RSI (Radio Science Investigation) involves both Earth and Rosetta based instrumentation. The system uses the communication between the Rosetta probe and tracking stations in Australia, Spain and the United States to create either a one-way (probe generated signal received on earth) or a two-way (a signal transmitted from Earth is received by the probe and re-transmitted back to Earth) radio link.

The RSI system will be used to investigate frequency shifts as a result of the movements of the probe and as a result of passing through ionised regions of space. This should give an indication of the motion of Rosetta alongside information regarding the forces acting on the probe and on the space the radio waves are travelling through.

It is envisioned that RSI will work alongside other instruments, such as OSIRIS, in order to provide information on the physical properties of the comet; such as its mass, density and gravity. It will also be able to assist in providing more focused information on the properties of the nucleus, coma and tail.

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