Microwave kinetic inductance detectors (MKIDs) are the most attractive radiation detectors for far-infrared and sub-mm astronomy. They combine ultimate sensitivity with the possibility to create very large detector arrays, in excess of 10000 pixels. This is possible by reading-out the arrays using RF frequency division multiplexing, which allows multiplexing ratios in excess of 1000 pixels per readout line. We describe a novel readout system for large arrays of MKIDs, operating in a 2-GHz band in the 4-8-GHz range. The readout, which is a combination of a digital frontand back-end and an analog upconverter and downconverter system, can read out up to 4000 detectors simultaneously with 1-kHz data rate. The system achieves a readout noise power spectral density of -98 dBc/Hz while reading 1000 carriers simultaneously, which scales linear with the number of carriers. We demonstrate that 4000 stateof-the-art aluminium-NbTiN MKIDs can be read out without deteriorating their intrinsic performance.

SPACEKIDS, a European Union FP-7 project, has recently been completed. It has focused on developing kinetic inductance detector (KID) arrays and demonstrating their suitability for space applications at far infrared and submillimetre wavelengths. KID arrays have been developed for both low-background (typical of astrophysical applications) and high-background (typical of Earth-observation applications), based on performance specifications derived from the science requirements of representative potential future missions. KID pixel and array designs have been developed, together with readout electronics necessary to read out large numbers of pixels. Two laboratory demonstrator systems have been built and used for comprehensive evaluation of large-format array characteristics and performance in environments representative of both astronomy and Earth observing applications. We present an overview of the SPACEKIDS project and a summary of its main results and conclusions.