Scaling Heat Rejection for High-Capability SmallSats: From Conduction to Deployable Two-Phase Radiators

The rapid growth of the SmallSat market has been driven by increased launch access and miniaturization and commercialization of spacecraft grade electronics, leading to steadily increasing onboard power and thus heat dissipation. As SmallSats evolve toward higher capability payloads, thermal control systems must reject greater heat loads while meeting aggressive Size, Weight, Power, and Cost (SWaP-C) constraints. This paper examines scalable heat rejection architectures for high-capability SmallSats, progressing from conduction-based approaches to advanced two-phase thermal solutions.

The assessment begins with conventional conductive heat spreading and fixed radiator architectures, identifying practical limitations as power density and heat transport distances increase. Constant conductance heat pipes (CCHPs) are then evaluated as a mature, low-risk option for improving isothermalization and radiator coupling. Pulsating heat pipes (PHPs) configured as radiator elements are introduced as an emerging solution that offers distributed heat rejection with reduced mass and mechanical complexity with additional up front design customization.

The paper then focuses on deployable radiator architectures enabled by additively manufactured loop heat pipes (AM LHPs). Loop heat pipes provide long-distance, low-thermal-resistance heat transport with passive operation, but their adoption in SmallSats has historically been limited by cost and lead time. Additionally, a brief assessment of pumped fluid loops is made for comparison looking to larger architectures.

Two AM LHP systems with deployable radiators are explored with configurations for 12U and an ESPA-class SmallSat to enable high heat rejection within constrained bus volumes. Design trades, manufacturing considerations, deployment mechanisms, thermal modeling, and thermal-vacuum testing are discussed, demonstrating a scalable path for thermal architectures supporting the next generation of high-power SmallSats.