Sentinel-3 Design

The Sentinel-3 mission consists of two satellites - Sentinel-3A and Sentinel-3B.

Sentinel details

Both Sentinel-3 satellites are 3-axis stabilised based on the new generation of avionics for the TAS-F LEO (Low Earth Orbit) platform. The nominal pointing is towards the local normal and yaw steering to compensate for the Earth rotation affecting the optical observations.

They have operational lifetimes of seven years, further details of all instrument platforms can be found in respective user handbooks.

Technical details of the platforms

Technical details

The table below lists the technical details of the Sentinel-3A and Sentinel-3B satellite platforms.

Parameters Details
Stowed Dimension & Mass 3.7 x 2.2 x 2.2 m³, 1250 kg
Solar Array Power 2.1 kW
Orbit Repeat Cycle 385 orbits in 27 days
Ground Track Control +/- 1 km
Ground Stations Kiruna for S-Band TTC (2 passes per day)
Svalbard for X-band dump (every orbit)
On-demand/Optional stations for X-Band local dump
S-Band Downlink 1 Mbit/s (or 123 kbit/s “Low Rate”) Packet-based
S-Band Uplink 64 kbit/s (16 kbit/s usable)
X-Band Downlink 2 x 280 Mbit/s
Platform Mass Memory 72 hours recording of all HKTM
Payload Mass Memory 576 Gbit (2 orbits storage)
Onboard Command Queues Position-based Schedule
Time-based Schedule
On-board Time Synchronised with UTC by GPS
AOCS Sensors (Nominal Mode) Star Trackers, GPS
AOCS Sensors (Safe Mode) Sun Acquisition Sensors, Coarse Gyroscopes, Magnetometer
Attitude Actuators (Nominal Mode) Reaction Wheels, Magnetotorquers
Attitude Actuators (Safe Mode) Reaction Wheels, Magnetotorquers
Propulsion 4 x 1N Thrusters (off-modulated), 116 kg hydrazine
 

Ocean and Land Colour Instrument (OLCI)

OLCI observes in 21 narrow spectral bands of the visible and near infrared spectrum at a resolution of 300 m.

With a swath width of 1270 km and five tilted cameras, which are specially optimised to reduce sun glint, the ocean and land colour instrument provides improved global coverage of ocean colour — in less than two days with two Sentinel-3 satellites in operation.

It expands the medium resolution ocean colour measurements collected by Envisat’s MERIS instrument (2002–2012).

Sea and Land Surface Temperature Radiometer (SLSTR)

The dual view, nine-channel SLSTR has a resolution of 500 m in the visible and shortwave infrared and 1 km in the thermal infrared and include two channels optimised for fire monitoring.

It continues and further improves the sea surface temperature record collected by the AATSR instruments flown on ERS and Envisat satellites. The aim is to collect highly accurate measurements to provide a reference dataset for other sea surface temperature missions on other satellites.

The design of SLSTR is improved from the previous AATSR instruments to include a wider swath of 1400 km in the nadir view and 740 km in the dual view.

As well as monitoring SST the instrument also monitors sea and land ice temperature, atmospheric aerosols and cloud properties and fires (both over land and for ocean gas flares).

Synthetic Aperture Radar Altimeter (SRAL)

The dual-frequency (Ku and C-band) Synthetic Aperture Radar Altimeter (SRAL) on board Sentinel-3 provides sea surface topography measurements in SAR (Delayed Doppler) mode, i.e. with a spatial resolution as narrow as 300 m. SRAL is used to determine sea and lake surface height, significant wave height, surface wind speed, and sea ice height and thickness.

SRAL is supported by a microwave radiometer for atmospheric correction and by a Precise Orbital Determination package (POD) to determine the altimeters position in space with pinpoint accuracy.

Precise Orbital Determination package (POD)

SRAL requires high accuracy radial orbit detection to meet its operational requirements. The POD package consists of three measurement systems that serve this purpose: the Global Navigation by Satellite System (GNSS), Doppler Orbitography by Radiopositioning Integrated by Satellite (DORIS), and a Laser RetroReflector (LRR).

Microwave radiometer (MWR)

The MWR is a two-channel passive microwave system that records brightness temperatures at 23.8 GHz and 36.5 GHz, providing information on respective atmospheric water vapour and liquid water content. These brightness temperatures are used with a radiative transfer model to infer the amount of water vapour and liquid water in the sub-satellite atmospheric column, and, thus, to calculate the WTC (correction to range) and the atmospheric attenuation (correction to σo) during ground station processing.

Ground Segment

The Sentinel-3 Ground Segment comprises of a number of interconnected sites with different responsibilities.

Ground stations, both S-Band and X-Band, are shared with Sentinel 1, 2 and other missions, and are managed by ESA as part of their service to EUMETSAT, under the respective agreements with the EC.

EUMETSAT has the responsibility for the operation of the Sentinel-3 Marine Centre, as well as the operation of the Flight Operations Segment, spacecraft operations, for routine operations.

Ground Segment Sites
Function Site
Core Ground Stations KSAT, Svalbard
Land Processing and Archiving Centres DLR, Oberpfaffenhofen (for OCLI)
ACRI, Sophia - Antipolis (for SLSTR and Synergy)
CLS, Toulouse (for SRAL)
Marine Centre EUMETSAT, Darmstadt
Payload Data Management Centre ESRIN, Frascati
Mission Performance Centre ACRI, Sophia - Antipolis
Precise Orbit Determination Service GMV, Madrid
Flight Operations Segment LEOP + Commissioning ESOC, Darmstadt
Flight Operations Segment Routine Operations EUMETSAT, Darmstadt

Core Ground Segment Elements

Ground Segment Overview
 
Ground Segment Overview (click to see details)
  • ESA and EUMETSAT Flight Operations Segment (FOSs): responsible for all aspects of the Sentinel satellite flight operations, including spacecraft monitoring and control.
  • Core Ground Stations: where the Sentinel X-Band data are down linked and the NRT land products are generated.
  • Offline Land Processing and Archiving Centres (PACs): where systematic offline data processing is performed. All data products are archived in a long term archive and are available online in a rolling archive for access by users.
  • Marine Centre: where NRT and offline marine products are systematically generated and the marine calibration, validation, quality control and mission performance activities are carried out. Marine Products/Data are archived in a long-term archive, made available in an online rolling archive and via EUMETCast.
  • Mission Performance Centre (MPC): responsible for land calibration, validation, quality control and mission performance activities and for support to the marine mission performance activities.
  • Sentinel Precise Orbit Determination (POD) service: providing precise orbits for the offline processing.
  • Copernicus Space Component Wide Area Network (CSC WAN): connects all centres and provides disseminated data products to the land users.
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