Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)

Mission Objectives

Space demonstration of a submillimeter sensor technology based on a superconductive mixer and 4-Kelvin mechanical cooler
Experiments of submillimeter limb-emission sounding of the atmosphere
Global observation of trace gases in the stratosphere and contribution to the atmospheric sciences

Specifications

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Observation Band	640 GHzBand
Target Gases	O₃, HCI, CIO, HO₂, H₂O₂, HOCI, BrO, HNO₃, SO₂,etc.
Altitude Range	10-60 km
Latitude Range	65N - 38S
Instruments	Offset Cassegrain Antenna SIS Mixer Receiver 4-Kelvin Mechanical Cooler Acousto-optical Spectrometer
Frequency Resolution	1.8 MHz
Sensitivity	1 K(rms) in a single scan

Submillimeter-Wave Sensor Operated at 4K in the shielded cryostat

SMILES instruments are protected against the ISS environmental electric field by payload panels designed as an electric shield (shielding of 14 dB).
Cryo-electronics unit, which deals with signal at lowest power levels, are shielded more by the cryostat (shielding of 40 dB).

SIS: Su~erconductor-Insulator-Su~erconduct

SMILES 640GHz SIS Reciever in the shielded crvostat

Stirling : 60-80W (AC 15Hz)
J-T Cooler : 30-37 W (AC 30 Hz)

Superconductive SIS mixer receivers have some 20 times higher sensitivity (lower noise) than conventional Schottky-barrier-diode (SBD) mixer receivers for frequencies less than 700 GHz. Sensitivity will be limited by the quantum limited noise (hf/k).

High-Quality Subsystem

Submillimeter Antenna (ANT)

SMILES's submillimeter antenna adpots an elliptical mirror with dimensions of 40 cm in vertical direction and 20 cm in horizontal. The mirror is not so large, but it is required to be highly accurate in shape for generating a high-quality beam at submillimeter wavelengths.

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Obserbation Frequency	624.32 - 650.32 GHz
Surface Accuracy	45 pm (rms)
HPBW	0.09 deg (El) x 0.18 deg (Az)
Beam Efficiency	>0.90 (2.5^*HPBW)

Acousto-Optical Spectrometer (AOS)

SMILES is equipped with two units of AOS, each has 1,500 channels over 1,200 MHz. This enables detection of more than 20 species involved in the atmospheric spectra.

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Input Frequency	1.55 - 2.75 GHz
Frequency Resolution	1.8 MHz (FWHM)
Channel Spacing	0.8 MHz / channel
Unit Averaging Period	0.47 sec

Measured Frequency resolution of the AOS (EM)

Global Data of Trace Gases with High Resolution

Global Coverage

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Covered Latitudes	68N - 35s (ISS Yaw: +15 deg) 65N - 38s (ISS Yaw: 0 deg) 61N - 42s (ISS Yaw: -15 deg)
T'rajectory for 24 Hours
Blue	ISS-SMILES Orbit
Red Dots	Sampled Area

Major Species of SMILES

Expected altitude profile of the volume-mixing-ratio is shown for nine major SMILES species according to a typical mid-latitude model atmosphere (45N).