Theoretical performance analysis of electrochromic radiators for space suit thermal control Jonathan G. Metts a,⇑ , James A. Nabity b , David M. Klaus a a University of Colorado at Boulder, 429 UCB, Boulder, CO 80309, USA b TDA Research, Inc., 12345 West 52nd Ave., Wheat Ridge, CO 80033, USA Received 14 April 2010; received in revised form 16 November 2010; accepted 18 November 2010 Available online 27 November 2010 Abstract Variable emissivity electrochromics have been proposed as an enabling technology for integrating a radiator capability into a space suit in order to augment or replace the traditional means of heat rejection achieved via water sublimation. Thermal analysis was per- formed to establish design trade spaces and to provide operational guidelines and performance specifications for electrochromic technol- ogy development. Based on using the available surface area of an entire space suit as a radiator and the projected infrared emissivity modulation capability of state-of-the-art electrochromic material, the proposed application for space suit heat rejection suggests the potential exists to reduce or eliminate reliance on water consumption for thermal control within a defined range of metabolic and envi- ronmental boundary conditions. Ó 2010 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Space suits; EVA; Life support; Thermal control; Radiators; Electrochromic 1. Background Since the Apollo program, space suits without umbilical connections have relied on a portable life support system (PLSS) that uses water sublimation to reject heat that would otherwise rapidly build up within the suit (NASA, 2006). Sources of heat include the astronaut’s metabolic output, power required for the suit’s avionics and PLSS components, and any environmental heat flux into the suit. Heat is collected throughout the suit’s interior by a Liquid Cooling and Ventilation Garment (LCVG), which inter- faces with a water and air heat exchanger in the PLSS, and from which the collected heat load is transferred to a self-regulating sublimator device. A porous metal plate exposes feed water to the low temperature and near- vacuum of space to create a thin sheet of ice that in turn sublimates directly to the vapor phase, thus removing heat collected by the LCVG. This vapor is vented away from the suit, carrying the rejected water mass and accompanying thermal energy as latent heat of sublimation. NASA is currently developing the Space Water Mem- brane Evaporator (SWME) to replace the sublimator (Bue et al., 2009). SWME is designed to be effective in pres- surized environments where sublimation does not occur, such as in the Martian atmosphere, as well as to be less prone to feed water contamination issues. The overall con- cept of rejecting heat using water consumption, however, remains similar to that of the sublimator. In contrast to the operational advantages that SWME offers, the evapo- rative phase-change process uses slightly more water for a given heat load than the legacy sublimator. Suit radiator concepts have been proposed that would cover only the relatively flat PLSS backpack with a radia- tor panel, but this approach offers limited heat rejection capability due to the small surface area and the dynamic reorientation (i.e., changing sink temperature) associated with EVA operations (Sompayrac et al., 2009). Variations on this theme have also been considered that rely on partial 0273-1177/$36.00 Ó 2010 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2010.11.018 ⇑ Corresponding author. Tel.: +1 205 435 0991. E-mail addresses: metts@colorado.edu (J.G. Metts), nabity@tda.com (J.A. Nabity), klaus@colorado.edu (D.M. Klaus). www.elsevier.com/locate/asr Available online at www.sciencedirect.com Advances in Space Research 47 (2011) 1256–1264