Interferometric Cartwheel payload: development status and current issues

The CNES interferometric cartwheel (ICW) system is based on a microsatellite constellation placed close enough to a conventional SAR radar to take opportunity from its Earth surface illumination. The microsatellite relative positions in time are such that at any moment, a vertical or an horizontal baseline may be constituted from a selection among the satellites for interferometric purposes. Due to the simultaneous acquisition of radar echoes on the various microsatellites, the expected performances are optimal with regard to time decorrelation effects. The microsatellite context will also allow for an overall cost optimization, these two points justifying the concept potential interest. A first application is expected to be launched by 2005, as a companion mission to the ASAR C-band synthetic aperture radar onboard the ESA ENVISAT satellite. This paper is focused on the microsatellite payload, which consists in a passive receiver, decomposed in : (i) a reflector based antenna sub-system, (ii) a RF analog receiver, (iii) a digital sub-system performing signal digitization, pre-processing, compression, and storing, (iv) a telemetry module, (v) a GPS receiver. The current interest for the ICW concept, and the existence of various possible missions in cooperation with SAR satellites, operating in L, C, and possibly X band has led to a search for genericity in the payload design, allowing it to evolve easily from a system concept to another. Special emphasis is given here on this genericity issue, and on Alcatel´s direct heritage for the payload development