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.
We carried out various tests of 800-mm-diameter aperture, lightweight optics that consisted wholly of carbon fiber-reinforced SiC composite, called HB-Cesic. A cryogenic optical test was performed on the primary mirror to examine any CTE irregularity as a surface change, and only small deformations were observed. The primary mirror was assembled with a convex secondary mirror into an optical system and tested under vacuum at the 6-m-diameter radiometer space chamber at Tsukuba Space Center of JAXA, where we have prepared interferometric metrological facilities to establish techniques to test large optical systems in a horizontal light-axis configuration. The wavefront difference between under vacuum and under atmosphere was confirmed to be less than 0.1 λ at λ=633 nm, if we realigned the optical axis of the interferometer and flat mirror under vacuum. We also demonstrated a stitching interferometry using the Φ800-mm optics by rotating a mask wheel of subapertures in front of the optical reference flat. The wavefront stitched from eight individual measurements of Φ275-mm subapertures differs from the full-aperture measurement without the mask by about 0.1 λ nm RMS, which showed the technique could able to be applied to test large telescopes especially for infrared wavelength region.
Owing to its high specific stiffness and high thermal stability, silicon carbide is one of the materials most suitable for large space-borne optics. Technologies for accurate optical measurements of large optics in the vacuum or cryogenic conditions are also indispensable. Within the framework of the large SiC mirror study program led by JAXA, we manufactured an 800-mm-diameter lightweight telescope, all of which is made of HB-Cesic, a new type of carbon-fiber-reinforced silicon carbide (C/SiC) material developed jointly by ECM, Germany and MELCO, Japan. We first fabricated an 800-mm HB-Cesic primary mirror, and measured the cryogenic deformation of the mirror mounted on an HB-Cesic optical bench in a liquid-helium chamber. We observed the cryo-deformation of 110 nm RMS at 18 K with neither appreciable distortion associated with the mirror support nor significant residual deformation after cooling. We then integrated the primary mirror and a high-order aspheric secondary mirror into a telescope. To evaluate its optical performance, we established a measurement system, which consists of an interferometer in a pressure vessel mounted on a 5-axis adjustable stage, a 900-mm auto-collimating flat mirror, and a flat mirror stand with mechanisms of 2-axis tilt adjustment and rotation with respect to the telescope optical axis. We installed the telescope with the measurement system into the JAXA 6-m chamber and tested them at a vacuum pressure to verify that the system has a sufficiently high tolerance against vibrations in the chamber environment. Finally we conducted a preliminary study of sub-aperture stitching interferometry, which is needed for telescopes of our target missions in this study, by replacing the 900-mm flat mirror with a rotating 300-mm flat mirror.
We present a test of optical metrology for 800-mm spaceborne optics in the 6-m radiometer thermal vacuum chamber at
JAXA's Tsukuba Space Center of JAXA. Under the framework of the JAXA's large-optics study program for astronomy
and Earth observations, we developed a test bench for interferometric metrology of large optics with an auto-collimation
method in the chamber. The optical system was aligned in a horizontal light-axis configuration within the facility limit to
handle a 3.5-m aperture telescope like SPICA. A high-speed interferometer was contained in an aluminum and titanmade
pressure vessel, which was mounted on the five-axis stage. We tested the 800-mm lightweight C/SiC optics using a
900-mm diameter flat mirror. Alignment changes in tilts of about ten arcseconds were observed as pressure went down
from 1 atm to vacuum. After we re-aligned the interferometer and flat mirror, the wavefronts through the optics under
vacuum were observed to increase in astigmatism aberration by 0.07λRMS at λ=633nm from under atmosphere, which
might be caused by a deformation in the test optics or flat mirror.
SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japan-led infrared astronomical satellite project
with a 3-m-class telescope in collaboration with Europe. The telescope is cooled down to temperature below 6 K in space
by a combination of mechanical coolers with radiative cooling in space. The telescope has requirements for its total
weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 μm at 6 K. The mirrors
will be made of silicon carbide (SiC) or its related material, which has large heritages of the AKARI and Herschel
telescopes. The design of the telescope system has been studied by the Europe-Japan telescope working group led by
ESA with European industries to meet the requirements. As for optical testing, responsibilities will be split between
Europe and Japan so that final optical verification at temperatures below 10 K will be executed in Japan. We present our
recent optical testing activities in Japan for the SPICA telescope, which include the numerical and experimental studies
of stitching interferometry as well as modifications of the 6-m-diameter radiometer space chamber facility at Tsukuba
Space Center in JAXA. We also show results of cryogenic optical testing of the 160-mm and 800-mm lightweight
mirrors made of a C/SiC material called HBCesic, which is a candidate mirror material for the SPICA telescope.
Chalcogenide glasses are compounded from chalcogen elements, such as sulphur, selenium, and tellurium. These
glasses are applied to commercial applications, e.g., night vision, because they transmit infrared in the spectral range of
0.8-16μm. Chalcogenide glasses have greater advantages over germanium (Ge), i.e., their wide spectral range of high
transmissivity and their small temperature dependence of the refractive index.
We have developed the Compact Infrared Camera (CIRC) with an uncooled infrared array detector (microbolometer)
for space applications. The CIRC has been scheduled to launch in 2013 to demonstrate the usability of a microbolometer
as a space application. The optics of the CIRC adopts two different kinds of materials for athermal optics. One is
germanium, and the other is GASIR1® which is a chalcogenide glass (Ge22As20Se58) developed by Umicore. However,
the radiation tolerance of GASIR® has not been investigated in the past.
We carried out irradiation tests to investigate the radiation tolerance of GASIR1®. We irradiated GASIR1® with
gamma-rays (Co60, 1.17 MeV and 1.33 MeV) up to 3Mrad. We measured the transmissivity and refractive index in the
infrared range before and after irradiation. In this paper, we report the results of the irradiation tests of GASIR1®.
The Compact InfraRed Camera (CIRC) is a technology-demonstration payload to be carried on the Small Demonstration
Satellite type-2 (SDS-2). The SDS program is a JAXA activity to demonstrate a variety of new technologies and new
missions. The CIRC is an infrared camera equipped with an uncooled infrared array detector (microbolometer). The
mission of the SDS-2/CIRC project is to demonstrate the potential of the microbolometer, especially for wildfire
detection but also for other applications. This paper introduces the detailed design and concept of CIRC. We also discuss
preliminary results of the feasibility study on wildfire detection using thermal infrared images.
We introduce a Japanese plan of infrared(z-band:0.9μm) space astrometry(JASMINE-project). JASMINE is
the satellite (Japan Astrometry Satellite Mission for INfrared Exploration) which will measure distances and
apparent motions of stars around the center of the Milky Way with yet unprecedented precision. It will measure
parallaxes, positions with the accuracy of 10 micro-arcsec and proper motions with the accuracy of ~ 4microarcsec/
year for stars brighter than z=14mag. JASMINE can observe about ten million stars belonging to the
bulge components of our Galaxy, which are hidden by the interstellar dust extinction in optical bands. Number of
stars with σ/π < 0.1 in the direction of the Galactic central bulge is about 1000 times larger than those observed
in optical bands, where π is a parallax and σ is an error of the parallax. With the completely new "map of the
bulge in the Milky Way", it is expected that many new exciting scientific results will be obtained in various fields
of astronomy. Presently, JASMINE is in a development phase, with a target launch date around 2015. We adopt
the following instrument design of JASMINE in order to get the accurate positions of many stars. A 3-mirrors
optical system(modified Korsch system)with a primary mirror of~
0.85m is one of the candidate for the optical
system. On the astro-focal plane, we put dozens of new type of CCDs for z-band to get a wide field of view. The
accurate measurements of the astrometric parameters requires the instrument line-of-sight highly stability and
the opto-mechanical highly stability of the payload in the JASMINE spacecraft. The consideration of overall
system(bus) design is now going on in cooperation with Japan Aerospace Exploration Agency(JAXA).
We explain simulation tools in JASMINE project (JASMINE simulator). The JASMINE project stands at the stage where its basic design will be determined in a few years. Then it is very important to simulate the data stream generated by astrometric fields at JASMINE in order to support investigations into error budgets, sampling strategy, data compression, data analysis, scientific performances, etc. Of course, component simulations are needed, but total simulations which include all components from observation target to satellite system are also very important. We find that new software technologies, such as Object Oriented(OO) methodologies are ideal tools for the simulation system of JASMINE(the JASMINE simulator).
In this article, we explain the framework of the JASMINE simulator.
We report an outline and a current status of developing a small, all-aluminum made telescope for Nano-JASMINE.
Nano-JASMINE is a nano-size astrometry satellite that will demonstrate some key technologies required for
JASMINE (Japan Astrometry Satellite Mission for Infrared Exploration) in a real space environment and will
measure absolute positions of bright stars (z ≤ 8 mag) with accuracies about 1 milli-arcsecond in a few years
mission. It has a Ritchey-Chretien type telescope with a 5-cm effective aperture, a 167-cm focal length and a field
of view of 0.5x0.5 degree. The telescope only occupies a volume about 15x12x12 cm, and weighs two kilograms
or less. Almost all of the structures and the optical elements of the telescope, including two aspherical mirrors
three flat mirrors and a dual-angled flat mirror that combines the beam from a relative angle of 99.5 degrees into
the primary mirror, are made out of aluminum alloy, being figured by diamond turning machines. The Bread
Board Model (BBM) of the telescope was now measured to be achieving a diffraction-limited performance at
The current status of the nano-JASMINE project is presented. Nano-JASMINE - a very small satellite weighing
less than 10 kg - aims to carry out astrometry measurements of nearby bright stars. This satellite adopts
the same observation technique that was used by the HIPPARCOS satellite. In this technique, simultaneous
measurements in two different fields of view separated by an angle that is greater than 90° are carried out; these
measurements are performed in the course of continuous scanning observations of the entire sky. This technique
enables us to distinguish between an irregularity in the spin velocity and the distribution of stellar positions.
There is a major technical difference between the nano-JASMINE and the HIPPARCOS satellites-the utilization
of a CCD sensor in nano-JASMINE that makes it possible to achieve an astrometry accuracy comparable to that
achieved by HIPPARCOS by using an extremely small telescope.
We developed a prototype of the observation system and evaluated its performance. The telescope (5cm)
including a beam combiner composed entirely of aluminum. The telescope is based on the standard Ritchey-
Chretien optical system and has a composite f-ratio of 33 that enables the matching of the Airy disk size to three
times the CCD pixel size of 15μm. A full depletion CCD will be used in the time delay integration (TDI) mode
in order to efficiently survey the whole sky in wavelengths including the near infrared.
The nano-JASMINE satellite is being developed as a piggyback system and is hoped for launch in 2008. We
expect the satellite to measure the position and proper motion of bright stars (mz < 8.3) with an accuracy of 1
mas, this is comparable to the accuracy achieved with the HIPPARCOS satellite.
We present the outline and the current status of the MAGNUM automated observation system. The operational objective of the MAGNUM Project is to carry out long-term multi-color monitoring observations of active galactic nuclei in the visible and near-infrared wavelength regions. In order to obtain these observations, we built a new 2 m optical-infrared telescope, and sited it at the University of Hawaii's Haleakala Observatory on the Hawaiian Island of Maui. Preliminary observations were started early in 2001. We are working toward the final form of the MAGNUM observation system, which is an unmanned, automated observatory. This system requirement was set by considering that the observation procedures are relatively simple, and the targets must be observed consistently over many years.
We report an infrared all sky cloud monitor operating at Subaru telescope at Mauna Kea, Hawaii. It consists of panoramic optics and a 10 μm infrared imager. Aspheric metal mirrors coated with gold (sapphire over-coated) are used in the panoramic optics, which is similar to the MAGNUM observatory's cloud monitor at Haleakala, Maui. The imager is a commercially available non-cooled bolometer array. The system is waterproof and (almost) maintenance-free. The video signals from the imager are captured, averaged over 50 frames, subtracted clear-sky frame and flat-fielded in two minutes interval. The processed cloud images are transferred to Subaru observational software system (SOSS) and displayed combined with telescope/targets information and also stored to Subaru Telescope data archive system (STARS). The processed images will be opened on Internet web site.
The MAGNUM Project is designed to carry out multi color monitoring observations of hundreds of AGNs over several years in order to measure the distance of these far away objects using simple physical principles and thereby determine cosmic parameters. The project has been funded by the Research Center of Early Universe. This project started in 1995 and observations are planned to begin in 1998. For the project, we are building a new remote controlled observatory with a 2 m automated telescope as well as new infrared and optical instruments. The telescope is optimized for infrared observations and for obtaining monitoring observations over many years. Our plane is to operate the observatory at the Haleakala summit on the Island of Maui, a suitable place for long time monitoring observations. The telescope is 2 m in diameter and has an alt-azimuth mount. The observatory will be equipped with such facilities as an automated instrument changer, weather monitor, environmental monitor and cloud cover monitor, making it easier to operate the telescope automatically and remotely. Observations will be carried out using an on-site scheduler, which will be commanded through a networked remote computer. Two observatory instruments are being built for the MAGNUM Project. The first is an infrared and optical imaging photometer which incorporates a dichroic beam-splitter and has an imaging capability over a wide wavelength range from 0.3 micrometers to 4 micrometers . It will be primarily used for AGN monitoring. The other is a wide field (33' field of view) 8K X 8K mosaic CCD camera.
We present the optical, mechanical and electronic design of MAGNUM-MIP. The MAGNUM project plans to carry out multi color monitoring observations for hundreds of AGNs over several years under remote and automated operation. MAGNUM- MIP has two channels that offer optical and IR broad-band imaging observations at the same time. The IR channel has a SBRC InSb 256 by 256 array which covers a wavelength range from 1 to 4 microns, and the optical channel uses a 1024 by 1024 SITE CCD which covers 0.35 micron to 1 micron. The two channels use the same optics and a beam splitter. We adopted a reflecting optical system in order to get good imaging quality over the wide wavelength range. Because the monitoring is expected to be carried out remotely for several years with minimum manual support and maintenance, the camera is designed to work with only semi-annual maintenance. It has a mechanical cooler, a low outgas design, and an automated vacuum system.