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Experiment

Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)

Last Updated: March 30, 2007

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

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)

Antenna (EFM)

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.


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)

Submillimeter Optics
Designed Antenna Pattern (637 GHz)

  • 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.


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

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).

VMR
Expected Resolution of SMILES Data
Upper Right:For a single scan data available in each 53 seconds
Lower Right:For a zonal averaged data available in each day
Resolution in VMR
 
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