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This paper presents a numerical method to propagate relative orbits. It can handle up to an arbitrary number of zonal and tesseral geopotential terms and can be extended to accommodate the effects of atmospheric drag as well as other perturbations. This method relies on defining a 'relative Hamiltonian,' which describes both the absolute and the relative motion of two satellites. Exploiting the separability of the solution, the Keplerian motion is described via analytical means whereas the effects of higher order terms are handled via a symplectic numerical integration scheme. The derivation and the numerical integration are designed to conserve the constants of the motion, resulting in better long term accuracy. When used within a relative orbit estimator, such a high precision relative orbit propagator should reduce the frequency of the required sensor input dramatically for a given estimation accuracy. We present results for a broad range of scenarios with large separations and show that sub-metre accuracy is possible over five days of propagation with a geopotential model containing 36 terms in tesseral and zonal harmonics. These results are valid for eccentricities reaching 0.5. Furthermore, the relative propagation scheme is significantly faster than differencing two absolute orbit propagations.

The purpose of a power subsystem is to ensure reliable delivery of electrical power compatible with all loads under all foreseeable operational states and environments, during all mission phases, and over the intended design life of the loads and of the space vehicle and the power subsystem is unarguably the most critical subsystem on a satellite. Therefore, reliability, efficiency, autonomy, redundancy and size features become critical issues in design and implementation of a satellite power system. Moreover, these parameters associated with the power subsystem usually determine the lifetime of a satellite. This paper describes the design details with redundancy concept, autonomous operation, single point free architecture and sizing of RASAT flight model power subsystem. Technical description and the qualification level of each power system module are also presented. For the battery charge regulator, the parallel operation and an effective MPPT algorithm will be presented in detail. Moreover, the power productionconsumption analysis and power system sizing will also be included for different scenarios.

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