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

Area of Science:

• Space-based climate monitoring
• Precision thermometry
• Phase-change material applications

Background:

• Orbital sensors require low-drift thermometry for climate change monitoring.
• On-orbit recalibration is currently unattainable.
• Phase-change materials (PCMs) are reliable ground references and potential candidates for orbital recalibration.
• Space Dynamics Lab (SDL) has developed miniaturized PCMs for orbital deployment.

Purpose of the Study:

• To assess the impact of microgravity on phase transitions of PCMs.
• To improve orbital temperature measurements for long-duration Earth observation and remote sensing.

Main Methods:

• Conducted experiments with the International Space Station (ISS) utilizing ITS-90 standard material (gallium, Ga).
• Compared phase-change temperatures of Ga in microgravity with Earth-based measurements.
• The Miniature On-Orbit Thermal Reference (MOTR) experiment was deployed on the ISS.

Main Results:

• Tested melting and freezing cycles of Ga in 6-hour intervals.
• Compared melt cycles on the ISS with pre- and post-launch ground-based measurements.
• Observed no significant difference in Ga melt temperature between 1g and microgravity conditions.

Conclusions:

• Gallium (Ga) exhibits consistent phase-change temperatures in microgravity and 1g.
• PCMs like Ga can be used for precise orbital temperature measurements with minimal uncertainty (a few mK).
• Validated the use of PCMs for recalibrating orbital thermometry.