NASA SP-118 SPACE-CABIN ATMOSPHERES 3 -2 8- Part ;IV,pngineering Tradeoffs of One- Grsus Two-Gas Systems6 A literature review by 6 Emanuel M. RothfiA4.D. Prepared under contract for NASA by Lovelace Foundation for Medical Education and Research, Albuquerque, New NIexico Scientific and Technical Information Division OFFICE OF TECHNOLOGY UTILIZATION 9 1967 10 c" )NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Washington, D.C.3 PREC€t?iNG PAGE BLANK NOT FILMQ. Foreword THISREPORT is Part Iv, the last volume of a study on Space-Cabin Atmospheres, conducted under sponsorship of the Directorate, Space Medicine, Office of Manned Space Flight, National Aeronautics and Space Administration. Part I, “Oxygen Toxicity,” was published as NASA SP47, Part 11, “Fire and Blast Hazards,” as NASA SP-48, and Part 111, “Physiological Factors of Inert Gases,” as NASA SP-117. This document provides a readily available summary of the open literature in the field. It is intended primarily for biomedical scientists and design engineers. The manuscript was reviewed and evaluated by leaders in the scientific com- munity as well as by the NASA staff. As is generally true among scientists, there was varied opinion about the author’s interpretation of the data compiled. There was nonetheless complete satisfaction with the level and scope of scholarly re- search that went into the preparation of the document. Thus, for scientist and engineer alike it is anticipated that this study will become a basic building block upon which research and development within the space community may proceed. JACK BOLLERUD Brigadier General, USAF, MC Acting Director, Space Medicine Office of Manned Space Flight iii FXECEDING PAGE BLANK NOT FILMX. Contents PAGE INTRODUCTTON ................................................................................................... vii Chapter 1: PHYSIOLOGICAL CONSIDERATIONS .................................................. 1 TOTAL PRESSURE ............................................................. 1 OXYGEN ........................................................................................................... 1 WATER VAPOR................................................................................................. 4 CARBON DIOXIDE............................................................................................. 4 DILUENT GAS ................................................................................................... 5 TOXIC SUBSTANCES AND ODORS ...................................................................... 6 DUSTS, AEROSOLS, AND IONS ........................................................................... 6 AIR CIRCULATION............................................................................................ 6 TEMPERATURE CONTROL................................................................................. 7 Radiation Heat Transfer ................................................................................. 7 Forced Convective Heat Transfer ..................................................................... 7 Free Convective Heat Transfer ........................................................................ 9 Evaporative Heat Transfer .............................................................................. 10 Combined Heat Transfer ................................................................................ 11 Chapter 2: ENGINEERING CONSIDERATIONS ..................................................... 17 WEIGHT CONSIDERATIONS............................................................................... 18 Structure of Cabin Wall .................................................................................. 18 Atmospheric Leakage ..................................................................................... 19 Tankage for Gas............................................................................................ 29 Air-conditioning System ................................................................................. 71 TRANSIENT PHENOMENA .................................................................................. 99 POWER SYSTEM FACTORS ................................................................................ 100 ECONOMIC AND OPERATIONAL FACTORS ......................................................... 100 Development Time ........................................................................................ 100 Uses of Existing Hardware and Equipment......................................................... 100 Maintenance and Convertibility ........................................................................ 100 Crew Acceptance.......................................................................................... 101 Contaminant Buildup ..................................................................................... 101 Qualification Testing...................................................................................... 101 Environment for Inflight Experiments ................................................................ 101 Complexity of Design and Operation ................................................................. 101 cost............................................................................................................ 102 Chapter 3: COMPARATIVE ANALYSIS OF ATMOSPHERE TRADEOFFS OF THE ENVIRONMENTAL CONTROL SYSTEM.............................................. 103 EFFECT OF MISSION LENGTH ON OVERALL ECS TRADEOFFS .......................... 107 SUMMARY OF TRADEOFFS IN THE SELECTION OF SPACE-CABIN ATMOSPHERES .............................................................................................. 109 REFERENCES ....................................................................................................... 115 Appendix A: NOMENCLATURE ............................................................................. 121 Appendix B: CONVERSION TABLES.................................................................... 125 V Introduction THE SELECTION of an ideal space-cabin atmosphere requires thorough analysis of physiological, physical, and engineering considerations of the problem. Since the basic function of a cabin atmosphere and its control system is to provide an environment for the optimum function of both crew and equipment, the specific interaction between the two must constantly be kept in mind. In this fourth part of the series on Selection of Space-Cabin Atmospheres, an attempt is made to consider this interaction in establishing valid criteria for engineering tradeoffs. It has been the general practice in this series to avoid relating the analysis of literature to any one specific space mission. This philosophy will be continued in the present study; however, meaningful engineering tradeoffs can be made only with rather well-defined physical constraints on the system. Because the manned- orbiting-laboratory concept allows adequate and realistic constraints to be set, it will be used as a model example in this analysis. Since the success and safety of each mission and crew are to a considerable extent dependent on the choice and design of atmospheric and thermal control systems, synthesis and optimization methods have become essential steps in atmosphere selection. Because every bit of weight and volume must be saved and every fraction of performance extracted from every subsystem, with no loss in reliability, and with economy of effort and at minimum cost, sophisticated analyses have been required for total systems integration. In the past, studies of this type have been of great value to the engineer in presenting heat- and mass-transfer data, as well as chemical process descrip- tions which include the direct influence of vehicle data, system variables, process selection, and reliability considerations. Very often the gas-specific factors have, by necessity, been included in the analyses, but their roles have not been pointedly delineated. It is hoped that the role of the gas-specific factors and the many biases surrounding their choice does become more clear as a result of the present analysis. The study begins with an evaluation of the physiological considerations which set boundaries for the physical environment within the cabin (ch. 1). The en- gineering analysis of chapter 2 is a review of the interaction between the physio- logical and hardware parameters of the environmental control system. An attempt is made to compare for each subsystem the effect of several physiologically accept- able gas mixtures on the weight and power penalties for missions of different types and durations. In chapter 3, the tradeoff criteria established in chapter 2 are used in an analysis of a typical mission-a two-man orbiting vehicle. The results of tradeoff analyses performed by several groups are compared to demonstrate the sensitivity of the final product to the physical, physiological, and engineering assumptions which were made. This mission was chosen only because of the avail- ability of several completely independent studies of the tradeoffs by the aerospace industry. These independent analyses offer the opportunity for evaluation of assumptions and biases which usually creep into any tradeoff study. It is hoped vii ... Vlll INTRODUCTION that this review will provide an adequate basis for unbiased atmospheric tradeoff studies of future missions. Several excellent reviews of analytical methods for atmospheric control processes have been used for basic source materials. 24,20,*0,95