Overview

SMILES (Superconducting Submillimeter-Wave Limb-Emission Sounder) is a mission aimed at observing the distribution of trace molecules in the Earth’s atmosphere with high precision. This mission was developed as a joint project between JAXA (Japan Aerospace Exploration Agency) and NICT (National Institute of Information and Communications Technology).

SMILES was installed on the Exposed Facility (JEM-EF) of the Japanese Experiment Module “Kibo” of the International Space Station (ISS) and conducted observations from October 12, 2009 to April 21, 2010.

From an orbit that circles the Earth in about 90 minutes, it observed the Earth’s atmospheric layer at altitudes of 10 to 60 km between 65 degrees north and 38 degrees south.

Observation Instruments

SMILES is the first observational instrument in space to use a superconducting low-noise receiver and a mechanical 4K refrigerator.
The instrument uses submillimeter waves to capture electromagnetic waves emitted by trace molecules in the atmosphere.
By pointing the antenna toward the limb of the Earth and moving it up and down, the altitude distribution of trace molecules can be observed in detail with an altitude resolution of about 3 km.
The atmospheric limb radiation collected by the antenna is guided to the Submillimeter Receiver (SRX), where the received submillimeter-wave signal is mixed with a reference signal (637.32 GHz) from a submillimeter-wave local oscillator (SLO) and guided to the SIS mixer via a pseudo-optical system consisting of a focusing mirror, a wire grid, and a sideband filter.
There are two SIS mixers, one for the upper sideband (USB: 649.12 GHz to 650.32 GHz) and one for the lower sideband (LSB: 624.32 GHz to 626.32 GHz), operating simultaneously to downconvert both sidebands to the intermediate frequency (IF) band between 11 GHz and 13 GHz.
The IF signal is further downconverted and amplified in an intermediate frequency amplifier (IFA) and then analyzed by two acousto-optical spectrometers within the Radio Spectrometer (AOS).

SMILES will observe approximately 100 points per orbit and approximately 1,600 points per day. This will enable detailed monitoring of the Earth’s atmospheric environment. The observational data will provide important information for understanding the variations in the ozone layer and the dynamics of other atmospheric trace molecules.

Achievements

SMILES observational data provided valuable information on the variation of the ozone layer and the distribution of trace molecules in the atmosphere, which has improved our understanding of the Earth’s atmospheric environment and provided useful data for environmental protection and climate change measures. In particular, it provided important data for evaluating the effectiveness of international regulations on substances that deplete the ozone layer.