“SMILES” aboard the ISS-JEM “KIBO” SMILES is a science and technology mission that is to be aboard the exposed facility of the ISS-JEM “KIBO” in 2005. Scientifically it is aimed at global observations of trace gases in the stratosphere that contribute ozone depletion. For the purpose, SMILES incorporates a new sensor technology for submillimeter-wave observations. So it is also a technology demonstration mission. SMILES

SMILES to Probe the Atmosphere SMILES is a completely passive sensor to detect thermal emissions of trace gases at submillimeter wavelengths. Molecular species in the atmosphere have lots of emission lines in the newly developed radio region. With a sensitive submillimeter sensor, we can probe the very site of ozone depletion in a global scale without being affected by the solar illumination. SMILES probes the atmosphere in the limb direction of the Earth with an antenna scanning the atmosphere vertically. By doing so, it can be sensitive to the height distribution of trace gases.

Ozone Depletion and the Role of “ClO” Ozone depletion is not a phenomenon that occurs only in the polar regions. It is clearly observed also in mid-latitudes in the past 20 years. Ozone is efficiently dissociated by catalysts such as chlorine monoxide (ClO), bromine monoxide (BrO) and other molecules. A pioneering millimeter-wave limb-emission sounder, UARS-MLS, has shown this mechanism occurring in the polar regions. SMILES will investigate such ozone-depleting mechanism in low- and mid-latitudes with high-precision data expected by its advanced submillimeter sensor. Ozone depletion is clear also in mid-latitude. (http://www.epa.gov/ozone/science/) “ClO” molecules destroy ozone in the Antarctic. (UARS-MLS)

Spectral Profiles at Submillimeter-waves Around 20 molecular species have emission lines in the submillimeter bands observed by SMILES, some are strong and others weak. The spectral profiles of those lines show variations dependent on the tangent altitude of the line-of-sight. This is due to the change of atmospheric pressure and the molecular content of the atmosphere. From these data we can derive the height distribution of each molecule. SMILES looks in “limb” directions of various tangent heights.

Submillimeter-wave Sensor at –269 C SMILES Superconductive Device: Nb/AlOx/Nb 640 GHz SIS Mixer 0.4 mm High sensitivity of SMILES is attributed to a superconductive sensor working at 4 Kelvin, i.e., –269 deg C. The sensor, which is called “SIS mixer,” is widely used as an ultra low-noise sensor for ground-based radio telescopes. In space, however, SMILES is the first attempt to use this attractive technology. SMILES incorporates a mechanical cooler to accommodate the sensor at 4 Kelvin. This cooler makes it possible to use the cryogenic sensor in space without a huge tank of liquid helium. 4 K 20 K 100 K 4 K Mechanical Cooler SIS: Superconductor-Insulator-Superconductor

Data-base for Predicting Ozone Trend SMILES covers latitudes of 65 N to 38 S. Thanks to its sensitivity, SMILES can produce a global map of ozone, HCl, ClO and some other molecules every day. Although BrO emissions are very weak, SMILES will be able to derive its latitudinal distribution averaged for a day. The output of SMILES will be fully used to check the atmospheric model. SMILES will thus contribute to predicting the future ozone trend. SMILES outputs the altitude distribution and its variation for trace gases.