SENTINEL-3 is a low Earth-orbit moderate size satellite compatible with small launchers including VEGA and ROCKOT. SENTINEL-3 is designed for a 7 year operational lifetime with 120 kg of hydrazine propellant allowing up to 12 years of continuous operations, including de-orbiting at the end of mission. The satellite layout is driven by the need to provide a large face viewing cold-space for thermal control, a modular design for payload accommodation and simplified management of all on-board interfaces. The satellite mechanical configuration and its flight attitude have been optimised through intensive mission analysis studies and system trade-offs performed during the mission definition, resulting in significant improvements in comparison to ENVISAT.
The main subsystems of the satellite are:
- Electrical Power System (EPS), comprising one solar array wing providing power to the spacecraft and payload.
- Attitude and Orbit Control System (AOCS) composed of a coarse sun sensor, magnetometers, coarse rate sensors, star trackers, a GNSS receiver and control actuators including thrusters, magneto-torquers and reaction wheels.
- Satellite management unit for satellite commanding and monitoring.
- Data handling and mass memory unit for payload data handling.
- Mass memory units for the satellite and its payload.
- Satellite telecommunication subsystems including an S-band subsystem for both telecommand (TC) uplink and telemetry (TM) downlink, and a dedicated high volume X-band subsystem for mission data downlink.
The main satellite platform characteristics are:
- Gyroless, three-axis stabilised platform with three star tracker heads, four reaction wheels and magnetic off-loading.
- Geodetic pointing and yaw steering.
- Eight 1 N hydrazine thrusters for in-plane and out-plane manoeuvres.
- Real-time on-board orbit accuracy determination of 3 m based on GPS and Kalman filtering.
- Launch Mass: 1 250 kg (with maturity and system margins, and fuel).
- Stowed dimensions (mm): (H) 3 710, (W) 2 202, (L) 2 207.
- Power: 2.1 kW rotary wing with 10 m2 triple junction GaAs European solar cells; Li Ion Battery Capacity: 160 Ah.
- Autonomy: position timeline and on-board sun ephemeris for greater than 2 weeks nominal autonomous operations.
- 64 kbps uplink, 1 Mbps downlink S-band command and control link (with ranging).
- 2 x 280 Mbps X-band science data downlink.
- 384 Gbit solid state mass memory.