SAE TECHNICAL PAPER SERIES 2008-01-2027 Testing the Celentano Curve: An Empirical Survey of Predictions for Human Spacecraft Pressurized Volume Marc M. Cohen Northrop Grumman Corporation 38th International Conference on Environmental Systems San Francisco, California June 29-July 2, 2008 400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-0790 Web: www.sae.org By mandate of the Engineering Meetings Board, this paper has been approved for SAE publication upon completion of a peer review process by a minimum of three (3) industry experts under the supervision of the session organizer. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. 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Printed in USA 2008-01-2027 Testing the Celentano Curve: An Empirical Survey of Predictions for Human Spacecraft Pressurized Volume Marc M. Cohen Northrop Grumman Corporation Copyright © 2008 SAE International ABSTRACT The history of human spaceflight -- from the earliest flights in tiny capsules to the capacious International In 1963, Celentano, Amorelli, and Freeman of North Space Station -- provides the baseline from which to American Aviation described a set of curves as an Index evaluate and test these predictions. What the historical of Habitability that can predict the amount of pressurized record affords is a metric to analyze how pressurized volume necessary per crewmember to conduct a volume varies with mission duration, crew size, and mission at “tolerable, performance, or optimal” levels. other causes. This paper presents an analysis of the “Celentano Curve” that depicts a relationship between spacecraft FIGURE 1 shows the original Celentano plot that pressurized volume and the duration of a space mission. features the volume prediction rising steeply over the shorter missions, but leveling out after six months at Since Yuri Gagarin flew in Vostok 1 in 1961, the US, about 700ft3 (19 to 20 m3). Celentano et al posited three Russia, and China have launched more than 250 human levels of accommodation “tolerable, performance, and spaceflights. This survey collects the empirical data and optimal,” but did not define them clearly. tests the Celentano curves against it. The statistical approach treats the Celentano curve as the hypothesis OBJECTIVES stating a causal relationship between mission duration and volume. Many authors have published variations of The objectives of this research are: the Celentano curve, and this author considers nine interpretations, plus three versions of the crew size • To determine what the facts are and what is true hypothesis and one functional operations hypothesis. about volume and mission duration. This analysis shows that pressurized volume increases • To provide an empirical baseline of historical as a function of mission duration, both as a power curve spacecraft and missions against which to compare and a logarithmic curve. This volume trend does not and perhaps validate volumetric designs in the level off but continues to rise throughout the historic future, and envelope of human spaceflight. • To identify the spacecraft volume and mission INTRODUCTION envelope issues to which architectural design research may make the greatest contribution. Since Celentano, Amorelli, and Freemans seminal paper, habitability researchers published dozens of CAVEAT: VOLUME ESTIMATION FROM FIRST citations, interpretations, and variations of the Celentano PRINCIPLES curves. This paper presents an analysis of the Celentano hypothesis and its acolytes, testing them This research does not address design guidelines and empirically against the historical data of human methodologies to size pressurized spacecraft and space spaceflight. In each case, the authors frame their habitats. Certainly, those topics are essential future predictions in terms of “meeting crew needs.” Most steps, but they exceed the scope of the present effort. notable among these predictions of volumetric “requirements,” NASA adopted an embodiment of the • The scope of this study extends only to identifying, Celentano curve in the 1987 Man-System Integration clarifying, and assessing the historical and empirical Standard (MSIS). record of human spaceflight. It is not a substitute for 1 calculating volume and mass requirements from first predict and plan these spacecraft parameters and principles in the design of crewed spacecraft. What requirements to meet crew needs across a broad this caveat means is that the human spaceflight range of functions, missions, and operations. community must develop and validate the tools to FIGURE 1. The original “Celentano Curve” 1963 shows Volume in ft3 on the Y-axis and Mission Duration in months on the X-Axis. The three curves appear from top to bottom as “Optimal, Performance, and Tolerable.” A further caveat is that this study addresses only gross 2. There is no agreement on how to measure habitable pressurized volume. It does not make distinctions volume or free volume or even how to define it, but among subtractive properties within the pressurized there is universal agreement that pressurized cabin, known variously as habitable volume, free volume is the entire space within the pressure volume, or living space. There are two reasons for this vessel that contains the crew cabin. choice: 1. There is good documentation available only on HISTORICAL CONTEXT actual pressurized volume. Very few spacecraft have any measurements available for the At the time Celentano, Amorelli, and Freeman posed subtractive volumes. At the same time, there are their hypothesis, human spaceflight was in its earliest sometimes inaccurate and conflicting values period of the Vostok, Mercury, Voskhod, and Gemini published for certain spacecraft volumes, so it may spacecraft. The experience of zero gravity was limited take real detective work to find the true data. to very small cabin volumes. Even the Apollo and Soyuz programs seemed far in the future, so that they had few data points for their theory. Never the less, by predicting 2 quantitative relationship between mission duration and in mass and volume for long duration missions such as a spacecraft size their paper became highly influential. Mars Transfer Vehicle (MTV) or at a moon or Mars This relationship is very important because the ability to surface base. predict cabin size will minimize huge potential variations Salyut Missions Mir Missions Testing the Celentano Curve: Spaceflight Mission Series Skylab Missions 1000.00 Mercury Missions Gemini Missions Apollo Missions Apollo-Soyuz Test Project Space Shuttle Missions ISS Expeditions Shuttle-Spacelab Missions Shuttle-SpaceHab Shuttle-Mir Missions 100.00 Vostok-Voskhod Missions Soyuz Missions All Shuttle Missions Power (Space Shuttle Missions) Power (Skylab Missions) Power (Shuttle-SpaceHab) Power (Shuttle-Spacelab Missions) Power (Shuttle-Mir Missions) 10.00 Power (Mir Missions) Log. (Salyut Missions) Volume per Crew Member in M^3 Log. (Mir Missions) Log. (ISS Expeditions) Power (ISS Expeditions) Power (Salyut Missions) Log. (Apollo Missions) Power (Apollo Missions) Log. (Mercury Missions) 1.00 Log. (Gemini Missions) 0.10 1.00 10.00 100.00 1000.00 Power (Vostok-Voskhod Missions) Duration in Days Log. (Vostok-Voskhod Missions) Log. (Space Shuttle Missions) FIGURE 2 shows the complete historic spaceflight data set for all spaceflights through the period of this study in 2006, omitting the outliers of Mercury and Vostok test flights for t<0.1 days. FIGURE 2 shows the record of human spaceflight by On reviewing the original Celentano, et al. spacecraft. How far has the space habitability paper, here is a summary of their experimental community progressed since Celentano? Christopher S. method: Allen, et al. (2003, p. 49) offered this stark assessment: “…They did a good job in describing the multiple There is currently no method available to factors that impact living space and habitability; determine with absolute certainty, the amount of however, my primary concern with their work is habitable space needed per crewmember for that their habitability index was based on missions beyond LEO. Until better data is studies done with very few subjects under available, designers should plan on allocating a controlled laboratory conditions for very short minimum of 16.99m3 (600ft3) of usable space durations from which they extrapolated to per crewmember (original emphasis. Allen, et multiple months. In particular, they based their al, 2000, p.47). habitability index on