Navigation Needs for ESA's Earth Observation Missions

This chapter outlines GNSS receiver requirements driven by navigation needs identified from applications in future ESA Low Earth Observation (LEO) satellites. In the domain of operational EO, the GMES mission Sentinel-3 (S3) poses the most demanding positioning requirements in real-time in order to aid the altimeter tracking and also in on-ground post-processing for POD. The Sentinel-1 (S 1) navigation requirements are also demanding in post-processing in view of differential interferometry applications with its SAR payload. Sentinel-2 has more relaxed navigation needs as compared to SI and S3. A series of these Sentinels is planned to be manufactured with a common receiver and a common processing procurement approach. Sentinel-3, and possibly other Sentinels too, will require Galileo-compatible receivers in-orbit from 2017. The Sentinel-5 precursor (S5p) mission for air-quality and the candidate mission to the 7th Earth Explorer (i.e. Biomass, CoreH2O, Premier) require GNSS solutions, but the navigation requirements are less demanding than for S3 and SI. Within meteorological missions, the GNSS Radio Occultation instrument on Post-EPS will need to meet very demanding along-track velocity requirements and requires a high number of channels compatible with multiple GNSS. Regarding Earth science missions, the high-resolution gravity monitoring with Post-GOCE implies demanding post-processing relative position and velocity noise measurements. As a general trend, besides a multi-GNSS capability (GPS and Galileo, at least), the capability of on-board POD, already partly considered in S3, is likely to become more of a common feature for all missions. The robustness and reliability of the navigation solution will also become increasingly important. This chapter also describes the key technology "building blocks", like the AGGA-4 digital GNSS processor to fulfill the requirements in these future missions.