Mechanical Coolers Research Articles

Suppression of cryocooler-induced microphonics in infrared imagers

Sophisticated portable infrared imagers developed for surveillance, reconnaissance, targeting and navigation play a vital role in the modern tactics used for carrying out military and antiterrorist operations. Their superior performance relies on novel optronic technologies and maintaining the infrared focal plane arrays at cryogenic temperatures using close cycle mechanical Stirling cryogenic coolers. Such coolers are well known sources of high-frequency interference contaminating the image signal and causing essential degradation in the overall imagery performance. This phenomenon is generally referred to as microphonics, which mostly manifests itself at the resonant frequencies of sensitive mechanical components of infrared packages. The ruggedizing of these components involves stiffening and dampening which are, evidently, not the best solutions to implement inside, say, an evacuated envelope, where the issues of added heat load, thermal mass, ageing, vacuum contamination due to outgassing are of the primary concern. The paper examines the idea of using externally mounted wideband dynamic absorbers for suppressing the above resonant responses and associated microphonic noise. The suggested analytical model relies on a set of complex frequency response functions experimentally captured on the original infrared package. The optimised dynamic absorber yields about a tenfold suppression of the resonant responses and a threefold attenuation of the overall RMS level of microphonic noise. The results of the analytical prediction are in fair agreement with experimental data.

AKARI—Infrared Satellite Mission—Present Status and Early Results

AKARI, formerly known as ASTRO-F, is a satellite mission dedicated to infrared astronomy for the first time in Japan. It has a 685-mm aperture telescope with two focal-plane instruments cooled by liquid helium (LHe) and mechanical coolers on board for observations in the 2–180 μm infrared spectral range. AKARI was launched on 2006 February 21 (UT) into a sun-synchronous polar orbit and started observations in May, 2006. It carried 179 liter LHe that lasted for 550 days and observations with LHe were carried out for more than 15 months. During the LHe holding period, AKARI made all-sky survey observations with six bands from 9 to 160 μm, which surpass the IRAS all-sky survey data in the sensitivity, spatial resolution, and spectral coverage. Together with the all-sky observation, AKARI also made pointing observations for about 10 min at a given position of the sky to execute deep imaging and spectroscopy from near- to far-infrared. Both focal-plane instruments work successfully on orbit and more than 90% of the sky was observed in the all-sky survey. After LHe exhaustion, near-infrared observations are planned to continue. This paper reports the in-orbit performance of AKARI and its early observational results so far obtained.

Design and Concept of the Compact Infrared Camera (CIRC) with Uncooled Infrared Detector

The compact infrared camera (CIRC) is one of technology demonstration payloads of Small Demonstration-Satellite type-3 (SDS-3). The CIRC is an infrared camera equipped with an uncooled infrared array detector (microbolometer). Microbolometers have an advantage of no requirement of cooling mechanisms such as a mechanical cooler. The main mission of the CIRC is the technology demonstration of the wildfire detection using the microbolometer. In this paper, we show the details of the design and concept of the CIRC. We also show preliminary results of feasibility study of the wildfire detection and other applications using thermal infrared images.

High Resolution Dynamics Limb Sounder: Experiment overview, recovery, and validation of initial temperature data

The High Resolution Dynamics Limb Sounder (HIRDLS) experiment was designed to provide global temperature and composition data on the region from the upper troposphere to the mesopause with vertical and horizontal resolution not previously available. The science objectives are the study of small‐scale dynamics and transports, including stratosphere‐troposphere exchange, upper troposphere/lower stratosphere chemistry, aerosol, cirrus and PSC distributions, and gravity waves. The instrument features 21 channels, low noise levels, high vertical resolution, and a mechanical cooler for long life. During launch most of the optical aperture became obscured, so that only a potion of an optical beam width at a large azimuth from the orbital plane on the side away from the Sun can see the atmosphere. Irrecoverable loss of capabilities include limitation of coverage to the region 65°S–82°N and inability to obtain longitudinal resolution finer than an orbital spacing. While this optical blockage also impacted radiometric performance, extensive effort has gone into developing corrections for the several effects of the obstruction, so that radiances from some of the channels can be put into retrievals for temperature. Changes were also necessary for the retrieval algorithm. The validation of the resulting temperature retrievals is presented to demonstrate the effectiveness of these corrections. The random errors range from ∼0.5 K at 20 km to ∼1.0 at 60 km, close to those predicted. Comparisons with high‐resolution radiosondes, lidars, ACE‐FTS, and ECMWF analyses give a consistent picture of HIRDLS temperatures being 1–2 K warm from 200 to 10 hPa and within ±2 K of standards from 200 to 2 hPa (but warmer in the region of the tropical tropopause), above which HIRDLS appears to be cold. Comparisons show that both COSMIC and HIRDLS can see small vertical features down to about 2 km wavelength. While further improvements in the data are expected, these data will allow HIRDLS to provide important support toward reaching the Aura objectives.

Thermal design and its on-orbit performance of the AKARI cryostat

The AKARI satellite (formerly known as ASTRO-F) is Japan’s first infrared astronomical satellite. AKARI is equipped with the infrared camera (IRC) and the far-infrared surveyor (FIS), which are cooled below 7 K. The AKARI’s 68.5 cm telescope, which is made of SiC, is also cooled below 7 K. A unique feature of the AKARI cryostat is that it uses both cryogen and mechanical coolers. Using mechanical coolers, the helium lifetime can be greater than one year with 170 L of liquid helium. AKARI was launched on February 21, 2006 (UT), from the Uchinoura Space Center (USC). It has been performing successfully in orbit.

Flight Performance of the AKARI Cryogenic System

Abstract We describe the flight performance of the cryogenic system of the infrared astronomical satellite AKARI, which was successfully launched on 2006 February 21 (UT). AKARI carries a 68.5 cm telescope together with two focal-plane instruments, Infrared Cameras and Far Infrared Surveyor, all of which are cooled down to cryogenic temperature to achieve superior sensitivity. AKARI has a unique cryogenic system, which consists of cryogen (liquid helium) and mechanical coolers (2-stage Stirling coolers). With the help of mechanical coolers, 179 L (26.0 kg) of super-fluid liquid helium can keep the instruments cryogenically cooled for more than 500 days. The on-orbit performance of the AKARI cryogenics is consistent with the design and a pre-flight test, and the boil-off gas flow rate is as small as 0.32 mg s$^{-1}$. We observed an increase in the major axis of the AKARI orbit, which can be explained by thrust due to the thermal pressure of vented helium gas.

High‐Precision CTE Measurement of SiC‐100 for Cryogenic Space Telescopes

ABSTRACTWe present the results of high‐precision measurements of the thermal expansion of sintered SiC, SiC‐100, intended for use in cryogenic space telescopes, in which minimization of thermal deformation of the mirror is critical, and precise information of the thermal expansion is needed for the telescope design. The temperature range of the measurements extends from room temperature down to ∼10 K. Three samples, Nos. 1, 2, and 3, were manufactured from blocks of SiC produced in different lots. The thermal expansion of the samples was measured with a cryogenic dilatometer, consisting of a laser interferometer, a cryostat, and a mechanical cooler. The typical thermal expansion curve is presented using an eighth‐order polynomial of the temperature. For the three samples, the coefficients of thermal expansion (CTE), α 1, α 2, and α 3, were derived for temperatures between 293 and 10 K. The average and the dispersion (1 σ rms) of these three CTEs are 0.816 × 10−6 and 0.002 × 10−6 K−1, respectively. No significant difference was detected in the CTE of the three samples from the different lots. Neither inhomogeneity nor anisotropy of the CTE was observed. Based on the CTE dispersion obtained, we performed a finite‐element method (FEM) analysis of the thermal deformation of a 3.5 m diameter cryogenic mirror made of six SiC‐100 segments. It was shown that the present CTE measurement has an accuracy that is sufficient for the design of the 3.5 m cryogenic infrared telescope mission SPICA (Space Infrared Telescope for Cosmology and Astrophysics).

AKARI (ASTRO-F): Flight performance and preliminary results

ASTRO-F, which is the first Japanese satellite mission dedicated to the infrared wavelength region, was successfully launched on February 21, 2006 (UT), and was named “AKARI”. The telescope has a 69 cm aperture, and is cooled to 6 K with super-fluid helium and mechanical coolers. AKARI is designed for the most advanced all-sky survey in the mid- and far-infrared wavelength region since the Infrared Astronomical Satellite (IRAS). We performed test observations using the performance verification period after the launch, and demonstrated that the instruments are mostly working well. The survey is on-going with six photometric bands including the first all-sky point source survey at 140 and 160 μm. In addition to the all-sky survey, deep imaging and spectroscopic surveys with pointed observations are being carried out in 13 wavelength bands from 2 to 160 μm for various scientific objectives.

Mid- and far-infrared astronomy mission SPICA

We present an overview and the current status of SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is an astronomical mission with a cryogenically cooled 3.5 m telescope optimized for mid- and far-infrared astronomy. Because of its high spatial resolution and unprecedented sensitivity in the mid- to far-infrared, SPICA can address a number of key problems in current astrophysics, ranging from the star-formation history of the universe to the formation of planets. To reduce the mass of the whole mission, SPICA carries no cryogen. SPICA will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system. This combination enables a 3.5-m class cooled (4.5 K) telescope in space. We also describe recent activities of the technology development programs for SPICA. The target year of the launch of SPICA is mid 2010s.

AKARI in Orbit—Scientific Potential for Understanding Galaxy Evolution

AbstractThe AKARI (formerly known as ASTRO-F) mission is the first Japanese satellite dedicated for large area surveys in the infrared (Murakami et al. 2004). AKARI was launched successfully on February 22nd 2006 (JST) from JAXA's Uchinoura Space Centre, Japan. AKARI is now orbiting around the Earth in a Sun-synchronous polar orbit at the altitude of 700 km. The 68.5 cm aperture telescope and scientific instruments are cooled to 6K by liquid Helium and mechanical coolers. The expected liquid Helium holding time is now found to be at least one year after the successful aperture lid-opening on 2006 April 13th (JST). AKARI will perform the most advanced all-sky survey in 6 mid- to far-infrared wavebands since the preceding IRAS mission over 2 decades ago. Deep imaging and spectroscopic surveys near the ecliptic poles with pointed observations are also on-going in 13 wavelength bands at 2-160 μm (see Table 1, details are given in Matsuhara et al. 2006). AKARI is a perfect complement to Spitzer in respect of its wide sky area and wavelength coverage. Two unique aspects of the pointing deep surveys with AKARI are: many imaging bands including the wavelength gap of Spitzer (8-24 μm), and the slitless spectroscopic capability (Ohyama et al. in this proceeding). Not only the All-Sky Survey but also the deep pointing surveys near the ecliptic poles over ~15 deg2 in total will be particularly well suited to construct the luminosity functions of the infrared galaxies, to evaluate their clustering nature, and also to discover rare, exotic objects at various redshifts out to z ~ 3. AKARI is also capable of detecting and measuring the spectrum and the fluctuations of the cosmic infrared background. The in-orbit sensitivity and spatial resolution of the surveys are found to be sufficient to achive the scientific goals listed above.

Mechanical coolers operating below 4.5 K for space application

This paper reports the 4 K- and 1 K-class mechanical coolers developed for space use. The 4 K-class cooler has been developed for Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES), which is to be operated onboard the International Space Station (ISS). The cooling capacity is 20 mW at 4.5 K, with the total input power of approximately 120 W. The 1 K-class cooler has been developed for cooling far-infrared detectors to 1.7 K in the Space Infrared Telescope for Cosmology and Astrophysics (SPICA). The cooling capacity is 10 mW at 1.7 K and the total input power to the cooler is about 180 W. A future possible cryogen-free cooling system for temperature below 0.1 K is also presented, which uses these coolers as a pre-cooler.

Neon dewar for the X-ray spectrometer onboard Suzaku

The X-ray spectrometer (XRS) onboard Suzaku is the first X-ray microcalorimeter array in orbit. The sensor array is operated at 60 mK, which is attained by an adiabatic demagnetization refrigerator and superfluid liquid helium. The neon dewar is a vacuum-insulated container for the XRS. The requirements for the XRS dewar are to maintain the detector and the cryogenic system under the mechanical environment at launch ( ∼ 15 G ), and to attain a lifetime of 3 years in a near-earth orbit. It is characterized with adoptions of solid neon as the second cryogen and a mechanical cooler, design optimization of the support straps for the neon tank to reduce the heat load as much as possible, and shock absorbers to mitigate the mechanical environment at launch. Microphonics from the mechanical cooler was one of the concerns for the detector performance, but the ground test results proved that they do not interfere with the detector. After about 1 month in orbit, its thermal performance showed that the dewar potentially achieves its design goals.

Performance verification of the Suzaku X-ray Spectrometer in the flight configuration

The X-ray Spectrometer (XRS) is a high resolution, non-dispersive cryogenic detector on board the X-ray satellite, Suzaku (Astro-E2), which was successfully launched on July 10, 2005. The XRS achieves an energy resolution of 6 eV at 6 keV (FWHM) and covers a broad energy range of ∼ 0.07 –10 keV. The XRS will enable powerful plasma diagnostics of a variety of astrophysical objects such as the dynamics of gas in clusters of galaxies. The XRS was integrated to the spacecraft in September 2004, and underwent a series of spacecraft tests until April 2005. We describe results of the XRS performance verification in the spacecraft configuration. First, the noise level was extremely low on the spacecraft, and most of the pixels achieved an energy resolution of 5–6 eV at 5.9 keV. Microphonic noise from the mechanical cooler was one of the concerns, but this was not a problem, when the dewar was integrated to the spacecraft and filled with solid neon. To attain the best energy resolution, however, correction of gain drift is mandatory. The XRS has a dedicated calibration pixel for that purpose, and drift correction using the calibration pixel is very effective when the gain variation is due to changes in the ∼ 60 mK heat sink temperature. On the other hand, the calibration pixel and the other pixels do not respond in the same way to variations of the helium and neon bath temperatures, and this effect requires further study.

Development of a valved linear compressor for a satellite borne J–T cryocooler

The provision of temperatures below 12 K is essential for sub-mm and FIR observations from satellite instruments. Historically this has been achieved with stored cryogens, however mechanical coolers could potentially provide higher reliability and flexibility. These cryocoolers typically incorporate a regenerative cold-finger, such as a pulse-tube, however this can be replaced by a recuperative Joule–Thompson stage to obtain the lowest temperatures required. The major change to the compressor is the requirement for steady flow. This paper describes the development of such a compressor using reed valves, based on space-qualified hardware. Long life potential was demonstrated by measuring the motion of the valves during operation. A model was also developed and validated to optimize performance.

FUTURE SPACE INFRARED TELESCOPE MISSION, SPICA

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an infrared astronomical satellite with a 3.5 m cooled telescope which is very powerful in mid- and far- infrared observations and makes complementary role to JWST and Herschel. SPICA will be launched at ambient temperature without any cryogen into the Sun-Earth L2 orbit and cooled down in space to 4.5 K with use of efficient radiative cooling and mechanical coolers. The present status of SPICA and the developments of the satellite system are reported.

Cooling of bulk material by electron-tunneling refrigerators

Improved refrigeration techniques have lead to scientific discoveries such as superconductivity and Bose-Einstein condensation. Improved refrigeration techniques also enhance our quality of life. Semiconductor processing equipment and magnetic-resonance imaging machines incorporate mechanical coolers operating below 10 K. There is a pressing need for refrigeration techniques to reach even lower temperatures because many next-generation analytical and astronomical instruments will rely on sensors cooled to temperatures near 100 mK. Here we demonstrate a solid-state, on-chip refrigerator capable of reaching 100 mK based on the quantum-mechanical tunneling of electrons through normal metal-insulator-superconductor junctions. The cooling power and temperature reduction of our refrigerator are sufficient for practical applications and we have used it to cool bulk material that has no electrical connection to the refrigerating elements.

New cooling methods for HPGE detectors and associated electronics

Despite the on-going development of room temperature semiconductors for use as gamma-ray detectors, the only material which can provide a solution to the combined requirements of stability, high-energy resolution and high-detection efficiency (at useful energies) is still germanium (HPGe). These properties of HPGe gamma-ray detectors make them invaluable in meeting the demands of the newly emergent and increasingly important applications relating to homeland security and the interdiction of smuggled nuclear material. However, HPGe detectors require cooling to cryogenic temperatures (<120 K) to operate as gamma-ray detectors. Traditionally, this cooling has been accomplished with liquid nitrogen (LN2). The use of LN2 as a coolant is, at best, inconvenient. Maintenance, operating cost, availability at remote locations, and the hazardous nature of the material all combine to limit the practicality of a LN2-cooled device, no matter how desirable it might be from other standpoints. Mechanical methods of achieving cryogenic temperatures have existed for many years. The first mechanically-cooled HPGe systems appeared commercially in the early 1980s.1 These systems had high cost, high power requirements, degraded system performance, were bulky in size, and unreliable. Other developments have produced prototype versions of portable (or transportable) mechanically-cooled HPGe systems. More recent advances in mechanical cooling technologies have the potential to make HPGe detectors easily adaptable to a wide variety of applications including battery-operated, truly man-portable systems for use in inspection, unattended monitoring, and Homeland Security. The major problems of mechanical coolers are degraded performance due to vibration and power consumption. The systems described here have reduced both of these to useable limits. The vibration or microphonic noise created in real-world systems is significantly reduced by optimizing the digital filter technology in the signal processing electronics associated with such detectors. Data presented here show reliability and performance results of the mechanically-cooled systems. These results show the improvements gained through the use of the optimally-matched digital filters.

The ASTRO-F mission: Large area infrared survey

ASTRO-F is the first Japanese satellite mission dedicated for large area surveys in the infrared. The 69 cm aperture telescope and scientific instruments are cooled to 6 K by liquid Helium and mechanical coolers. During the expected mission life of more than 500 days, ASTRO-F will make the most advanced all-sky survey in the mid- to far-infrared since the Infrared Astronomical Satellite. The survey will be made in six wavebands and will include the first all sky survey at >100–160 μm. Deep imaging and spectroscopic surveys with pointed observations will also be carried out in 13 wavelength bands from 2 to 160 μm. ASTRO-F should detect more than a half million galaxies tracing the large-scale structure of the Universe out to redshifts of unity, detecting rare, exotic extraordinarily luminous objects at high redshift, numerous brown dwarfs, Vega-like stars, protostars, and will reveal the large-scale structure of nearby galactic star forming regions. ASTRO-F is a perfect complement to Spitzer Space Telescope in respect of its wide sky and wavelength coverage. Approximately 30% of pointed observations will be allocated to an open-time opportunity. Updated pre-flight sensitivities as well as the observation plan including the large-area surveys are described.

SPICA: A 3.5 m space infrared telescope for mid- and far-infrared astronomy

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is a Japanese astronomical infrared satellite project optimized for mid- to far-infrared observations. It will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system, a combination of which allows us to have a 3.5-m class cooled (4.5 K) telescope in space. SPICA will give us deep insights into a number of key problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets, owing to its high spatial resolution and unprecedented sensitivity in the mid- to far-infrared. We have made successful progress in the development of mechanical coolers, whereas silicon carbide and carbon-fiber reinforced silicon carbide have been extensively investigated as primary candidates for the SPICA telescope mirrors. We present the current status of the SPICA project as well as the results of technology developments.

Development of 1 K-class mechanical cooler for SPICA

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a future mission to launch a large infrared observatory to the second Sun–Earth Lagrangian liberation point (L2) by H-IIA rocket. A unique feature of its cryogenic system is a warm launch system using radiative cooling and closed-cycle mechanical coolers in orbit to cool its detectors and mirrors down to about 4.5 and 1.7 K. The 1 K-class cooler, which consists of a two-stage Stirling cooler and a Joule–Thomson (JT) cooler with 3He as the working fluid, has been developed for cooling the far infrared detectors to 1.7 K. Designed cooling capacity of the cooler is 10 mW at 1.7 K and the total input power to the cooler is about 180 W without driver electronics. This paper describes the preliminary design and the results from preliminary test of the prototype cooler for the 1 K-class cooler.