Publisher's Note: This paper, originally published on 30 July 2024, was replaced with a corrected/revised version on 8 November 2024. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
High precision sub-arcsecond pointing stability has become a capability widely utilized in the balloon-borne community, in particular for high resolution optical systems. However, many of these applications are also pushing the state-of-the-art with regards to detector technology, many forms of which require some level of cryogenic cooling and active dissipative cooling systems to achieve target performance specifications. Built on the success of the Super-pressure Balloon-borne Imaging Telescope (SuperBIT) experiment, we present the results of improved technologies and design methodologies applied to the EXoplanet Infrared TElescope (EXCITE), which uses active cryogenic systems to achieve detector performance while requiring pointing stability at the 100 milliarcsecond level. Results from EXCITE's recent balloon-borne campaign are presented within the context of Super-pressure Balloon (SPB) and Long Duration Balloon (LDB) applications.
The EXoplanet Climate Infrared TElescope (EXCITE) is a near-infrared spectrograph (0.8-3.5 μm, R∼50) designed for measuring spectroscopic phase curves of transiting hot Jupiter-type exoplanets that operates off a high-altitude balloon platform. Phase curves produce a combination of phase curve and transit/eclipse spectroscopy, providing a wealth of information for characterizing exoplanet atmospheres. EXCITE will be a firstof- kind dedicated telescope uniquely able to observe a target nearly uninterrupted for tens of hours, enabling phase curve measurements, and complementing JWST. The spectrometer has two channels, a 0.8-2.5 μm band and a 2.5-3.5 μm band, providing a spectrum with a spectral resolution of R≥50. Two Off-Axis Parabolic (OAP) mirrors reimage the telescope focal plane to provide on-axis, diffraction-limited performance, wth a CaF2 prism providing dispersion. The spectrum is imaged with a single JWST flight spare Teledyne H2RG detector, providing Nyquist sampling of each channel. Here, we discuss the spectrograph’s mechanical design, acceptance testing, assembly, and cryostat integration.
The EXoplanet Climate Infrared TElescope (EXCITE) is an instrument designed to measure spectroscopic phase curves of extrasolar hot Jupiters from a long duration balloon platform. EXCITE will fly a moderate resolution spectrometer housed inside of a cryogenic receiver actively cooled by two linear pulse tube cryocoolers. Here we provide the current status of the design and performance of the cryogenic receiver, its heat rejection mechanism, and associated control electronics. A recirculating methanol fluid loop rejects heat from the cryocoolers and transports it to sky-facing radiator panels mounted to the gondola. The cryocoolers are controlled by drive electronics with active vibration reduction functionality to minimize the impact of vibrations on pointing stability. We discuss the thermal and vibrational performance of the cryogenic receiver during ground-based pointing tests in its 2023 field campaign in Ft. Sumner, NM and present its current status as EXCITE prepares for its 2024 test flight campaign.
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.
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.
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