Abstract-We will show that ocean-reflected signals from the global positioning system (GPS) navigation satellite constellation can be detected from a low-earth orbiting satellite and that these signals show rough correlation with independent measurements of the sea winds. We will present waveforms of ocean-reflected GPS signals that have been detected using the experiment onboard the United Kingdom's Disaster Monitoring Constellation satellite and describe the processing methods used to obtain their delay and Doppler power distributions. The GPS bistatic radar experiment has made several raw data collections, and reflected GPS signals have been found on all attempts. The down linked data from an experiment has undergone extensive processing, and ocean-scattered signals have been mapped across a wide range of delay and Doppler space revealing characteristics which are known to be related to geophysical parameters such as surface roughness and wind speed. Here we will discuss the effects of integration time, reflection incidence angle and examine several delay-Doppler signal maps. The signals detected have been found to be in general agreement with an existing model (based on geometric optics) and with limited independent measurements of sea winds; a brief comparison is presented here. These results demonstrate that the concept of using bistatically reflected global navigation satellite systems signals from low earth orbit is a viable means of ocean remote sensing.

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The optimal controllers for the management of 3-axis reaction-wheel momentum of rigid Earth-pointing satellites are analyzed in detail using magnetorquers and/or thrusters. Especially, two novel, optimal combined control schemes are proposed in order to achieve rapid, propellant-saving reaction wheel momentum dumping control by employing magnetorquers and thrusters. Finally, simulation results are presented to demonstrate the superiority of these algorithms. These two combined algorithms could easily be applied in real-time onboard an LEO Earth-pointing satellite.

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The modernisation of GPS and the introduction of Galileo will introduce the use of Binary Offset Carrier (BOC) modulation. BOC will be implemented as either a sine or cosine sub-carrier modulation, which affects the spectral properties of the signal and the receiver search, acquisition and tracking processes. This paper addresses the effect of the various forms of BOC modulation on the receiver search process. Theory is developed to draw comparisons between search techniques and verified with computer simulation models.