Subspace mass sensors instantly detect mass readings and movement of objects up to a distant from the ship determined by the originating nation's technology level. The readings are used both for early warning and navigation when traveling at sublight speeds. The readings are not very detailed and cannot detect objects of less than 60,000 kg.
A type of detection system found in many modern civilizations, it widely differs in detection range due to technological level. Nations like Yamatai and Nepleslia had ranges of light years compared to the new comers to galactic politics like the Abwehrans who have detection ranges of Astronomical Units.