Masumichi Seta

Submillimeter Limb-emission Sounder JEM/SMILES aboard the Space Station

A submillimeter limb-emission sounder, that is to be aboard the Japanese Experiment Module (JEM, dubbed as KIBO) at the International Space Station, has been designed. This payload, Superconducting Submillimeter-wave Limb-emission Sounder (SMILES), is aimed at global mappings of stratospheric trace gases by means of the most sensitive submillimeter receiver ever operated in space. Such sensitivity is ascribed to a Superconductor-Insulator- Superconductor (SIS) mixer, which is operated at 4.5 K in a dedicated cryostat combined with a mechanical cooler. SMILES will observe ozone-depletion-related molecules such as ClO, Hcl, HO2, HNO3, BrO and O3 in the frequency bands at 624.32-626.32 GHz and 649.12-650.32 GHz. A scanning antenna will cover tangent altitudes from 10 to 60 km in every 53 seconds, while tracing the latitudes form 38 S to 65 N along its orbit. This global coverage makes SMILES a useful tool of observing the low- and mid- latitudinal areas as well as the Arctic peripheral region. The molecular emissions will be detected by two units of acousto-optic spectrometers (AOS), each of which has coverage of 1.2 GHz with a resolution of 1.8 MHz. This high-resolution spectroscopy will allow us to detect weak emission lines attributing to less-abundant species.

Mechanical cooler and cryostat for submillimeter SIS mixer receiver in space

This paper reports on a space-qualified cooling system for submillimeter SIS mixer receiver (SIS: superconductor- insulator-superconductor). Designed cooling capacity of the system is 20 mW at 4.5 K, 200 mW at 20 K, and 1000 mW at 100 K. The combination of two-stage Stirling cooler and Joule- Thomson one has demonstrated the capacity with a power consumption of less than 300 W, including losses of drive electronics. The cryostat has a thermal insulation structure of S2-GFRP straps to fasten its 100 K stage. 20 K stage of the cryostat is held with GFRP pipes on the 100 K stage, while 4 K stage is supported with CFRP pipes on the 20 K stage. The cooling system accommodates two SIS mixers at 4.5 K, two IF amplifiers at 20 K, and two more IF amplifiers at 100 K. The mass of the cooling system is 40 kg for the mechanical cooler itself, 26 kg for the cryostat, and 24 kg for the driver electronics. The system has been developed for a 640 GHz receiver for an atmospheric limb-emission sounder SMILES, which is to be aboard the International Space Station in 2005. The engineering model of the system has been built and tested successfully.

JEM/SMILES limb-sounding of stratospheric trace species I: retrieval algorithm and simulator

In order to estimate measurement capability of the Superconducting Submillimter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) and to clarify the scientific impacts of the JEM/SMILES, we are developing the JEM/SMILES simulator. The simulator consists of the forward model and the inversion model. The forward model calculates a brightness temperature by applying the radiative transfer formula to a limb sounding geometry and simulates the effects of the JEM/SMILES sensor characteristics including optics superconductor-insulator-superconductor (SIS) mixers, Acousto-Optical Spectrometer (AOS), and so on, to it. Because it is important to estimate the effects of the sensor for the retrieval, we develop carefully simulated sensor model. The forward model also calculates weighting functions of molecular, the temperature, the pressure and so on. This paper describes how the brightness temperature and weighting functions are calculated in the forward model and how the effects of the sensor are taken into account in the simulator, and finally shows how the optical estimation method (OEM) is applied to our retrieval model.

Demonstration of superconducting sub-millimeter-wave limb emission sounder (SMILES) for observing trace gases in the middle atmosphere using the exposed facility of the Japanese experimental module (JEM) of the international space station

The sub-millimeter wavelength region is advantageous for high-precision observations of trace species in the stratosphere. A Superconducting Sub-Millimeter-wave Limb Emission Sounder (SMILES) is scheduled to demonstrate the measurements of extremely faint sub-millimeter-wave emissions of the atmospheric trace gases on the Exposed Facility (EF) of the Japanese Experimental Module (JEM) of the International Space Station in 2003. The applications of superconductivity and mechanical 4K-refrigerator in space will be demonstrated in the experiment. JEM/SMILES obtains the diurnal and seasonal variability in the global three-dimensional distributions of the stratospheric trace gases for quantitative understanding of the stratospheric ozone depletion and its effect on the climate change with respect to the relationships among chemical reaction processes and their relationships with atmospheric dynamics. JEM/SMILES utilizes the 640GHz band to measure the vertical profiles of trace gases involved in the stratospher...

Development of a Superconducting Submillimeter-Wave Limb Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS)

NASDA and CRL are planning to develop a spaceborne SMILES, which is to be installed in the Exposed Facility (EF) on the JEM of the ISS. By observing gases such as ClO, HCl, NO, N2O, HO2 and BrO in the stratosphere, JEM/SMILES can trace the chemical reactions concerning the ozone depletion and climate change. Global distribution of those gases will be mapped with a height resolution of about 2 km. JEM/SMILES receives low-intensity signals from those gases with highly sensitive SIS (Superconductor-Insulator-Superconductor) mixers at 640 GHz, which are cooled to 4.2 K by a space-qualified mechanical cooler. The mission target is to demonstrate the effectiveness of the submillimeter-wave limb emission sounding and to establish space applicability of the low-noise SIS mixers and a mechanical 4-K cooler. JEM/SMILES is expected to be launched in 2003, and the experiments will last a year or more.