NAVCOM Short Description

Modelling Hybrid Communication - Navigation Systems for Formation Flying Satellites (HybridNAVCOM)

HybridNAVCOM project aimed to study the possibilities to define a dual band carrier hybrid communication-navigation model for precise relative position and attitude measurements and estimation. Our secondary objectives were the study and modeling of various waveforms and communication protocols for improved synchronization, detection and estimation, design, implementation, simulation and validation of new navigation algorithms for coarse and fine metrology, and collision detection functions using communication system data.

Unlike single spacecraft missions where a single processor executes all guidance and control functions, in formation flying missions, the spacecraft must act in a cooperative way as a whole, and therefore the tasks are divided between different processors on different platforms. The envisaged models are developed for a group of two satellites and are relied on the exploitation of waveform diversity, scattering mechanisms, channel capacity estimation, estimation of various signal forms, frequencies and polarization, combined with possible interferometric techniques for accurate ranging and positioning. The master processes information related to formation guidance, estimation and control functions, and commands the second one. This allows for optimal collision free trajectories estimation. Formation flying assumes inter-satellite synchronization, inter-satellite distance measurement and inter-satellite orientation/direction estimation. Formation state estimation is an essential function to be performed in formation flying systems and generally each spacecraft must be equipped with sensors that measure the relative position between itself and the other element of the formation. The estimation has to be performed on board, in real time, and to account for the delays, communication drops and time-variant topologies. Investigated range based positioning methods are: received signal strength, time of arrival, time difference of arrival, propagation delay based on pseudo random code or phase variation.

The development and validation of the proposed dual carrier hybrid communication-navigation model, consisting of a new communication protocol and formation flying algorithms tailored to a unique hardware platform for ISL and navigation, was based on a custom implementation upon NI USRP 2952R software define radio platform. Functionality and performance testing of the hybrid communication-navigation model was carried out using the dynamic test bench in GMV's platform-art© laboratory in Madrid.

Fig. 1 Dynamic test bench in GMV's platform-art© laboratory.

ACKNOWLEDGEMENT
This work was supported by a grant of the Romanian Space Agency, STAR2 program.