Ariel is the M4 mission of the ESA’s Cosmic Vision Program 2015-2025, whose aim is to characterize by lowresolution transit spectroscopy the atmospheres of over one thousand warm and hot exoplanets orbiting nearby stars. It has been selected by ESA in March 2018 and adopted in November 2020 to be flown, then, in 2029. It is the first survey mission dedicated to measuring the chemical composition and thermal structures of the atmospheres of hundreds of transiting exoplanets, in order to enable planetary science far beyond the boundaries of the Solar System. The Payload (P/L) is based on a cold section (PLM – Payload Module) working at cryogenic temperatures and a warm section, located within the Spacecraft (S/C) Service Vehicle Module (SVM) and hosting five warm units operated at ambient temperature (253-313 K). The P/L and its electrical, electronic and data handling architecture has been designed and optimized to perform transit spectroscopy from space during primary and secondary planetary eclipses in order to achieve a large set of unbiased observations to shed light and fully understand the nature of exoplanets atmospheres, retrieving information about planets interior and determining the key factors affecting the formation and evolution of planetary systems.
The Start-Planet Activity Research CubeSat (SPARCS) is a NASA-funded mission led by Arizona State University, devoted to characterizing the UV emission of low-mass stars. During its nominal one-year mission, SPARCS will observe close to 20 low-mass stars, with the goal of understanding their short and long-term UV variability. SPARCS will be ready for launch in 2025. SPARCS’ payload is a 9-cm telescope paired with two delta-doped charge-coupled devices (CCDs). The data calibration converts the raw instrument counts into an average flux within the two ultraviolet bands (153 - 171 nm, 258 - 308 nm). While the system is only weakly sensitive in the infrared, the target stars are very bright at long wavelengths. This requires careful correction of the data for out-of-band emission. The system is being fully characterized on the ground to provide supporting calibration data. The calibration uses observations of very stable white dwarfs to achieve the 10% photometric accuracy requirement in both bands.
We discuss the final assembly, integration, and testing of the Star-Planet Activity Research CubeSat. SPARCS is a 6U CubeSat mission designed to monitor the dual-channel, far-UV (153-176 nm) and near-UV (258-308 nm) photometric activity of nearby low mass stars to advance our understanding of their evolution, activity, and the habitability of surrounding exoplanets. This paper details the assembly of the SPARCS instrument and the testing process to characterize and validate the performance of the payload prior to spacecraft integration. To test SPARCS, we have established a customized CubeSat AIT laboratory and thermal vacuum chamber at ASU equipped to handle CubeSats requiring meticulous contamination control for work in the FUV. After a brief overview of these facilities and the testing plan, we will detail the methods and data used to verify the performance of SPARCS and generate calibration products to reduce raw flight data to high-quality science products. The result will be the delivery of the first highly sensitive FUV astrophysics CubeSat which will inform exoplanet environments and future observations of these systems by facilities like the Habitable Worlds Observatory.
UV-SCOPE is a mission concept to determine the causes of atmospheric mass loss in exoplanets, investigate the mechanisms driving aerosol formation in hot Jupiters, and study the influence of the stellar environment on atmospheric evolution and habitability. As part of these investigations, the mission will generate a broad-purpose legacy database of time-domain ultraviolet (UV) spectra for nearly 200 stars and planets. The observatory consists of a 60 cm, f/10 telescope paired to a long-slit spectrograph, yielding simultaneous, almost continuous coverage between 1203 Å and 4000 Å, with resolutions ranging from 6000 to 240. The efficient instrument provides throughputs < 4% (far-UV; FUV) and < 15% (near-UV; NUV), comparable to HST/COS and much better than HST/STIS, over the same spectral range. A key design feature is the LiF prism, which serves as a dispersive element and provides high throughput even after accounting for radiation degradation. The use of two delta-doped Electron-Multiplying CCD detectors with UV-optimized, single-layer anti-reflection coatings provides high quantum efficiency and low detector noise. From the Earth-Sun second Lagrangian point, UV-SCOPE will continuously observe planetary transits and stellar variability in the full FUV-to-NUV range, with negligible astrophysical background. All these features make UV-SCOPE the ideal instrument to study exoplanetary atmospheres and the impact of host stars on their planets. UV-SCOPE was proposed to NASA as a Medium Explorer (MidEx) mission for the 2021 Announcement of Opportunity. If approved, the observatory will be developed over a 5-year period. Its primary science mission takes 34 months to complete. The spacecraft carries enough fuel for 6 years of operations.
Within this paper, we describe architecture and functionality of the Fine Guidance Sensor (FGS), one of two instruments on-board ESA ARIEL mission. We present a conceptual design, development models, related challenges, and opportunities as seen at iPDR milestone.
The Star-Planet Activity Research CubeSat (SPARCS) is a 6U CubeSat under construction that is devoted to the photometric monitoring of M stars in the far-UV (FUV) and near-UV (NUV), to measure the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation. We report on the progress made in the assembly, integration and test of the instrument payload at Arizona State University using a custom TVAC chamber and optical stimulus that provides calibration light sources and the custom contamination control environment that the FUV demands. The payload consists of a custom 90mm clear aperture telescope developed by Hexagon/Sigma Space, combined with a dichroic plate to separate the FUV and NUV beams developed by Teledyne Acton and Materion, married with twin focal plane array cameras separately optimized for their bandpasses as developed by JPL.
The Atmospheric Remote-Sensing Infrared Exoplanet Large-survey, ARIEL, has been selected to be the next (M4) medium class space mission in the ESA Cosmic Vision programme. From launch in 2028, and during the following 4 years of operation, ARIEL will perform precise spectroscopy of the atmospheres of ~1000 known transiting exoplanets using its metre-class telescope. A three-band photometer and three spectrometers cover the 0.5 µm to 7.8 µm region of the electromagnetic spectrum.
This paper gives an overview of the mission payload, including the telescope assembly, the FGS (Fine Guidance System) - which provides both pointing information to the spacecraft and scientific photometry and low-resolution spectrometer data, the ARIEL InfraRed Spectrometer (AIRS), and other payload infrastructure such as the warm electronics, structures and cryogenic cooling systems.
KEYWORDS: Ultraviolet radiation, Stars, Atmospheric modeling, Space operations, Space telescopes, Planets, Telescopes, Sensors, Exoplanets, Control systems
Roughly 40 billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1–0.4 AU). Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M stars in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation.
NESSI (New Mexico Exoplanet Spectroscopic Survey Instrument) was originally conceived, designed and built under a NASA NM-EPSCoR funded effort as a near-infrared multi-object spectrograph for characterizing exoplanet transits at the Magdalena Ridge Observatory. With the help of funding from JPL, we are moving NESSI to its new home on the Hale telescope in early 2018. Salient features of the New NESSI include a 6.5 arc minute field-of-view, low (R~250) or moderate (R~1100) spectral resolutions across J, H and/or K bands, the ability to stare at transits with high frame-rates, and finally a suite of on-board filters for imaging applications. We present the new design of NESSI, lessons learned in the refurbishment process, as well as an update for next steps in the process.
ATLAST is a particular realization of the Large Ultraviolet Optical Infrared telescope (LUVOIR), a ∼10-m diameter space telescope being defined for consideration in the 2020 Decadal Review of astronomy and astrophysics. ATLAST/LUVOIR is generally thought of as an ambient temperature (∼300 K) system, and little consideration has been given to using it at infrared wavelengths longward of ∼2 μm. We assess the scientific and technical benefits of operating such a telescope further into the infrared, with particular emphasis on the study of exoplanets, which is a major science theme for ATLAST/LUVOIR. For the study of exoplanet atmospheres, the capability to work at least out to 5.0 μm is highly desirable. Such an extension of the long wavelength limit of ATLAST would greatly increase its capabilities for studies of exoplanet atmospheres and provide powerful capabilities for the study of a wide range of astrophysical questions. We present a concept for a fiber-fed grating spectrometer, which would enable R=200 spectroscopy on ATLAST with minimal impact on the other focal planet instruments. We conclude that it is technically feasible and highly desirable scientifically to extend the wavelength range of ATLAST to at least 5 μm.
An exoplanet mission based on a high-altitude balloon is a next logical step in humanity’s quest to explore Earthlike planets in Earthlike orbits orbiting Sunlike stars. The mission described here is capable of spectrally imaging debris disks and exozodiacal light around a number of stars spanning a range of infrared excesses, stellar types, and ages. The mission is designed to characterize the background near those stars, to study the disks themselves, and to look for planets in those systems. The background light scattered and emitted from the disk is a key uncertainty in the mission design of any exoplanet direct imaging mission, thus, its characterization is critically important for future imaging of exoplanets.
NESSI: the New Mexico Tech Extrasolar Spectroscopic Survey Instrument is a ground-based multi-object
spectrograph that operates in the near-infrared. It will be installed on one of the Nasmyth ports of the
Magdalena Ridge Observatory (MRO) 2.4-meter Telescope. NESSI operates stationary to the telescope
fork so as not to produce differential flexure between internal opto-mechanical components during or
between observations. In this paper we report on NESSI's detailed mechanical and opto-mechanical design,
and the planning for mechanical construction, assembly, integration and verification.
NESSI: the New Mexico Tech Extra(solar)planet Spectroscopic Survey Instrument is a ground-based multi-object
spectrograph that operates in the near-infrared and is being deployed this fall at the Magdalena Ridge Observatory 2.4 m
telescope. When completed later this year, it is expected to be used to characterize the atmospheres of transiting
exoplanets with unprecedented ground-based accuracies down to about K = 9 magnitude. The superior capabilities of
NEESI for this type of work lay, in part, in the design philosophy used for the instrument which is well-focused on the
exoplanet case. We report here on this design philosophy, detail and status of the design and assembly, and preparation
for first light in the fall of 2012.
KEYWORDS: Sensors, Spectroscopy, Space telescopes, Telescopes, Planets, Stars, Space operations, Mid-IR, Long wavelength infrared, Short wave infrared radiation
The Exoplanet Characterisation Observatory (EChO) is a space mission dedicated to undertaking spectroscopy of
transiting exoplanets over the widest wavelength range possible. It is based around a highly stable space platform with a
1.2 m class telescope. The mission is currently being studied by ESA in the context of a medium class mission within
the Cosmic Vision programme for launch post 2020. The payload suite is required to provide simultaneous coverage
from the visible to the mid-infrared and must be highly stable and effectively operate as a single instrument. In this
paper we describe the integrated spectrometer payload design for EChO which will cover the 0.4 to 16 micron
wavelength band. The instrumentation is subdivided into 5 channels (Visible/Near Infrared, Short Wave InfraRed, 2 x Mid Wave InfraRed; Long Wave InfraRed) with a common set of optics spectrally dividing the input beam via dichroics.
We discuss the significant design issues for the payload and the detailed technical trade-offs that we are undertaking to
produce a payload for EChO that can be built within the mission and programme constraints and yet which will meet the
exacting scientific performance required to undertake transit spectroscopy.
FINESSE (Fast INfrared Exoplanet Spectroscopic Survey Explorer) will provide uniquely detailed information on the
growing number of newly discovered planets by characterizing their atmospheric composition and temperature structure.
This NASA Explorer mission, selected for a competitive Phase A study, is unique in its breath and scope thanks to broad
instantaneous spectroscopy from the optical to the mid-IR (0.7 – 5 micron), with a survey of exoplanets measured in a
consistent, uniform way. For 200 transiting exoplanets ranging from Terrestrial to Jovians, FINESSE will measure the
chemical composition and temperature structure of their atmospheres and trace changes over time with exoplanet
longitude. The mission will do so by measuring the spectroscopic time series for a primary and secondary eclipse over
the exoplanet orbital phase curve. With spectrophotometric precision being a key enabling aspect for combined light
exoplanet characterization, FINESSE is designed to produce spectrophotometric precision of better than 100 parts-per-million
per spectral channel without the need for decorrelation. The exceptional stability of FINESSE will even allow
the mission to characterize non-transiting planets, potentially as part of FINESSE’s Participating Scientist Program. In
this paper, we discuss the flow down from the target availability to observations and scheduling to the analysis and
calibration of the data and how it enables FINESSE to be the mission that will truly expand the new field of comparative
exoplanetology.
KEYWORDS: Exoplanets, Planets, Infrared spectroscopy, Space telescopes, Signal to noise ratio, Space operations, Telescopes, Atmospheric chemistry, Calibration, Spectroscopy
THESIS, the Transiting Habitable-zone Exoplanet Spectroscopy Infrared Spacecraft, is a concept for a medium/Probe
class exoplanet mission. Building on the recent Spitzer successes in exoplanet characterization, THESIS would extend
these types of measurements to super-Earth-like planets. A strength of the THESIS concept is simplicity, low technical
risk, and modest cost. The mission concept has the potential to dramatically advance our understanding of conditions on
extrasolar worlds and could serve as a stepping stone to more ambitious future missions. We envision this mission as a
joint US-European effort with science objectives that resonate with both the traditional astronomy and planetary science
communities.
Less than 20 years after the discovery of the first extrasolar planet, exoplanetology is rapidly growing with more than
one discovery every week on average since 2007. An important step in exoplanetology is the chemical characterization
of exoplanet atmospheres. It has recently been shown that molecular signatures of transiting exoplanets can be studied
from the ground. To advance this idea and prepare more ambitious missions such as THESIS, a dedicated spectrometer
named the New Mexico Tech Extrasolar Spectroscopic Survey Instrument (NESSI) is being built at New Mexico Tech
in collaboration with the NASA Jet Propulsion Laboratory. NESSI is a purpose-built multi-object spectrograph that
operates in the J, H, and K-bands with a resolution of R = 1000 in each, as well as a lower resolution of R = 250 across
the entire J/H/K region.
KEYWORDS: Planets, Stars, Space telescopes, Exoplanets, Space operations, Telescopes, Photometry, Signal to noise ratio, Atmospheric chemistry, Spectroscopic atmospheric monitoring techniques
THESIS is a concept for a medium class mission designed for spectroscopic characterization of extrasolar planets
between 2-14 microns. The concept leverages off the recent first-steps made by Spitzer and Hubble in characterizing
the atmospheres of alien gas giants. Under favourable circumstances, THESIS is capable of identifying
biogenic molecules in habitable-zone planets, thereby determining conditions on worlds where life might exist.
By systematically characterizing many worlds, from rocky planets to gas-giants, THESIS would deliver
transformational science of profound interest to astronomers and the general public.
It is commonly accepted that highly challenging planet finding missions such as Darwin and TPF need precursors on the
ground, for both technological demonstration and study of the exozodiacal clouds around potential targets. A first
instrument, GENIE, designed to be implemented in the interferometric laboratory of the VLTI, was studied by ESA and
scientific/industrial teams. In this paper we present a concept for ALADDIN, an operational nulling instrument to be
implemented at Dome C in Antarctica, and discuss the comparison with GENIE from the instrumental point of view.
Our preliminary design involves moderate ~1m size telescopes mounted on a 40m long rotating beam allowing
baselines up to 30m and feeding a 2-arm nulling beam combiner. When compared to GENIE, the rotating beam design
has the advantage of removing the need for both long-stroke delay line and dispersion control equipments. As a side
effect, the instrumental arrangement of ALADDIN finds itself more representative of what Darwin will be.
Furthermore, critical issues like phase control, photometric balance and instrumental background suppression are
expected to be relaxed by the improved atmospheric conditions, lower temperature, and simpler optical trains.
Calibration of geometrical stellar leakage will make advantage of the continuously adjustable baseline. As results, a
simpler instrument showing improved performance is expected. In conclusion, we see our ALADDIN concept as a
valuable alternative to GENIE, with a quite stronger scientific potential and a considerably simplified instrumental
design.
The ESA Darwin space mission will require a ground based precursor to i/ demonstrate nulling interferometry
in an operational context and ii/ carry out some precursor science, such as the characterization of the level
of exozodiacal light around the main Darwin targets. These are the stated objectives of the GENIE nulling
instrument that was studied for the VLTI.
We argue here that the same objectives can be met in a more efficient way by an antarctic-based nulling
experiment. The ALADDIN mission concept is an integrated L-band nulling breadboard with relatively modest
collectors (1m) and baseline (40m). Because of its privileged location, this is suffcient to achieve a sensitivity
(in terms of detectable zodi levels) which is 1.6 to 3.5 times better than GENIE at the VLTI, bringing it below
the 20-zodi threshold value identified to carry out the Darwin precursor science. The integrated design enables
top-level optimization and full access to the light collectors for the duration of the experiment, while reducing
the complexity of the nulling breadboard.
KEYWORDS: Telescopes, Space telescopes, Optical instrument design, Motion models, Control systems design, 3D modeling, Device simulation, Adaptive optics, Domes, Control systems
Studies by Mark Swain and a colleague at the Max Planck Institut fur Astronomie, coupled with results from past and ongoing projects at Harvey Mudd College, strongly suggest that it may be possible to achieve imaging performance comparable to the Hubble Space Telescope at relatively low cost using available, commercial products. This is achievable by placing a 2.4 m telescope, with readily available adaptive optics, on a 30 m tower located at a high-elevation geological "dome" in Antarctica. An initial project surveyed relevant tower design approaches, then generated and evaluated six concept designs for telescope towers. Using data for typical and extreme wind at Dome C to generate wind loads, finite element analysis yielded lateral deflections at the top of 0.3 mm for typical winds and 12.1 mm for extreme gusts, with the lowest resonant frequency at 0.7 Hz; some tower concepts are innovative and allow for easy shipment, setup, and relocation. A subsequent project analyzed a tower designed by Hammerschlag and found fundamental resonance frequencies at 4.3 Hz for bending and 5.9 Hz for torsion; this project also designed and simulated an active telescope control system that maintained 17 milliarcsecond pointing error for the telescope atop the tower during typical wind conditions.
We present preliminary results of a comparison of possible Antarctic telescope locations based on the results of a
regional climate model. The simulation results include predictions for temperature, wind speed, seeing, precipitable
water vapor, and cloud cover. The domain of the simulation is the entire Antarctic continent for the 2004 winter season.
By incorporating lateral forcing, our simulation captures the effects of weather systems that can affect even the interior
regions of the Antarctic plateau. The simulation also shows maritime air advection into the plateau interior. We find the
model predictions are generally in good agreement with measurements made at the South Pole and Dome C. The
simulation results suggest that the Dome F and Dome A regions are potentially very good sites and are generally
superior to Dome C.
In realizing the scientific potential of locating an astronomical interferometer at one of the Antarctic domes, it will be necessary to retire risks and reduce costs. One way of doing this is to build the interferometer away from Antarctica, test the instrument, and then transport the system as modules to the final location. This novel approach can only be undertaken after it has been shown that such a system will survive the trip without damage, and that calibration of the system will be possible at a very low cost. The authors undertook such a study, measuring the shocks likely to be encountered during shipment, and then establishing that in all but one case, the shocks can be reduced by commercially available vibration isolators to <5g. The one shock not reducible to <5g occurred when the instrument was transferred from an icebreaker to the ice, and will require more careful handling by the shippers. The team also developed and modeled configurations for the delay lines and optics tables to reduce shipment risk while providing a backbone for the delay lines. The study supports the feasibility of a "preassembled" Antarctic interferometer.
Mid-infrared (8-13μm) nulling is a key observing mode planned for the NASA-funded Keck Interferometer at the Keck Observatory on the summit of Mauna Kea in Hawaii. By destructively interfering and thereby canceling the on-axis light from nearby stars, this observing mode will enable the characterization of the faint emission from exo-zodiacal dust surrounding these stellar systems. We report here the null leakage error budget and pre-ship results obtained in the laboratory after integration of the nulling beam combiner with its mid-infrared camera and key components of the Keck Interferometer. The mid-infrared nuller utilizes a dual-polarization, modified Mach-Zehnder (MMZ) beam combiner in conjunction with an atmospheric dispersion corrector to achieve broadband achromatic nulling.
We report on a novel approach for implementing a dual Bracewell nulling interferometric beam combiner using miniature conductive waveguides contained in a single monolithic structure. We present modeling results for these devices at mid-infrared wavelengths. Potential applications for these devices in the Terrestrial Planet Finder mission are discussed.
We propose a science demonstrator for the Antarctic Plateau Interferometer. It is a comparatively much simpler system than API but dedicated to the goal of obtaining the first low-resolution spectra in the thermal infrared of a few "hot Jupiter" type exoplanets. It would provide a unique platform to acquire operational experience on antarctic stellar interferometry, and build up an extensive database on the relevant site properties, as a preparation for API.
Observations of the nucleus of NGC 4151 at 2.2 μm using the two 10-meter Keck telescopes as an interferometer show a marginally resolved source less than or equal to 0.1 pc in diameter. These observations are the first measurement of an extragalactic source with an optical/IR interferometer. These observations represent a ten-fold improvement in angular resolution when compared to previous near-infrared measurements of AGN and make it possible to test the subparsec-scale, near-infrared emission models of NGC 4151.
The Antarctic Planet Interferometer is a concept for an instrument designed to detect and characterize extrasolar planets by exploiting the unique potential of the best accessible site on earth for thermal infrared interferometry. High-precision interferometric techniques under development for extrasolar planet detection and characterization (differential phase, nulling and astrometry) all benefit substantially from the slow, low-altitude turbulence, low water vapor content, and low temperature found on the Antarctic plateau. At the best of these locations, such as the Concordia base being developed at Dome C, an interferometer with two-meter diameter class apertures has the potential to deliver unique science for a variety of topics, including extrasolar planets, active galactic nuclei, young stellar objects, and protoplanetary disks.
The first high-dynamic-range interferometric mode planned to come on line at the Keck Observatory is mid-infrared nulling. This observational mode, which is based on the cancellation of the on-axis starlight arriving at the twin Keck telescopes, will be used to examine nearby stellar systems for the presence of circumstellar exozodiacal emission. This paper describes the system level layout of the Keck Interferometer Nuller (KIN), as well as the final performance levels demonstrated in the laboratory integration and test phase at the Jet Propulsion Laboratory prior to shipment of the nuller hardware to the Keck Observatory in mid-June 2004. On-sky testing and observation with the mid-infrared nuller are slated to begin in August 2004.
The Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) is a space-based imaging and spectral ("double Fourier") interferometer with kilometer maximum baseline lengths for imaging. This NASA "vision mission" will provide spatial resolution in the far-IR and submillimeter spectral range comparable to that of the Hubble Space Telescope, enabling astrophysicists to extend the legacy of current and planned far-IR observatories. The astrophysical information uniquely available with SPECS and its pathfinder mission SPIRIT will be briefly described, but that is more the focus of a companion paper in the Proceedings of the Optical, Infrared, and Millimeter Space Telescopes conference. Here we present an updated design concept for SPECS and for the pathfinder interferometer SPIRIT (Space Infrared Interferometric Telescope) and focus on the engineering and technology requirements for far-IR double Fourier interferometry. We compare the SPECS optical system requirements with those of existing ground-based and other planned space-based interferometers, such as SIM and TPF-I/Darwin.
Recent site seeing testing campaigns conducted by our team from University of Nice1 show that Dome C represents the best site on Earth for astronomical high angular resolution (HAR) observations at optical and IR wavelengths. The dramatic gain over relevant HAR parameters r0, L0, θ0 and τ0, added to very low temperatures during the polar winter nights (-70°C), the dry atmosphere and the possibility of continuous observations during several nights make Dome C the ideal site for deploying a kilometric optical interferometer before the 2015 horizon. Here we describe the concept of Kiloparsec Explorer for Optical Planet Search (KEOPS) that is studied by our group at LUAN. KEOPS is an interferometric array of 36 off-axis telescopes, each 1.5m in diameter. Its kilometric baselines open sub-mas snap-shot imaging possibilities to detect and characterize extra-solar planetary systems, especially exo-Earths out to 300 parsecs from the visible to the thermal IR. KEOPS can be considered as a DARWIN/TPF challenger but at a much lower cost.
Delay lines provide the pathlength compensation that makes the measurement of interference fringes possible. When used for nulling interferometry, the delay line must control pathlengths so that the null is stable and controlled throughout the measurement. We report on a low noise, low disturbance, high bandwidth optical delay line capable of meeting the TPF interferometer optical path length
control requirements at cryogenic temperatures.
Ultimately, after the Single Aperture Far-IR (SAFIR) telescope, astrophysicists will need a far-IR observatory that provides angular resolution comparable to that of the Hubble Space Telescope. At such resolution galaxies at high redshift, protostars, and nascent planetary systems will be resolved, and theoretical models for galaxy, star, and planet formation and evolution can be subjected to important observational tests. This paper updates information provided in a 2000 SPIE paper on the scientific motivation and design concepts for interferometric missions SPIRIT (the Space Infrared Interferometric Telescope) and SPECS (the Submillimeter Probe of the Evolution of Cosmic Structure). SPECS is a kilometer baseline far-IR/submillimeter imaging and spectral interferometer that depends on formation flying, and SPIRIT is a highly-capable pathfinder interferometer on a boom with a maximum baseline in the 30 - 50 m range. We describe recent community planning activities, remind readers of the scientific rationale for space-based far-infrared imaging interferometry, present updated design concepts for the SPIRIT and SPECS missions, and describe the main issues currently under study. The engineering and technology requirements for SPIRIT and SPECS, additional design details, recent technology developments, and technology roadmaps are given in a companion paper in the Proceedings of the conference on New Frontiers in Stellar Interferometry.
We have proposed to develop a prototype 0.5-meter far-infrared telescope and heterodyne receiver/spectrometer system for fully-automated remote operation at the summit of Dome A, the highest point on the Antarctic plateau. The unparalleled stability, exceptional dryness, low wind and extreme cold make Dome A a ground-based site without equal for astronomy at infrared and submillimeter wavelengths. HEAT, the High Elevation Antarctic Terahertz Telescope, will operate in the atmospheric windows between 150 and 400 microns, in which the most crucial astrophysical spectral diagnostics of the formation of galaxies, stars, planets, and life are found. At these wavelengths, HEAT will have high aperture efficiency and excellent atmospheric transmission most of the year. The proposed superheterodyne receiver system will be comprised of 0.8, 1.4 and 1.9 THz channels which will observe the pivotal J=7-6 line of CO, the J=2-1 line of atomic carbon, and the far-infrared fine structure lines of N+ and C+, the brightest emission lines in the entire Milky Way Galaxy. When combined with the HEAT telescope, the receiver system represents a uniquely powerful instrument for reconstructing the history of star formation in our Galaxy, with application to the distant Universe. The receiver system itself serves as a valuable testbed for heterodyne Terahertz components, using leading-edge mixer, local oscillator, low-noise amplifier, cryogenic, and digital signal processing technologies that will play essential roles in future Terahertz observatories. The proposed study will pave the way for future astronomical investigations from Dome A.
To properly characterize the atmospheric properties of a site for a future large telescope or interferometer, it is insufficient to measure quantities, such as the full-width at half-maximum of a stellar image, that have been integrated over the entire atmosphere. A knowledge of the turbulence distribution as a function of height is necessary, since this affects the ease and degree to which adaptive optics systems can improve the telescope’s resolution. Furthermore, some astronomical measurements, such as narrow-field differential astrometry at microarcsecond precision, depend critically on the amount of turbulence high in the atmosphere (up to 20km). In order to obtain the necessary site-testing data at remote sites such as those on the Antarctic plateau, we have designed a robust and reliable instrument based on an 85 mm refractive telescope, a gimbal-mounted sidereostat mirror, and a Multi-Aperture Scintillation Sensor (MASS). The instrument uses the spatial structure of single-star scintillation to measure vertical turbulence profiles from 0.5 to 20km. The MASS system is designed to operate completely autonomously throughout the Antarctic winter. It also has potential applications at existing observatory sites for quantifying the turbulence characteristics of the atmosphere in real-time.
The primary limitation to ground based astronomy is the Earth's atmosphere. The atmosphere above the Antarctic plateau is different in many regards compared to the atmosphere at temperate sites. The extreme altitude, cold and low humidity offer a uniquely transparent atmosphere at many wavelengths. Studies at the South Pole have shown additionally that the turbulence properties of the night time polar atmosphere are fundamentally different to mid latitudes. Despite relatively strong ground layer turbulence, the lack of high altitude turbulence combined with low wind speeds presents favorable conditions for interferometry. The unique properties of the polar atmosphere can be exploited for Extrasolar Planet studies with differential astrometry, differential phase and nulling intereferometers. This paper combines the available data on the properties of the atmosphere at the South Pole and other Antarctic plateau sites for Extrasolar Planet science with interferometry.
We report on the progress in developing cryogenic delay lines and
integrated optics components. These are some of the critical components needed to enable far-IR direct-detection interferometers. To achieve background-limited performance in the 40 to 400 μm region, th einterferometer optics and delay lines must be cooeld to near liquid Helium temperatures. Our cryogenic delay line designs incorporate a number of novel features and has been operated at liquid nitrogen temperatures. Our integrated optics effort has focued on producing single-mode spatial filters and beam combiners.
Laser induced, micro-chemical etching is a promising new technology that can be used to fabricate three dimensional structures many millimeters across with micrometer accuracy. Laser micromachining possesses a significant edge over more conventional techniques. It does not require the use of masks and is not confined to crystal planes. A non-contact process, it eliminates tool wear and vibration problems associated with classical milling machines. At the University of Arizona we have constructed the first such laser micromaching system optimized for the fabrication of THz and far IR waveguide and quasi-optical components. Our system can machine many millimeters across down to a few microns accuracy in a short time, with a remarkable surface finish. This paper presents the design, operation and performance of our system, and its applications to waveguide devices for sub millimeter and far IR interferometry.
The control of longitudinal dispersion, which determines the position of the null fringe as a function of wavelength, is central to the problem of producing deep broadband interferometric nulls. The dispersion is the sum of terms due to environmental factors such as the dry-air and water-vapor atmospheric seeing, the unbalanced air column due to the unequal delay-line paths between the telescopes the combiner, and to the distance from the central fringe. The difference between an achromatic nuller and a normal constructive combiner operating at its first (chromatic) null can be thought of as an added longitudinal dispersion, which for the case of the Keck Interferometer is smaller than the environmental terms. We demonstrate that the sum of these effects can be adequately compensated by an appropriate thickness of ZnSe combined with an additional achromatic pathlength. The Keck Interferometer nulling combiners take advantage of this result. They are intrinsically constructive combiners made to produce achromatic nulls by inserting a ZnSe dispersion corrector into each of the four input beams. We describe the null fringe stabilization control algorithm and present calculations of the required loop bandwidth and precision. A potentially important advantage of the present approach is that the system will be able to function as either a destructive or constructive combiner, depending on the value of a single control-loop parameter (the target fringe phase).
The W.M. Keck Observatory is conducting a focused effort to identify and mitigate facility vibrations that significantly affect optimal optical performance. This effort should improve the performance of both Keck adaptive optics systems, the laser guide star, the AO instruments, and the interferometer, and will benefit future high precision instruments.
We present our strategy for mitigating vibrations in a large ground-based telescope. Our approach is to establish reasonable confidence in identifying the facility vibration sources that most significantly deteriorate optical performance. For the interferometer we completed vibration surveys that correlate vibrations on the interferometer beam path with direct vibration measurements on the telescope structure and facility. We developed a metric to evaluate the effect of vibrations on the entire interferometer beamline. From our surveys, we prioritized facility components to be addressed, and developed approaches to mitigate key vibrations contributions. Initial results show large local improvements, and global improvements to our vibration environment.
The Keck Interferometer is entering a regular limited observational phase. A restricted number of observers are expected to use the instrument over the course of the next few years in a shared-risk capacity. To facilitate this, the W. M. Keck Observatory and the Jet Propulsion Laboratory are following a Handover procedure consisting of a number of stages related to the science modes of the instrument as they reach completion. The first of these is the Visibility Science mode that involves only the two Keck telescopes. Other modes to follow are Nulling, Differential Phase, Astrometry, and Imaging. The process includes defining a reasonable level of functionality of each mode, training observatory staff to maintain and schedule tasks related to the upkeep of each mode, and defining and documenting each of the subsystems related to each mode. Here we discuss the outline of the Handover plan and report on its progress to date.
Far infrared interferometers in space would enable extraordinary measurements of the early universe, the formation of galaxies, stars, and planets, and would have great discovery potential. Since half the luminosity of the universe and 98% of the photons released since the Big Bang are now observable at far IR wavelengths (40 - 500 micrometers ), and the Earth's atmosphere prevents sensitive observations from the ground, this is one of the last unexplored frontiers of space astronomy. We present the engineering and technology requirements that stem from a set of compelling scientific goals and discuss possible configurations for two proposed NASA missions, the Space Infrared Interferometric Telescope and the Submillimeter Probe of the Evolution of Cosmic Structure.
We discuss concepts for deploying direct-detection interferometers in space which are optimized for the wavelength range 40 micrometers to 500 micrometers . In particular, we introduce two missions in NASA's current strategic plan: SPIRIT (SPace InfraRed Interferometric Telescope) and SPECS (Submillimeter Probe of the Evolution of Cosmic Structure).
We present the motivation and development of the novel `differential phase' technique being developed for the Keck Interferometer with the goal of detecting faint companions near a bright source. The differential phase technique uses simultaneous phase measurements at several infrared wavelengths to detect the astrophysical signature produced by a chromatic, asymmetric brightness distribution. We discuss the origin of the differential phase signature and present results of test observations taken at the Palomar Testbed Interferometer. One important test result is the larger than expected effect of water vapor turbulence on these multi-wavelength observations due to the infrared dispersion of water. In order to reach the design goal of 0.1 milliradians, the phase noise caused by both temperature and water vapor fluctuations in the atmosphere must be corrected, and we discuss several ways to achieve this.
The South Pole Imaging Fabry-Perot Interferometer (SPIFI) is a direct detection, imaging, submillimeter spectrometer. The spectral resolving elements are a pair of cryogenic, scanning Fabry-Perot interferometers which use a free- standard Ni mesh for the etalon mirrors. The detectors for SPIFI are a 5 X 5 array of bolometers coupled to the focal plane with Winston cones. An adiabatic demagnetization refrigerator cools the bolometers to approximately 60 mK while a 3He system operates simultaneously as a thermal guard. SPIFI is intended to operate on the ASO/RO submillimeter telescope at the South Pole and on the JCMT telescope on Mauna Kea and will be used to study the gas- phase reservoirs of carbon in star-forming regions in our own and near-by galaxies. SPIFI takes advantage of three things: (1) Advanced bolometers that achieve background limited performance at very high resolving powers. (2) The imaging capability and high spectral resolving power of Fabry-Perot interferometers. (3) The superb atmospheric transmission in submillimeter bands possible from the South Pole. The SPIFI uses state-of-the-art monolithic silicon bolometers fabricated at the NASA Goddard Space Flight Center. The cryogenic, scanning Fabry-Perots in SPIFI were designed and built at Cornell and are an evolution of the design used with great success for the Kuiper Wide Field Camera. The 1.7 m Antarctic Submillimeter Telescope/Remote Observatory exploits what is thought to be the best submillimeter observing site in the world.
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