Home > Instruments onboard SPICA

Large-aperture Cryogenic Telescope

SPICA will employ a 2.5 m diameter Ritchey-Chretien telescope with a field of view of 30 arc minutes, whose mirror is polished to achieve the diffraction limit at the wavelength of λ = 20 μm. The entire telescope will be kept cooled to below 8 K (-265 ℃) during observations to decrease its own infrared radiation and thus achieve high sensitivity.

This large telescope is required to be lightweight. To obtain clear images, the telescope also needs to be made of a material having small distortion. Hence as the material for the telescope, SPICA will adopt light and tough Silicon Carbide (SiC), which has been successfully used in previous missions such as AKARI and Hershel. Thus, despite the largeness of the telescope, its total mass is estimated to be no more than about 600 kg.

ESA (The European Space Agency) is responsible for development of the telescope.

Fig. 1   Schematic view of the SPICA telescope assembly

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Focal Plane Instruments

The following two focal plane instruments will be onboard SPICA: the SMI (SPICA Mid-Infrared Instrument) and the SAFARI (SpicA FAR-infrared Instrument).

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SPICA Mid-infrared Instrument; SMI

A number of dust band emissions are found in the mid-infrared range (e.g., λ = 20 - 40 μm). Among these, observations of nearby galaxies have shown that band emissions from PAH (Poly-Aromatic Hydrocarbon) dust are an indicator of star formation activity. In spite of this importance, a high-sensitivity observation in the mid-infrared band has yet to be performed.

The SMI is designed to conduct imaging and spectroscopy in λ = 20 - 40 μm with a unprecedentedly high sensitivity. Three channels consisting of SMI - LRS, SMI - MRS and SMI - HRS covers this wavelength range. The SMI Consortium consisting of mainly ISAS and Japanese universities is responsible for development of the SMI.

  • SMI-LRS (Low-Resolution Spectroscopy)
    A prism spectrometer with 4 slits with a 10 arc-minutes field of view. It is designed to conduct high-speed spectroscopic imaging in λ = 17 - 36 μm, with a moderate wavelength resolution (R=Δλ/λ=50). It aims at detecting PAH dust emission as a clue of distant galaxies and emission of minerals from planet formation regions around stars.
  • SMI-MRS (Low-Resolution Spectroscopy)
    An infrared spectrometer with Echelle diffraction grating, covering λ = 18 - 36 μm. Its high sensitivity for line emission with a relatively high wavelength resolution (R = 2,000) enables characterization of distant galaxies and planet formation regions detected by SMI-LRS.
  • SMI-HRS (High-Resolution Spectroscopy)
    An infrared spectrometer with immersion grating covering λ = 12 - 18 μm. With its extremely high wavelength resolution (R = 28,000), SMI-HRS can study the dynamics of molecular gas in planet formation regions around stars.

* See "For Astronomers" for the latest information on the SMI performance.

Fig. 2   Block diagram of the basic functions of SMI

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SPICA Far-infrared instrument; SAFARI

The SAFARI is a diffraction grating spectrometer designed to achieve the highest-ever sensitivity for line emission in the wide far-infrared wavelength range of λ = 34 - 210 μm (TBD) with a moderate wavelength resolution (R=300). The SAFARI will employ a TES (Transition Edge Sensor) bolometer developed by SRON (Netherlands Institute for Space Research) as a far-infrared detector. An additional function enabling high-resolution observations (R=3,000) by a combination of a Fabry‐Perot interferometer with the diffraction grating is under consideration. With its beam steering mirror, it can perform imaging observations of a 2 arc minute square region on the sky. This function is effective to observe diffuse celestial objects. The SAFARI Consortium consisting of institutes/universities from Europe, Canada and U.S.A is responsible for development of the SAFARI.

In the SAFARI wavelength range, there are various bright emission lines from ionized gas. With its high sensitivity, the SAFARI can reveal star formation history in galaxies and evolution of supermassive black holes at their center, by detecting these emission lines from distant galaxies.

* See "For Astronomers" for the latest information on the SAFARI performance.

Fig. 3   Overview of SAFARI Cold Unit

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