Improving Rosetta's Return-Link Margins

G.P. Calzolari et al.

The Rosetta mission is designed to study in-situ a cometary nucleus’ environment and its evolution in the inner Solar System. To be launched in January 2003 by an Ariane-5, Rosetta will rendezvous with Comet P/Wirtanen in 2011, after one Mars- and two Earth-gravity assists, and two asteroid fly-bys. The near-comet operations, which are scheduled to last about 1.5 years, will require a minimum return-link telemetry data rate of 5 kbit/s to meet the scientific goals, with about 14 hours of daily coverage.

Rosetta will operate in the frequency bands allocated by the Geneva-based International Telecommunications Union (ITU) to deep-space missions operating 2 million kilometres or more from Earth. These bands enjoy stringent protection requirements, making them virtually free of radio-frequency interference from other services. Moreover, the limited number of such missions makes it acceptable to adopt coding and modulation schemes that are optimum for power-limited as opposed to bandwidth-limited systems. This article describes the efforts currently being made to optimise Rosetta’s communications capabilities in this respect.