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Objectives
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This work was carried out in the frame of development and qualification of key equipments for application in payloads or platform (sub) systems to enhance their capabilities or to match specific opportunities in the multimedia domain. It aimed at the development and qualification of a Coarse Sun Sensor (CSS), suitable for the Attitude and Orbit Control Subsystem of telecom-satellite platforms for multi-media applications, like the Spacebus-4000 platform. The sensor is a European product, built with components free of export restrictions imposed by US ITAR legislation.
The Coarse Sun Sensor (CSS) from TNO – sometimes called Sun Acquisition Sensor (SAS) – is a pyramid sun sensor, which provides 2-axis coarse sun position information in the form of analogue voltage signals in a near hemispherical FOV.
The sensor consists of an aluminium structure with a truncated pyramid in the centre of shadowing rims. On the four faces of the pyramid, dual chip detector devices are installed, such that their lines of sight are inclined with respect to the boresight viewing direction and at 90 degrees apart (see pictures). In this way the four dual-detectors span a hemispherical FOV, constrained by the shadow from the outer rims of the structure. These rims can be shaped to specific mission requirements by strap-on baffles, attached to the main structure of the sensor. The detectors act as optical sensing elements, sensitive to sunlight. The dual construction leads to built-in redundancy of the sensor outputs.
Challenges
The key issue of the CSS project was to produce a fully European Coarse Sun Sensor, based on an European detector. Furthermore, the qualification program of the European detector included a 10,000 thermal cycles test between extreme temperatures of -90°C to +125°C, which makes the Coarse Sun Sensor equipped with these detectors compliant with the requirements of the long-duration major European telecommunication and multi-media satellite platforms. This is further supported by the use of epitaxial silicon material for the detector, which makes the sensor radiation hardened.
Plan
The development and qualification of the European dual chip detector has been successfully performed by OSI Norway in 2008 under TNO specification. The newly developed detectors have then been integrated by TNO in the Coarse Sun Sensor EQM for equipment level qualification testing to comply with requirements obtained from Spacebus-4000 and Alphabus mission types. This test program was successfully completed by TNO early in 2009 and the test results have been successfully reviewed at system level by Thales in spring the same year, confirming the compliance of this CSS with both the SB-4000 and Alphabus multimedia platforms.
Current Status
The program has been successfully completed early 2009. The Final Presentation was organised at Estec in October 2009.
