ESA GNC Conference Papers Repository

In the framework of the EU-led Global Monitoring for Environment and Security (GMES) program, ESA is undertaking the development of a series of five Sentinel missions with the objective to provide operationally Earth observation data for the implementation of operational GMES and national services. As part of the GMES Space Component, the Sentinel-1 mission is based on a constellation of two satellites (A and B units) each carrying a C-band SAR instrument providing all-weather and day-and night imaging capability. The Sentinel-1 end-to-end system is specifically designed to acquire systematically and provide routinely SAR data and information products for GMES Ocean, Land and Emergency services. These services include applications such as monitoring sea ice zones and the arctic environment, surveillance of marine environment, monitoring land surface motion risks, mapping of land surfaces, and mapping in support of humanitarian aid in crisis situations. Thales Alenia Space Italy (TAS-I) is Prime Contractor for the system and the spacecraft. In particular the spacecraft is based on the PRIMA platform design, enhanced to support the specific Sentinel-1 challenging performance requirements. The Sentinel-1 satellite embarks a SAR payload that is able to acquire images according to multi-resolution, multi-swath and multi-polarization modes of operation on a wide area access. It can also transmit to ground the science data through the Optical Communication Payload (OCP) via the EDRS telecommunication satellite. The OCP is an optical-laser transceiver that allows to transmit data to remote counter terminals pointing the laser beam with a two degree of freedom movable telescope. The key requirements are: overall pointing accuracy better than 6.75 mDeg also during OCP slewing; in-orbit position determination 10 m; velocity determination 0.01 m/s; instrument bursts synchronization better than 5 ms commanded as a position tag. The mission reference orbit has to be kept with 100 m (RMS) error with no out of services. An AOCS safe mode based on independent hardware and software resources is also required. The avionics subsystem provides to Sentinel-1 all satellite functions required for safe operations of the satellite during all mission phases, including also non-nominal situations: command and control, data handling, attitude and orbit control, autonomous failure detection, isolation and recovery.