Defining a Discretized Space Suit Surface Radiator With Variable Emissivity Properties

Abstract

Heat rejection for space suit thermal control is typically achieved by sublimating water ice to vacuum. Converting the majority of a space suit's surface area into a radiator may offer an alternative means of heat rejection, thus reducing the undesirable loss of water mass to space. In this work, variable infrared (IR) emissivity electrochromic materials are considered and analyzed as a mechanism to actively modulate radiative heat rejection in the proposed full suit radiator architecture. A simplified suit geometry and lunar pole thermal environment is used to provide a first-order estimate of electrochromic performance requirements, including number of individually controllable pixels and the emissivity variation that they must be able to achieve to enable this application. In addition to several implementation considerations, two fundamental integration architecture options are presented—constant temperature and constant heat flux. With constant temperature integration, up to 48 individual pixels with an achievable emissivity range of 0.169–0.495 could be used to reject a metabolic load range of 100 W–500 W. Alternatively, with constant heat flux integration, approximately 400 pixels with an achievable emissivity range of 0.122–0.967 are required to reject the same load range in an identical external environment. Overall, the use of variable emissivity electrochromics in this capacity is shown to offer a potentially feasible solution to approach zero consumable loss thermal control in space suits.

Planetary extravehicular activity (EVA) risk mitigation strategies for long-duration space missions

“…The time it takes for such a concept has been demonstrated in the order of seconds, and while this device has not been approved for spaceflight yet, it has been evaluated in space-like environments and shows promise for future missions 14 . Another approach involves the use of variable infrared emissivity electrochromic materials (pixels) to actively modulate heat rejection 17 . This constant temperature architecture rejected 100–500 W using an emissivity range of ~0.169–0.495 17 .…”

“…Another approach involves the use of variable infrared emissivity electrochromic materials (pixels) to actively modulate heat rejection 17 . This constant temperature architecture rejected 100–500 W using an emissivity range of ~0.169–0.495 17 . The constant heat flux variation allowed for the same amount of metabolic workload rejection (100–500 W), but used a variable emissivity range of 0.122–0.967 17 .…”

“…This constant temperature architecture rejected 100–500 W using an emissivity range of ~0.169–0.495 17 . The constant heat flux variation allowed for the same amount of metabolic workload rejection (100–500 W), but used a variable emissivity range of 0.122–0.967 17 . Both of these approaches have no loss of consumables, less overall mass, and no system power requirements 17 .…”

Numerical Modeling of the Thermal Insulating Properties of Space Suits

“…The adopted model has the shape of a multilayer cylindrical partition, with a 40 mm inner radius from the axis, which corresponds to the astronaut's forearm. The remaining parts of the suit may contain electrical elements and other systems, causing changes in the obtained results [31]. In the case of a repeatable shape and thermal conditions, the typical procedure is to introduce only a part of the structure during the calculations.…”