Observational study: microgravity testing of a phase-change reference on the International Space Station

Abstract

BACKGROUND: Orbital sensors to monitor global climate change during the next decade require low-drift rates for onboard thermometry, which is currently unattainable without on-orbit recalibration. Phase-change materials (PCMs), such as those that make up the ITS-90 standard, are seen as the most reliable references on the ground and could be good candidates for orbital recalibration. Space Dynamics Lab (SDL) has been developing miniaturized phase-change references capable of deployment on an orbital blackbody for nearly a decade. AIMS: Improvement of orbital temperature measurements for long duration earth observing and remote sensing. METHODS: To determine whether and how microgravity will affect the phase transitions, SDL conducted experiments with ITS-90 standard material (gallium, Ga) on the International Space Station (ISS) and compared the phase-change temperature with earth-based measurements. The miniature on-orbit thermal reference (MOTR) experiment launched to the ISS in November 2013 on Soyuz TMA-11M with the Expedition 38 crew and returned to Kazakhstan in March 2014 on the Soyuz TMA-10 spacecraft. RESULTS: MOTR tested melts and freezes of Ga using repeated 6-h cycles. Melt cycles obtained on the ground before and after launch were compared with those obtained on the ISS. CONCLUSIONS: To within a few mK uncertainty, no significant difference between the melt temperature of Ga at 1 g and in microgravity was observed. INTRODUCTIONThe Committee for Earth Science and Applications from Space has articulated a scientific need for orbital temperature knowledge to support infrared radiance measurements with 0.1-K uncertainty 1 over a period of at least 10 years. As temperature uncertainty is only one of the contributors to the desired 0.1-K uncertainty, the goal for on-orbit temperature knowledge must be smaller (in the range of 0.01 K) to leave margin for other uncertainties in the calibration chain. Onboard references utilizing phase transitions have been identified as the most likely means for realizing International System of Units (SI) traceability for temperature measurements in orbit.The 3) identifies several phase-change materials (PCMs) with reliable fixed points that can be reproduced and used as references with submilli-kelvin absolute uncertainties for ground-based calibrations. Three PCMs with fixed points in the range required to calibrate Earth-observing sensors are gallium (Ga), water, and mercury with melt points of 302.9146, 273.16, and 234.3156 K, respectively. 3 However, the ITS-90 description of procedures and apparatuses does not translate easily into a design for an automated orbital implementation. ITS-90 describes fixed-point cells that use fragile materials such as plastic or glass to contain PCMs and require sensors to be placed in reentrant wells within relatively large volumes of 250 ml or more of the PCM. The described procedures do not apply directly to in situ sensor calibrations such as those that will be required on an orbital blackbody.In early 2006, the suitability of ...

RAVAN: CubeSat Demonstration for Multi-Point Earth Radiation Budget Measurements

“…This behavior has been noted previously. Topham et al experienced gallium supercooling in their on-orbit International Space Station experiment evaluating the effect (if any) of microgravity on gallium phase changes [33]. In any case, gallium melts were used exclusively for RAVAN radiometer stability measurements; the freezing behavior had no effect.…”

Modular integrated thermal control system in scientific experimental express rack on space station

“…Besides, TEC has the merits of non-noise and high integration [12,13]. There are already extensive applications of TEC in space experiment like biologic sample separation [14]. TEC has also been successfully applied to the modular equipment, such as space telescope infrared camera [15], quartz crystal microbalance [16], membrane evaporator [17], etc.…”

An invar-based fabry-perot cavity refractometer with a gallium fixed-point cell for assessment of pressure

“…To realize such an instrumentation, we present here an Invarbased DFPC refractometer that has been equipped with an automated temperature regulating and assessment system. Similar to what previously has been demonstrated by deployment on the International Space Station (ISS) [7], the latter employs an automated, miniaturized, custom-made fixed-point cell based upon the well-defined melting point of gallium. By the use of a thermocouple working close to zero temperature difference, the temperature of the cavity assembly is constantly assessed with respect to this melting point.…”