We have planned the Lunar observatory project, TSUKUYOMI aiming to meter-wavelength observations on the Moon. One of the scientific objectives is to observe the 21 cm global signal from the Dark Ages using the 1–50 MHz observing frequency range. The receiving system must have a noise temperature sufficiently lower than the foreground noise and also requires the flat bandpass response. To cover the ultra-wide bandwidth, an electrically-short dipole antenna and a preamplifier with high input impedance will be employed. This paper focuses on a feasibility study of the system performance. The environment of and around the observation site, such as the lunar surface dielectric constant and the antenna height from the ground plane, affects the sensitivity because it alters important parameters such as the antenna beam pattern and impedance. The investigation results of relationship between the surrounding environment and the sensitivity will be also reported.
Aim to Japan's participation in the Artemis program in the 2030s in mind, we pursue the feasibility studies of lunar telescope, including astronomical observations. Focusing on the meter-wavelength observations (observing frequency of lower than 50MHz), which cannot be observed in the harsh environments on the ground from the Earth, including the ionosphere and radio frequency interference, we have reported on conceptual design based on the results of our feasibility studies in Japan. The main scientific objectives we have studied so far are broadly covering the following three areas: astronomy and astrophysics, planetary science, and lunar science. In astrophysics, the observing frequency range of 1- 50MHz gives us an opportunity to observe the 21 cm global signal (spatial average temperature) from the Dark Ages, which is determined purely by cosmology and is not affected by first-generation star formation and cosmic reionization. In astronomy, it provides the images of the Milky Way galaxy at meter wavelengths. In planetary science, it will be possible to study the environments of exoplanets through 1) radio waves from auroras on gas giant exoplanets like Jupiter and 2) stellar radio-wave bursts. In lunar science, it has the potential to observationally study the lunar ionosphere, subsurface structure, and dust environment. At present, we plan the meter-wavelength interferometric array as lunar telescope, including the single-dish observations. In this paper, focused on the scientific requirements from cosmology, we will report the design concepts of Japanese lunar telescope project, including the advanced feasibility studies of antenna, receiver, signal chain and spectrometer that are compared as other studies in US, China and Europe. We named this project TSUKUYOMI.
Direct detection of Earth-like exoplanets requires a high-contrast imaging system to suppress bright stellar light that prevents the detection. The wavefront sensing and control technique which is one component of the high-contrast imaging system can suppress stellar scattered light (speckles) caused by wavefront aberrations. However, deformation of the system due to temperature changes in space telescopes or atmospheric turbulence in ground-based telescopes cause speckles that fluctuate faster than the wavefront sensing and control. As the post-processing technique, the Coherent Differential Imaging on Speckle Area Nulling (CDI-SAN) method was proposed to suppress the fast-fluctuating speckles. We are conducting the laboratory demonstration of the CDISAN method using two types of experimental facilities. One of them is equipped with a deformable mirror and a field programmable gate array. In our initial laboratory demonstration, we achieved 10−8 level contrast. To achieve higher contrast, we are updating our facility. The other facility is equipped with a spatial light modulator (SLM). In this facility, the contrast was improved by 10−1 using the CDI-SAN method.
Low-frequency radio observations below 50 MHz on the Moon are not subject to some radio interference, allowing for the study before the formation of the first star, which is impossible from the Earth. Our lunar observatory project, TSUKUYOMI, aims to observe the 21cm global signal from the Dark Ages, requiring wideband observations covering 1-50MHz to spot absorption features of ∼ 40 mK relative to the CMB. Considering the radiation from the Milky Way, which is the main foreground noise source and the reception characteristics of the short dipole antenna, a pre–amplifier with a noise lower than 2nV/√ Hz and an input capacitance of 25pF will result in a system noise well below foreground noise over the entire bandwidth and a roughly flat wideband response. Managing the input/floating capacitance and using a lumped constant circuit is crucial for wideband performance. This paper outlines the wideband system and delves into the system performance requirements.
GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is one of the three candidates of ISAS/JAXA’s Strategic L-class mission for the 2030s. The 1.2 m aperture, 50 K cryogenic space telescope with the wide-field camera (WFC) will provide the 1,260 square arcmin field-of-view for five photometric bands between 2 and 8 μm. The high resolution spectrometer (HRS) will observe the 10–18 µm with a wavelength resolution of 30,000. The GREX-PLUS WFC field-of-view is 130 times larger than that of the James Webb Space Telescope and similar to those of Euclid and Roman Space Telescope. Since these two survey missions are limited to the wavelength less than around 2 µm, GREX-PLUS will extend the wavelength coverage beyond 2 μm, providing versatile legacy imaging survey significantly improved from previous Spitzer imaging survey in the same wavelength range. The spectral resolution of the GREX-PLUS HRS is 10 times higher than that of the James Webb Space Telescope, opening a new window of the mid-infrared high-resolution spectroscopy from space. The main scientific themes are the galaxy formation and evolution and the planetary system formation and evolution. The GREX-PLUS WFC aims to detect the first generation of “bright” galaxies at redshift z > 15. The GREX-PLUS HRS aims to resolve the Kepler motion of water vapor molecules and identify the location of the water “snowline” in ∼ 100 proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of super massive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on. This paper presents the status of the concept design of GREX-PLUS, including telescope system, WFC, HRS, cooling system, and spacecraft bus system.
KEYWORDS: Prisms, Calibration, Polarizers, Polarization, Spectroscopes, Spectral resolution, Equipment, Target detection, Space telescopes, Signal to noise ratio
The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will demonstrate spectroscopy of planets and polarization measurements of disks. The spectroscopy and polarization modes utilize Amici and Wollaston prism designs. The spectroscopy mode, designed and built and Goddard Space Flight Center (GSFC), has a resolution of R50 in 15% bands centered at 660nm and 730nm. The Wollaston design and optics are contributed by the Japanese Aerospace Exploration Agency, with final alignment and testing at GSFC. We present the requirements, ground-to-orbit calibration, and deployable slit operations. We also detail on the design, results from the as-built flight assemblies.
Various types of high-contrast imaging instruments have been proposed and developed for direct detection of exoplanets by suppressing nearby stellar light. Stellar speckles due to wavefront aberration can be suppressed by the appropriate wavefront control, called the dark hole control. However, the speckles, which fluctuate faster than the dark hole control due to atmospheric turbulence in ground-based telescopes or instrument deformation caused by temperature changes in space telescopes, cannot be suppressed by the control and remain in focal plane images. The Coherent Differential Imaging on Speckle Area Nulling (CDI-SAN) method was proposed to overcome such fast fluctuating speckles and detect exoplanetary light. We constructed an optical setup in a laboratory to demonstrate the CDI-SAN method. With the dark hole control and the CDI-SAN method, we achieved 10−8 level of contrasts.
The atmospheric characterization of habitable candidates is one of the effective approaches for search for life out of the solar system. However, it is much hard by high planet-star flux contrast, 10-8 - 10-10 . A coronagraphic mask proposed by Itoh & Matsuo (2020) can suppress host stellar light but is imposed by a strict wavelength range limit of 0.3%. A spectroscopic coronagraph that combines the diffraction-limited coronagraph with a spectrograph is expected to achieve enlarges the effective bandwidth. On the other hand, a non-common path error, which is induced by the spectrograph, could limit the achievable contrast. We designed a high-accuracy spectrograph motivated for the spectroscopic coronagraph and measured its wavefront error. The common path error is 9.9 nm RMS, which is mostly caused by the alignment error between the convex grating and spherical mirror of the spectrograph. The achievable contrast of the spectroscopic coronagraph was also estimated from the non-common path error measurement. We found that the contrast of 10-8 could be achieved with a bandwidth of 5%, which is a promising result as the first step.
Recently, we have proposed a fourth-order coronagraph with inner working angles (IWA) of ∼ 1λ/D applicable with segmented telescopes, by deriving some complex-valued focal-plane mask patterns with the value between the interval [-1,1]. The mask pattern is implementable achromatically with a custom-patterned half-waveplate sandwiched between two linear polarizers orthogonal to each other. To enhance the system’s spectral bandwidth, we are now investigating the methods from various perspectives. One method to widen the system’s spectral bandwidth is to disperse point spread functions (PSF) incident to the focal-plane mask to the direction orthogonal to the mask pattern using a diffraction grating. Because the mask pattern is one-dimensional, we can optimize the mask pattern for each PSF dispersed by each wavelength (spectroscopic coronagraph). Another method focuses on the fact that the stellar leak due to a wide spectral bandwidth is flat at the Lyot stop and thus reducible with the successive use of the multiple coronagraph systems. Because the practical successive use of the multiple coronagraph systems requires a high off-axis throughput of the focal-plane mask, we derived new mask patterns by modifying the original pattern. This method can bring additional enhance of spatial resolution, although the current optimization limits the working angle to the separation angles of 0.7–1.4λ/D (super-resolution coronagraph or double coronagraph). Our fundamental simulation shows that both the methods can deliver a contrast of 10−10 at wavelengths of 650–750nm.
GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a new mission concept for ISAS/JAXA’s strategic L-class mission program in the 2030s. With a 1.2 m aperture, a 50 K cryogenic space telescope will have a < 1, 400 arcmin2 wide-field camera with 6 bands in the 2–10 μm wavelength range and a high-dispersion spectrometer with a wavelength resolution of < 30, 000 in the 10–18 μm band. The cryogenic infrared mission concept of GREX-PLUS is based on SPICA, exploiting the technical resources so far studied and developed, such as an active cooling system. The high-dispersion spectrometer of GREX-PLUS is based on the high-dispersion channel of the SPICA Mid-Infrared Instrument (SMI). The wide-field camera of GREX-PLUS is also based on previous concept studies for the ISAS/JAXA’s WISH mission concept. GREX-PLUS is a concept proposal for a Japan-led mission but international collaborations are also welcome.
The mid/far infrared hosts a wealth of spectral information that allows direct determination of the physical state of matter in a large variety of astronomical objects, unhindered by foreground obscuration. Accessing this domain is essential for astronomers to much better grasp the fundamental physical processes underlying the evolution of many types of celestial objects, ranging from protoplanetary systems in our own milky way to 10-12 billion year old galaxies at the high noon of galaxy formation in our universe. The joint ESA/JAXA SPICA mission will give such access for the astronomical community at large, by providing an observatory with unprecedented mid- to far-infrared imaging, polarimetric and spectroscopic capabilities.
Measurements in the infrared wavelength domain allow us to assess directly the physical state and energy balance of cool matter in space, thus enabling the detailed study of the various processes that govern the formation and early evolution of stars and planetary systems in the Milky Way and of galaxies over cosmic time. Previous infrared missions, from IRAS to Herschel, have revealed a great deal about the obscured Universe, but sensitivity has been limited because up to now it has not been possible to fly a telescope that is both large and cold. Such a facility is essential to address key astrophysical questions, especially concerning galaxy evolution and the development of planetary systems.
SPICA is a mission concept aimed at taking the next step in mid- and far-infrared observational capability by combining a large and cold telescope with instruments employing state-of-the-art ultra-sensitive detectors. The mission concept foresees a 2.5-meter diameter telescope cooled to below 8 K. Rather than using liquid cryogen, a combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With cooling not dependent on a limited cryogen supply, the mission lifetime can extend significantly beyond the required three years. The combination of low telescope background and instruments with state-of-the-art detectors means that SPICA can provide a huge advance on the capabilities of previous missions.
The SPICA instrument complement offers spectral resolving power ranging from ~50 through 11000 in the 17-230 µm domain as well as ~28.000 spectroscopy between 12 and 18 µm. Additionally, SPICA will be capable of efficient 30-37 µm broad band mapping, and small field spectroscopic and polarimetric imaging in the 100-350 µm range. SPICA will enable far infrared spectroscopy with an unprecedented sensitivity of ~5x10-20 W/m2 (5σ/1hr) - at least two orders of magnitude improvement over what has been attained to date. With this exceptional leap in performance, new domains in infrared astronomy will become accessible, allowing us, for example, to unravel definitively galaxy evolution and metal production over cosmic time, to study dust formation and evolution from very early epochs onwards, and to trace the formation history of planetary systems.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.