Pleiades

The PLEIADES optic component is composed of two "small satellites" (mass of one ton) offering a spatial resolution at nadir of 0.7 m and a field of view of 20 km. Their great agility enables a daily access all over the world, essentially for defence and civil security applications, and a coverage capacity necessary for the cartography kind of applications at scales better than those accessible to SPOT family satellites. Moreover, PLEIADES will have stereoscopic acquisition capacity to meet the fine cartography needs, notably in urban regions, and to bring more information when used with aerial photography.


HISTORY

As to international satellite company, SPOT IMAGE of France is going to launch Pleades sequence satellites in 2005.


SPECIFICATIONS

The main design drivers for the satellite architecture are the image quality, the agility and the image location accuracy. The image quality drives the instrument size. A high agility requires a very compact design, with a few stiff appendages. As a consequence, the instrument is integrated inside the bus. A high image location accuracy is achieved by minimizing the interface between the instrument and the bus. The star trackers and the gyroscope heads are directly supported by the instrument to avoid any thermal distortion that could be induced by the bus.

The bus structure is build on an hexagonal shape, with three solar arrays at 120 deg, and three star trackers in a quasi tetrahedron configuration, optimizing the attitude determination accuracy. This configuration authorizes accommodation of the instrument focal plane radiator for maximum heat dissipation. An antenna support structure is used to carry the Earth-pointing antennas and for the instrument baffle.

The solar arrays are mounted directly on the bus structure without any drive mechanism to ensure a maximum stability. Their first flexion mode frequency is increased by the use of stiffeners when deployed. Moreover the high compacity and low mass of the satellite (<1000 kg) make it compatible with a large series of low cost small launchers (among them Soyouz and Rockot). The two Pleiades satellites will be launched by Soyouz from Europe's spaceport in Kourou, French Guiana.

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