TRAJECTORY ESTIMATION STUDIES FOR LONG COASTING PHASE OF MARS MISSION

Abstract

At Sriharikota range, configuration of down range tracking network, Real-time tracking and trajectory estimation play a critical role during a satellite launch for flight safety as well as mission monitoring. Criticality is more when the mission parameters vary during the launch window to meet the mission requirements. PSLV-C25, the 320 T XL version is intended to inject the 1337.24 Kg MARS Orbiter into 250 Km * 23500 Km * 19.2 deg Sub-GTO orbit. MARS Orbiter Mission [MOM] is the first Indian interplanetary mission to orbit a spacecraft around MARS in an elliptical orbit of 360km * 80000 km. This paper deals with the trajectory estimation and prediction methodologies studied and established at Sriharikota Range for this launch. The major challenge in the Mars orbiter mission is to configure the Down range network of Telemetry stations in view of large variation in the Argument of Perigee (AOP) requirement ranging from 276 0 to 289 0 during injection over the period of launch window. Requisite AOP facilitates transit of the Spacecraft from Earth to Mars using minimum energy Hohmann transfer. The change in the requirement of AOP each day in turn demanded a new trajectory with its characteristic changes in long coasting duration, fourth stage ignition time and subsequent MARS Orbiter injection time into sub-GTO. It is mandatory to capture the Telemetry data during those critical events to assess the success of the mission. The flight duration was around 3000s and the coasting duration was 1600s before the ignition of the PS4 stage. Study of configuration of mobile Telemetry stations on Shipborne terminals is carried out to cater to visibility requirements of critical events such as fourth stage ignition time and subsequent MARS Orbiter injection. State vector accuracy studies are carried out for the Ship-borne radar data of the vehicle during long coasting using Linear Kalman filter. Also a trajectory extrapolation algorithm is designed and studied to provide extrapolated trajectory during the long coasting period after 3 rd stage burn out which in turn is used to compute and display trajectory parameters to mission executives and provide antenna-pointing information to the ship-borne terminals. This paper presents the trajectory estimation methodology proposed, extrapolation techniques adopted and accuracies achieved for the long coast duration.