Slated for launch in 2025, SPHEREx will be NASA’s next astrophysics explorer mission. Optimized to meet rigorous requirements to precisely map the Universe’s large scale structure, produce deep maps of the diffuse extra-galactic background, and to survey the Milky Way’s biogenic ice content, the SPHEREx telescope’s widefield optical design utilizes a series of custom near infrared linear variable filters to survey the entire sky spectroscopically. This unique instrument has now completed its construction phase and is fully assembled for flight. To precisely focus and calibrate the optical and spectroscopic properties of SPHEREx, a custom optical-cryogenic facility was developed and commissioned. In this overview, we describe the implementation of the recently completed instrument integration and testing campaign, delivering a well characterized imaging spectrometer to be integrated with the rest of the observatory.
The Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) is an upcoming all-sky near-infrared spectroscopic survey satellite designed to address all three primary science goals of NASA’s Astrophysics Division. SPHEREx employs a series of Linear Variable Filters (LVFs) to create 102 spectral channels across the wavelength range of 0.75 to 5 µm, with spectral resolutions R between 35 and 120. This paper presents the spectral calibration setup used for SPHEREx and discusses the various challenges encountered during the measurement process. Ultimately, we demonstrate the spectral responses for all 25 million pixels in SPHEREx.
The extragalactic background light (EBL) is the integrated diffuse emissions from unresolved stars, galaxies, and intergalactic matter along the line of sight. The EBL is regarded as consisting of stellar emissions and thus an important observational quantity for studying global star formation history throughout cosmic time. Intensity and anisotropy in the near-infrared EBL as measured by the Cosmic Infrared Background ExpeRiment (CIBER), NASA’s sounding rocket experiment, and previous infrared satellites exceed the predicted signal from galaxy clustering alone. The objective of CIBER-2 is to unveil the EBL excess by observing it at extended wavelengths into the visible spectrum with an accuracy better than CIBER. The onboard instrument of CIBER2 comprises a 28.5-cm telescope cooled to 90K, and three HAWAII-2RG detectors coupled with dual-band filters for photometric mapping observations in six wavebands simultaneously and with linear variable filters for lowresolution spectroscopy. Although CIBER-2 made a successful first flight from White Sands Missile Range in New Mexico in 2021, technical problems such as contamination of thermal radiation from the rocket chassis and degradation of the mirror coat were recognized. Despite a successful second flight in 2023 solving the problems with the revised onboard instrument, the experiment was aborted because of trouble with the rocket tracking system. In this paper, we describe the parachute-recovered payload rebuilt after the second flight and the testing, and we report the successful flight on May 5th 2024.
SPHEREx is a NASA Medium Explorer mission planned for launch in early 2025. It will produce an all-sky near infrared spectral survey from 0.75µm to 5µm with 6.2”x 6.2” pixels and spectral resolving power ranging between R=35 and R=130.
Each focal plane assembly (FPA) comprises three 2048x2048 H2RG detector arrays. The H2RG detector is paired with a Linear Variable Filter, placed just above the detector, that defines a spectral response that varies over the detector along one spatial direction. Two FPAs view the sky through a dichroic beamsplitter, where the short-wave FPA uses three 2.5µm cutoff H2RGs and the mid-wave FPA uses three 5.3µm cutoff H2RGs. We developed a novel laboratory setup to carry out spectral response measurements of every pixel by coupling a cryogenic Winston Cone and integrating spheres to a grating spectrometer which allows us to measure the full 2x3.5°x11.3° field of view simultaneously. This presentation will present the design of the test apparatus and results.
Selected as the next NASA Medium Class Explorer mission, SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer is planned for launch in early 2025. SPHEREx calibration data products include detector spectral response, non-linearity, persistence, and telescope focus error measurements. To produce these calibration products, we have developed a dedicated data acquisition and instrument control system, SPHERExLabTools (SLT). SLT implements driver-level software for control of all testbed instrumentation, graphical interfaces for control of instruments and automated measurements, real-time data visualization, processing, and data archival tools for a variety of output file formats. This work outlines the architecture of the SLT software as a framework for general purpose laboratory data acquisition and instrument control. Initial SPHEREx calibration products acquired while using SLT are also presented.
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