The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is to be launched into orbit around the second Lagrangian point (L2) in the Sun-Earth system. Taking advantage of the thermal environment in L2, a 2.5m-class large IR telescope is cooled below 8K in combination with effective radiant cooling and a mechanical cooling system. SPICA adopts a cryogen-free system to prevent the mission operation lifetime being limited by the amount of cryogen as a refrigerant. Currently, the mechanical cooler system with the feasible solution giving a proper margin is proposed. As a baseline design, 4K / 1K-class Joule-Thomson coolers are used to cool the telescope and thermal interface for Focal Plane Instruments (FPIs). Additionally, two sets of double stage stirling coolers (2STs) are used to cool the telescope shield. In this design, nominal operation of FPIs can be kept when one mechanical cooler is in failure. In this paper, current baseline configuration of the mechanical cooler system and current status of mechanical coolers developments which need to satisfy the specific requirements of SPICA cryogenic system are presented.
We present an overview of the cryogenic system of the next-generation infrared observatory mission SPICA. One of the most critical requirements for the SPICA mission is to cool the whole science equipment, including the 2.5 m telescope, to below 8 K to reduce the thermal background and enable unprecedented sensitivity in the mid- and far-infrared region. Another requirement is to cool focal plane instruments to achieve superior sensitivity. We adopt the combination of effective radiative cooling and mechanical cryocoolers to accomplish the thermal requirements for SPICA. The radiative cooling system, which consists of a series of radiative shields, is designed to accommodate the telescope in the vertical configuration. We present thermal model analysis results that comply with the requirements to cool the telescope and focal plane instruments.
The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.
KEYWORDS: Sensors, Frequency modulation, Temperature metrology, Cryocoolers, Vibration isolation, X-rays, Space operations, Spectroscopy, Fermium, Head
The soft x-ray spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from microvibration from cryocoolers mounted on the dewar. This is mitigated for the flight model (FM) by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the FM was verified before launch of the spacecraft in both ambient condition and thermal-vacuum condition, showing no detectable degradation in energy resolution. The in-orbit detector spectral performance and cryocooler cooling performance were also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the microvibration could degrade the cryogenic detector is shown. Lessons learned from the development to mitigate unexpected issues are also described.
The soft x-ray spectrometer (SXS) was a cryogenic high-resolution x-ray spectrometer onboard the Hitomi (ASTRO-H) satellite that achieved energy resolution of 5 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator (ADR). The cooling chain from room temperature to the ADR heat sink was composed of two-stage Stirling cryocoolers, a He4 Joule–Thomson cryocooler, and superfluid liquid helium and was installed in a dewar. It was designed to achieve a helium lifetime of more than 3 years with a minimum of 30 L. The satellite was launched on February 17, 2016, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the helium tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and the cryocoolers.
Very lightweight mirror will be required in the near future for both astronomical and earth science/observation missions. Silicon carbide is becoming one of the major materials applied especially to large and/or light space-borne optics, such as Herschel, GAIA, and SPICA. On the other hand, the technology of highly accurate optical measurement of large telescopes, especially in visible wavelength or cryogenic circumstances is also indispensable to realize such space-borne telescopes and hence the successful missions.
We have manufactured a very lightweight Φ=800mm mirror made of carbon reinforced silicon carbide composite that can be used to evaluate the homogeneity of the mirror substrate and to master and establish the ground testing method and techniques by assembling it as the primary mirror into an optical system. All other parts of the optics model are also made of the same material as the primary mirror.
The composite material was assumed to be homogeneous from the mechanical tests of samples cut out from the various areas of the 800mm mirror green-body and the cryogenic optical measurement of the mirror surface deformation of a 160mm sample mirror that is also made from the same green-body as the 800mm mirror.
The circumstance and condition of the optical testing facility has been confirmed to be capable for the highly precise optical measurements of large optical systems of horizontal light axis configuration. Stitching measurement method and the algorithm for analysis of the measurement is also under study.
KEYWORDS: X-rays, Sensors, Spectroscopy, Space operations, Lithium, Field effect transistors, Satellites, Calibration, Single crystal X-ray diffraction, Magnetic sensors
We present the overall design and performance of the Astro-H (Hitomi) Soft X-Ray Spectrometer (SXS). The instrument uses a 36-pixel array of x-ray microcalorimeters at the focus of a grazing-incidence x-ray mirror Soft X-Ray Telescope (SXT) for high-resolution spectroscopy of celestial x-ray sources. The instrument was designed to achieve an energy resolution better than 7 eV over the 0.3-12 keV energy range and operate for more than 3 years in orbit. The actual energy resolution of the instrument is 4-5 eV as demonstrated during extensive ground testing prior to launch and in orbit. The measured mass flow rate of the liquid helium cryogen and initial fill level at launch predict a lifetime of more than 4 years assuming steady mechanical cooler performance. Cryogen-free operation was successfully demonstrated prior to launch. The successful operation of the SXS in orbit, including the first observations of the velocity structure of the Perseus cluster of galaxies, demonstrates the viability and power of this technology as a tool for astrophysics.
We present the new design of the cryogenic system of the next-generation infrared astronomy mission SPICA under the
new framework. The new design employs the V-groove design for radiators, making the best use of the Planck heritage.
The new design is based on the ESA-JAXA CDF study (NG-CryoIRTel, CDF-152(A)) with a 2 m telescope, and we
modified the CDF design to accommodate the 2.5 m telescope to meet the science requirements of SPICA. The basic
design concept of the SPICA cryogenic system is to cool the Science Instrument Assembly (SIA, which is the
combination of the telescope and focal-plane instruments) below 8K by the combination of the radiative cooling system
and mechanical cryocoolers without any cryogen.
KEYWORDS: Infrared telescopes, Space telescopes, Telescopes, Optical instrument design, Cryogenics, Infrared radiation, Cooling systems, Space telescopes, Cryogenics, Electrical breakdown, James Webb Space Telescope, Space operations
The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is a pre-project of JAXA in collaboration
with ESA to be launched in the 2020s. The SPICA mission is to be launched into a halo orbit around
the second Lagrangian point in the Sun-Earth system, which allows us to use effective radiant cooling in combination
with a mechanical cooling system in order to cool a 2.5m-class large IR telescope below 8K. Recently,
a new system design in particular thermal structure of the payload module has been studied by considering
the technical feasibility of a cryogenic cooled telescope within current constraints of the mission in the CDF
(Concurrent Design Facility) study of ESA/ESTEC. Then, the thermal design of the mechanical cooler system,
for which the Japanese side is responsible, has been examined based on the CDF study and the feasible
solution giving a proper margin has been obtained. As a baseline, 4K / 1K-class Joule-Thomson coolers are
used to cool the telescope and thermal interface for Focal Plane Instruments (FPIs). Additionally, two sets of
double stirling coolers (2STs) are used to cool the Telescope shield. In this design, nominal operation of FPIs
can be kept when one mechanical cooler is in failure.
LiteBIRD is a next generation satellite aiming for the detection of the Cosmic Microwave Background (CMB) B-mode polarization imprinted by the primordial gravitational waves generated in the era of the inflationary universe. The science goal of LiteBIRD is to measure the tensor-to-scaler ratio r with a precision of δr < 10-3♦, offering us a crucial test of the major large-single-field slow-roll inflation models. LiteBIRD is planned to conduct an all sky survey at the sun-earth second Lagrange point (L2) with an angular resolution of about 0.5 degrees to cover the multipole moment range of 2 ≤ ℓ ≤ 200. We use focal plane detector arrays consisting of 2276 superconducting detectors to measure the frequency range from 40 to 400 GHz with the sensitivity of
3.2 μK·arcmin. including the ongoing studies.
The Hitomi (ASTRO-H) mission is the sixth Japanese X-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. After a successful launch on 2016 February 17, the spacecraft lost its function on 2016 March 26, but the commissioning phase for about a month provided valuable information on the on-board instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.
We summarize all the in-orbit operations of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H (Hit- omi) satellite. The satellite was launched on 2016/02/17 and the communication with the satellite ceased on 2016/03/26. The SXS was still in the commissioning phase, in which the setups were progressively changed. This article is intended to serve as a reference of the events in the orbit to properly interpret the SXS data taken during its short life time, and as a test case for planning the in-orbit operation for future micro-calorimeter missions.
The Soft X-ray Spectrometer (SXS) is a cryogenic high-resolution X-ray spectrometer onboard the ASTRO-H satellite, that achieves energy resolution better than 7 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator. The cooling chain from room temperature to the ADR heat sink is composed of 2-stage Stirling cryocoolers, a 4He Joule-Thomson cryocooler, and super uid liquid He, and is installed in a dewar. It is designed to achieve a helium lifetime of more than 3 years with a minimum of 30 liters. The satellite was launched on 2016 February 17, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the He tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and cryocoolers.
KEYWORDS: Vibration isolation, Sensors, Cryocoolers, X-rays, Spectroscopy, X-rays, Space operations, Temperature metrology, Fermium, Frequency modulation, Head
Soft X-ray Spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from micro-vibration from cryocoolers mounted on the dewar. This is mitigated for the flight model by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the flight model was verified before launch of the spacecraft in both ambient condition and thermal-vac condition, showing no detectable degradation in energy resolution. The in-orbit performance was also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the micro-vibration could degrade the cryogenic detector is shown.
Sumitomo Heavy Industries, ltd. (SHI) has been developing cooler and Dewar technology for space application with
Japan Aerospace Exploration Agency. SHI has four types of coolers to cover temperature range from 1.7K to 80K or
more. Those are Single stage Stirling coolers for 80K, two-stage Stirling coolers for 20K, 4K-class cooler and 1K-class
cooler. 4K and 1K class coolers consist of a Joule-Thomson cooler and a two-stage Stirling as a pre-cooler. SHI also
provided Dewars. In this paper, SHI’s cooler and Dewar technology are described.
The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is a pre-project of JAXA in collaboration with ESA to be launched around 2025. The SPICA mission is to be launched into a halo orbit around the second Lagrangian point in the Sun-Earth system, which allows us to use effective radiant cooling in combination with a mechanical cooling system in order to cool a 3m large IR telescope below 6K. The use of 4K / 1K-class Joule-Thomson coolers is proposed in order to cool the telescope and provide a 4K / 1K temperature region for Focal Plane Instruments (FPIs). This paper introduces details of the thermal design study for the SPICA payload module in the Risk-Mitigation-Phase (RMP), in which the activity is focused on mitigating the mission’s highest risks. As the result of the RMP activity, most of all the goals have been fully satisfied and the thermal design of the payload module has been dramatically improved.
We present the mission design of LiteBIRD, a next generation satellite for the study of B-mode polarization and inflation from cosmic microwave background radiation (CMB) detection. The science goal of LiteBIRD is to measure the CMB polarization with the sensitivity of δr = 0:001, and this allows testing the major single-field slow-roll inflation models experimentally. The LiteBIRD instrumental design is purely driven to achieve this goal. At the earlier stage of the mission design, several key instrumental specifications, e.g. observing band, optical system, scan strategy, and orbit, need to be defined in order to process the rest of the detailed design. We have gone through the feasibility studies for these items in order to understand the tradeoffs between the requirements from the science goal and the compatibilities with a satellite bus system. We describe the overview of LiteBIRD and discuss the tradeoffs among the choices of scientific instrumental specifications and strategies. The first round of feasibility studies will be completed by the end of year 2014 to be ready for the mission definition review and the target launch date is in early 2020s.
We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of < 7eV in the energy range of 0.3 – 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.
The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is a 3.2m cooled (below 6K) telescope
mission which covers mid- and far-IR waveband with unprecedented sensitivity. An overview of recent design
updates of the Scientific Instrument Assembly (SIA), composed of the telescope assembly and the instrument
optical bench equipped with Focal Plane Instruments (FPIs) are presented. The FPI international science and
engineering review is on-going to determine the FPI suite onboard SPICA: at present the mandatory instruments
and functions to perform the unique science objectives of the SPICA mission are now consolidated. The final
decision on the composition of the FPI suite is expected in early 2013. Through the activities in the current pre-project
phase, several key technical issues which impact directly on the instruments’ performances and the science
requirements and the observing efficiency have been identified, and extensive works are underway both at
instrument and spacecraft level to resolve these issues and to enable the confirmation of the SPICA FPI suite.
WISH, Wide-field Imaging Surveyor for High-redshiftt, is a space mission concept to conduct very deep and widefield
surveys at near infrared wavelength at 1-5μm to study the properties of galaxies at very high redshift beyond the
epoch of cosmic reionization. The concept has been developed and studied since 2008 to be proposed for future
JAXA/ISAS mission. WISH has a 1.5m-diameter primary mirror and a wide-field imager covering 850 arcmin2. The
pixel scale is 0.155 arcsec for 18μm pitch, which properly samples the diffraction-limited image at 1.5μm. The main
program is Ultra Deep Survey (UDS) covering 100 deg2 down to 28AB mag at least in five broad bands. We expect to
detect <104 galaxies at z=8-9, 103-104 galaxies at z=11-12, and 50-100 galaxies at z<14, many of which can be feasible
targets for deep spectroscopy with Extremely Large Telescopes. With recurrent deep observations, detection and light
curve monitoring for type-Ia SNe in rest-frame infrared wavelength is also conducted, which is another main science
goal of the mission. During the in-orbit 5 years observations, we expect to detect and monitor <2000 type-Ia SNe up to
z~2. WISH also conducts Ultra Wide Survey, covering 1000deg2 down to 24-25AB mag as well as Extreme Survey,
covering a limited number of fields of view down to 29-30AB mag. We here report the progress of the WISH project
including the basic telescope and satellite design as well as the results of the test for a proto-model of the flip-type filter
exchanger which works robustly near 100K.
LiteBIRD [Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background
Radiation Detection] is a small satellite to map the polarization of the cosmic microwave background (CMB)
radiation over the full sky at large angular scales with unprecedented precision. Cosmological inflation, which
is the leading hypothesis to resolve the problems in the Big Bang theory, predicts that primordial gravitational
waves were created during the inflationary era. Measurements of polarization of the CMB radiation are known as
the best probe to detect the primordial gravitational waves. The LiteBIRD working group is authorized by the
Japanese Steering Committee for Space Science (SCSS) and is supported by JAXA. It has more than 50 members
from Japan, USA and Canada. The scientific objective of LiteBIRD is to test all the representative inflation models that satisfy single-field slow-roll conditions and lie in the large-field regime. To this end, the requirement
on the precision of the tensor-to-scalar ratio, r, at LiteBIRD is equal to or less than 0.001. Our baseline design
adopts an array of multi-chroic superconducting polarimeters that are read out with high multiplexing factors in
the frequency domain for a compact focal plane. The required sensitivity of 1.8μKarcmin is achieved with 2000
TES bolometers at 100mK. The cryogenic system is based on the Stirling/JT technology developed for SPICA,
and the continuous ADR system shares the design with future X-ray satellites.
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated
by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the highenergy
universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV.
These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3–12 keV with
high spectral resolution of ΔE ≦ 7 eV, enabled by a micro-calorimeter array located in the focal plane of
thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5–80 keV, located in the focal plane of
multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4–12 keV,
with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera
type soft gamma-ray detector, sensitive in the 40–600 keV band. The simultaneous broad bandpass, coupled
with high spectral resolution, will enable the pursuit of a wide variety of important science themes.
The conceptual design of the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) has been studied as a
pre-project of the Japan Aerospace Exploration Agency (JAXA) in collaboration with ESA to be launched in 2018. The
SPICA is transferred into a halo orbit around the second Lagrangian point in the Sun-Earth system, where radiant
cooling is available effectively. The SPICA has a large IR telescope 3 m in diameter, which is cooled without cryogen to
below 6 K by the radiant and mechanical cooling system. Therefore, the SPICA mission will cover mid- and far-IR
astronomy with high sensitivity and spatial resolution during a long period of over 5 years for goal. Most heat radiation
from the sun and spacecraft is blocked by the Sun Shield and thermal radiation shields covered with Multi-Layer
Insulator (MLI) to limit heat radiation to the Scientific Instrument Assembly (SIA). The SIA, which is composed of the
primary mirrors and optical benches equipped with Focal Plane Instruments (FPIs), is refrigerated to below 6 K by two
sets of 4K-class Joule-Thomson (JT) cooler with a cooling power of 40 mW at 4.5 K. The Far-IR detector is refrigerated
to 1.7 K by two sets of 1K-class JT coolers with a cooling power of 10 mW at 1.7 K. Improvements for the higher
reliability and sufficient cooling performance are required in the development of SPICA mechanical cryocoolers.
Thermal analysis indicates that the SPICA cryogenic system works effectively to limit the total heat load on the SIA to
41.2 mW. This paper describes the conceptual design of the SPICA cryogenic system, which was established with
thermal feasibility for nominal operation mode.
KEYWORDS: Galactic astronomy, Space telescopes, Telescopes, Mirrors, Near infrared, Optical filters, Staring arrays, Ultraviolet radiation, James Webb Space Telescope, Sensors
WISH is a new space science mission concept whose primary goal is to study the first galaxies in the early universe.
We will launch a 1.5m telescope equipped with 1000 arcmin2 wide-field NIR camera by late 2010's in order to conduct
unique ultra-deep and wide-area sky surveys at 1-5 micron. The primary science goal of WISH mission is pushing the
high-redshift frontier beyond the epoch of reionization by utilizing its unique imaging capability and the dedicated
survey strategy. We expect to detect ~104 galaxies at z=8-9, ~3-6x103 galaxies at z=11-12, and ~50-100 galaxies at
z=14-17 within about 5 years of the planned mission life time. It is worth mentioning that a large fraction of these
objects may be bright enough for the spectroscopic observations with the extremely large telescopes. By adopting the optimized strategy for the recurrent observations to reach the depth, we also use the surveys to detect transient objects.
Type Ia Supernova cosmology is thus another important primary goal of WISH. A unique optical layout has been
developed to achieve the diffraction-limited imaging at 1-5micron over the required large area. Cooling the mirror and
telescope to ~100K is needed to achieve the zodiacal light limited imaging and WISH will achieve the required
temperature by passive cooling in the stable thermal environment at the orbit near Sun-Earth L2. We are conducting the
conceptual studies and development for the important components of WISH including the exchange mechanism for the
wide-field filters as well as the primary mirror fixation.
SPICA is a next generation infrared astronomy mission to reveal the origin of planets and galaxies. The mission is led by
Japan Aerospace Exploration Agency (JAXA) in collaboration with the European Space Agency (ESA) and international
consortiums in Japan, Europe, USA, and the Republic of Korea. SPICA is an "observatory" based on the heritage of
AKARI's "all sky survey". ESA provides a 3-m class telescope using technology heritage of Herschel. The SPICA will
achieve superior sensitivity in the mid- to far- infrared astronomy to be launched into space. SPICA has a completely
new cooling system, which utilizes efficient mechanical coolers. This system enables a large, cryogenically cooled
telescope in space. SPICA system concept and requirements are clear, but it is not easy to design. SPICA spacecraft
consists of the Payload Module (PLM) and the Bus Module (BM). The PLM includes mechanical coolers and passive
thermal shields, which enable to cool down the telescope and scientific instruments below 6K. The PLM is connected to
the BM with low thermal conductivity truss structure to keep the PLM cool and the BM warm. This paper describes how
to meet the system requirements to establish the feasible design of SPICA spacecraft.
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated
by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the
high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular
resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination
of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray
mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV)
provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD
camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray
detector (40-600 keV) . The micro-calorimeter system is developed by an international collaboration led
by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of
ΔE ~7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be
pursued.
The Soft X-ray Spectrometer (SXS) is a cryogenic high resolution X-ray spectrometer onboard the X-ray astronomy
satellite ASTRO-H. The detector array is cooled down to 50 mK using a 3-stage adiabatic demagnetization
refrigerator (ADR). The cooling chain from room temperature to the ADR heat-sink is composed of superfluid
liquid He, a 4He Joule-Thomson cryocooler, and 2-stage Stirling cryocoolers. It is designed to keep 30 L of liquid
He for more than 3 years in the nominal case. It is also designed with redundant subsystems throughout from
room temperature to the ADR heat-sink, to alleviate failure of a single cryocooler or loss of liquid He.
We present the science and an overview of the Soft X-ray Spectrometer onboard the ASTRO-H mission with
emphasis on the detector system. The SXS consists of X-ray focusing mirrors and a microcalorimeter array and
is developed by international collaboration lead by JAXA and NASA with European participation. The detector
is a 6×6 format microcalorimeter array operated at a cryogenic temperature of 50 mK and covers a 3' ×3' field
of view of the X-ray telescope of 5.6 m focal length. We expect an energy resolution better than 7 eV (FWHM,
requirement) with a goal of 4 eV. The effective area of the instrument will be 225 cm2 at 7 keV; by a factor of
about two larger than that of the X-ray microcalorimeter on board Suzaku. One of the main scientific objectives
of the SXS is to investigate turbulent and/or macroscopic motions of hot gas in clusters of galaxies.
The SXS (Soft X-ray Spectrometer) onboard the coming Japanese X-ray satellite NeXT (New Exploration Xray
Telescope) and the SXC (Spectrum-RG X-ray Calorimeter) in Spectrum-RG mission are microcalorimeter
array spectrometers which will achieve high spectral resolution of ~ 6 eV in 0.3-10.0 keV energy band. These
spectrometers are well-suited to address key problems in high-energy astrophysics. To achieve these high spectral
sensitivities, these detectors require to be operated under 50 mK by using very efficient cooling systems including
adiabatic demagnetization refrigerator (ADR). For both missions, we propose a two-stage series ADR as a cooling
system below 1 K, in which two units of ADR consists of magnetic cooling material, a superconducting magnet,
and a heat switch are operated step by step. Three designs of the ADR are proposed for SXS/SXC. In all three
designs, ADR can attain the required hold time of 23 hours at 50 mK and cooling power of 0.4μW with a low
magnetic fields (1.5/1.5 Tesla or 2.0/3.0 Tesla) in a small configuration (180 mmφ× 319 mm in length).
We also fabricated a new portable refrigerator for a technology investigation of two-stage ADR. Two units of
ADR have been installed at the bottom of liquid He tank. By using this dewar, important technologies such as an operation of two-stage cooling cycle, tight temperature control less than 1 μK (in rms) stability, a magnetic
shielding, saltpills, and gas-gap heat switches are evaluated.
The Soft X-ray Spectrometer (SXS) onboard the NeXT (New exploration X-ray Telescope) is an X-ray spectrometer
utilizing an X-ray microcalorimeter array. Combined with the soft X-ray telescope of 6 m focal length,
the instrument will have a ~ 290cm2 effective at 6.7 keV. With the large effective area and the energy resolution
as good as 6 eV (FWHM), the instrument is very suited for the high-resolution spectroscopy of iron K emission
line. One of the major scientific objectives of SXS is to determine turbulent and/or macroscopic motions of the
hot gas in clusters of galaxies of up to z ~ 1. The instruments will use 6 × 6 or 8 × 8 format microcalorimeter
array which is similar to that of Suzaku XRS. The detector will be cooled to a cryogenic temperature of 50 mK
by multi-stage cooling system consisting of adiabatic demagnetization refrigerator, super fluid He, a 3He Joule
Thomson cooler, and double-stage stirling cycle cooler.
The SPICA mission has been proposed to JAXA as the second Japanese IR space telescope to be launched in 2017. The
SPICA spacecraft, launched with an H-IIA launch vehicle, is to be transferred into a halo orbit around the Sun-Earth L2,
where effective radiant cooling is feasible owing to solar rays and radiant heat fluxes from the Earth constantly coming
from the same direction. That optimal thermal environment enables this IR space telescope to use a large 3.5-mdiameter-
single-aperture primary mirror cooled to 4.5 K with advanced mechanical cryocoolers and effective radiant
cooling instead of a massive and short-lived cryogen. As a result of thermal and structural analyses, the thermal design of
cryogenic system was obtained. Then, mechanical cryocoolers have been developed to meet cooling requirement at 1.7
K, 4.5 K and 20 K. The latest results of upgrading of the 20 K-class two-stage Stirling cooler, the 4K-class JT cooler,
and the 1K-class JT cooler indicate that all cryocoolers gain a sufficient margin of cooling capacity with unprecedentedly
low power consumption for the cooling requirement. It is concluded that the feasibility of the SPICA mission was
confirmed for the critical cryogenic system design, while some attempts to achieve higher reliability, higher cooling
capacity and less vibration have been continued for stable operations throughout the entire mission period.
The ESI instrument (European SPICA Instrument) is a proposed imaging spectrometer for the 30-210μm band for the JAXA SPICA mission. The instrument will have unprecedented spatial resolution and sensitivity due to the large 03.5m telescope aperture, cold fore-optics (~5K) and high sensitivity detectors (NEP~10-19W/√Hz). One of the key technical challenges of the design of the instrument is the thermal architecture due to the mass and cryogenic heat load constraints and the need for very low temperatures. Two candidate detector technologies have been pre-selected for inclusion in the instrument Phase-A study; Photoconductors and TES Bolometers.
An overview of thermal architecture of the SPICA spacecraft is presented in order to explain the thermal interface constraints imposed on the instrument. Proposed thermal architectures for the instrument for both the TES and the Photoconductor options will be outlined including a novel design for a lightweight hybrid cooler for achieving sub 100-mK detector temperatures. This novel cooler architecture utilizes a combination of ADR and sorption coolers. Several design solutions for achieving high thermal isolation generic to both detector options are presented.
This paper describes that the feasibility of the next Japanese infrared astronomical SPICA mission is verified in thermal design by numerical analyses and developed technologies. In this advanced cryogenic mission, in order to cool the large primary mirror and focal plane instruments down to 4.5 K for 5 years or longer without cryogen, the mechanical cooling is employed with effective radiant cooling, which compensates the limited cooling capacity of the JT cryocooler for 4.5 K upgraded from that developed for the "JEM/SMILES" mission on the International Space Station. First, thermal design of the telescope is numerically discussed with thermal mathematical models. Some configurations of radiators, shields and solar-array paddles are investigated and compared in technical and mission feasibilities. Next, the development status of the 3He-JT circuit with the Stirling cryocooler for one detector operated at the lowest temperature of 1.7 K is reported. The recent results of experiments give that the breadboard model of the 1.7 K cryocooler successfully exceeds the required cooling capacity of 10mW at 1.7K with small power consumption. Finally, the heat rejection system from those cryocoolers is discussed. As a promising candidate, the loop heat pipe is chosen and suitably designed.
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