Relative Navigation

BACKGROUND

The Indian Space Research Organisation (ISRO) is the premier space agency of the Government of India. As project trainees, we worked with senior scientists at Flight Dynamic Group (FDG) at ISAC to develop a satellite tracking routine for docking micro satellites. The work included application of filtering techniques to de-noise proximity data from on-board sensors and deriving system of equations for estimation of orbital location of the satellite

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METHODOLOGY

Two IMS (Indian Micro Satellite) Spacecrafts, one designated as target and the other designated as chaser, are launched by a PSLV launcher into two slightly different orbits. No communication link between the target and chaser during the far range rendezvous phase in which relative separation is around 50 km to 5 km range is envisaged and this phase is a ground guided phase. In the docking phase of the mission, docking sensors such as Laser Range Finder during the relative separation of 5 km to 0.25 km, Docking Camera during the relative separation of 300 m to 1 m, Visual Camera for real time imaging during the relative separation of 1 m to docking are used respectively.

We were required to carry out design and development of software for the following:

1. CW (Clohessy Wiltshire) equation for relative state propagation as it is one of the constituent for the onboard navigation software based on Kalman filter technique and foreseeing a need for relative state propagation for longer duration in the absence of measurements.

2. Kalman filtering technique for relative state estimation using range measurements and measurements from visual camera for onboard application.

We used C++ as our platform for programming. The resulting outputs were subsequently simulated using MATLAB. The results were plotted to analyse the various parameters and constraints involved, and were compared to the data provided to us by the senior sicentists.

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OUTCOME

Worked with the senior scientists at FDG at ISAC to design software for the docking of IMS (Indian Micro Satellite). The the work was evaluated as 'excellent' by the FDG reviewers. Submitted a technical report- Relative Navigation for Rendezvous Docking Experiment to ISAC. The results were also presented to university committee in a seminar, as part of graduation requirements, and was awarded A+.

Gained insight into how a technical literature survey is done and how theoretical formulations are implemented in real-world software. Also obtained understanding of concepts of orbital mechanics and relative navigation as applied to satellite navigation systems.