Advanced Life Support Equivalent System Mass Guidelines

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NASA/TM-2003-212278

Advanced Life Support Equivalent System Mass Guidelines

Document

Julie A . Levri, John W Fishel; Harry W Jones, Ph.D.

Am es Resea rch Centel; MofSett Field, California

Alan E. Drysdale, Ph.D.

The Boeing Company, Kennedy Space Centel; Florida

Michael K. EwertJohn son Space Centel; Houston, Texas

Anthony J. Hanford, Ph.D.

Lockheed Martin Space Operations, Houston, Texas

John A. Hogan, Ph.D.

Rutgers, T he State U niversity ofNew Jersey, New Brunswick, N ew Jersey

Jitendri A. Joshi, Ph. D.

Universities Sp ace Research Association, Washington, D. C.

Da vid A. Vaccari, Ph.D., D.E.E.

Stevens Institute of Technology, Hoboken , New Jersey

Nat ional Aeronaut ics and

Spa ce Adm inis tra t ion

Am es Research Cen ter

Mo ffet t F ie ld , Cal i fo rn ia 94035-1000

September 2003



Available from:

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076-1320

(301) 621-0390

National Technical Information Service5285 Port Royal Road

Springfield, VA 22161

(703) 487-4650



ALS Equivalent System Mass Guidelines D ocument

TABLE OF CONTENTS

NASNTM-2003-2 12278

1 ABSTRACT ......................................................................................................................................... 1

2 INTRODUCTION ............................................................................................................................... 2

2.1 PURPOSEOFTHIS DOCUMENT........................................................................................................... 2

2.2 DOCUMENTCONTROL....................................................................................................................... 2

2.3 ESM DEFINITION.RATIONALEAND APPLICATION........................................................................... 3

2 .4 TH EELEMENTARYESM EQUATIONA ND A SIMPLEEXAMPLE .......................................................... 3

2.5 PURPOSESOF THE ESM CONCEPT..................................................................................................... 6

2.6 USERS............................................................................................................................................... 7

3 ESM COMPUTATIONAL METHO D ............................................................................................. 8

3.1 DEC~SIONSAN D ASSUMPTIONSABOUT THE ANALYSIS...................................................................... 8

3.2 ESM EQUATION............................................................................................................................... 20

3.3 DISCUSSIONOF LOCATIONFACTORS............................................................................................... 35

4 ESM RESULTS.................................................................................................................................. 37

4.1 RESULTSCONFIDENCE..................................................................................................................... 37

4.2 RESULTSREPORTING....................................................................................................................... 38

5 REFERENCES................................................................................................................................... 40

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ALS Equivalent System Mass Guidelines Document

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ALS Eq uivalent System Mass Guidelines Docum ent NASM TM-2003-2 12278

SYMBOLS

cooling requirement of subsystem i [kWth]

the mass equivalency factor for the cooling infrastructure of subsystem i

[k g /k Wd

crewtime requirem ent of subsystem i [CM-Wy]

mass equivalency factor for the crewtime of subsystem i [kg/CM-h]

duration of the m ission segment of interest [y]

ESM value o f the entire life suppo rt system (the sum of the crewtime andnon-crewtime po rtions of ESM) [kg]

crewtime portion of ESM [kg]

non-crewtime portion (considers mass, volum e, power, and cooling on ly)of ESM [kg]

ES M valu e of the entire life support system (the sum of the crewtime andnon-crewtime p ortions ofESM) [kg]

location facto r for the segm ent of interest [kg/kg]

initial mass of subsystem i [kg]

time- or ev ent-dependent mass of sub system i [kg/y]

power requ irement of subsystem i [kW,]

mass e quivalency factor for the power generation support infrastructure ofsubsystem i [kg/kW,]

initial mass stowage factor for subsystem i [kg/kg]

time- or ev ent-dependent mass stowa ge factor for subsystem i [k g k g ]

Systems Integration, Modeling and Analysis

crewtime that is required to maintain the life support system (a subsetof

C WORK) [CM-wyl

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ALS E quivalent Sys tem Mass Guidelines Document NASN TM-2003-2 12278

tMISSlON

tWORK

VI

VTD

AL S

AU

BVAD

ESM

ETCS

ITC S

LEO

NASA

RMD

R&TD

crewtim e that is used in performing scien tific, mission -oriented work (a

su bs et o f tWORK) [CM-My]

total crewtime allotted for work (not dev oted to time such as eating,sleeping, exercising, personal time, etc.) [CM -My]

mass equivalenc y factor for the pressurized volume su pport infrastructureof subsystem i [kg/m3]

initial volume o f subsystem i [m3]

time- or event-dependent volume of subsy stem i [m3]

ACRONYMS

Advanced Life Support

Astronomical Unit

Baseline Values and Assumptions Document

Equivalent System M ass

External Th ermal Control System

Internal Thermal Control System

Low-Earth Orbit

National Aeronautics and Space Administration

Reference Missions Document

Research and Technology Development

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ALS Equivalent System Mass G uidelines Document NASNTM-2003-212278

1 ABSTRACT

Equivalent System Mass (ESM ) is often applied to ev aluate trade study op tions in theAdvan ced Life Support (ALS) Program. ESM can be used to identify which of several

options that meet all specified requirements have the lowest launch cost, as related to themass, vo lume, power, cooling and crewtime needs.

This doc umen t provides an introductionto the ESM co ncept, an explanation of thecomp utational method, and a discussion of results interpretation and reporting. Anyresearcher with a basic understanding of the integration issues of an Advan ced L ifeSupport system may apply the m ethods in this documen t to perform an effective ESM-based trade analysis.

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ALS Equivalent System M ass G uidelines Document NASN TM-2003-2 12278

2 INTRODUCTION

2.1 Purpose of this Docum ent

This document provides a definition of Equ ivalent System Mass (ESM), describes how tocalculate ESM, and discusses interpreta tion of ESM results, in the interests of theAdvanced Life Support (ALS) Project. The ESM computational method described in thisdocument has evolved ov er several years and is consistent with the meth od used in theAdvanced Life Support Project 2001 Metric Document (Drysdale and Hanford, 2002).

This document provides guidelines for performing an ESM evaluation for trade study ’purposes. The docum ent is designed to prov ide detailed instructive material forresearchers who are performing E SM evaluations for the first time. It docu ments the A LSSystems Integration, Mod eling and Ana lysis (SIMA ) Element position o n ESM, toprovide consistency in ESM ev aluations. This document also addresses ESM issues thathave been frequen tly raised by ALS research ers.

2.2 Docum ent Control

This document was created under the SIM A Element of the ALS Project. Thus, the finaldocument w ill be un der the controlof the SIM A Lead. Please send docum ent comm entsto the primary author and the SIMA Lead.

Julie A. LevriNASA A mes Research Center(650) 604-6917 (voice)

[email protected]

Michael K. EwertNASA Johnson Sp ace Center(281) 483-9134 (voice)

Michael.K.Ewert(4NASA. gov

’ It is critical to note the difference betw een a “trade study” and an “ESM evaluation”. An ESM evaluation

is one of several possible too ls that may be used in a trade study. A trade study may include variousquantitative and qualitative criteria in evaluating technology o ption s. In this document, the words “study”

and “analysis” are used interchangeably. A trade study is a com parison of trade-offs for various options. A

an ESM value for a single technology may be co mp uted, but the value can only be compared to other

options that are evaluated under iden tical assum ption s. Moreover, a n ESM value shou ld never be

“unconditionally” assigned to a technology, since most ESM valu es are scenario-specific.

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ALS Equivalent System M ass Guidelines Docum ent * NASA/TM-2003-212278

2.3 ESM Definition, Rationale and Application

ESM is typically used a s a transportation cost measure in ALS trade studies, to avoid thecomp lications, both technical and political, of using dollar costs for com parisons.Because the co st to transport a payload is proportional to the mass o f that payload, a

mass-based measure such as ESM is used to qua ntify the launch cost of the life supportsystem and associated infiastructure.An ESM value represents the sum of the life supportsystem2 mass and appropriate fractions of supporting system masses, includingpressurized3volume, pow er generation, cooling, and crew time, for maintaining a crewover the d uration of a specified mission.

ESM should rarely be the o nly metric applied in a trade study.As a cost me tric, ESMmay not be capable of capturing reliability, safety and perform ance differences betweentrade study options. Thus, for ESM to be applied approp riately, the trade study optionsmust meet som e comm on prerequisites, and some characteristics might requirecomp arison by m eans other than ESM. (This issue is discussed in Section3.1 .)

2.4 The Elementary ESM Equ ation and a Simple Exam ple

ESM could include any aspect of the system that exerts an effect on system mass, but inpractice the parame ters of interest4 are typically narrowed down to the following:

* As it is used here, “system ” may pertain to a com plete life support s ystem, or any subset of a complete life

support system and supportive infrastructure.

In reality, all volum e in the habitat will be pressurized unless there a re some materials or equipment that

don’t require pressurization (or possibly requ ire less pressurization, such as a large plant chamber).

How ever, if it is necessary for the crew to access materials and eq uipment that are unpressu rized or

pressurized below that of h uman requiremen ts, an EV A expedition or temporary repressurization of that

chamber would be required. Because of this, in typical missions, life support system equipment to which

the crew might require access is pressurized. However, the possibility for alternative scenarios exists,

whic h is the reason for the “pressurized” qualifier in this sentence.

As with all aspects of a trade study, the parameters to inclu de in an ESM analysis are subject to scrutiny

by the analyst. If there is low confidence in a particular data value or equivalency factor, then the analystshould judge whether to include that parameter in the ESM evaluation or to qualify the issue in some other

manner. In particular, crewtime data tends to be uncertain at low stages of technology development,

although crewtime is a very critical and decisive part of typical human-rated space missions. (For example,

EVA crewtime drove a major redesign of the International Space Station when it was determined that the

crew could not support as much EVA as the design required.)

4

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ALS Equivalent System M ass Guidelines Document NASN TM-2003-2 12278

0 Mass’

0 volume5

0 Power

0 Cooling

0 Crewtime

Although these five parameters could be related to one another in a variety of ways, ESMis calculated as the su m o f the m ass equivalencies of these parameters.

Equation 1 is provided as a simplified version of the comp lete ESM equ ation (presentedin Section 3.2). Equation 1 is provided for explanatory purpos es only, for simpleexpression of the ESM con cept for first-time ESM users. If an actual ESM com putation isperformed, the analyst should understand the complete ESM equation in Section 3.2.

ESM = M + (V Ve,)+ (P .P,,)+ (C C,, )+ (C T D CT,, ) Equation 1

where E S M = the equivalent system mass value of the system o f interest [kg],

A4 = the total mass o f the system [kg],

V = the total pressurized volum e of system [m 3],

Ye , = the mass equiv alency factor for the pressurized volume infrastructure [kg/m3],

P = the total power requirem ent of the system [kWe] 6,

P,, = the mass equivalency factor for the power generation infrastructure [kg/kWe],

C = the total cooling requirement o f the system [kw th]’,

C,, = the mass equivalency factor for the cooling infrastructure [kg/kWth],

CT = the total crewtime requireme nt of the system[CM-Wy],

D = the duration of the mission segm ent of interest [y],

CT,, = the mass equivalency factor for the crewtime support [kg/CM -h].

This parameter may have both initial and time-dependent components. See Eq uation 2.

kW , = kW electrical

’kW,h= kW thermal

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ALS Equivalent System Mass Guidelines Document NA SNT M-2 003-212 278

Mass equivalency factors (Veq,Peq,Ceq,and CT,,) are used to convert the non-massparameters ( V , P , C an d CT) to mass equivalencies. Equivalency factors are determinedby com puting the ratio of the unit mass of infrastructure required per unit of resource. F orexam ple, consider a structure used for pressurized volume that is based upon a designthat has a total volume capacity at launch of 300 m3 and a total empty mass of 30,000 kg.

Such a design has a mas s equivalency factor for volume of: Veq= (30,000 kg/300 m3)=100kg/m3 . Thus, if a subsy stem in the ESM e valuation requires 4m3 of pressurizedvolume at launch, it would have a volume cost (V .V,,) of (4m3 * 100kg/m3), or 400 kg.

Mass equivalency factor values may be obtained from the ALS Baseline Values andAssumptions D ocument (BVA D) (Hanford, 2002). However, it is also acceptable for aresearcher to develop mas s equivalenc y factors that are more app ropriate for a particularinvestigation. In such a case, an explanation of the equ ivalency factor values an dreferences should be pro vided in the analysis final report.

Each distinct segm ent of a mission should be considered individually in E SM

evaluations. Q uantifying the benefits of off-loading (e.g. venting, dum ping) mass inbetween propulsion events requires segment-specific ESM computations. For example,consider two technologies that are being evaluated for the transit habitat of a M arsmission. If o ne o f the technologies is able to off-load expended mass before launchingfrom Mars orbit to Low-Earth Orbit (LEO), that advantage will only appear if the E SMfor each mission segment is computed separately. Location factors may be required forsegment-specific ESM values if those values are to be summed linearly or com pared.This topic is discussed in Section 3.3.

Th e following simple ESM calculation is meant to serve as an exa mple for conv eyingbasic co ncepts to first-time ESM users. The exam ple is not a trade study comparison, asonly one technology option is evaluated. Some values in the exam ple are based uponvalues provided in D oll and Eckart (1999).

Assume that the sys tem of interest’ is a carbon dioxide scru bbing device being ra ted for a

Mars outbound transit mission (duration,D = 0.49 y). The inv estigator sizes the devicefor the appro priate processing rate, based upon assum ptions about the mission of intere st,and determ ines the followin g values. The hardw are, expen dables, and spares’ requ ired

Recall that in this docum ent, “system” may pertain to a complete life support system, or any subset of a

complete life support sy stem and supportive infrastructure. For explanatory purposes, the sy stem in th is

example is pu rposely restricted to a single hardware device. The appropriate system to define depend s upon

the ob jectives of the analysis and the extent and detail of the system necessary to reflect the total costimpact of each trade option. This issue is discussed further in Section 3.1.

8

’ In the ES M descriptions after this section, most hardware is accounted under an “initial mass” term, and

most exp end ables and spares are accounted under a “time-dependent mass” term. However, for simp licity

in this example, initial and time-dependent m ass (and initial and time-dependent v olume) are not

distinguished.

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ALS Equivalent System Mass Guidelines Do cument NASNTM-2003-212278

over the entire duration of the mission weigh 91.6 kg (M>.The volume of the system is0.45 m3 (V). The power requirement of the sys tem is 0.9 kWe (P),thus the coolingrequirem ent of the sy stem is 0.9 kwth (c).The crewtime requirement is 4 C M-h/y (CT).

Ass ume tha t the investigator chooses to apply equ ivalency factors provided in the ALS

BVA D (Hanford, 2002) for a Mars transit mission. Thus, Veq= 215.5 kg/m3,Peg= 237kg/kW,, C,, = 60 kg/kWth, and CT,, = 1.14 kg/CM-h in Equation 1.

App lying the above values, the compu tation of ESM according to Equation 1 is:

E S M = 91.6 kg + (0.45 m3 . 215.5 kg/m3)+ (0.9 kWe.* 237 kg/kWe) +......+ (0.9 kWth * 60 kg/kwth) + (4 CM -h/y * 0.49 y 1.14 kg/CM-h) = 458 kg

Every piece of hardware in the system of interest may have m ass, volume, pow er, coolingand crew time requirements. However, in AL S trad e studies the real quantity of interest inan ESM analysis is comparison of the total system impact of trade options, which is oftenmo re complicated than simple accoun ting of hardware items. Determination of the totalsystem impact often involves determining the qu antities of w orking materials in thesystem that are necessar y to maintain crew h ealth over the entire mission duration. To dothis, the investigator should define the sy stem to the approp riate extent and level of detailto comprehensively capture cost impacts of trade options. Th ese issues are explainedfurther in Section 3.1.

2.5 Purposes of the ESM Concept

Th e primary purpose of ESM is to serve as one of the tools used in life support tradestudies of ALS system options” for space miss ions or ground-based test beds.Exam ination of transportation cost impacts using ESM, in conjunction with evaluation of

other pertinent issues not addressed by ESM , can fac ilitate decision s on research andtechnology development. ESM also currently serves as a tool for comp uting the ALSMetric’ ’ that is reported to NASA H eadqua rters and, ultimately, Cong ress.

ESM evaluations can also be used to evaluate test-bed design and performance. Inplanning fo r post-test-bed ESM evaluations, data collected during the test should includemas s, volume, power, cooling, and crewtim e information . After a test-bed run, ESMevaluation s may be used to provide an asses sme nt of mission transportation cost for theparticular system hardware, configuration and control appro ach used in the test bed.

The word “option” is used here to represent technology, hardware, configuration and/or control app roachI O

options.

Th e ALS Metric is based u pon ES M evaluations of candida te, future long-duration mission scenarios.1 1

The ALS Metric concept and computational method is documented in de tail in Drysdale and Hanford

(2002).

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ALS Equivalent System Mass Guidelines Document NASM TM-2003-2 12278

Similarly, ESM can be calculated for particular implementations o f potential referencemissions, such as m issions in the ALS Reference Missions Do cumen t (RMD ) (Stafford et

al., 2001). The effects of variations on life support system designs or transportationarchitectures for a reference mission can be considered using ESM , in co njunction withevaluation of other impo rtant features, to rank various options for that mission.

2.6 Users

Users of ESM can include:

0 System Analysts

0 Researchers

Technology D evelopers

0 Managers

Typically, the role of c ompu ting ESM is assigned to life supp ort system analysts, who

obtain technology data from researchers and technology deve lopers as well as fromhistorical documents, reports and d atabases. The results from ESM analyses are thenpresented and explained to various members of the comm unity, including researchers,technology develope rs, and manag ers. Community mem bers m ay use the results of ESMevaluations, along with o ther important criteria, to m ake decisions about research andtechnology development (R&TD) direction, an do r test bed and reference missiontechnology options.

How ever, analysts are not necessarily the only individuals that compu te ESM. In somecases, researchers, technology developers, and m anagers may perform ESM evaluations.This d ocum ent is designed to guide any individual in performing m eaningful andconsistent ESM evaluations.

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ALS Equivalent System Mass G uideline s Document NASN TM-2003-2 12278

3 ESM COMPUTATIONAL METH OD

ESM calculations involve significan t am oun ts of data and a ssum ptions, and thecalculation s should be performed in a consistent fashion if the results are to be

compa rable and useful for trade study purposes. This section of the document discussesdecisions and assumptions about the analysis, as well as application of the ESM equation.

3.1 Decisions and Assum ptions about the Analysis

An analysis requires consideration of the following six interconnected facets, whiledocumenting all critical assum ptions.

1) Determination of analysis objectives

2) Determination of the mission of interest and related assum ptions

3) Determination of the system characteristics that should be cap tured in the an alysis

4) Definition of the system e xtent and level of detail

5) Application of data

6) Interpretation of resu lts

As illustrated in Figure 1,because kno wledge is gained during the analysis process, theanalys is steps may b e iterative'*. At any point in the an alysis process, it may be necessaryto reiterate a previous step. As the p rocess is iterated, the inves tigator should take the

opp ortunity to review the analy sis objectives, critical chara cteristics, system definitionand data application and chang e them if necessary. Because AL S inherently deals w ithmissions that are incompletely defined, the analyst should also m ake an effort todocum ent all design assumptions during the course of the study .

3.1.1 Determination of Analysis O bjectives - Analysis objectives drive all facets of theESM computation. Objectives should be thoroughly defined in order for the investigatorto determine the mission of interest and system c harac teristics to capture in the stu dy,define the extent and detail of the syste m, and apply d ata.

Ideally, analysis objectives are defined at the inc eption of the stud y, in an appropria televel of detail. However, in reality, the ne ed fo r further clarification of the objectivesoften arises during the course of the research. This docum ent provides examp les that

'' One commonly useful iteration approach is to compu te rough estimates of ES M values at the inception of

the study, in order to iden tify critical issues, before embarking o n study deta ils.

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ALS Equivalent System M ass Guidelines Document NASNTM-2003-212278

+

portray the need for c lear, appropriately detailed analysis objectives. With e xperience, ananalyst can gain foresig ht into the proper level of detail that is required in defining thestudy o bjectives.

Determine the systemcharacteristics that should

be captured in the analys is.

3.1.1

3.1.2

3.1.3

3.1.4

3.1.5

Initiate study .E,Determine analysis

objectives.r.Determine the miss ion of

interest and relatedassumptions.

tI I

I. Y Apply data.

4

Terminate study.

Figure 1 . Flow chart for the ESM analysis process.

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ALS Equivalent System Mas s Guidelines Document NASN TM-2003-2 12278

3.1.2 Determination of the Mission of Interest and Related Assump tions - The resultsof a n ESM analysis depend on the assumptions made about the operating environment,the subsystem of interest, and the surrounding system. Cons equently, an ESM analysismu st be done with a particular mission and set of assum ptions in mind.

Th e ALS RMD is one source that analysts can use for selection of a particular referencemission for consideration in a trade study. Indeed, if the mission of interest is addressedin the RM D, it is recommend that the Rh4D assumptions be used in the study baseline. Ifnot, RM D missions can possibly be used as a starting point, and mission chan ges can bedocumented.

Top-level assumptions that are related to RM D m issions are documented in the A LSBVAD. Such assumptions include, for example, m i~s ion -s pe cif ic'~mass equivalencyfactor values, the number o f crew members, numbe r of visits to each site, missionduration, habitable volum e, infrastructure costs, crewmem ber body mass, an d typicalmetabo lic loads. When deemed applicable by the analyst, the values provided in theBVA D m ay be applied to trade studies. If other estimates are applied in lieu of BVADvalues, the investigator should provide appropriate d o~ um en ta ti on '~for those values.

In addition to the top-level mission assumptions, notions about the details of s ystemhardw are, configuration and control are inherently made throughout a trade s tudy. Alltop-level and system detail assumptions shou ld be well desc ribed, referenced an dorganized throughout the trade stud y documentation.

3.1.3 D etermination of the Characteristics of Interest and the Means by W hich toCa pture those Characteristics in the Stud y - Based upon the an alysis objectives, theinvestigator determines which characteristics should be captured in the trade study. Th einvestigator must then determine the means by which tho se characteristics will be

captured in the trade study.

Characteristics of interest may be consideredprerequisites for inclusion in the study, orthey may be compared (q~ant i ta t ive ly '~an do r qualitatively'6 , between trade study

l 3 An equivalency factor only has value in the context of an actual mission scenario from which analysts

can asses s the infrastructure costs.

If the documentation is well-known and reliable, a simple reference is adequate. Otherwise, derivation of14

the values should be provided in the analysis documentation.

Other methods of quantitative comparison that are deemed appropriate by the analyst for the study might15

be unrelated to ESM, or they might be some modification of ESM. For an example of a comparative

measure that is a modification of ESM for evaluation of food systems, see Cruthirds (2001).

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ALS Equivalent System Mass Guidelines Document NASMT M-2003-2 12278

the rest of the system remains identical between trade study o ptions. This section presentstwo brief exam ples to illustrate these concepts: 1) com parison of 1Om2 of salad crop to10m2of wheat crop, and 2) comparis on of oxygen generation via bioregen eration (greenplants) to oxygen ge neration via water electrolysis. For th e purposes of Advanced LifeSupport, the system extent may range from the entire life support system and interfaces2'

to any subset thereof.

Th e system should be defined to the appropriate extent. The analyst should consider anyportion of the life sup port system that has a significan t effect upon, o r is significantlyaffected by the trade options. For examp le, if a comparis on is being made betweengrowing 10m2of salad crop versus growing 10m2of wheat crop, in addition to thedifferences in crop production specifics, the evaluation sh ould include significantdifferences outside of the biomass production system . For ex ample, the wheat crop optionmay require significantly more food processing resources (equipment mass, volume,power, cooling and crewtime) than the salad crop option. The wheat crop option may alsobe more effective in generating oxygen, removing carbon dioxide and producing food

energy than the salad crop op tion, resulting in sizing differences in air revitalizationequipment and prepackaged food stores. The different crops may also result in differenttype s and quantities of wastes, resulting in differences in the necessary waste sub system .Depending on the analysis objectives an d the investigator's judgement, it may benecessary to inc lude such subsystems when defining the sy stem for study.

Th e system should be defined to the appropriate level of detail. In the com parison of10m2of salad crop and 10m2 of wheat crop, issues such as nutritional (macro- and micro-nutrient) differen ces, palatability differences and differences in crew psycho logicalbenefits betwee n the two options may be difficult to reflect in the ESM comp utation. Inthat case, if considered by the analys t to be im portant, such differences should beaddressed , qualitatively and/or quan titatively, elsewhere in th e study . Som e differences,such a s the sensitivity of the different crop types to sy stem perturbations , may be, intheory, quan tifiable in the ESM computation. How ever, the data necessary for suchquantification may not be available. If inadequate data exists for reve aling criticaldifferences between options , or if the ESM method i s unable to reflect the differences,then those differences should be discussed quantitatively and/or qualitatively in someother manner in the study.

Identification of the appropriate system extent and level of de tail for an ESM evaluationmay be complicated by major functional differences between options. In some cases,technologies of interest might have some overlapping functionality and some non-

Th e reader is referred to the ALS Baseline Values and A ssumption s Document (Hanford, 2002),Table

2.4.1 and Table 2.4.2, for descriptions of ALS Subsystems and Interfaces. ALS Subsystems include Air,

Biomass, Food, Thermal, Waste and Water. ALS Interfaces include Crew, Cooling, Extravehicular Activity

Support, Human Accommodations, In-Situ Resource Utilization, Integrated Control, Power and Radiation

Protection.

21

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overlapping functionality. For examp le, oxygen generation via bioregeneration (greenplants) may be comp ared to oxyg en generation via water electrolysis, because there issom e overlapping functionality (oxygen generation). However, because green plants a lsoprovide other critical functions, such as carbo n dioxide scrubb ing and water pu rification,the investigator should ma ke an effort to define at least functionally comp arable systems.

For example, a carbon diox ide scrubber and water purification system m ay be ad ded tothe water electrolysis option. Food proc essing and waste system s may also be modifiedfor comparable functionality. Howeve r, the two options m ay still differ in degree ofwater purification (quality of the output water). Depen ding on the o bjectives of theanalysis, the analyst may cho ose to either further mod ify the options to achieve an evengreater degree of com mon ality or to qualitatively discuss the purification differences. Th eappropriate approach depends o n the potential impact on analysis results and the degreeof resources (Le. time and m oney) that hav e been assigned for the investigation.

Regardless of the system definition approach, a justification of th e system ex tent andlevel of detail should be p rovided in the analysis report, so that the analysis choices canbe scrutinized.

3.1.5 Application of Data - Raw data provided by researchers and technology developersmay require some modification in order to fit into the context of a particular ESMevaluation. Data m odifications may include, but are not limited to, develo pmen t stateadjustment, and or system scaling. Although d evelopm ent state adjustment and systemscaling are the most com mo n types of data modification in an ESM analysis, other typesofmodification may b e necessary. All data modifications should be explained andquantified in the analysis report.

3.1.5.1 Development State Adjustment: Depen ding upon the objectives of the analysis,some data may require adjus tment for the appropriate developm ent state22.InALS trade

studies, the flight-ready developm ent state is typically of g reatest interest for ESMevaluation^^^. How ever, because there is n o official definition of the flight-ready

development state, the analysts judgem ent m ust be used to d etermine the modificationsthat are appropriate for the p articular analysis.

“Development state” is analogous, in some situations, to Technology Readiness Level (TRL). TRL is a

scale of nine technology development increments that is often used within NASA to characterize the

development status of a technology. Although the ALS Program is typically interested in the flight-ready

development state, other states, su ch as the current state or ground-based test-ready state could po tentially

be of interest.

23 In predicting the efficiency of flight-ready technology, the theoretical best performance may be of

interest. Particularly, flight-ready performance may be difficult to predict for a technology in the early

stages of research and development (TR L 1) . In such a case, the researcher may cho ose to base

performance predictions on the theoretical best performance that could be achieved. If the theoretical best

performance is assumed in a study, this should be clarified in the analysis docum entation.

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ALS Equ ivalent System Mass Gu idelines Docum ent NASA/TM-2003-212278

For trade study com parisons, all equipment data sho uld be “normalized” to the samedevelopment state24.Norm alizing data to a future development state often requires thatthe investigator make assumptions in orderto modify values or to estimate m issingvalues. All such assum ptions and their reasoning should be thoroughly docum entedsothat the analysis results can be understood in the ap propriate context.

For ex ample, in determ ining a flight-ready developm ent stateESM, the analyst maypredict that advances through R&TD will result in improved design soph istication suchas m aterial types, autom ation, and processor e fficiency, thereby reducing the flight-readyESM . Similarly, critical system characteristics may necessitate mod ification of the rawdata to appropriately capture those qu alities in the analysis.

To adjust raw d ata for a flight-ready developm ent state, in addition to im provem ents inthe techno logy during developmen t, the investigator should account for the environm entof the m ission and an y other anticipated mission requireme nts. A list of possiblemotivations for data adjustment to flight-ready status are listed in Table1.As there are

currently no official guidelines for q uantifying such factors in an an alysis, the analystshould judge the im portance of such ad justments against the availability of da ta and th eanalysis resources needed to mak e the mod ifications.

Requirem ents of future missions are (by definition) uncertain, and the information neededto m ake da ta adjustments is often unavailable. Probably the most difficult issue incompa ring flight ready options with developmen tal options is the am ount of detailed dataavailable. Flight equipm ent is by definition com plete, thus necessary data is available.Developm ental equipment, however, might have no data on maintenance costs or crewtime, and may not have all the pieces necessary for safely operating the equipm ent in aspace environmen t. For exam ple, a bench-top electrolysis unit might not have all of thesensors and safety equipme nt required to prevent a hydrogen explosion. It might not

have been run long enough to know the lifetime of the consum ables and spares.As analternative to modifying da ta for a flight-ready development state, an an alyst may stateassump tions that flight equipmen t is similar to some earlier design stage. Suchassump tions are often necessary, since the data neede d for developm ent state adjustmentsis often unavailable.An investigator may ch oose to qualitatively discuss necessary d ataalterations, rather than a ttempt to quantify the m odifications. Regardless of the approach,

24 Wh atever the developm ent state of interest, proper com parisons should be m ade in trade studies. For

example, it is inappropriate to com pare an ESM value for the current development state of on e carbon

dioxide scrubber to the ESM value for the flight-ready development state of another carbon dioxide

scrubber. Th e analyst should make a decision of which development state is appropriate fo r the trade stud y

and normalize the data to that chosen state. In some non-trade-study cases of ESM compu tations, it may

be necessary to com pute ESM values for different developm ent states for one set of hardware. For

example, both the current development state ESM and the flight-ready development state ESM of one set of

hardware may be of interest to project managers to estimate the ESM change between those two states.

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ALS Equivalent System Mass G uidelines Document NASN TM -2003-2 12278

all development state data m odifications deemed appropr iate for the study should beclearly explained in the analysis documentation.

Motivation

Technology

improvementsduring research anddevelopment

Gravity conditions

Dust conditions

Sunlight conditions

Planetary protectionrequirements

Radiationconditions

Launch forces

Noise level &associatedfrequencyrequirements

Safety requirements

Availabilityrequirements

Example

The analyst may predict that equipmen t may be better autom ated

for a flight, thereby reducing the crew time requirement.

The level of gravity during different phases o f a missio n will affectequipment structural strength requirements, an d may drivemodification of processes to accom mod ate differences in phaseseparation, convection and o ther characteristics.

Equipment exposed to the Mars surface may require m odificationto enable operation during dust storms.

A M ars greenhouse may require som e degree of artificial lightingin order for plants (that have evo lved in Earth condition s) toacceptably thrive.

If implemented on the Mars surface, technologies that vent gas tothe external environment m ay require modification to prevent therelease of possible biomarkers (in interest of the integrity of thesearch for life on the Mars surface).

It may be necessary to mod ify hardware materials to those whichare less susceptible to radiation dam age.

Equipment might be required to surv ive 3 g during launch fromEarth. Parts of a technology (brittle materials, delicate instruments,fragile connections, etc.) may also be su sceptible to launch

vibratory forces, therefore requiring m odification.Locations without an atmosphere externa l to the habitat (e.g. LEO )will have m ore stringent constraints on noise levels an d associatednoise frequencies.

Safety devices may be neede d to bring equipment to a greater (Le.flight-ready) safety level or to bring options in a trade study tocomr>arablesafetv levels.

Redundant equipment may be necessary to increase equipmentavailability or to bring options in a trade study to co mpa rableavailability levels.

Table 1. Some Possible Motivations for Data Adjus tment to Flight-Ready S tatus

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AL S Equivalent System M ass Guidelines Document NASNTM -2003-2 12278

3.1.5.2 System Suing and Data Scaling: Raw da ta received from researchers mayrequire scaling for representation of the app ropriately-sized system. For exam ple, atechnology develope r may provide processor hardware param eters25for a laboratoryprototype that processes only a fractionof the flow that would require processing in anactual mission or test bed. If the objective of the analysis is to comp are functionally

similar processors for a spe cific mass throughput, system sizing and data scaling isnecessary.

Hardware is comm only sized according to a characteristic parameter. Lacking otherinformation, throughput, or mass flowrate26through the equipm ent, is often a goodcorrelating parameter. For examp le, in sizing an ox ygen generation device, a typicalapproach is to m ultiply the num ber of crewmem bers by the historical, individual, averageoxygen demand.

The level of detail necessary for defining the system o f interest determines the level ofdetail necessary in the sizing effort. In this respect, the investigator’s judgemen t should

be used to determine which m aterial compounds should be included in the sizing effort. Ifa material comp ound has a relatively minor effect on system sizing, then it may beappropriate to exclude that particular compound from the sizing effort, in the interest ofanalysis time and funding. However, it is critical that the analyst contemp lates the entiresystem of interest in the sizing effort, to include any non -intuitive yet significant sizingimpacts. Sizing efforts often require that the investigator make assumptions abou t thehardware, con figuration, and control approaches in the system. These assum ptions shouldbe clearly stated in reporting the evaluation results,so that the results can be consideredin context of those assum ptions.

Depending on the objectives of the analysis, the sizing effort may range from steady-stateto transient2’ conditionsz8.In other words, system sizing efforts may lie anywhere in

25 In this document, “hardware parameters” pertain to the mass, volume, pow er, cooling and crew time

requirements ofthe hardware,which are inputs to the ESM equation, as shown in Section 3.2.

In some cases, processo r mass flow rate is directly proportiona l to the num ber of crewmembers in a

mission scenario, thus hardware parameters may be scaled proportionally to the number of crewmembers.

Such an approach may also be acceptable when the range of scale is small between raw data hardware

parameters and those implemented in an analysis.

26

2’ “Transient” is often considered to be synonymous with “dynamic”

Power generation system sizing approaches also range in complexity. Th e simplest approach is to su m

the daily-average power draw of each subsystem to size the power generation system. The most comp lex

approach is to simulate the mission to identify peak power needs for sizing the power generation system.

Sizing approaches m ay lie anywhere in between (or include) these two extremes.

28

September 2003 17



AL S Equivalent System Mass Gu idelines Document NASMTM-2003-2 12278

between (or include) these two appro ache^^^. A steady-state s izing effort requires lessanalysis effort but is less realistic than the m ore effo rt-intensive transient sizing effort 30

Steady-state sizing efforts can be easily implemented using spreadsh eet software,wherea s transient sizing efforts are mo st easily performed through the use of transientsimulation tools3’. If batch or s emi-batch processors exist in the system , an alternative

between resource-intensive transient sim ulation and (possibly) inaccurate steady-stateestimates may be necessary. In such a case, the analyst might choos e to modify stead y-state flowrates to agree with the batch or sem i-batch nature of t he processors.

In this sam e vein, the investigator sho uld decide whether to size the system for solelynom inal (no fault) operation, or if the sys tem should be sized for s pecific off-nominaleven ts (faults). Thus, system sizing possibilities span a space boun ded by 1) steady-statewith nom inal operation, 2) steady-state with off-nom inal events, 3) transient withnom inal operation, and 4) transient with off-nominal events. For each individual study,the an alyst’s judgement shou ld be used to determine the m ost ap propriate sizing tactics.Th e most common approach to date for system sizing efforts has been steady-state massflow calculations of daily loads, under no minal operation.

Once the appropriate sizing parameter values through hardware have been determined,the investigator should implem ent factors to scale the hardw are parameters to thosevalues. A simple approach is to scale hardware para meters linearly with respect to thesizing parameters. How ever, more accurate hardware param eters might be obtained byusing scaling factors (which a re not necessarily linear) provided by the technologydevelope r or by using compo nent-specific scaling factors that are standard to thechem ical industry. (Th e reader is referred to Yeh , e t . al., 2001, for examp les of scalingfactors used in the Chem ical Industry.) As a sim plification, the entire piece of hardware

For example, if a steady-state sizing effort is performed, the analyst may choose apply “corrections” to29

the results in order to reflect known sizing characteristics of the system.

30 Th e easiest design to size is one that provides a processor with steady-state flow. How ever, when

necessary, transien t system sizing allows for m ore accurate processor si zing for peak ‘flows an d or the

necessary b uffers to bring flows as close as possible to steady-state.

To clarify, if a transient simulation (Le. dyn amic simulation) is performed, the analyst uses the results of

that sim ulatio n to size processors as well as any necessary buffers (e.g. greywater ta nks and potable w ater

tank s in the case of water processor sizing). In some simulation cases, proces sors may require sizin g for the

maxim um or minimum flowrate that is needed during the simulation in order to satisfy som e other

con dition s, such as requirements on the sup ply rate of a resource or constraints on holding tank capacity ofa resource. Also, in some simuulation cases, buffer tanks may requi re sizing acco rding to specified

con dition s such as requirements on the receiving rat e of a resource or constraints on the processing rate of a

resource. W hatever the requirements and constraints on the simula tion, the processors should be sized to

the maximum flowrate and buffers should be sized to the maximum capacity seen during the simulation.

Such “maximums” are the parameters that feed into the ES M equation ( M , V , P , C and C7).

31

Septem ber 2003 18



ALS E quivalent System Mass Guidelines Docum ent NASNTM-2003-212278

can be scaled to one sizing parameter. However, because there can be components ( e gcontrols) of a piece of hardw are that are not size-dependenton sizing parameters (such a smass flowrate), more accurate sizing parameters should be used for those compo nents, ifreadily available. Whatever the approach, sizing parameters, scaling factors andassociated assumptions should be adequately explained in the analysis docum entation.

September 2003 19



ALS Equivalent System M ass Gu idelines Document NASA/TM-2003-2 12278

where E S M = the equivalent system mass value of the system o f interest [kg],

M I , = initial mass of subsystem i [kg],

SFI i= initial mass stowage factor for subsystem i [kg/kg],

V I j= initial volume o f subsystem i [m3],

= mas s equivalency factor for the pressurized volum e support infrastructure of“eqj

subsystem i [kg/m3],

P, = power requirement of subsystem i [kW,],

= mas s equivalency factor for the power genera tion support infrastructure of% j

subsystem i [kg/kW,],

C j= cooling requirement of sub system i [kWth],

Ceqi= mas s equivalency factor for the coo ling infrastructure of subsystem i [kg/kWth],

CT = crewtime requirement of sub system i [CM-Wy],

D = duration of the mission seg men t of interest [y],

CTeqi= mass equivalency factor for the crewtime of subsystem i [kg/CM-h],

M T D i= time- or event-dependent mass o f subsystem i [kg/y],

Equation 2 is oriented toward spreadsheet acc ountin g of comm odity use by subsystem parameters. In32

some cases (such as when transient simulation is used to determine the siz e of the power gene rationsystem), assignment of commodity use to specific subsystems is not straightforward, and a modified

accounting method should be used. Specific examples of such situations are provided later in this

document.

33 Italics are used to denote symbols used in equations in this docum ent.

September2003 20



ALS Equivalent System M ass Guidelines Document NASNTM-2003-212278

SFrDi=time- or event-depend ent mass stowage factor for subsystem i [kg/kg], and

VTDi= time- or event-depende nt volume of sub systemi [m3].

The terms in the ESM e quation are summed over i = 1 to n subsystems. A “subsystem” as

written in this docume nt pertains to an y subset of the system that was defined for thestudy. A sp readsheet example is included with this docum ent, as a po ssible template foritemizing ESM subsystems. Figure 2 shows the main view of the ESM Temp late. In theESM Temp late, a separate row is provided for each subsystem , divided as deem edappropriate by the an alyst. Currently, only three rows are provided for d ata entry (Item 1Item 2, and Item3), so the investigator should add rows as necessary, while assuring thatthe “Total” row correctly sums the values for each parameter in the spreadsheet.

The most comm on approach to date for defining subsystems has been at the hardwarelevel. Generally, the sy stem shou ld at least be divided into subsystems as nece ssary toreflect subsystem -specific stowage an d equivalency factors and to allow for

straightforward critique by others. Typ ically, subsystem-specific equivalencies(Veq,P e g ,Ceq,an d CTeq)are not ne cessary; one equivalency factor value is applied to allsubsystems for a p articular mission segment34.Therefore, the ESM Template has beendesigned so that “System-Applicable Equivalency Factors” can be entered and used asthe default values for all subsystems in the results documentation.

Th e spreadsheet nature of th e ESM Tem plate makes it most suited to system sizing viasteady-state sizing. The template sho uld be mod ified, or other reporting metho ds sh ouldbe u sed if regarded necessary by the analyst. For exam ple, ifan investigator chooses tosize a system acco rding to transient simulation results, it may be difficult to assignportions of the peak power and cooling needs to specific ~ u b s y s te m s ~ ~ .Thus, the analyst

34 As a specific counter-example, one subsystem may be relatively impervious to environmental radiation,

while another subsystem may be relatively vulnerable to environmental radiation. If the necessary radiation

shielding is not built onto the hardware itself and counted as initial mass (MI) ,then the latter technology

would require a larger volume equivalency factor to account for the additional radiation protection.

Additionally, one subsystem could associate resource needs to multiple infrastructure sources. For example,

both solar and nuclear power could, in theory, be utilized during a Mars surface mission. In such a case, a

particular piece of hardware could obtain part of it’s power needs from the solar power generation system

and the remainder of it’s power needs from the nuclear power generation system. In su ch a case, an analy st

performing an ESM computation should take care to assign appropriate mass equivalency factors for power

use to the distinct resource needs, without “double-booking” the hardware power requirements.

35 On e approach to such a dilemma to allocating portions of the total power “peak” to the different

subsystems may be to assign the necessary mass of the power system according to the particular hardware’s

influence on the overall power system design. Thus, if a particular piece of hardware requires 4 kW at the

design point (peak) of the power system design simulation, thereby driving the size of the pow er system

from 16kW to 20kW, then those 4kW might b e “billed” to that specific hardware.

September 2003 21



ALS Equivalent System Mass Guidelines Document NASA/TM-2003-2 12278

migh t choose to use only the mass, volume a nd crewtime portions of the template andspecify the peak pow er and cooling dem ands in a different manner. In such a case , theassum ptions behind the simulation configuration that lead to that peak pow er and c oolingneeds sh ould be explained.

The goal of an ESM trade study evaluation is to size the system differences between tradeoptions. Thu s, even though this document go es to great lengths to detail all types ofmaterials that might be accounted in a system , the analyst only needs to co nsider thethings that differ between options for a particular analysis. Additionally, categorization ofmaterials accord ing to ESM parameters is not clear-cut. For example, som e analysts maycho ose to categorize the mass of cabin atmospheric gas es under th e initial mass term(MI),wh ile other analysts choose to categorize those gases under the time-d ependen tmass term (MTD).In fact, the exact means o f materials categorization is inconseq uential,as long a s all critical materials are quantified correctly over the en tire mission du ration.

In the E SM Template, cells are provided for each o f the parameters in Equation 2. Thecolumn s for each parameter can be “unscrolled” to reveal background inform ation thatmay b e necessary for proper referencing and explanation of data. The unscrolled colu mnsinclude sub-columns for:

. Original Data V alue, Source and Description;

= Develo pmen t State Adjustment Explanations, Quan tifications and So urces; and

. Scaling Explanations, Quantifications and Sou rces.

Oth er ALS researchers should be able to understand and critique the data that are appliedin the analysis. Thus, it is critical that applied values be appropriately doc umen ted, so

that the evolution of values (from original to imp lemented ) can be tracked . Figure 3show s the columns for background information for the initial mass term ( M ~ Y F I )of theESM calculation. Although not shown in the figure, such colum ns are repeated for thevolum e, power, cooling, crewtime, time-dependent mass and time-dep endent volum eterms.

Each parameter, stow age factor, and equivalency factor in Equation 2 w ill now b ediscussed in detail.

Septem ber 2003 22



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ALS Equivalent System Mass Guidelines Docum ent NASNT M-2003-2 12278

3.1.6 Explanation of Parameters- The parameters for initial mass ( M I ) ,initial volume( V I ) ,power (P) , cooling (C),crewtime (CT),time-dependent mass ( M T D ) and time-depend ent volume (VTD)in Equation 1 will now be ex plained in detail.

3.1.6.1 Initial Mass ( M I ) :Initial mass, M I in Equation 2, pertains to any mass in the

system of interest that is not dependent upon the duration of the m ission segm ent, andthat is not accounted for in volume, power and co oling terms. (Th e volume terms ac countfor the mass of structure required for pressurized volume, the power term accounts fo r themass of the power generation system, and the cooling term accounts for the m ass of theheat rejection system.) The initial mass of a system can include 1) hardware, 2 )associated hardware connections such as plumbing, and 3) any working mass, such as

water in tanks (Doll, 1999).

Th e hardware accounted in the initial mass param eter should include all hardwarenecessary for proper op eration of the system, other than replacemen t of time-dependentitems such as consum ables and spare parts. (Time -depende nt items are counted in thetime-dependent mass parameter, MTD.)The proper hardw are to includ e in the initial massterm may include more than th e obvious main equipm ent and tanks. The initial mass termshould also include subsys tem thermal control devices, such as equipment fans,coldplates, heat exchang ers, equipment for heat distribution (includ ing the cabin fan ifappropriate) and associated fluids. Also, any power distribution an d storage equipm entwithin the system of interest are included in the initial mass, wh ile power generation andsystem-level storage or distribution equipment is included in the power term in Equation2, ( P P e 4 ) .The initial mass term should also include any necessary controls hardware,such as control panels, sam pling devices, and m onitoring equipm ent.

Asso ciated hardware connections may include plumb ing, ducting, or wiring either withinor between subsystem s. How ever, in some cases, such equipm ent is not a large portion of

the ESM and may be excluded from the analysis. The cho ice of whether or not to includehardw are connections in the study should be m ade by the investigator. If hardwareconnection s are deemed a considerable part of the system , the analyst sho uld decide uponwhere to account for inter-subsystem conn ections when tab ulating results. Suchconnections might be appropriately assigned to one particular subsystem, or theconnection s might be counted as a separate entity. If counting conn ections as a separateentity in the ESM T emplate, the investigator simply adds an additional row for data entry.

Wo rking mass pertains to a material36(such as water or oxygen gas) that must betransported in order for the system to operate properly. Th e working m ass values may beaffected by the selected sizing approach, that may range from steady-state to transient

estimates.

Working mass includes the atmospheric gasses in the system, when app ropriate.36

September 2003 24



ALS Equivalent System Mass Guidelines Document NASNTM-2003-212278

For example, consider the case w here a steady-state mass balance is performed todetermine the quantities of working fluids. In a steady-state mass balance, working massmay be estimated as the mass of material in storage awaiting processing, plus the amountthat occupies the processor at steady-state. Working mass for a particular processorrepresents the am ount of useful material that is “tied up” in the processor and is therefore

unavailab le to the rest of the system (Levri et al, 2000).Thus, if processing speed is veryfast (or residence time is low), the working mass fo r that processo r will becorrespondingly low; if the processing speed is very slow (or residence time is high), theworking m ass for that processor will be correspondingly high.

If a stead y-state sizing effort is performed, but th e analyst wishes to properly reflect thenature of batch or sem i-batch processors, then working m ass m ay be the time-averagedmass contained in the reactors and buffers during one residence time. A dditionally, if asteady-state sizing effort is performed but the investigator has further know ledge aboutthe behavior of the system, then the analyst may make corrections to working massestimates and tank sizes. Such an endeavor may account for some time-driven material

quantities withou t perform ing a full transient sizing effort.

Sizing a system through transient simulation may require a different approach toaccounting for working m ass. In the case of a closed or sem i-closed life support system,accumulation of a compound in one location necessarily reduces the amount of thatcom pound in another location. Thus , in the case of transien t simulation sizing, it isdifficult to assign (categorize) working mass to specific subsystems. In such a case, theworking m ass of a material for the entire system of interest may be accounted as anindividual subsystem, by using a separate row of data in the ESM Template.

3.1.6.2 Initial V olume (VI) :Initial volume, VI in Equation 2, pertains to any p ressurized

volum e required for housing the system of interest that is associated with initial massquantities, and any space required for crew access to equipment. Thus, initial volume fora com plete life support system includes any pressurized volume n ecessary to support lifesupport hard ~ar e .~’ .

Care should be taken such that crew access volume is appropriately accounted. In caseswhere crew access space is strategically planned around unit change-out, the volum erequired for that change-out may po ssibly be disregarded. For example, it may bepossible to restrict crew access (in addition to the sp ace between the tops o f the plantsand the lamps) to replace lamps in a plant growth system to the interval between

37 Although the m ass of gas that occupies crew free space is accounted in the initial mass term, for

computation of the ALSMetric, the AL S Project Office has mandated that crew fre e volume will not be

included in the ca lculation, in order to prevent misleading metric improvement through restriction of cabin

volum e and associated reduction in habitat structure and radiation shielding ma ss.

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AL S Equivalent System Mas s Guidelines Document NA SN TM -200 3-2 12278

harvesting and replanting3'. In such a case, space in addition to the plant growth v olum eis not required.

3.1.6.3 Power (P):Power, P in Equation 2, pertains to the electrical power requirem entsfor sizing the powe r ge neration system. The suitability of Equation 2 (and the ESM

Template) in accoun ting for system power requirements depends on the approac h that isused to size the power generation system.

Power generation system sizing approach es range in com plexity. The sim plest approachis to sum the daily-average power draw of each sub system to size the power generationsystem. The most complex approach is to sim ulate the mission to identify powe r need sfor sizing the power gen eration system. The investigator should determin e if the mo stappropriate approach to power system sizing is 1 ) sum ming daily-average powe r draws ,2) simulating the sy stem power draw , or 3) some intermediate approach. The analystshould understand the system power dynam ics in order to incorporate the mostappropriate power generation sy stem sizing methods.

If the investigator choo ses to sum daily-average power draws , and power availability andcost are not time-dependent, then application of Equ ation 2 (and the ESM T emp late) isstraightforward. Th e accuracy of such an approach dep ends largely on the powe r storagecapacity (Le. buffering) of th e power system , and the behavior and control appro ach ofthe life support system . Such an approach is m ost representative of the power need fo r asystem that runs continuo usly at steady-state.

If the analyst chooses to simu late the system power draw, application of the power term( P P,,) in Equation 2 (and the ESM T emplate) is less straightforward. System pow erdraw fluctuates with subsys tem transient power requirement^^^ and process scheduling4'.Thus, rather than sum ming sub system power requirements, the simulated power draw

profile might be exam ined to determine the most appro priate value to represent the powerrequirement of the entire sys tem of interest. The peak p ower requirement d uring thesimulation may be a good value fo r sizing the power generation system. Howe ver, indesign of an actual system, processes might be rescheduled to reduce the peak sy stempower needs. Some degree of pow er storage might also be used (at som e cost) to reduce

38 This may be a reasonable assump tion, given likely lamp sizes and lifetimes

39 As an example of transient power requirements for a particular hardware item, an incinerator that uses a

heat exchanger to heat inflow air and cool outflow air may have a large power draw during start-up of the

process, followed by a relatively low power draw once the process has reached steady-state.

As an example of power fluctuation with process scheduling, a system that incorporates crop production40

may experience the highest power demands during illumination of the crop. Thus, the peak pow er need

might be reduced by illuminating the crop during the crew's night, when there is little power-demanding

activity elsewhere in the system.

September 2003 26



ALS Equivalent System Mass Guidelines Document NASM TM-2003-212278

peak system power requiremen ts. The investigator should select the most approp riatepoint on a sim ulated powe r profile and decide upon adjustments (if any), based uponknow ledge of system operation.

If sum ming daily-average power draws is too inaccu rate and simu lating the system pow er

draw is too resource-intensive, the analyst may choose to use an intermediate approach tosizing the power generation system. For examp le, for some su bsystems, the inve stigatormight consider the nominal subsystem power draws to b e m ore representative of realitythan daily-average power draw s. As an example, an incinerator may be run only afterevery 10-day crop harvest interval, encouraging the use of a value other than the dailyaverage power draw.

3.1.6.4 Cooling (C): Cooling, C in Equation 2, pertains to heat rejection requirements forsizing of the internal and external thermal control systems.As with pow er, the suitabilityof Equation 2 (and the ESM Temp late) in accou nting for system cooling requirementsdepends o n the approa ch that is used to size the thermal control system.

Mo st power that is consum ed in the life support system must eventually be rejected asheat41. Thus, in the case of direct application of E quation 2 (and the ESM Te mplate)subsystem co oling needs are typically equivalent to the subsystem power needs.Similarly, in the case o f power system sizing by transient simulation, the thermal co ntrolsystem may generally be sized according to the system powe r requirement. How ever,there are cav eats to equating cooling requirements with pow er requirements. Forexamp le, any exo thermic reactions (e.g. human metabolism, oxidative waste processes)or endotherm ic reactions (water e.g. electrolysis, photosynthesis) in the system should beconsidered in sizing the thermal control system. Another exam ple is the direct use ofsunlight for power, such a s in a planetary greenhouse.In such a situation, only a smallamou nt of power may b e needed for solar powe r collection and distribution, but arelatively large thermal heat load would ultimately have to be rejected from the system.Thus, the c ooling requirement for the direct use of sunlight may be greater than that ofthe pow er requirement.

3.1.6.5 Crewtime (CT):Crewtime, CT in Equa tion 2, pertains to any time that the crewspends in system operation or maintenance. Operation and maintenance includes anycrewtime spent in processing steps that require crew intervention (including start-up andshutdown ), monitoring an d control, changing out parts, cleaning, and other maintenance.For an ESM evaluation in which only nominal operation of the system is considered, onlycrewtime spent in schedu led maintenance is included in the an alysis. Unsched uled

.4 ' Ther e is a caveat to this generalization. Th e colder the location of the m ission, the greater the rate of

passive loss of heat from the habitat. Simi larly, during environmental temperatures g reater than the habitat

temperature, heat rejection is required i n excess of that generated w ithin the habitat. However, this cavea t is

generally disregarded for ALS trade studies.

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ALS Equivalent System Mass Guidelines Document NA SN TM -200 3-2 12278

mainten ance (troubleshooting and repair) would be included in ESM evaluations thatconsider off-nom inal events.

Crewtim e that is spent on mission-oriented or scientific work is not in cluded in the ESMevaluation. Thus, because extra-vehicular activity (EV A) is typically con sidered mission-

oriented work, it has traditionally not been counted as crewtime in ES M evaluations.However, in a case where a life support technology requires that a portion o f EVA tim ebe s pent in maintaining the life support system, an appropriate quantity of EV A timeshould be counted in the ESM crewtime term. For example, in a case wher e noxiouswas tes are disposed outside of the habitat on a planetary surface4*,any EVA time (e.g.waste transfer, mon itoring pressures) spent maintaining that subsystem s hould be coun tedin the crewtime term.

3.1.6.6 Time-Dependent Mass (MTD):Time-dependent mass, M TDin Equation 2,pertains to any mass in the system that is dependent upon the miss ion seg ment duration.Such item s may include, but are not limited to, consumable resources, proces sexpend ables and spare parts43.Consumable resources may include clothing, prepackagedfood and other materials. Howev er, depending on the sizing effort approach, there maynot be a clear distinction between consumable resources (included in the time-depend entmass term) and work ing mass (included in the initial mass term ). The categorization ofmaterials is not particularly important, as long as all critical materials in the sys tem areappropriately quantified and included in the analysis.

3.1.6.7 Time-Dependent Volume (VT D):Time-dependent vo lume, VTDin Equation 2,pertains to any pressurized volum e in that is associated with th e time-depen dent mass

(MTD).

The an alyst should take care that time-dependent volume isn’t dou bly booked in an ESM

evaluation. Configurations that are prone to volume double booking include those thattake advantage of dynam ically changing space in the habitat. For examp le, in a casewhere emptied food lockers are used to store stabilized waste rn a t e r i a l ~ ~ ~ ,the investigator

Th e environmental impact in suc h a case might be an issue. Howev er, the case is simplified for the42

purp ose of providing a uncomplicated example.

If the ESM evaluation considers only nominal system operation, then o nly expen dables and spares43

associated with nominal operation and maintenance should be included in the study. If the ESM evaluation

considers off-nominal events, then expendables and spares for appropriate contingency sho uld be includedin the study.

This exam ple is solely for illustrative purposes. In reality, because o f possible sa fety hazards, storing44

waste material, even if stabilized, in close proximity to unused food stores may violate mission

requirements.

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ALS Eq uivalent System Mass Guidelines Docum ent NASMTM-2003-2 12278

should not to dou ble-book that volume in both the food subsystem and the w aste

subsystem.

3.1.7 Stowa ge Factors and Mass Equivalency Facto rs - In Equation 2, stowage factors(SF1an d SFTD)are app lied to initial and time-dependent masses, when necessary, to

account for additional hardware, such as racks, needed to fasten dow n and containequipment.

Also in Equation 2, subsystem volume (V , and VTD),power (P),cooling (0and crewtime(CT)requirements are converted to units of mass by assignment of a fraction of theinfrastructure cost, according to the fraction of resource use. Th e ratio of the resourcecost (in units of mass) to resource use is termed a mass equivalency factor.

Num erical values for stowage factors and mass equivalency factors are provided in theALS BVAD, along with the assum ptions that were used to gen erate those values.Insituations where alternative values are more appropriate for a particular ESM evaluation,

the reasoning and value derivation45should be provided in the study report.

3.1.7.1 Stow age Factors (SFIan d SFTD):Most items must be secured to the inside ofthe habitat in som e manner. Large items may be fastened directly to the primarystructure. For m any com ponents of hardware, a simp le rack, such as those used o n theInternational Space Station, may be used for securing equipm ent. For sm all, loose items,such as food packages, packa ges of hygiene wipes, rolls of toilet paper, etc., som eadditional equipme nt, such as a tray, is necessary for containm ent.

Stowage factors may b e ap plied, if necessary, to a subsystem’s initial and time-depen dentmass (M Ian d MTD),as a relative representation of the item’s need for additional holdingstructure. How ever, stowag e factors should only be use d to the degree necessary tocomp ensate for unavailable information on the equipment that is required for stowage.Thu s, some initial and time-dependent mass values in an ESM evaluation may require noalteration by stowage factors, and other data values m ay require significant alteration bystowage factors.

For exa mple, if the m ass of rack structure needed for a com ponent of equipm ent is welldocum ented, that rack mass c an be included in the initial mass of the eq uipmen t, and theequipment can be given a 1.O stowage factor46.As an other example, if the mass o f foodlockers needed for individual food items is known , but the mass o f the rack needed to

45 A reference may b e provided in lieu of the derivation, if the derivat ion exists in a readily-available

reference.

A value of 1.O is the minimum value tha t may be applied as a stow age factor and implies that no46

modification to the mass data for stowag e requirements is necessary.

September 2003 29



ALS Equivalent System Mass Guidelines Document NA SNT M -2003-2 12278

secure the lockers is unkno wn, then the time-dependent fo od and associated lockers canbe given a stowage factor that is greater than 1.O.

In the ESM Template, a default stowage factor of 1.O is assigned to each subsystem. Thisdefault value may be chan ged for each su bsystem , as necessary . Each stowage facto r

colum n can be unscrolled to provide inform ation on the explanation and source of eachstowage factor that is applied.

3.1.7.2 Volume Equivalency Factor (Veq):As m entioned previously, the ratio of theresource cost (in units of mass) to resource use is termed an equivalency factor.

In practice, volume equiv alency factors, Veq,are driven by pressure loads, andrequirements for radiation protection and meteoroid shielding. Most designs assum e thatall parts of the system hav e sim ilar supportive structure and ar e shielded and pressurizedequally. In such cases, the sam e equivalency factor is applied to all subsystems. (Thesystem-applicable volum e equivalen cy factor in the ESM Tem plate may be emplo yed.)However, if some portions of th e habitat are shielded o r pressurized differently thanothers or use a different suppor tive structure, then subsystem -specific volumeequivalency factors should be used. For exam ple, a shielding-intensive “storm shelter’’migh t be designed into a habitat to protect the crew fro m short periods of high radiationlevels. Similarly, plants migh t be grown in a cham ber that is less shielded4’ and at a lowerpressure than the crew habitat48.In this case, separate volume equivalencies should beused for the crew and p lant habitats49(and an airlock would be needed between them).

The habitat structure must w ithstand the stress caused by the internal pressure loads. Inaddition, during events of internal or ex ternal pressure chang e, the structure must be ab leto maintain an acceptable form . The habitat may also require thermal shielding such asradiant o r ablative coverings50.In those cases, the therm al shielding is proportional to the

volum e enclosed, with larger cabins requiring larger heat shielding.

47 Plants are less radiosensitive than human s.

Such an approach may reduce the necessary mass of atmospheric gases and the air leakage rate. Plant48

growth rates might also be increased.

Alternatively, the lower of the two volume equivalencies could be used in the computation, and the mass

of the extra shielding required fo r the crew could be accou nted for in the initial mass term. As another

exam ple, if a habitat requires a stor m shelter for high-radiation even ts, the shelter could be accounted for byexplicitly adding shielding mass to the initial mass term, rather than by using a different volume

equivalency factors for different parts of the habitat.

49

Th e tiles on Shuttle are an exam ple of a radiant covering, w hile the heat sh ield on the base of earlier crew50

capsules are an example of ablative shielding.

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ALS Equivalent System Mass Guidelines Document NASNTM -2003-2 12278

Requirem ents on radiation shielding can have a large effect on equivalency factors forpressurized volume. Ra diation shielding requirements vary with the age, sex, nutrition,and g enetics of the crew, the time in the solar cycle, distance from the Sun, and localeffects such as the Van Allen Belts. In free spac e near 1 Astro nom ical Unit'' (AU), a thinaluminum skin may be adequ ate to protect human s from short exposures to the ultraviolet

radiation and the less penetrating solar radiation. During solar particle events and in theVan Allen B elts, radiation levels can be high enoug h to require ad ditional shielding toprevent acute radiation sickness. It is harder to sh ield against the m ore energe tic cosmicradiation, making it a concern for long duration missions.

Depen ding on the m ission location, meteoroid shielding could be required for so mehabitats. Significant quantities of d ebris particles are found in LE O,somore shieldingwould be required than during Mars transit or on the M oon. M ars has a thin atmosp here,whic h would provide some meteoroid protection and possibly som e radiation shieldingfor a M ars surface habitat.

Accepted values for volume equivalency factors for specific mission segm ents areprovided in the BVAD.

3.1.7.3 Pow er Equivalency Factor (Peq):As with the v olume eq uivalency factor, thepow er equivalency factor,Peq,is the ratio of the resource cost (in units of mass) toresource use. Th us, the powe r equivalency factor is determined by d ividing the massof

the power generation system by the electrical power output.

Th e power equivalency factor should reflect all aspects of the power generation system,including any nec essary power storage, heat rejection for the power system, and powerdistribution a nd control. All of these characteristics vary w ith the type of pow ergeneration system.

Mo st designs assum e that all parts of the system utilize power from the sam e powergeneration system. In such cases, the same equivalency factor is ap plied to allsubsystems. (The system-ap plicable power e quivalency factor in the ESM Temp late maybe employed.) However, if portions of the habitat are powered by d ifferent powergeneration sy stems, then subsystem-specific power equivalency factors shou ld be used.For examp le, consider the case of using solar power in which power storage is necessaryduring the nighttime. Such a system would requ ire that the solar power system be sizedfor the pea k day time load and o versized for constant draw o f power to recharge batteries,which are sized for the peak nighttime load. Thus, different power e quivalency factors beapplied to equipment that require power during the day (solar power system ) versus

equipm ent that require power during the night (batteries). If some equipmen t were used

1 AU = 149,597,870.691kilometers. An Astronomical Unit is the mean distance between the Earth and

the S un. It is a derived constant and used to indicate distances w ithin a solar system. The Earth orb its at a

distance of 1 AU from the Sun.

51

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ALS Equivalent System Mass Guidelines Document NAS NTM -2003-2122 7s

during both the day and night, the larger of the two equivalency factors would be appliedto those particular hardware pieces52.

Currently, the twomost comm only assumed approaches to power generation for ALS

reference missions are nuclear reactors an d so lar collectors. Accepted v alues for pow er

equivalency factors for specific mission se gmen ts are provided in the BVA D.

3.1.7.4 Cooling Equivalency Factor (Ceq):As with the volume and power equ ivalencyfactors, the cooling equivalency factor, Ceq,is the ratio of the resource cost (in units o fmass) to resource use. Thus, the cooling equ ivalency factor is determined by dividing th emass o f the thermal control system by the h eat rejection capacity of that system .

There are three types of thermal control equipm ent to consider in an ESM an alysis:

1) subsystem thermal control equipm ent that transports heat from the subsystemhardware to the internal thermal contro l system (ITCS ),

2) ITCS equipment that transports heat from the subsystem thermal controlequipment (or the cabin air in the ca se of atmospheric cooling) to the externalthermal control system (ETCS), and

3) ETCS equipment that transports heat from the ITCS to the environment.

Subsystem thermal control equipment m ay inc lude hardware-associated fans, coldplates,heat exchangers, fluids and controls. ITCS ha rdware m ay include lines, pum ps, heatexchang ers, fluids and controls that are inside the habitat but not within the subsy stemcooling equipment. The ETCS requires radiators, piping, heat exchangers, pum ps, fluidsand controls.

Subsy stem thermal control equipment should alw ays be accounted in the initial massterm (M I ) .ITCS equipment is most easily accounted by app lying an ITCS coolingequivalency factor to the subsystem (or system) cooling dem and53.ETCS equipm ent is

Normally, for a solar power system , the BVAD provides po wer equivalency factor estimates for52

continuous power usage and for daytime-only pow er usage. Values for systems that only operate at night

are not included.

In the case of an analysis of a complete life supp ort system, the ITCS equipment may be accounted as a

separate subsystem (with its own mass, volume, power, cooling and crewtime demands). This can be doneif the analyst has the appropriate ITCS knowledge and such an approach is expected increase results

accuracy. In such an endeavor, the analyst must be certain not to double-book the subsystem cooling

demands as both sub system and ITCS cooling d emands. While this second approach is recommen ded and

encouraged for overall system analysis, SIMA recognizes that even for an overall system analysis it may

not be practical in all cases, especially if the analyst is not familiar with thermal control sys tems .

53

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ALS Equivalent Sy stem Mass Guidelines Docum ent NASNTM -2003-2 12278

accounted by app lying an ETC S cooling equivalency factor to the subsystem (or system )cooling demand. If the IT CS is accounted via a cooling equivalency factor, the IT CScooling equivalency factor and the E TCS cooling equivalency factor (both in units ofkg/kWth)may be sum med an d applied as one factor to the subsystem cooling dem and.Values for internal and external thermal control system co oling equ ivalency factors are

provided as both comb ined values and as separate values in the BV AD. Using co mb inedcooling equivalency factors is the recommended approach and the approach that isconsistent with Equation 2.

For m ost sp ace missions, radiation is the only feasible mec hanism of ETCS heatrejection. In som e locations such as the surface of Mars, during periods of lowenvironmen tal temperature, significant heat loss may occur simp ly due to the temperaturegradient between the crew habitat and the external environment. How ever, radiator sizingdepends o n the difference betw een the fourth power of the radiator temperature an d thefourth power o f the heat sink temperature. Thus, even in con tinuously cold locations,thermal control systems ma y still be necessary to maintain a continuously comfortable

cabin temperature.

3.1.7.5 Crewtim e Equivalency Factor (CT,,):The key assum ption behind theapplication of the crewtime equ ivalency factor is that time occupied in operation an dmaintenance of the life suppo rt system detracts from the time that is available formission-oriented work (Levri et al., 2000)54.If it is assum ed that the main go al of themission is to achieve spe cific, scientific objectives, then a ny cre w hours spent on the lifesupport system underm ine crew hours needed to achieve the mission goals.

For ex ample, if half of the crew’s designated work time is con sum ed by life suppo rtmaintenance, the size of the crew and associated life supp ort system mu st (in theory) beapproxima tely doubled in order to achieve the scientific goals of the m ission. Likewise, if

three-fourths of the crew’s available work time were consum ed by the life supportsystem, the size of the crew and life support system would have to be multiplied by fourin order to achieve the mission goals. Thus, as the a moun t of time available for scientificwo rk app roaches zero, the num ber of crewmembers and size of the associated life supportsystem would ap proach infinity.

Levri e t a1 (200 0) presents a disc ussion of the mathem atical theory behind the crew timeequivalency factor, whic h is sum marized here. If the total amo unt of time that is available

54 As with all m ass equivalency factors, if the analyst finds the underlying assumptions to be inappropriate

to the study at hand, then alternative assumptions can be declared and used to com pute different

equivalency factors. For examp le, if it is believed that crewtime will be readily available and in low

demand during a particular mission, then the analyst may decide to apply a crew time equivalency factor of

zero. S uch a decision is perfectly acceptable, as long as the justification is reasonable and clearly

docum ented in the an alysis report.

September2003 33




to the crew for work is categorized into mission -oriented (scientific) work and lifesupport-o riented work , the follow ing equation can be written:

WORK = MISSION + ~ L S S Equation 3

where t W o R K = total crewtime allotted for work (not devoted to time such as eating,

sleeping, exercising, persona l time, etc.) [CM -h/y],

tMISSION = crewtime that is used in performing scientific, missio n-oriented work (a subse t

of WORK) [CM-Wyl,

t L s s = crewtim e that is requ ired to m aintain the life su ppo rt sys tem ( a su bset of tWORK)[CM-Wy].

Similarly, if the total ESM of a life support system is categorized into crewtim e ESM andnon-crewtime (mass, volume, power and cooling) ESM, the following equation can bewritten:

Equation 4

where E S M T O T A L ~ ~= the ESM value of the entire life support system (the sum of thecrewtime and non-crewtime portions of ESM) [kg],

ESMNCT= the non-crew time portion (mass, volum e, powe r, and cooling ) of ESM [kg],

ESMCT= the crewtime portion of ESM [kg].

Follow ing the logic that as time for mission work decreases, the number of crew and sizeof the life support system increas es proportion ally, the follow ing equation can be w ritten:

Equation 5(~:Z:NESMTOTAL= E S M N C T

If Equation 4 is comb ined with Equation 5 , the following equation is achieved:

Equation 6IMISSION -‘JESMCT = ESMNCT

The crewtime cost is the life support system mass that is required per CM-Wy, thus, thecrewtime equivalency factor may be w ritten as follows:

Equation 7

“ss

ESMTOTAL is synonym ous wi th “E SM” in Equ ation 1 and Equation 2. ESMToTAL is used in this do cum ent55

to remain consistent with the BVAD and the original derivation of the crewtime equivalency factor (Levri,

et a l . ) .

September 2003 34



ALS Equivalent System Mass Guidelines Document NASA/TM-2003-212278

Manipulation of Equation 4 through Equation 7 provides the following equation:

Equation 8

Equation 8 show s that the crewtime equivalency factor varies as the ratio of the non -

crewtime po rtion of the life support system and the time available for mission-orientedwork.

As a sim plification to compu ting the crewtime equivalency factor, assumptions can b emade about ESMNCTand tMIssIoN fo r various m ission segm ents, based upo n p ast AL Sme tric calcula tions, resulting in standard CT, value s for ALS referenc e missions. ThoseCT,, values and their associated assumptions are documen ted in the ALS BVA D.Application of ALS BVAD crewtime equivalencyfacto rs is the most straight-forward

approach approach to computing the crewtime portion of ESM.

Application of standard CT,, values in the ALS B VA D is most app ropriate when the life

support system of interest has a ESkf,,cp’tMIssIoN value similar to the values used to derivethe standard CT,, values. How ever, if the ESM,&tMI~S~oN value for the specific lifesupport system of interest is known and is very different from the values used to developthe BVAD CT,, values, then analysis-specific crewtime equivalencies shou ld becomp uted an d implem ented according to Equation8 . However, the ESA&cdtMIssIoN value

is typically not kn own u nless one considers the entire life support system, rather than asubset of the life support system.

3.3 Discussion of Location Factors

Accelerating m ass to d ifferent locations in space can require different amounts of fue l,making transportation co st per unit mass a location-dependent characteristic. Thus, in

order to compare the costsof the various segments, ESM should be com putedindividually for each seg ment and then “normalized”.

Segme nt-specific ESM values can be no rmalized by applying location factors (Fisheret

al. 2003). A location factor represents the cost of transporting mass between one startinglocation and destination, relative to the cost of transporting that sam e amo unt of m assbetween a reference start ing locat ion and de ~ ti n a t i o n ~ ~ .Different location factors shouldbe u sed fo r different mission segments.A mission segm ent may be defined as a portionof a mission separated by c hanges in velocity (i.e. separated by distinct propulsion

56 Fo r example, a po ssible reference starting location and destination might be the Earth’s surface and LEO,

respectively.

September 2003 35



ALS Equivalent System Mass G uidelines Docume nt NASMTM-2003-2 12278

events). For example, a mission to Mars and back mig ht have the following missionsegmentss7,each of which has a distinct location factor:

1) Earth to L EOs8

2) LEO to M ars orbit

3) Within Mars Orbit

4)

5) On the Mars surface

6)

7) Mars orbit to LEO

8) LEOtoEarth

In order to appropriately compare costs of m ission segments, each segment’s ESM valueshould first be multiplied by the appropriate location factor. Such “normalized” costs can

then be legitimately compared across segm ents.

Mars orbit to Mars surface

Mars surface to M ars orbit

Application of a location factor to an ESM comp utation results in the following equation:

ESM = Le, * 5 [( M I , SFIi )+ (VI,. .Ye,, )+(Pi.Peq,)+(c,.Ceqi)+ ...i = l

.. .+ (CTi * D CT,,, )+ ( M m , .D .SF,, ,)+ (Yo, .D .veqi)] Equation 9

where Le, = the location factor for the seg me nt of interest [kglkg].

Location factors depend on the type of propulsio n used. Lo cation factor values are

currently being developed for various propulsion options and mission segments for thenext revision of the ALS BVAD. See Fisher et al . (200 3) for a detailed discussion ofequivalency factors.

Other architectures could have different segments. For exam ple, a direct ascent mission might have only57

two segments: Earth to Mars surface and Mars surface to Earth.

If Earth to LEO were also the reference starting location an d destina tion, then the location factor58

associated with that segment would have a value of 1.

September 2003 36



ALS E quivalent System Mass Guidelines Docum ent NASNTM -2003-2 12278

4 ESM RESULTS

4.1 Results Confidence

The co nfidence of an ESM value is driven by the accu racy of raw data used in theevaluation as well as the d egree of effort put into modifying that data.

Researchers that provide raw da ta for an ESM evaluation may exe cute various levels ofrigor in the data co llection process. In addition, if raw data is obtained fromdocum entation, rather than d irectly from a researcher, error propagation in data valuescan be a concern. On the other hand, data from sources with a very rigorous reviewprocess can be q uite reliable. Consequ ently, an a nalyst may be faced with data from arange of sources and various degrees of accuracy. Because the accuracy of raw data feedsinto the co nfidence of ESM results, the inv estigator should have at least a basicimpression of raw data quality59.

Confidence in results is also affected by decisions affecting the rigor of developm entstate ad justments and scaling efforts. Application of appropriate equivalency factors,storage factors and location factors also affects the qu ality of ESM results. The analystshould balance the degree o f effort needed for adeq uate results confidence with resourceavailability during each step of th e ESM evaluation process.

To legitimately impleme nt ESM results in a selection process, the ESM results must b emo re a ccurate than the degree of separation between option results.Thus, a roughcalculation may be adequate to rank two options, if the result values are grossly differentfrom each other. In other cases, a high level of accuracy is required to make comp arisonsof options that have very similar ESM values6'. If the results of an ESM comp arison are

too close to make a judgement, then both options may be equally good from the ESMperspective, and other issues are likely to drive technology selection.

Th e deg ree of results separation that is necessary to conclude a sign ificant difference (i.e.jud ge one option preferable over another) depends upo n the degree of confidence in thedata used an d the degree of accuracy in the analysis methods. Data confidence andanalysis accuracy is analysis-specific. Therefore, the de gree of results sep aration that isrequired to de clare one o ption preferable to ano ther is also ana lysis-specific. The

59 Ideally, error ranges wo uld be supplied w ith each point of data in an ESM analy sis, allowing for

com puta tion of the result's confidence lim its. However, in reality, error ranges are rarely reported in data

obtained for ESM evaluations, impeding estimation of the degree of confidence in results.

6o However, if the difference between ESM values is small, the trade study selection will most likely be

made based on other information, such as the state of the development, or functional differences (though

any option must meet the requirements to be considered).

September 2003 37



ALS Equivalent System Mass Guidelines Document NASN TM-2003-2 12278

investigator’s judgem ent s hould be used to determ ine the analysis-spe cific necessarydegree of results separation.

If data accuracy is uncertain, a reaso nable assumption is that an ord er of mag nitude ofseparation (i.e. factor of 1 0) betwee n ESM results is adequate to conclud e a significant

difference between options (D oll and Eckart, 1999).A difference of a few percent islikely to be sensitive to assum ptions. However, the degree of confidence in technologydata generally improves a s the technology is further develope d. Thus, ES M comparisonsof trade options at advanced development stages may require less of a degree ofseparation between results in order t o declare a significant difference betw een options.

4.2 Results Reporting

All assum ptions (both top-level and m ore detailed), input data, sources, and analysismetho ds should be describe d (and well organized) throughout th e trade studydocumentation.

Som etimes the greatest value of an a nalysis can be the identification of superior orinferior input data and their sou rces. In this same vein, unreferenced data values canmake a calculation suspect.

ESM results are analysis-spe cific and should always be reported in con text, rather than assolitary values. For this reason, resu lts reporting should be done with adequa te rigor toallow for verification by other researchers . All input data, sources, analysis appro achesand critical assumptions made on the hardware, configuration, and control approach es inthe system should be clear ly stated in reporting the evalua tion results, so that the resultscan be considered in context. Even if the ALS BVAD is used to determine values for ananalysis, the analysis docum entation shou ld identify which va lues we re applied and

explain the implied assumptions.

ESM results documentation should include the following material, and all associatedassumptions, as a minimum:

1) Description of analy sis objectives.

2)

3)

4)

5)

6)

Explanation of chara cteristics deemed w orthy of exam ination (e.g. criticalcharacteristics).

Explanations of which (if any) critical characteristics are cap tured by E SM andwhich are reflected by som e other quantitative or qualitative means.

Justification of the s ystem ex tent and level of detail chosen for the ESMevaluation.

Raw data values for ESM parameters, their sources, and a brief ex planation ofthose values implemented.

Justification of develo pme nt state adjustments, sizing method s and s calingapproach, including quantification and references.

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ALS Equivalent System Mas s Guidelines Docum ent NASNTM-2003-212278

7 )

8)

Justification of stow age factors, equivalency factors and location factors chosenfor the ESM evaluation.

A discussion of the expected accuracy of results and associated interpretation.

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ALS Equivalent System Mass Guidelines Document NASNTM-2003-212278

5 REFERENCES

Cruthirds, J., Perchonok, M . and Kloeris, V. (20 02) “Mathematical M odeling ofFood Systems for Long-Term Space Missions”. 32nd International Conference onEnvironmental Sy stems, SAE Technical Paper #20 02-0 1-2290.

Drysdale, A.E. and Hanford, A.J. (2002) “Advanced L ife Support Research andTechnology Development Metric - Fiscal Year 2001” JSC 47787, CTSD -ADV-482, Crew and Therm al Systems Division, NASA Johnson Space Center,Houston, TX.

Doll, Susan and Eckart, Peter (1999) Environmental Control and Life S upportSystems (ECLS S). in Human Spaceflight: Mission A nalysis and Design, Larsonand Pranke (eds), McG raw-Hill, New York.

Fisher, John W.; Levri, Julie A. and Jones, Harry W. (200 3) “The Effect of

Mission Location on Mission Costs and Equivalent System Mass”. 33rdInternational Confer ence on Environmental Systems , SAE Technical Paper#2003-01-2633.

Hanford, A.J. and Ew ert, M.K. (2002) “Advanced Life Suppo rt Baseline Valuesand Assumptions Document”, CTSD-ADV-484, JSC 47804, NASA JohnsonSpace Center, Houston, TX.

Levri, J.A.; Vaccari, D.A.; Drysdale, A.E. (200 0) “Theory and A pplication of theEquivalent System Mass M etric”. 30thInternational Conferenc e on EnvironmentalSystems, SAE Technical Paper #2000-01-2395.

Stafford, K.W.; Jerng, L .T.; Drysdale, A.E.; Maxw ell, S.; Levri, J.A. (2001)“Advanced Life Support Systems Integration, Mod eling, and Analysis ReferenceMissions Document,” edited by Ewert, M.K. and Hanford . A.J., JSC-39 502,Revision A, NA SA Johnson Space Center, Houston, Tex as.

Yeh, H.Y.; Jeng, Frank; Brown, Ch eryl; Lin, Chin; and Ewert, Mich ael (2001)“Advanced Life Supp ort Sizing Analysis Tool”. 3 1St International Conferenc e onEnvironmental Systems, SA E Technical Paper #2001-01-2304.

September 2003 40



REPORT DOCUMENTATION PAGE

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4. TITLE AND SUBTITLE

Advanced L ife Suppor t Equiva lent System Mass Guide l ines Document

I Ju lie A. L e d ; Alan E. Drysdale, Ph.D.**;Michael K. Ew ert***; John W, Fisher';

Anthony J. Han ford, Ph.D .t; John A. Hogan, Ph.D .tt; Harry W. Jones, Ph.D.*;

Jitendra A. Joshi, Ph.D.$; David A. Vacca ri, Ph.D., D.E.E?*

*AmesResearch Center, Moffett Field, CA ; **TheBoeing Company, K ennedy

Space Center, FL; ***JohnsonSpace Cente r, Houston, TX ; tLockheed Martin Space

Operations, Houston, TX; ttRu tgers , The State University of New Jersey, NewBrunswick, NJ; m nive rsitie s Space Research Association, Washington, D.C.;

*$StevensInstitute of Technology, Hoboken , NJ

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

9. SPONSORlNGlMONlTORlNG AGENCY NAME(S) AND ADDRESS(ES)

Nationa l Aeronaut ics and Sp ace Adminis t ra t ionWa sh ing ton , DC 20546- 0001I

i. FUNDING NUMBERS

131-20- 10-26

3. PERFORMING ORGANIZATIONREPORT NUMBER

A-03 10698

IO . SPONSORlNGlMONlTORlNGAGENCY REPORT NUMBER

NASA/TM-2003-212278

11. SUPPLEMENTARY NOTES

Point of Contac t : Jul ie A. Levr i , Am es Research Center , MS 239-8, Moffe t t F ield , CA 94035-1000

(650) 604-6917, Julie [email protected]

12a. DlSTRlBUTlONlAVAlLABlLlTY STATEMENT 12b. DISTRIBUTION CODE

Unclass i f ied-Unlimited

Subjec t Ca tegory 54 Dis t r ibut ion: Nonstandard

Avai labi li ty: NA SA CA S1 (301) 621-0390

I13. ABSTRACT (Maxlmurn200 w ords )

Equiv a lent System M ass (E SM ) is of ten appl ied to eva lua te trade s tudy opt ions in the Advanced L ife

S uppor t (ALS) P r ogr am . ES M c a n be used to identify which of several options that meet all specif ied

requirements have th e lowest laun ch cost , as re lated to the mass , volum e, power , cool ing, and c rewtim e.

This docum ent provides an in t roduc t ion to the ESM concept , an explana t ion of the computa t iona l method ,

and a discussion of results interpretation and reporting. Any researcher with a basic understanding of the

integra t ion issues of an Advanced Life Suppor t sys tem may apply the methods in th is document to perform

an effective ESM-based trade analysis.

Advanced Life Support Equivalent System Mass Guidelines

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Transcript of Advanced Life Support Equivalent System Mass Guidelines