Astronomy at far-infrared (far-IR) wavelengths is essential to our understanding of the evolution of the cosmos, from the star formation history of galaxies to how the ice distribution affects the formation of extrasolar planetary systems. The Hubble Space Telescope, James Webb Space Telescope, and the Atacama Large Millimeter Array have already produced ground-breaking astronomical observations with high angular resolution spanning the visible to sub-millimetre wavelength regimes. However, this presents a gap in the far-IR, from roughly 30−400μm, where ground-based observations are largely intractable due to the opacity of Earth’s atmosphere. Indeed, no telescope, observatory, or interferometry array has ever achieved sub-arcsecond angular resolution over this wavelength range. A space-based solution is needed. However, a space-based far-IR telescope capable of subarcsecond angular resolution and high sensitivity, at a cost comparable to the largest space missions to date, presents unique physical, practical, and engineering challenges. In this paper, we envisage what a far-IR Great Observatory class mission might look like in the context of the already-studied Origins Space Telescope (OST) and the Space Infrared Interferometric Telescope (SPIRIT). We begin with a historical reflection of far-IR missions, including OST and the recommendations by the Astro2020 Decadal Survey for a de-scoped mission. We use this to motivate the recommendation of a space-based interferometer as a reasonable path towards sub-arcsecond angular resolution at far-IR wavelengths. Using the SPIRIT mission concept as inspiration, we consider multiple point designs for a two element, structurally connected spatial-spectral space-based far-IR interferometer to understand the implications on achieved angular resolution and estimate total mission cost in context of the Decadal Survey recommended far-IR Great Observatory cost cap. This paper illustrates the unique capabilities only possible through a space-based far-IR double Fourier interferometry mission capable of sub-arcsecond resolution.
A space-based far-infrared interferometer could work synergistically with the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA) to revolutionize our understanding of the astrophysical processes leading to the formation of habitable planets and the co-evolution of galaxies and their central supermassive black holes. Key to these advances are measurements of water in its frozen and gaseous states, observations of astronomical objects in the spectral range where most of their light is emitted, and access to critical diagnostic spectral lines, all of which point to the need for a far-infrared observatory in space. The objects of interest – circumstellar disks and distant galaxies – typically appear in the sky at sub-arcsecond scales, which rendered all but a few of them unresolvable with the successful and now-defunct 3.5-m Herschel Space Observatory, the largest far-infrared telescope flown to date. A far-infrared interferometer with maximum baseline length in the tens of meters would match the angular resolution of JWST at 10x longer wavelengths and observe water ice and water-vapor emission, which ALMA can barely do through the Earth’s atmosphere. Such a facility was conceived and studied two decades ago. Here we revisit the science case for a space-based far-infrared interferometer in the era of JWST and ALMA and summarize the measurement capabilities that will enable the interferometer to achieve a set of compelling scientific objectives. Common to all the science themes we consider is a need for sub-arcsecond image resolution.
Carbon dioxide (CO2) is an atmospheric trace gas; therefore its accurate sensing is of great interest. Optical sensors exploiting the midinfrared (mid-IR) light absorption of CO2 provide high sensitivity and are widely used in medical diagnostics, atmospheric monitoring, remote sensing, and industrial applications. In this work, we demonstrated accurate CO2 gas sensing at a 4.2-μm wavelength. In addition, detecting the weak mid-IR molecular absorption bands of gases at low concentrations requires using increased optical path lengths. The most obvious method that can expand the potential beam path in a spectroscopic system is to use a longer linear gas cell, which in some situations may be adequate; however, space and volume requirements need to be considered. A circular multireflection (CMR) cell was used to reflect the radiation back and forth through the sample medium multiple times, thus greatly reducing the size footprint compared with a linear cell of equivalent optical path length. A CMR cell was designed and constructed to allow for multireflections within the cell. The optical alignment of the cell and the convenience of changing the optical path length by adjusting its position with respect to the incident light beam were also used to maximize the advantages of the device. The cell has an inner diameter of 6.5 cm, and the path length can reach up to 123.5 cm, which is equivalent to 19 beam passes of reflections. This work will be used as the groundwork for designing an instrument for the high-resolution measurement of CO2 gas in planetary atmospheres.
Carbon dioxide (CO2) is an atmospheric trace gas, and its accurate sensing is therefore of great interest. Optical sensors exploiting the mid-infrared (mid-IR) light absorption of CO2 provide high sensitivity and are widely used in medical diagnostics, atmospheric monitoring, remote sensing, and industrial applications. In this work, we demonstrated an accurate CO2 gas sensing at 4.2 µm wavelength. In addition, detecting the weak mid-IR molecular absorption bands of gases at low concentrations requires increasing optical path lengths to be used. The most obvious method that can expand the potential beam path in a spectroscopic system is to use a longer linear gas cell, which in some situations may be adequate; however, space and volume requirements need to be considered. In this work, a circular multi reflection (CMR) cell was used to reflect the radiation back and forth through the sample medium multiple times, thus greatly reducing the size footprint compared to a linear cell of equivalent optical path length. A CMR cell was designed and constructed to allow multi-reflections within the cell. The optical alignment of the cell and the convenience of changing the optical path length by adjusting its position with respect to the incident light beam were also used to maximize the advantages of the device. This work will be used as the groundwork for designing an instrument for the high-resolution measurement of CO2 gas in planetary atmospheres.
Validation of global climate models (GCMs) for planets in our solar system requires observational data, but observations from the orbit of Mars and its surface are limited in number and are constrained by their orbit or landing site. Ground-based observations of Mars can help by providing data across the entire Martian hemisphere, yet historically, ground-based observations at submillimeter wavelengths have been limited to disk-average, or at best, a few resolution elements across Mars. We used Atacama Large Millimeter/submillimeter Array (ALMA) observations of Mars to determine the spatial distribution of carbon monoxide in the Martian atmosphere, which can be related to the atmospheric temperature. ALMA’s comparably high spatial and spectral resolutions in the submillimeter wavelengths could allow the mapping of abundances and temperature profiles, and the comparison of these data to simulations generated by the Laboratoire de Météorologie Dynamique (LMD) Mars GCM. However, the long baselines associated with the high spatial resolution of ALMA introduced systematic errors that resulted in radiative transfer modeling degeneracies. We serve to provide insight to facilitate proposed ALMA observations of Mars in the future so that the systematic errors encountered within these observations might be avoided.
Mid-infrared (IR) laser spectroscopy is broadly used to study trace gas species in medical diagnostics, atmospheric monitoring, remote sensing, and industrial applications. Its capability to measure fundamental rovibrational bands due to the chemical functional groups in the most relevant gas molecules allows for high instrumental sensitivity. In this work, we used a target mid-IR wavelength laser diode to measure the concentration of CO2 gas. In addition, detecting the weak mid-IR molecular absorption bands of gases like CO2 at low concentrations requires increasing optical path lengths to be used. There are a number of methods that can potentially be used to lengthen the beam path in a spectroscopic system; the most obvious being to use a longer linear gas cell, which in some situations may suffice; however, space and volume requirements need to be considered. In this work, we used a circular multi-reflection (CMR) cell, which reflects the radiation back and forth through the sample medium multiple times greatly reducing the footprint size compared to a linear cell of equivalent path length. A CMR cell is designed and constructed so that it allows multi-reflections within the cell. The optical alignment of the cell and the convenience of changing the optical path length by adjusting its position with respect to the entering light beam are key advantages. This work will be used as the groundwork for designing an instrument for high-resolution measurement of gas abundances in planetary atmospheres.
Pamela Clark, Tilak Hewagama, Shahid Aslam, James Bauer, Michael Daly, Lori Feaga, Dave Folta, Nicolas Gorius, Kyle Hughes, Terry Hurford, Donald Jennings, Timothy Livengood, Michael Mumma, Conor Nixon, Jessica Sunshine, Geronimo Villanueva, Kevin Brown, Ben Malphrus, Aaron Zucherman
Here we describe the Primitive Object Volatile Explorer (PrOVE), a smallsat mission concept to study the surface structure and volatile inventory of comets in their perihelion passage phase when volatile activity is near peak. CubeSat infrastructure imposes limits on propulsion systems, which are compounded by sensitivity to the spacecraft disposal state from the launch platform and potential launch delays. We propose circumventing launch platform complications by using waypoints in space to park a deep space SmallSat or CubeSat while awaiting the opportunity to enter a trajectory to flyby a suitable target. In our Planetary Science Deep Space SmallSat Studies (PSDS3) project, we investigated scientific goals, waypoint options, potential concept of operations (ConOps) for periodic and new comets, spacecraft bus infrastructure requirements, launch platforms, and mission operations and phases. Our payload would include two low-risk instruments: a visible image (VisCAM) for 5-10 m resolution surface maps; and a highly versatile multispectral Comet CAMera (ComCAM) will measure 1) H2O, CO2, CO, and organics non-thermal fluorescence signatures in the 2-5 μm MWIR, and 2) 7-10 and 8-14 μm thermal (LWIR) emission. This payload would return unique data not obtainable from ground-based telescopes and complement data from Earth-orbiting observatories. Thus, the PrOVE mission would (1) acquire visible surface maps, (2) investigate chemical heterogeneity of a comet nucleus by quantifying volatile species abundance and changes with solar insolation, (3) map the spatial distribution of volatiles and determine any variations, and (4) determine the frequency and distribution of outbursts.
Bryan J. Holler, Stefanie N. Milam, James M. Bauer, Charles Alcock, Michele T. Bannister, Gordon L. Bjoraker, Dennis Bodewits, Amanda S. Bosh, Marc W. Buie, Tony L. Farnham, Nader Haghighipour, Paul S. Hardersen, Alan W. Harris, Christopher M. Hirata, Henry H. Hsieh, Michael Kelley, Matthew M. Knight, Emily A. Kramer, Andrea Longobardo, Conor A. Nixon, Ernesto Palomba, Silvia Protopapa, Lynnae C. Quick, Darin Ragozzine, Vishnu Reddy, Jason D. Rhodes, Andy S. Rivkin, Gal Sarid, Amanda A. Sickafoose, Amy A. Simon, Cristina A. Thomas, David E. Trilling, Robert A. West
We present a community-led assessment of the solar system investigations achievable with NASA’s next-generation space telescope, the Wide Field Infrared Survey Telescope (WFIRST). WFIRST will provide imaging, spectroscopic, and coronagraphic capabilities from 0.43 to 2.0 μm and will be a potential contemporary and eventual successor to the James Webb Space Telescope (JWST). Surveys of irregular satellites and minor bodies are where WFIRST will excel with its 0.28 deg2 field-of-view Wide Field Instrument. Potential ground-breaking discoveries from WFIRST could include detection of the first minor bodies orbiting in the inner Oort Cloud, identification of additional Earth Trojan asteroids, and the discovery and characterization of asteroid binary systems similar to Ida/Dactyl. Additional investigations into asteroids, giant planet satellites, Trojan asteroids, Centaurs, Kuiper belt objects, and comets are presented. Previous use of astrophysics assets for solar system science and synergies between WFIRST, Large Synoptic Survey Telescope, JWST, and the proposed Near-Earth Object Camera mission is discussed. We also present the case for implementation of moving target tracking, a feature that will benefit from the heritage of JWST and enable a broader range of solar system observations.
Gas Abundance Sensor Package (GASP) is a stand-alone scientific instrument that has the capability to measure the concentration of target gases based on a non-dispersive infrared sensor system along with atmospheric reference parameters. The main objective of this work is to develop a GASP system which takes advantage of available technologies and off-the-shelf components to provide a cost-effective solution for localized sampling of gas concentrations. GASP will enable scientists to study the atmosphere and will identify the conditions of the target’s planetary local environment. Moreover, due to a recent trend of miniaturization of electronic components and thermopiles detectors, a small size and robust instrument with a reduction in power consumption is developed in this work. This allows GASP to be easily integrated into a variety of small space vehicles such as CubeSats or small satellite system, especially the Micro-Reentry Capsule (MIRCA) prototype vehicle. This prototype is one of the most advanced concepts of small satellites that has the capability to survive the rapid dive into the atmosphere of a planet. In this paper, a fully-operational instrument system will be developed and tested in the laboratory environment as well as flight preparation for a field test of the instrument suite will be described.
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