- Buyers Guide
Pre-launch preparations for the Sentinel-1A satellite, carrying an Airbus Defence and Space built radar instrument, are in full swing at Europe´s Kourou Spaceport in French Guiana. The satellite, built by Thales Alenia Space Italy as prime contractor, set to be launched on 3 April 2014 by a Soyuz launcher, will mark a new era of Earth observation.
Sentinel-1A carries the Synthetic Aperture Radar (SAR) Antenna Subsystem (SAS) which will be able to acquire an immense amount of data due to its continuous operation capability. Although complex data compression mechanism are provided, the Sentinel-1A satellite communication system will deliver up to 8,000 Gbits of imagery data every day for the next 7 years.
The antenna is made up of 5 panels. Four of them are folded down for launch onto a support frame on the sides of the satellite and are released and deployed in orbit. Integrated on these panels are 280 dual polarised small transmitters delivering a total RF signal of just over 5 kW. These transmitters and their associated receive elements which provide all the electronic beam steering capabilities are supplied by Thales Alenia Space and are implemented as Transmit/receive multichip hybrid modules integrated into Electronic Front-End (EFE) equipment. By steering the beam across the observation track in a series of 80 km wide strips next to each other on the ground, a medium resolution image for wider swaths of up to 400 km can be assembled. The high transmit power presented a thermal design challenge in addition to the already complex mechanical design task of creating the required highly stable structure of the 800kg antenna.
Its counterpart, i.e. the SAR Electronics Sub-system (SES) has to drive the antenna and has to provide the complex timing and control of the radar creating its highly stable radar signals. It is also the unit upon which the synchronization and imaging control responsibility falls. The timing has to ensure a 2.5 m pixel positioning accuracy on a 400 km wide target nearly 1000 km away on the ground while travelling at 7 km per second. This was the driver to implement at mission and satellite level a sophisticated mechanism for extremely accurate real time orbit prediction on board, and determination of very precise timing to synchronize the SAR image data take acquisition.
To deliver the radar part of the mission’s performance, the Space Systems teams built and tested at Friedrichshafen (Germany) a 12.3 m x 0.9 m antenna, electronically integrated with the SAR Electronics Subsystem designed in Portsmouth (UK), which provides the signal processing, timing and system control. Sentinel-1A, a SAR imaging satellite, will be joined by its’ twin (Sentinel-1B) around the end of next year to form the European Radar Observatory. This will complete the Sentinel-1polar orbiting constellation, which will significantly improve accessibility and time performance of the overall system (revisit and response time), further reinforcing the system capability to provide continuous all-weather round the clock imagery for marine, land monitoring and emergency services.
The two SAR instruments, which make these satellites the flexible and powerful tools that they are, were developed by Airbus Defence and Space who have a long history of Earth observation Radar instruments for the European Space Agency ESA. As well as having had overall industrial responsibility for the European ERS-1/ERS-2 satellites launched in 1991 and 1995 respectively and Envisat launched in 2001, Airbus Defence and Space has also developed and built the AMI (ERS), ASAR (Envisat) and ASCAT (MetOp) radar payloads. On top of this, Airbus Defence and Space has been the prime contractor for the German TerraSAR-X and TanDEM-X radar satellite projects.