To address the scientific goals of NASA's astrophysics division, the JPL and Caltech's SPHEREx mission conducts the first near-infrared all-sky spectral survey in low-earth-orbit using a ...passively-cooled, cryogenic telescope. Several unique water contamination issues arise due to the combination of cryogenic operation temperatures and the limited temperature control authority of passive cooling. Because water molecules have adsorption bands within the wavelengths of interest for SPHEREx's survey, it is imperative that water contamination be controlled and minimized. In this work, a model is developed for the SPHEREx mission to predict the transport and accumulation of outgassed water onto sensitive payload components. The model utilizes the time dependent thermal profiles of the individual payload components, initial water content, and spacecraft geometry to calculate the time dependent water diffusion, transport, and adsorption. This model is subsequently used to predict water contamination risks and design decontamination solutions for each risk. Two major water contamination risks were predicted, water accumulation during cooldown and on cryogenic surfaces during the mission. The first risk occurs during the cooldown of the payload to cryogenic temperatures, predicting water accumulation on optical surfaces in excess of the allowable levels. To mitigate this accumulation, the temperature of the optical surfaces is controlled during cooldown through a combination of heaters and spacecraft pointing. The second risk is unavoidable water accumulation onto the payload thermal system's cryogenic surfaces. This possibly jeopardizes thermal performance and temperature stability, both of which are required for science success. To decontaminate any water that had collected onto cryogenic thermal system surfaces, a decontamination maneuver was designed. In this decontamination maneuver, cryogenic surfaces of the thermal system are warmed to a temperature where water will desorb by spacecraft pointing while still meeting all avoidance constraints, and thereby avoiding undue risk to the observatory hardware. Through application of the developed analytical model and inclusion of the decontamination maneuver in the mission design, SPHEREx can confidently demonstrate that it is able to decontaminate, at the start of and during the mission as needed to meet its end of life science performance requirements.
We report the measurement of the relative permeability of Metglas 2714A at 4.2
K temperature and at frequencies up to 1
MHz. We find that at ∼300
kHz, the real part of the relative permeability ...begins to drop towards unity, while the magnitude of the imaginary part increases. Our data can be used to design transformers and EMI filters for low temperature applications.
Measurements of Casimir effects in 4He films in the vicinity of the bulk superfluid transition temperature Tλ have been carried out, where changes in the film thickness and the superfluid density are ...both monitored as a function of temperature. The Kosterlitz-Thouless superfluid onset temperature in the film is found to occur just as the Casimir dip in the film thickness from critical fluctuations becomes evident. Additionally, a new film-thickening effect is observed precisely at Tλ when the temperature is swept extremely slowly. We propose that this is a non-universal Casimir effect arising from the viscous suppression of second sound modes in the film.
Measurements of Casimir effects in super(4)He films in the vicinity of the bulk superfluid transition temperature T sub(lambda) have been carried out, where changes in the film thickness and the ...superfluid density are both monitored as a function of temperature. The Kosterlitz-Thouless superfluid onset temperature in the film is found to occur just as the Casimir dip in the film thickness from critical fluctuations becomes evident. Additionally, a new film-thickening effect is observed precisely at T sub(lambda) when the temperature is swept extremely slowly. We propose that this is a non-universal Casimir effect arising from the viscous suppression of second sound modes in the film.
We reexamine mass flow in a superfluid gyroscope containing a superfluid Josephson weak link. We introduce a frequency-dependent hydrodynamic inductance to account for an oscillatory flow of the ...normal fluid component in the sensing loop. With this hydrodynamic inductance, we derive the thermal phase noise, and hence the thermal rotational noise of the gyroscope. We examine the thermodynamic stability of the system based on an analysis of the free energy. We derive a quantum phase noise, which is analogous to the zero-point motion of a simple harmonic oscillator. The configuration of the studied gyroscope is analogous to a conventional superconducting RF SQUID. We show that the gyroscope has very low intrinsic noise (1.9x10{sup -13} rad s{sup -1}/{radical}(Hz)), and it can potentially be applied to study general relativity, Earth science, and to improve global positioning systems (GPS)
We present a formal thermodynamic treatment of superfluid flow in a Josephson junction. We show that the current i(s) and the phase difference phi are thermodynamic conjugate variables. We derive ...quantitative expressions for the rms fluctuations of i(s) and phi. Also, we discuss the thermodynamic stability and the thermal activation to the phase-slip region. We apply the developed formalism to show why an array of apertures in 4He can exhibit the Josephson effect near the lambda transition despite strong thermal fluctuations.
This work presents three large-format 2048 x 2048 pixel arrays integrated into passively cooled assemblies able to image in the short and medium-wave infrared range. Continuous spectral selectivity ...is achieved by means of linear variable filters mounted above the detector arrays.
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