Small, inexpensive satellites called CubeSats are commonly used for conducting academic and commercial space research. Typically, there is no thermal control system to dissipate heat from the CubeSat avionics, limiting onboard computing power. UC Davis is investigating the use of sublimators as a CubeSat cooling technology. Sublimators are a small-volume, passive thermal control technology with proven flight history which may allow CubeSats to fly more powerful computers and conduct more complex experiments. During sublimation of ice to water vapor, significant thermal energy (heat) is transferred from a heat source into the vacuum of space due to water’s high latent heat. Although sublimators utilize water, a consumable, their size and passive nature is especially appropriate for CubeSat missions with volume constraints and short durations. In a typical sublimator, liquid water from a supply line freezes in a porous component, and heat from the electronics transforms the ice into water vapor. The porous component passively regulates the sublimation rate and avionics heat rejection by providing a resistance to water vapor flow exiting the sublimator.  

For 60 years, sublimation phase-change technology has been successfully utilized as a heat rejection mechanism to cool astronauts on spacewalks. Despite its success, there are aspects of the heat and mass transfer processes which are not fully understood.  The I-SCHREAM team is investigating the driving factors in a sublimator, including the development of an analytical model of gaseous flow through the porous component, developing a set of requirements for incorporating sublimation cooling technology into a CubeSat, and eventual model validation and fully integrating testing in a vacuum environment.