A constant gain Kalman filter approach for the prediction of re-entry of risk objects

The accurate estimation of the predicted re-entry time of decaying space debris objects is very important for proper planning of mitigation strategies and hazard assessment. This paper highlights the implementation strategies adopted for the online re-entry prediction using Kalman filter approach with constant gains with the states being the semi-major axis, eccentricity and ballistic coefficient and using the measurements of the apogee height and perigee height derived from the Two Line Elements provided by agencies like USSPACECOM. Only a very simple model is utilised for the orbit propagation and a basic feature of the present approach is that any unmodellable state and measurement errors can be accounted for by adjusting the Kalman gains which are chosen based on a suitable cost function. In this paper we provide the details of validating this approach by utilising three re-entries of debris objects, namely, US Sat. No. 25947, SROSS-C2 Satellite and COSMOS 1043 rocket body. These three objects re-entered the Earth's atmosphere on 4th March 2000, 12th July 2001 and 19th January 2002, respectively.