Application of GNSS CORS in Earth Observation Satellites Ground Station Selection and Control for Nigeria Space Programme

Abstract

In order to maximize global scientific collaboration on the utilization of data products from NigeriaSat payloads, there may be need to have additional ground stations in Nigeria, across Africa, Asia and Europe, etc. Ground station network is the means by which satellites stay in contact with the Earth, through which data reception and satellite controls are realized. The Global Navigation Satellite System (GNSS) Continuously Operating Reference Station (CORS) Infrastructure in Nigeria and IGS around are relevant in the site selection, data facility evaluation and EOS tracking/control of the Nigeria satellites payloads. The study used the GNSS CORS data of February 2010 and the Two Line Element (TLE) set of NigeriaSat-1 (N-1) Orbit to make sky visibility analysis for EOS ground Station selection in Nigeria and the trend analysis of N-1 orbital behavior for a period of seven years (1st January 2004 – 1st January 2011). The optimized DOP values of majority of the eleven stations were consistently poor (well above 4) between the hours of 10:20-11:00GMT and 13:10-14:00GMT respectively, but with mean values ranging between 2.4 and 3.2 (i.e. 2.4:DOP: 3.2). This technique is only one of many supporting technical and logistic criteria for ground station selection using GNSS-based LEOS tracking and control. NigeriaSat-1 showed a total orbital angular drift of about 00o 19’ 03” of arc (equivalent to about 34. 29km, about 4.3km/year), towards the earth pole between 27th September 2003 and 27th September 2010. The eccentricity of the Orbit ellipse of the NigeriaSat-1 was slightly unstable and irregular in September 2004, which might have resulted in in-ordinate imaging of same ground area or swath on the earth during the period. The TLE set analysis shows that the N-1 Coefficient of Drag was small; hence not subjected to extreme vertical and lateral drag in orbit, which may not be unconnected with its light weight/mass of 98kg (micro-satellite). For sustainability of the Nigeria Space programme, periodic monitoring of the NigeriaSat-2 and NigeriaSat-X orbital status with the TLE set from the on-set of launch and completion of in-orbit callibration is imperative. This is because their weights/masses are quite higher than than that of N-1; hence would be more susceptible to drag in orbit. Secondly, due to periodic and sudden changes in space weather that could cause some orbit and altitude pertubations on the spacecrafts.