Air Revitalization Demonstration on the JEM (KIBO) for a Manned Space Exploration

Abstract

To further advance manned space exploration, a critical issue that must be addressed is recycling of resources, especially air revitalization and water reclamation. Japan is already a leader in terrestrial environmental technologies, and aims to apply this know-how to develop air and water recycling technologies for space applications. To support proposed post- ISS missions such as manned lunar or asteroid exploration and an Earth-Moon Lagrange point (EML1) space station, JAXA is developing an air revitalization system for an on-orbit demonstration on the International Space Station (ISS) early in the extended ISS operation period (2015-2020). The requirements for this technical demonstrator have been investigated and its specifications established. Regenerative life support functions include oxygen recovery from carbon dioxide using a combination of CO 2 reduction by a Sabatier process and O 2 generation by electrolysis. Each air and water re-vitalization subsystem is planned to be transported to the ISS separately by successive H-II Transfer Vehicle (HTV)launches in the sequence Water Reclamation → Water Electrolysis → CO 2 Reduction. This paper presents the air re-vitalization system developed by JAXA, and gives details of water electrolysis in microgravity.

Electrolysis in reduced gravitational environments: current research perspectives and future applications

“…The stack itself is operated at 75 A, corresponding to 350 mA cm −2 with an average cell voltage of 1.72 V 15 . Pt based catalysts designated as E-50 by General Electric 8,16 are used on the anode side and Pt Black is utilized on the cathode side 15 . The PEM electrolyzer can produce between 2.3 and 9.2 kg of oxygen per day at a selectable rate in continuous operation.…”

“…Another, more advantageous system to improve reliability and lifespan is passive phase separation using porous glass membrane separators. Further efforts are however necessary to improve passive phase separation in general e.g., with respect to the required membrane size 15,16 . Alongside improved separation processes, an alternative approach is to inject water only on the cathode side to avoid mixing gaseous oxygen and liquid water 8,15,16 .…”

Magnetic phase separation in microgravity

“…"Introduction", electrolyzers stand out as some of the most interesting applications. Electrolyzers are utilized for oxygen production in the Oxygen Generation Assembly on the International Space Station and suffer from the absence of buoyancy as gas bubble removal from the electrode surface is hindered 1,2,7,8 . The first studies of this phenomenon were carried out in the 1960s within the frame of developing a reliable spacecraft environmental control system for oxygen production 83 .…”

“…A forced water flow can be employed to remove the froth layer from the electrode surface, but the approach has limited efficiency and involves the use of heavy and unreliable liquid circuits 7 . The operation of electrochemical devices with gaseous products or reactants is therefore complicated in reduced gravitation and results in increased complexity, mass, and power consumption.…”

“…Numerous phase separation methods have been developed for microgravity conditions. Centrifuges 1,2 , forced vortical flows 3,4 , rocket firing 5,6 , membranes 7,8 , and surface-tensionbased technologies 9,10 , which include wedge geometries [11][12][13][14] , springs 15 , eccentric annuli 16 , microfluidic channels 17 , or porous substrates 18,19 , among others, are the most traditional solutions. As an alternative, the use of electrohydrodynamic forces has been studied since the early 1960s 20 and successfully tested for boiling [21][22][23] , two-phase flow management 24,25 , and conduction pumping 26 applications.…”