We report on the performance of lumped-elements Kinetic Inductance Detector (KID) arrays for mm and sub-mm wavelengths, operated at 0.3 K during the stratospheric flight of the OLIMPO payload, at an altitude of 37.8 km. We find that the detectors can be tuned in-flight, and their performance is robust against radiative background changes due to varying telescope elevation. We also find that the noise equivalent power of the detectors in flight is significantly reduced with respect to the one measured in the laboratory, and close to photon-noise limited performance. The effect of primary cosmic rays crossing the detector is found to be consistent with the expected ionization energy loss with phonon-mediated energy transfer from the ionization sites to the resonators. In the OLIMPO detector arrays, at float, cosmic ray events affect less than 4% of the detector samplings for all the pixels of all the arrays, and less than 1% of the samplings for most of the pixels. These results are also representative of what one can expect from primary cosmic rays in a satellite mission with similar KIDs and instrument environment.

Millimetron is a Russian-led 12 m diameter submillimeter and far-infrared space observatory which is included in the Space Plan of the Russian Federation for launch around 2017. With its large collecting area and state-of-the-art receivers, it will enable unique science and allow at least one order of magnitude improvement with respect to the Herschel Space Observatory. Millimetron will be operated in two basic observing modes: as a single-dish observatory, and as an element of a groundExp Astron (2009) space very long baseline interferometry (VLBI) system. As single-dish, angular resolutions on the order of 3 to 12 arc sec will be achieved and spectral resolutions of up to a million employing heterodyne techniques. As VLBI antenna, the chosen elliptical orbit will provide extremely large VLBI baselines (beyond 300,000 km) resulting in micro-arc second angular resolution.

We present the theoretical fundamentals and features of development of cryogenic cooling systems for receivers in the range 0.1-1 THz. The results of development of cryogenic systems for sustaining the temperatures in the range from 150 to 0.3 K are considered. The systems are based on a wide class of cryogenic devices employing various principles and thermodynamic cycles. The described developments are based on the unity of the thermal and radiophysical complexes of the cooled receiver and the cryosystem. The discussed cryosystems are specifically used to cool receivers with the mixers based on Schottky-barrier diodes and superconductor-insulatorsuperconductor structures, as well as on various bolometers. The problems of heat insulation against the surrounding medium and heat transfer from the receiver to the cryogenic liquid, the features of the input/output of signals in a wide frequency range and of mechanical vacuum-tight thermo-decoupled inputs to the cryostat, and the control systems for cryoelectronic complexes are considered in detail. The presented results can be used for both laboratory experiments and practical applications in radio astronomy, atmosphere spectroscopy, and other fields.

We describe the in-flight performance of the horn-coupled Lumped Element Kinetic Inductance Detector arrays of the balloon-borne OLIMPO experiment. These arrays have been designed to match the spectral bands of OLIMPO: 150, 250, 350, and 460 GHz, and they have been operated at 0.3 K and at an altitude of 37.8 km during the stratospheric flight of the OLIMPO payload, in Summer 2018. During the first hours of flight, we tuned the detectors and verified their large dynamics under the radiative background variations due to elevation increase of the telescope and to the insertion of the plug-in room-temperature differential Fourier transform spectrometer into the optical chain. We have found that the detector noise equivalent powers are close to be photon-noise limited and lower than those measured on the ground. Moreover, the data contamination due to primary cosmic rays hitting the arrays is less than 3% for all the pixels of all the arrays, and less than 1% for most of the pixels. These results can be considered the first step of KID technology validation in a representative space environment.

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