Sentinel-3 Design

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

Sentinel details

Platform

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

They will both have operational lifetimes of seven years.

The table below lists the technical details of the Seintiel-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
 

Instruments

Sentinel-3 carries several instruments, the three from which EUMETSAT collects data and disseminates are:

Ocean and Land Colour Instrument (OLCI)

OLCI will observe 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 will provide improved global coverage of ocean colour — in less than two days with two Sentinel-3 satellites in operation.

It will expand the medium resolution ocean colour measurements collected by Envisat’s MERIS instrument (2002-2012).

Sentinel details

Sea and Land Surface Temperature Radiometer (SLSTR)

The dual view, nine-channel SLSTR will have 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 will continue and further improve 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 will also monitor 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 Synthetic Aperture Radar Altimeter (SRAL) on board Sentinel-3 will provide sea surface topography measurements in SAR mode, i.e. with a spatial resolution as narrow as 300 m.

SRAL is supported by a microwave radiometer for atmospheric correction and by a DORIS receiver, Global Navigation Satellite System, and laser retroreflector to determine its position in space with pinpoint accuracy.

The SRAL will be used to determine sea and lake surface height, significant wave height, surface wind speed, and sea ice height and thickness.

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