Radio Science measurements in presence of data on optical and RF links

Abstract

Radio Science (RS) experiments currently rely on unmodulated CW RF signal carrier for spectral purity and maximized signal-to-noise ratio. This requires missions to carefully schedule them away from periods of high rate telemetry. In the era of optical communications, current systems experience the same problem. In this paper, we derive a data processing architecture that will yield high-accuracy RS or link science type of information on the ground from communication signals readily transmitted from space assets, in a broad range of communication frequencies, from RF to optical. This technique is intended to save power, bandwidth and scheduling demands on the spacecraft. Our proposed technical approach is applicable to a broad suite of modulations (phase and/or intensity), of receiver types (coherent and/or non- coherent), and carrier frequencies (e.g., microwave, optical), thus providing an architectural improvement to present state-of-the-art communication systems utilized by NASA as well as to future systems. This method is an additional module to the existing communication receiver architecture, and does not require modifications to their operation. We propose a practical system that approaches the ultimate theoretical performance for estimating the amplitude, phase, and frequency variations due to the changes in the planet atmosphere. For optical links with intensity modulated laser transmission or phase modulated CW laser communications the proposed optical receiver provides both data detection and signals required to extract RS data such as amplitude, phase and frequency due to planetary atmospheric changes. We can extract the same information required for RS data by using differential methods of encoding and at the optical receiver a local laser, a phase shifter, and an array of photon detectors are used.