The EXoplanet Climate Infrared TElescope (EXCITE) experiment is a balloon-borne, purpose-designed mission to measure spectroscopic phase curves of short-period extrasolar giant planets (EGPs, or “hot Jupiters”). Here, we present EXCITE’s principal science instrument: a high-throughput, single-object spectrograph operating in the 0.8-2.5 µm and 2.5-4.0 µm bands with R≥50. Our compact design achieves diffraction-limited, on-axis performance with just three powered optics: two off-axis parabolic mirrors and a CaF2 prism. We discuss the optical and mechanical design, the expected optical performance of the spectrograph, and summarize the tolerances needed to achieve that performance. We also discuss plans for establishing alignment of the optics and verifying the optical performance.
The EXoplanet Climate Infrared TElescope (EXCITE) is a 0.5 meter near-infrared spectrograph that will fly from a high altitude balloon platform. EXCITE is designed to perform phase-resolved spectroscopy – continuous spectroscopic observations of a planet’s entire orbit about its host star – of transiting hot Jupiter-type exoplanets. With spectral coverage from 0.8 – 4 um, EXCITE will measure the peak of a target’s spectral energy distribution and the spectral signatures of many hydrogen and carbon-containing molecules. Phase curve observations are highly resource intensive, especially for shared-use facilities, and they require exceptional photometric stability that is difficult to achieve, even from space. In this work, we introduce the EXCITE experiment and explain how it will solve both these problems. We discuss its sensitivity and stability, then provide an update on its current status as we work toward a 2024 long duration science flight.
The EXoplanet Climate Infrared TElescope (EXCITE) is an instrument dedicated to measuring spectroscopic phase curves of extrasolar giant planets. EXCITE will carry a moderate resolution near-infrared spectrograph and will fly on a long duration balloon mission. We give an overview of the mechanical and thermal design and development status of the EXCITE cryogenic receiver. Active cooling for the EXCITE cryostat is provided by two linear pulse-tube cryocoolers. We discuss cryocooler thermal performance, integration of the spectrometer and detector, and the mounting scheme that attaches the cryostat to the backplate of the telescope. To reject heat power from the cryocoolers, gravity-assisted copper-methanol thermosyphons will maintain cryocooler temperatures within 20 ◦C of ambient temperature during operation. We discuss the results of preliminary thermal modeling of the thermosyphons as well as performance testing of a prototype built for in-lab verification.
Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) is an ESA M class mission aimed at the study of exoplanets. The satellite will orbit in the lagrangian point L2 and will survey a sample of 1000 exoplanets simultaneously in visible and infrared wavelengths. The challenging scientific goal of Ariel implies unprecedented engineering efforts to satisfy the severe requirements coming from the science in terms of accuracy. The most important specification – an all-Aluminum telescope – requires very accurate design of the primary mirror (M1), a novel, off-set paraboloid honeycomb mirror with ribs, edge, and reflective surface. To validate such a mirror, some tests were carried out on a prototype – namely Pathfinder Telescope Mirror (PTM) – built specifically for this purpose. These tests, carried out at the Centre Spatial de Liège in Belgium – revealed an unexpected deformation of the reflecting surface exceeding a peek-to-valley of 1µm. Consequently, the test had to be re-run, to identify systematic errors and correct the setting for future tests on the final prototype M1. To avoid the very expensive procedure of developing a new prototype and testing it both at room and cryogenic temperatures, it was decided to carry out some numerical simulations. These analyses allowed first to recognize and understand the reasoning behind the faults occurred during the testing phase, and later to apply the obtained knowledge to a new M1 design to set a defined guideline for future testing campaigns.
Ariel (Atmospheric Remote-Sensing Infrared Exoplanet Large Survey) is the adopted M4 mission in the framework of the ESA “Cosmic Vision” program. Its purpose is to conduct a survey of the atmospheres of known exoplanets through transit spectroscopy. Launch is scheduled for 2029. Ariel scientific payload consists of an off-axis, unobscured Cassegrain telescope feeding a set of photometers and spectrometers in the waveband between 0.5 and 7.8 µm and operating at cryogenic temperatures (55 K). The Telescope Assembly is based on an innovative fully-aluminum design to tolerate thermal variations avoiding impacts on the optical performance; it consists of a primary parabolic mirror with an elliptical aperture of 1.1 m of major axis, followed by a hyperbolic secondary that is mounted on a refocusing system, a parabolic re-collimating tertiary and a flat folding mirror directing the output beam parallel to the optical bench. An innovative mounting system based on 3 flexure-hinges supports the primary mirror on one side of the optical bench. The instrument bay on the other side of the optical bench houses the Ariel IR Spectrometer (AIRS) and the Fine Guidance System / NIR Spectrometer (FGS/NIRSpec). The Telescope Assembly is in phase B2 towards the Preliminary Design Review to start the fabrication of the structural model; some components, i.e., the primary mirror, its mounting system and the refocusing mechanism, are undergoing further development activities to increase their readiness level. This paper describes the design and development of the ARIEL Telescope Assembly.
The Atmospheric Remote-Sensing Infrared Exoplanet Large-survey, ARIEL, has been selected to be the next M4 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 about 1000 known transiting exoplanets using its metre-class telescope, a three-band photometer and three spectrometers that will cover the 0.5 µm to 7.8 µm region of the electromagnetic spectrum. The payload is designed to perform primary and secondary transit spectroscopy, and to measure spectrally resolved phase curves with a stability of < 100 ppm (goal 10 ppm). Observing from an L2 orbit, ARIEL will provide the first statistically significant spectroscopic survey of hot and warm planets. These are an ideal laboratory in which to study the chemistry, the formation and the evolution processes of exoplanets, to constrain the thermodynamics, composition and structure of their atmospheres, and to investigate the properties of the clouds.
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