SPICA provided the next step in mid- and far-infrared astronomical research and was a candidate of ESA's fifth medium class Cosmic Vision mission. SAFARI is one of the spectroscopic instruments on board SPICA. The Focal Plane Unit (FPU) design and analysis represent a challenge both from the mechanical and thermal point of view, as the instrument is working at cryogenic temperatures between 4.8K and 0.05K. Being a large instrument, with a current best estimate of 148,7kg of mass, its design will have to be optimized to fit within the mission´s mass and volume budget. The FPU will also have to be designed for its modularity and accessibility due to the large number of subsystems that SAFARI had to accommodate, highlighting Fourier Transform Spectrometer Mechanism (FTSM) and the three grating-based point source spectrometer modules (GM) which operates at 1.7K in the FPU, the latter representing 60% of the total mass of the instrument
The far infrared instrument SAFARI spectrometer on board the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) provides moderate resolution spectra (R~300) with simultaneous coverage over 34 to 230 μm. With the high sensitivity TES detectors, the SAFARI can reach the sensitivity down to ~7×10-20 W/m2. In order to provide accurate calibration for the TES readout circuit, a calibration source assembly (CSA) is developed to provide a stable and absolute flux radiation to the spectrometer over the whole spectral range. The CSA has a primary function during observations to take periodic reference measurement to correct for drift, subtracting backgrounds, etc from the detector. The CSA is composed of three microlamps and one integrating sphere. The microlamps are made of resistance wires by microlithography to mimic square blackbody sources. By combining an 81K microlamp and a 24K microlamp, a reasonably flat spectrum can be produced at the output of the integrating sphere. The radiation to the transition edge sensor detector pixel is around 1×10-16 W. The integrating sphere can also provide a uniform output to cover the size of SAFARI field of view including the target and sky pixels. In this paper, the CSA design and the prototype results of the microlamp and the integrating sphere are presented.
This paper describes the end-to-end opto-mechanical design of the SAFARI instrument on SPICA and the analysis of the spectrometer optical performances. SAFARI instrument is a high sensitivity grating-based spectrometer operating in the 34-230 μm wavelength range. The scientific drivers lead to the implementation of two modes of operation. The Low- Resolution (LR) or nominal mode (R~300) and the High-Resolution (HR), that implies to include a Martin-Puplett Fourier Transform Spectrometer (MP-FTS) to achieve the required spectral resolution (R~2000-11000). The optical system is all-reflective and consists of three main modules. The input optics module (IOM) is an unobscured reflective Offner relay. In the IOM a Beam Steering Mirror (BSM) is included for spatial modulation and to allow efficient sky mapping. The Band and Mode Distributing Optics (BMDO) module splits the radiation band into the four different spectral bands and includes the MP-FTS. The field image existing at the output of the BMDO constitutes the entrance to the Grating Module Optics (GM). These modules provide spectral dispersion by means of linear and reflective diffraction gratings and the final image onto the detectors. Performances of the GMs are high demanding with a detector divided into 2 sub-bands with a different pixel size for each sub-band.
SAFARI is a point source spectrometer for the SPICA mission, which provides far-infrared spectroscopy and high sensitivity. SPICA mission, having a large cold telescope cooled to 6K above absolute zero, will provide an optimum environment where instruments are limited only by the cosmic background. SAFARI is a grating-based spectrometer with two modes of operation, Low Resolution (LR), or nominal mode (R~300) and High Resolution, (HR) (R~2000-11000). The SAFARI shall provide point source spectroscopy with diffraction-limited capability in four spectral bands over 34-230μm and a field of view (FoV) on sky over 2’×2’. Due to the complexity of the optical design of the SAFARI instrument a modular design was selected. Four principal modules are defined: Calibration Module (CS), Input Optics Module (IOM), Beam and Mode Distribution (BMDO) and Grating Modules (GMs). The present work is focused in the last module. Dispersive optical systems inherently demand the need of volume allocation for the optical system, being this fact somehow proportional to the wavelength and the required resolving power. The image sampling and the size of the detector elements are key drivers in this optical modular design. The optimization process has been performed taking into account the conceptual design parameters obtained during this phase such as collimator and camera optics focal lengths, subsystem diameters and periods and AOIs of the diffraction gratings.
SpicA FAR infrared Instrument, SAFARI, is one of the instruments planned for the SPICA mission. The SPICA
mission is the next great leap forward in space-based far-infrared astronomy and will study the evolution of galaxies,
stars and planetary systems. SPICA will utilize a deeply cooled 2.5m-class telescope, provided by European industry, to
realize zodiacal background limited performance, and high spatial resolution. The instrument SAFARI is a cryogenic
grating-based point source spectrometer working in the wavelength domain 34 to 230 μm, providing spectral resolving
power from 300 to at least 2000.
The instrument shall provide low and high resolution spectroscopy in four spectral bands. Low Resolution mode is the
native instrument mode, while the high Resolution mode is achieved by means of a Martin-Pupplet interferometer.
The optical system is all-reflective and consists of three main modules; an input optics module, followed by the Band
and Mode Distributing Optics and the grating Modules. The instrument utilizes Nyquist sampled filled linear arrays of
very sensitive TES detectors.
The work presented in this paper describes the optical design architecture and design concept compatible with the
current instrument performance and volume design drivers.
Ingenio/SEOSAT is the flagship mission for the Spanish Space Plan 2007-2011, as is currently under development by a
Spanish industrial consortium in the framework of an ESA contract. Ingenio/SEOSAT is a multi-spectral high-resolution
optical satellite for Earth Remote Sensing, designed to provide imagery to different Spanish civil, institutional and
governmental users, and potentially to other European users in the frame of GMES and GEOSS. SEOSAT/Ingenio is a
Low Earth Orbiting mission. It features a Primary Payload (PP) with one 2.5 meter resolution panchromatic channel and
four 10 meter resolution visible/near infrared spectral channels. The PP swath close to 55 km ensures a frequent revisit
period, and offers quick accessibility to any point on Earth in emergency situations. In this paper are described the main
characteristics and development status of the instrument from an opto-mechancial point of view, as well as the estimated performance data.