Abstract
The satellite imaging service used to be very expensive and mainly explored by government for civil and military applications. With the development and commercialisation of space industry, there is increasing demand on the timely satellite imagery service. Therefore the performance analysis of the service delivery delay of the satellite imaging system becomes important. Currently the performance of satellite imaging service is mostly analysed based on system simulation results or real sample data from service providers, which are usually accurate but not systematic. Also the effects of system parameters are not direct viewing. Theoretical modelling approach, however, captures the feature of the system and provides direct systematic performance evaluation, which is a useful guide in designing satellite system according to the user's requirements in timely service delivery. Therefore this work is motivated to model the satellite imaging system analytically. In this work we consider a satellite imaging system with single satellite, single ground station and limited onboard storage. Queueing theory is applied for the performance modelling. Since there are two tandem service stages: image capture and image download, the system is modelled using a two-node tandem queue with blocking. At first we propose a continuous-time two-dimensional Markov chain for describing the satellite imaging system. The model works well but has its limitations and disadvantages. In order to have a better model for the satellite imaging system, we conduct a further research on the service mechanism of the image capture and image download. Using satellite geometric models, we derive the stochastic features of image capture and download service, in terms of the probability of having an operation opportunity each orbital period, and the probability distribution of the inter-time between operation opportunities. We propose discrete-time clocking models for the image capture and download service respectively, with queue status defined on a discrete-time orbit- by-orbit basis, and with transition probabilities between system states derived from the stochastic analysis. We then concatenate these two queues and propose a tandem clocking model for the complete satellite imaging service system. The discrete-time clocking models have been evaluated by comparison with simulation results using different target location distributions. The models are proven to be very successful for general distributed target locations, with above 95% high accuracy for the mean system queue length. Using the tandem clocking model, we conduct performance analysis for the key service performance measure: average waiting time, and also investigate system parameters' effects on the system performance. With this work, we are enabled to provide information about the general performance of a satellite imaging system, which caters to the customer's concern and also is very helpful for system optimisation in satellite design and control.