The cold start of the space GPS receiver, i.e. the start without any information about the receiver position, satellite constellation, and time, is complicated by a large Doppler shift of a navigation signal caused by the satellite movement on the Earth orbit. That increases about five times the search space of the navigation signals compared to the standard GPS receiver. The paper investigates a method of the acceleration of the GPS receiver cold start time designed for the pico- and femto-satellites. The proposed method is based on a combination of the parallel search in Doppler frequency and PRN codes and the serial search in code phase delay. It can shorten the cold start time of the GPS receiver operating on LEO orbit from about 300 to 60 seconds while keeping the simplicity of FPGA signal processor and low power consumption. The developed algorithm was successfully implemented and tested in the piNAV GPS receiver. The energy required for the obtaining of the position fix was reduced five times from 36 on to 7.7 Joules. This improvement enables applications of such receiver for the position determination in smaller satellites like Pocket Cube or femto-satellites with a lower energy budget than the Cube Satellite.

The objective of the research was to develop the Attitude Control System algorithm to be implemented in the Earth Observation Satellite System composed of leader-follower formation. The main task of the developed Attitude Control System is to execute attitude change manoeuvres required to point the axis of the image acquisition sensor to the fixed target on the Earth’s surface, while the satellite is within the segment of an orbit, where image acquisition is possible. Otherwise, the satellite maintains a nadir orientation. The control strategy is realized by defining the high-level operational modes and control laws to manage the attitude control actuators: magnetorquers used for desaturation of the reaction wheels and reaction wheels used for agile attitude variation. A six-degree-of-freedom satellite model was used to verify whether the developed Attitude Control System based on PID controllers for actuators performs attitude control in line with the requirements of an Earth Observation System. The simulations done for a variety of combinations of orbital parameters and surface target positions proved that the designed Attitude Control System fulfils the mission requirements with sufficient accuracy This high-level architecture supplemented by a more detailed control system model allowed proving efficient functionalities performance.