  Future astrophysics and cosmic microwave background space missions operating
in the far-infrared to millimetre part of the spectrum will require very large
arrays of ultra-sensitive detectors in combination with high multiplexing
factors and efficient low-noise and low-power readout systems. We have
developed a demonstrator system suitable for such applications. The system
combines a 961 pixel imaging array based upon Microwave Kinetic Inductance
Detectors (MKIDs) with a readout system capable of reading out all pixels
simultaneously with only one readout cable pair and a single cryogenic
amplifier. We evaluate, in a representative environment, the system performance
in terms of sensitivity, dynamic range, optical efficiency, cosmic ray
rejection, pixel-pixel crosstalk and overall yield at at an observation centre
frequency of 850 GHz and 20% fractional bandwidth. The overall system has an
excellent sensitivity, with an average detector sensitivity NEPdet=3x10^-19
W/rt(Hz) measured using a thermal calibration source. At a loading power per
pixel of 50fW we demonstrate white, photon noise limited detector noise down to
300 mHz. The dynamic range would allow the detection of 1 Jy bright sources
within the field of view without tuning the readout of the detectors. The
expected dead time due to cosmic ray interactions, when operated in an L2 or a
similar far-Earth orbit, is found to be <4%. Additionally, the achieved pixel
yield is 83% and the crosstalk between the pixels is <-30dB. This demonstrates
that MKID technology can provide multiplexing ratios on the order of a 1000
with state-of-the-art single pixel performance, and that the technology is now
mature enough to be considered for future space based observatories and
experiments.
