  We have developed an imaging Fourier transform spectrometer (FTS) for
space-based far-infrared astronomical observations. The FTS employs a newly
developed photoconductive detector arrays with a capacitive trans-impedance
amplifier, which makes the FTS a completely unique instrument. The FTS was
installed as a function of the far-infrared instrument (FIS: Far-Infrared
Surveyor) on the Japanese astronomical satellite, AKARI, which was launched on
February 21, 2006 (UT) from the Uchinoura Space Center. The FIS-FTS had been
operated for more than one year before liquid helium ran out on August 26,
2007. The FIS-FTS was operated nearly six hundreds times, which corresponds to
more than one hundred hours of astronomical observations and almost the same
amount of time for calibrations. As expected from laboratory measurements, the
FIS-FTS performed well and has produced a large set of astronomical data for
valuable objects. Meanwhile, it becomes clear that the detector transient
effect is a considerable factor for FTSs with photoconductive detectors. In
this paper, the instrumentation of the FIS-FTS and interesting phenomena
related to FTS using photoconductive detectors are described, and future
applications of this kind of FTS system are discussed.
