system are detected as they enter the range of navigational radar at about 100,000km, or a few hours away. Even if a burn has not been detected prior to that, any reasonably alert military ship would pick up an incoming ship, burning or not. At about 5,000 km tactical radar picks up targets and is able to be very discriminating about what is coming in and allows you to distinguish ship classes.

Space Detection Networks synthesise system-wide data from station space traffic control radars, navigational radars on passing merchants, outlying bases, asteroid mines, and orbital wide-band EMR telescopes. All homeworlds, colonial capitals and very rich colonies have such Space Detection Networks as standard.

An SDN looking for a non-burning incoming vessel would would expect to have a 90% chance of detection of anything substantial (Class 5000 / Capital Ship size) up to 100 million km out. The detection range would be a little closer for smaller vessels, but would expect to be 99% effective at detecting a pacifier-sized target at 1 million km.

Much depends on circumstances - a ship coming in along the plane of the ecliptic might be a bit harder to detect, but would also be at very high risk itself from damage caused by dust and micro-meteorites impacts (unless moving extremely slowly - in which case the SDN has a lot longer to detect and it is therefore easier to spot).