A Prediction Model Oriented Approach for Space Exploration Mission Design and Operation

The continuous development of payload and ground segment technologies enables the use of higher frequency bands also for space communication systems. Whereas the X band has been of standard use for 30 years for these applications, Ka band systems have been only recently tested by the SMART-1 KaTe payload [1] and are now currently used by the NASA Mars Reconnaissance Orbiter [2]. Also the ESA Bepi-Colombo mission will exploit Ka band for down-linking large data volumes produced by the scientific instruments and for Radio Science experiments. The next step in term of technology and frequency bands is represented by the use of the Q and W frequency bands. However, due to the increasing use of Ka band by SatCom systems worldwide, it can be expected that these systems will gradually move into Q/V bands. Therefore, considering the advantages given by the large available bandwidth, smaller antenna size (for the same gain), the possible improvements of payload/ground segment RF technologies, the use of W frequency band could be an option for the manned and unmanned exploration of the solar system. One of the main problems for the use of any frequency above 10 GHz and even more for the W band, is represented by the Earth’s atmosphere radiowave propagation [3]. Atmospheric losses and atmospheric sky noise temperature experienced at lower frequencies by ground stations increase dramatically at W band. This issue is even more relevant for Space Research ground stations, due to the need to track the spacecraft down to low elevation angles, and the use of low-noise components for the receiver required by the low signal level. In this framework, ESA/ESTEC initiated a study aimed at investigating the feasibility and performance of W band radio communication link for Solar System space exploration and the development of a Space Design Tool. In particular, as experimental data at W-band frequencies lack, statistical prediction models of the propagation impairments, which constitute the bulk elements of the Space Design Tool for the feasibility and performance analysis of different space missions, have been revised and tested against physical prediction models. An accurate model to calculate the sky noise temperature, as a function of the path extra attenuation, has been purposely developed during the study and implemented into the Space Design Tool. Moreover, to the conventional design of a space mission that makes use of a direct downlink between the spacecraft and the Deep Space ground station (1-hop), the possibility of a 2-hop downlink through one or more data relay satellites [4] is implemented into the Space Design Tool. The activity was carried out by a consortium constituted by Politecnico di Milano (Italy), acting as prime contractor, Università di Roma ‘La Sapienza’ (Italy), and Scuola Universitaria della Svizzera Italiana (SUPSI, Switzerland), acting as subcontractors.