Non-cooperative satellites: a reference filter detects small manoeuvres that conventional methods miss

By controlling the manoeuvre probability via an independent filter, the RD-IMM method detects discrete thrusts in geostationary orbit and reduces the position error by more than half.

Knowing when a foreign satellite is quietly changing orbit is a central issue in space surveillance. Interactive Multiple Model (IMM) filters, used to identify these unannounced maneuvers, are based on a matrix of transition probabilities that must be set without knowing the actual frequency of the target's maneuvers. Variants that adjust this matrix continuously suffer from a feedback loop: they can maintain an alert when there is no maneuver, or on the contrary stifle it when a surge occurs.

A judge outside the filter

The proposed method, RD-IMM, entrusts this adjustment to a reference filter which assumes a thrust-free trajectory and is not mixed with the rest of the device. The difference between its forecasts and the observations is continuously translated into the probability of switching to manoeuvre mode, which breaks the loop.

Tested with four space-based optical sensors following a geostationary target, the method detects small thrusts that a conventional IMM does not see, with few false alarms during unmanoeuvrable passages. After a small thrust in the direction of travel, it reduces the position error by more than 50% compared to single-filter approaches.