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.
The Cosmology Large Angular Scale Surveyor (CLASS) is a polarization-sensitive telescope array located at an altitude of 5,200 m in the Chilean Atacama Desert. CLASS is designed to measure “E-mode” (even parity) and “B-mode” (odd parity) polarization patterns in the Cosmic Microwave Background (CMB) over large angular scales with the aim of improving our understanding of inflation, reionization, and dark matter. CLASS is currently observing with three telescopes covering four frequency bands: one at 40 GHz (Q); one at 90 GHz (W1); and one dichroic system at 150/220 GHz (G). In these proceedings, we discuss the updated design and in-lab characterization of new 90 GHz detectors. The new detectors include design changes to the transition-edge sensor (TES) bolometer architecture, which aim to improve stability and optical efficiency. We assembled and tested four new detector wafers, to replace four modules of the W1 focal plane. These detectors were installed into the W1 telescope, and will achieve first light in the austral winter of 2022. We present electrothermal parameters and bandpass measurements from in-lab dark and optical testing. From in-lab dark tests, we also measure a median NEP of 12.3 aW√ s across all four wafers about the CLASS signal band, which is below the expected photon NEP of 32 aW√ s from the field. We therefore expect the new detectors to be photon noise limited.
We have developed a suite of novel infrared-blocking filters made by embedding scattering particles in a polymer aerogel substrate. Our developments allow us to tune the spectral performance of the filters based on both the composition of the base aerogel material and the properties of the scattering particles. Our filters are targeted for use in a variety of applications, from ground-based CMB experiments to planetary science probes. We summarize the formulations we have fabricated and tested to date, including several polyimide base aerogel formulations incorporating a range of size distributions of diamond scattering particles. We also describe the spectral characterization techniques used to measure the filters’ optical properties, including the development of a mm-wave Fourier transform spectrometer testbed.
Infrared-blocking scattering aerogel filters have a broad range of potential applications in astrophysics and planetary science observations in the far-infrared, sub-millimeter, and microwave regimes. Successful dielectric modeling of aerogel filters allowed the fabrication of samples to meet the mechanical and science instrument requirements for several experiments, including the Sub-millimeter Solar Observation Lunar Volatiles Experiment (SSOLVE), the Cosmology Large Angular Scale Surveyor (CLASS), and the Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM). Thermal multi-physics simulations of the filters predict their performance when integrated into a cryogenic receiver. Prototype filters have survived cryogenic cycling to 4 K with no degradation in mechanical properties.
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.
The Cosmology Large Angular Scale Surveyor consists of four instruments performing a CMB polarization survey. Currently, the 40 GHz and first 90 GHz instruments are deployed and observing, with the second 90 GHz and a multichroic 150/220 GHz instrument to follow. The receiver is a central component of each instrument's design and functionality. This paper describes the CLASS receiver design, using the first 90 GHz receiver as a primary reference. Cryogenic cooling and filters maintain a cold, low-noise environment for the detectors. We have achieved receiver detector temperatures below 50mK in the 40 GHz instrument for 85% of the initial 1.5 years of operation, and observed in-band efficiency that is consistent with pre-deployment estimates. At 90 GHz, less than 26% of in-band power is lost to the filters and lenses in the receiver, allowing for high optical efficiency. We discuss the mounting scheme for the filters and lenses, the alignment of the cold optics and detectors, stray light control, and magnetic shielding.
The Cosmology Large Angular Scale Surveyor (CLASS) aims to detect and characterize the primordial Bmode signal and make a sample-variance-limited measurement of the optical depth to reionization. CLASS is a ground-based, multi-frequency microwave polarimeter that surveys 70% of the microwave sky every day from the Atacama Desert. The focal plane detector arrays of all CLASS telescopes contain smooth-walled feedhorns that couple to transition-edge sensor (TES) bolometers through symmetric planar orthomode transducer (OMT) antennas. These low noise polarization-sensitive detector arrays are fabricated on mono-crystalline silicon wafers to maintain TES uniformity and optimize optical efficiency throughout the wafer. In this paper, we discuss the design and characterization of the first CLASS 93 GHz detector array. We measure the dark parameters, bandpass, and noise spectra of the detectors and report that the detectors are photon-noise limited. With current array yield of 82%, we estimate the total array noise-equivalent power (NEP) to be 2.1 aW√s.
EBEX is a balloon-borne telescope designed to measure the polarization of the cosmic microwave background radiation. During its eleven day science flight in the Austral Summer of 2012, it operated 955 spider-web transition edge sensor (TES) bolometers separated into bands at 150, 250 and 410 GHz. This is the first time that an array of TES bolometers has been used on a balloon platform to conduct science observations. Polarization sensitivity was provided by a wire grid and continuously rotating half-wave plate. The balloon implementation of the bolometer array and readout electronics presented unique development requirements. Here we present an outline of the readout system, the remote tuning of the bolometers and Superconducting QUantum Interference Device (SQUID) amplifiers, and preliminary current noise of the bolometer array and readout system.
Spider is a balloon-borne array of six telescopes that will observe the Cosmic Microwave Background. The 2624
antenna-coupled bolometers in the instrument will make a polarization map of the CMB with approximately
one-half degree resolution at 145 GHz. Polarization modulation is achieved via a cryogenic sapphire half-wave
plate (HWP) skyward of the primary optic. We have measured millimeter-wave transmission spectra of the
sapphire at room and cryogenic temperatures. The spectra are consistent with our physical optics model, and
the data gives excellent measurements of the indices of A-cut sapphire. We have also taken preliminary spectra of
the integrated HWP, optical system, and detectors in the prototype Spider receiver. We calculate the variation
in response of the HWP between observing the CMB and foreground spectra, and estimate that it should not
limit the Spider constraints on inflation.
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.