July 2010 

NASA/TP–2010-216722 

OLTARIS: On-Line Tool for the 

Assessment of Radiation in Space 

Robert C. Singleterry, Jr., Steve R. Blattnig, Martha S. Clowdsley, Garry D. Qualls, 

Christopher A. Sandridge, Lisa C. Simonsen, and John W. Norbury 

NASA Langley Research Center, Hampton, Virginia 

Tony C. Slaba and Steven A. Walker 

Old Dominion University, Norfolk, Virginia 

Francis F. Badavi 

Christopher Newport University, Newport News, Virginia 

Jan L. Spangler 

Lockheed Martin Operations Support, Hampton, Virginia 

Aric R. Aumann 

Analytical Services and Materials, Inc., Hampton, Virginia 

E. Neal Zapp, Robert D. Rutledge, and Kerry T. Lee 

NASA Lyndon B. Johnson Space Center, Houston, Texas 

Ryan B. Norman 

University of Tennessee, Knoxville, Tennessee 
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July 2010 

NASA/TP–2010-216722 

OLTARIS: On-Line Tool for the 

Assessment of Radiation in Space 

Robert C. Singleterry, Jr., Steve R. Blattnig, Martha S. Clowdsley, Garry D. Qualls, 

Christopher A. Sandridge, Lisa C. Simonsen, and John W. Norbury 

NASA Langley Research Center, Hampton, Virginia 

Tony C. Slaba and Steven A. Walker 

Old Dominion University, Norfolk, Virginia 

Francis F. Badavi 

Christopher Newport University, Newport News, Virginia 

Jan L. Spangler 

Lockheed Martin Operations Support, Hampton, Virginia 

Aric R. Aumann 

Analytical Services and Materials, Inc., Hampton, Virginia 

E. Neal Zapp, Robert D. Rutledge, and Kerry T. Lee 

NASA Lyndon B. Johnson Space Center, Houston, Texas 

Ryan B. Norman 

University of Tennessee, Knoxville, Tennessee 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

Acknowledgments 

This work was supported by the Human Research Program in the Advanced Capabilities 

Division under the Exploration Systems Mission Directorate and performed by the 

members of the Design Tool Project in the Space Radiation Program Element. 

Trade names and trademarks are used in this report for identification only. Their usage does not constitute 

an official endorsement, either expressed or implied, by the National Aeronautics and Space 

Administration. 
Contents

Executive Summary vii

1 Introduction and Background 1

2 OLTARIS Description and Functionality 1

2.1 Web interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Thickness Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Material Properties 8

3.1 Heavy Ion Nuclear Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . 8

3.2 Nucleon and Light Ion Nuclear Cross Sections . . . . . . . . . . . . . . . . . . 8

3.3 Atomic Cross Sections or Stopping Powers . . . . . . . . . . . . . . . . . . . 9

4 Radiation Environment or Boundary Conditions 9

4.1 Solar Particle Event Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.2 Galactic Cosmic Rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.3 Earth Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.3.1 Galactic Cosmic Rays . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.3.2 Omni-directional Trapped Protons . . . . . . . . . . . . . . . . . . . . 12

4.3.3 Atmospheric Albedo Neutrons . . . . . . . . . . . . . . . . . . . . . . 13

4.4 Lunar Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5 Particle Transport 13

6 Response Functions 16

6.1 Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6.2 Dose Equivalent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.3 TLD-100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6.4 Integral and Differential Linear Energy Transfer (LET) . . . . . . . . . . . . . 18

6.5 Tissue Equivalent Proportional Counter (TEPC) . . . . . . . . . . . . . . . . . 19

6.6 Effective and Organ Averaged Dose Equivalent . . . . . . . . . . . . . . . . . 19

7 Summary and Future Work 20

A Example Use Case 22

References 24

iii
List of Figures

1 Program Flow for OLTARIS . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Body Phantom Zone Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

List of Tables

1 Deceleration Parameters for Preset OLTARIS GCR Scenarios . . . . . . . . . . 12

2 OLTARIS Transported Isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3 NCRP 132 Organs and their weights . . . . . . . . . . . . . . . . . . . . . . . 20

iv
Acronyms

OLTARIS On-Line Tool for the Assessment of Radiation In Space

AP8MAX Aerospace corporation Proton version 8 at solar MAXimum

AP8MIN Aerospace corporation Proton version 8 at solar MINimum

CAD Computer Aided Design

CAF Computerized Anatomical Female

CAM Computerized Anatomical Male

CSDA Continuous Slowing Down Approximation

DSNE Design Specification for Natural Environments

EO Earth Orbit

FAX Female Adult voXel phantom

GCR Galactic Cosmic Ray

HZETRN2005 High Z and Energy TRaNsport 2005 - basic particle transport code used

in OLTARIS

ICRP International Commission on Radiological Protection

IGES Initial Graphics Exchange Specification

ISS International Space Station

ITAR International Traffic in Arms Regulations

LEO Low Earth Orbit

LET Linear Energy Transfer

MAX Male Adult voXel phantom

MC Monte Carlo

NCRP National Council on Radiation Protection

NUCFRG2 NUClear FRaGmentation Version 2 - basic heavy ion cross sections

used in OLTARIS

SGE Sun Grid Engine

SIREST Space Ionizing Radiation Environment and Shielding Tools

SPE Solar Particle Event

STS Space Transportation System - shuttle

TEPC Tissue Equivalent Proportional Counter

TLD-100 lithium-fluoride Thermo-Luminescent Detector version 100

v
Nomenclature

Dose amount of energy deposited into a certain quantity of material

Dose Equivalent tissue dose converted to biological effects in humans - ICRP-60

Effective Whole-Body

Dose Equivalent organ weighted dose equivalent - NCRP-132

m proton mass, 1.67 × 10−27kg or 938 MeV

E particle kinetic energy per mass unit, MeV

amu

or AMeV

φ differential particle flux or fluence, #

cm2−AMeV−[day or event]

QICRP−60

quality factor to multiply by energy deposited (dose) to calculate a human response (dose equivalent), Sv

Gy

vi
Executive Summary

The On-Line Tool for the Assessment of Radiation In Space (OLTARIS) is a World Wide Web

based tool that assesses the effects of space radiation on humans and electronics in items such

as spacecraft, habitats, rovers, and spacesuits. This document explains the basis behind the interface and framework used to input the data, perform the assessment, and output the results to

the user as well as the physics, engineering, and computer science used to develop OLTARIS.

The transport and physics is based on the HZETRN2005 and NUCFRG2 research codes. The

OLTARIS website is the successor to the SIREST website from the early 2000’s. Modifications

have been made to the code to enable easy maintenance, additions, and configuration management along with a more modern web interface. Overall, the code has been verified, tested, and

modified to enable faster and more accurate assessments.

The interface and data input/output are based on user needs determined through user interviews and the creation of use cases. The code is broken down into five basic elements: Radiation

Environment (Boundary Conditions), Material Properties, Geometry (slab or vehicle thickness

distributions), Transport, and Response Functions. The path through these elements and the

data input/output is based on the use case being executed. As new use cases are created, only

the code necessary to complete each use case is generated (code is reused), the web interface is

updated for the new functionality, and new web scripts are created to tie the assessment together.

All code is tested with module and functional testing. These tests are updated whenever new

use cases are implemented. If any code is changed or added, the whole system is tested to make

sure functionality is not compromised and the test answers do not change in an unintended

manner over time. This continuous verification is an important part of OLTARIS. It ensures

reliability over time even as modifications and improvements are made to ensure state-of-theart predictions.

As new use cases are generated, new algorithms are also needed to implement them. Currently under development is a ray-by-ray calculation, which will allow any number of materials

in any order to be analyzed in a spacecraft geometry. Other new use cases can be added as needs

dictate. The next major areas of modification are more accurate transport algorithms, better uncertainty estimates, and electronic response functions. Improvements in the existing algorithms

and data occur continuously and are logged in the change log section of the website.

vii
1 Introduction and Background

Particle transport algorithms and methods needed to assess the radiation shielding in spacecraft

are difficult to solve and master. When non-experts are asked to utilize them in their normal

work flow, the functionality of these algorithms and methods needs to be simple, clear, and

straightforward. The answers that they give need to be accurate, characterized by an uncertainty, and reproducible [1, 2]. Achieving these goals entails numerous characteristics: modularity, version control, modern user interface, maintainability, verification, and validation. Data

interfaces and formats need to be established between modules, clear paths need to be established for data flow, and user interfaces need to feed the proper data into and out of the system

so that a non-expert user can understand the input and results.

The SIREST website [3] attempted to enable this type of functionality for space radiation

analysis. OLTARIS, its successor, contains improved methods for handling complex geometries and an increased level of code verification and manageability. The URL is listed as

https://oltaris.larc.nasa.gov/. The first task was to establish acceptable user interactions with

the website. This was achieved through interviewing potential users about how they envisioned

working with this type of data. Use cases were generated to capture this desired work flow

and functionality. From these initial use cases and other programmatic requirements, an initial

capability was defined.

Current, state-of-the-art, research-based radiation analysis tools were identified and utilized in the construction of OLTARIS. The research-based particle radiation transport code

HZETRN2005 [4, 5] is the basis for OLTARIS. HZETRN2005 has embedded response functions that were greatly expanded in OLTARIS. New response functions not in HZETRN2005

were also added. The NUCFRG2 [6, 7, 8] code was used for heavy ion cross sections with

HZETRN2005 embedded light ion cross sections [9]. The rest of the paper will describe the

current capability and how that capability was implemented within OLTARIS.

2 OLTARIS Description and Functionality

The OLTARIS architecture is divided into two main parts, the website, on which users interact

through a browser, and the execution environment, where the computations are performed. This

architecture enables maximum flexibility and is scalable as demand increases. The website is

built primarily with standard open source components. The core is Ruby on Rails [10] with a

MySQL [11] database running on an Apache [12] web server. The only licensed, server-side

component is an Adobe Flash plugin which allows the users to plot and examine results using a

standard, free plugin that most browsers already have.

The execution environment is primarily FORTRAN executables tied together with some Perl

and Ruby scripts running on a computational cluster. Data is passed between the web server and

the cluster using XML files. Jobs are managed with the open-source Sun Grid Engine (SGE)

[13]. There are benefits to having SGE serve as a mediator between the user interface and

1
Figure 1: Program Flow for OLTARIS

the computations. First, additional nodes or clusters can be easily added as demand increases.

Also, the web interface can easily be replaced with a desktop client sometime in the future, if

requirements dictate.

Figure 1 shows the program and data flow for OLTARIS. The boxes indicate different components or modules of the system. This modular system makes it easy to maintain and upgrade

as new algorithms, methods, and capabilities are developed. Each module has a clearly defined

input and output data format so that the individual module developers don’t have to know about

the coding details of the other modules; however, they can easily interface with all the other

modules they need. For example, if requirements dictate the development of another radiation

environment, the new radiation environment will plug into the process cleanly, as long as its

outputs are in the same format as every other environment model.

The green boxes indicate the data that the user needs to supply: a slab definition or a thickness distribution of their vehicle (see Section 2.2), and mission parameters that will determine

how the external radiation environment is computed. The blue boxes indicate data that the user

can either download from the web server or data used in the calculations and stored on the execution host. This includes material data with associated cross section databases (see Section 3)

and body-thickness distributions used in the calculation of whole-body effective dose equivalent. The downloadable content includes ray distributions and a phantom human CAD (Com2
puter Aided Design) object that can be used to prepare the vehicle thickness distributions. The

gold boxes represent the computations which are performed on the execution host and consist

of three modules: the environmental model, the particle transport, and the response functions.

The environment module is where the external radiation environment is computed. The user

can currently choose from four different types of environments: an historic Solar Particle Event

(SPE) or a linear combination of SPEs, free-space Galactic Cosmic Rays (GCR), Lunar Surface,

or Earth Orbit (EO). The output of these environments is a spectral flux or fluence. The units

are particles

cm2−AMeV−time , where time is given in events for SPE (fluence) and days for GCR and EO

(flux). This flux/fluence is then used as the boundary condition for the transport. More details

about the environments can be found in Section 4.

The transport module is composed of two paths depending on the type of geometry the user

selects, either slab or thickness distribution. Both paths use nuclear transport methods based on

HZETRN2005, which have been greatly improved, verified, and validated [14, 15, 16, 17, 18,

19]. The slab computation transports particles from the chosen boundary condition, through

any user defined materials and thicknesses, to generate fluxes/fluences at the material interfaces

and at the end boundary. The computation for the case of a thickness distribution is a series of

transport runs for an array of depths for each material that the user needs. OLTARIS currently

supports aluminum, polyethylene, and tissue for possible materials in a vehicle. The output is an

array of flux/fluence versus energy and thickness for every combination of material thicknesses.

The selection of the spatial grid (thickness intervals) and the energy grid is dependent on the

boundary condition and is not user selectable at this time. Further details about the transport

method can be found in Section 5.

The response function module takes the resulting flux/fluence calculated with the transport

module and computes selected responses for each depth of the various materials and the total responses at the end of the slab or at the selected vehicle location. For thickness distributions, an

array of response function versus depth curves are computed for the same set of material spatial

grids selected for the flux/fluence transport. Total quantities along each ray in the thickness distribution are calculated by interpolating over the response function versus depth database just

computed. The total quantity at a target point is then calculated by integrating over all of the

rays. In the case of whole body effective dose equivalent (or effective dose), an added step is

performed to combine the vehicle thickness distributions with the body thickness distributions

for a large number of target points in a human phantom. The process for calculating dose equivalent at a single target point is then repeated for each body target point and a weighted average

of these values is taken. Details about all the possible responses can be found in Section 6.

Finally, all the results are transferred back to the user’s account on the website for viewing,

plotting, or download.

2.1 Web interface

Users need to register on the OLTARIS website and receive approval before they can enter the

website. This is required because some of the content falls under the purview of the Interna3
tional Traffic in Arms Regulations (ITAR) [20], but registration also allows for regulating and

maintaining limited computer resources by permitting only those with a real need and knowledge to access the site. Once the user account has been activated by a site administrator, the

user can login and start using the tools.

The first page the user sees after login is the Projects page. Each project is the complete

encapsulation of a calculation; it includes the definition of the radiation environment, the selection of a thickness distribution or slab, and a selection of desired responses. This page allows

the user to create new projects, edit existing projects, submit new jobs to the compute cluster,

and access the results of previous jobs. A job is an instantiation of a project that is packaged

for processing. When a new project is created, the user is stepped through a series of pages that

allows the user to define the different aspects of the problem. Help pages are available at any

point in the process if the user needs more information. Once the project is saved, the user is

returned to the Projects page and can submit a job to the compute cluster. A project can include

multiple jobs so that if the user wants to change particular elements of the project, say select a

different environment or response, the user can do so and create an additional job that can be

submitted under that same project.

Once a job is submitted, the user can check its status from the Jobs page for a particular

project. When a job is complete, an email is sent to the user from the grid scheduler (SGE) and

the user can view the results by selecting Display/Download Results for the completed job on

the Jobs page. The results page will list some of the results directly in tabular form and allow

the user to plot data, such as dose versus depth curves and flux/fluence data. The plot page has

the option to copy the plotted data to the user’s clipboard so that it can be pasted into various

local applications on their computer. The user also has the option to download the data to their

desktop computer in the form of a text file or can cut-and-paste directly into EXCELTM.

Another section of the website is the Thickness Distributions page which is selected from

one of the main tabs across the top of the page. This page presents a list of the user’s current

thickness distributions and allows the user to upload new ones. Once a thickness distribution is

uploaded to the site, it is available for selection from a project page. Thickness distributions are

uploaded to the site in the form of an XML file. A document describing the format of the file

and sample files can be downloaded from the Thickness Distributions page. The user can also

download a phantom CAD object that represents a human geometry. This can be positioned

and oriented in the user’s CAD model to help select the proper target points in their vehicle

geometry and compute effective dose responses. The next section of this paper describes this

process in more detail.

The Slabs and Materials sections, selected from the tabs at the top of each page, are used

to create user-defined slabs of any material the user desires. The user first defines the materials

they want to use at the Materials tab by entering the material’s elemental mass percentage, its

molecular mass percentage, or its chemical formula. Once the material is defined, the user can

submit the material definition to the computational grid so that the material cross sections (see

Section 3) can be computed for later use. Once the cross section database is available, the user

can then go to the Slabs tab and define a layup of materials of any thickness, in any order the

4
user chooses. This capability is useful for comparing new material or structural concepts. Once

a slab is created, it can be selected for a project from the Projects page.

The previous discussion describes the current layout of the website; however, the developers

are continuing to add content and update models, so a Change Log is accessible from each page

to communicate any changes or updates to the site or its underlying code/data. There are also

links on each page to send an email to the developers to offer suggestions or report problems.

Feedback from users is encouraged and is very important in prioritizing new capabilities.

2.2 Thickness Distributions

In order to compute a response in a realistic vehicle geometry, a representation of the vehicle

geometry, in the form of a material thickness distribution, is required. This thickness distribution is computed using a process called ray tracing. Ray tracing uses a directionally distributed

set of rays emanating from the same point to determine how much material is surrounding that

point in each ray direction. The point source of the rays is commonly called a target point.

The intersections of the rays and the various components of the vehicle CAD model are used to

determine the along-the-ray thicknesses of the components, which are stored along with their

associated material types.

OLTARIS currently supports only three materials - aluminum, polyethylene, and human

tissue in vehicle geometries, as mentioned previously. For example, one ray could intersect a

human being, which would be a thickness of tissue, followed by some shielding material, such

as polyethylene, and then the vehicle structural components, which could be a thickness of aluminum. Rays typically intersect multiple objects, so there can be many separate material thicknesses along each ray. The current version of OLTARIS will sort and combine these thicknesses

so that the outermost layer of shielding is composed of all the collected aluminum thicknesses

along that ray, the next layer of shielding represents the total thickness of polyethylene along

that ray, and the innermost layer represents the total amount of tissue along that ray.

Any angular distribution of rays may be used, as long as they are distributed evenly enough

that each ray can approximately represent an equal solid angle of shielding surrounding its

target point. However, to compute an effective whole-body dose equivalent using OLTARIS,

the user will need to use one of the many ray distributions that are available for download from

the Thickness Distributions page. Those currently available include distributions with 42, 492,

512, 968, 1002, 4002, 9002, or 10,000 rays. If the user needs to take into account a specific

body phantom orientation with respect to their vehicle, OLTARIS provides a process that makes

this possible.

To calculate an effective dose, OLTARIS combines uploaded vehicle thickness distributions

with pre-computed body phantom thickness distributions. The process used to combine these

distributions provides the ability to analyze a specific body orientation relative to a vehicle

shielding model and the ability to capture the local variation of radiation intensity inside the

vehicle. This local variation could be due to variations in the amount of shielding surrounding

5
different regions of the vehicle interior and might, for example, yield a situation in which the

phantom’s head is less shielded than its feet.

In order to accurately represent the user’s desired phantom orientation within a vehicle

model, the user will need to download one of two specially developed CAD models from the

OLTARIS web site. These CAD models are proxies for the male and female body phantoms that

are available for use in OLTARIS. The user will need to load this model into their CAD software, as a new component in their shielding model. The models have been made available in an

IGES (Initial Graphics Exchange Specification) file format to gain broad compatibility with the

widest possible array of CAD software. Each body phantom proxy CAD model includes eight

reference points.

The three points used to establish the phantom orientation have been colored green and

labeled “A”, “B”, and “C” (see Figure 2). Once oriented, the user will record the (x, y, z)

coordinates of these three points, taking care to use the same reference coordinate system that

will be used for ray tracing. The coordinates of these three points can be entered into a form

on the OLTARIS website to generate a custom ray distribution, rotated to take into account

the phantom orientation. The form used to create these ray distributions can be accessed from

the Thickness Distributions page. The user should use this ray distribution to ray trace vehicle

thickness distributions that correspond to that phantom orientation.

The other five reference points included with each IGES phantom proxy are colored red and

are used to capture the effects of shielding variation within the vehicle interior. These five points

correspond to five body zones, as shown in Figure 2. To use this feature, the user will need to

perform five separate vehicle ray traces and calculate five separate vehicle thickness distributions, each centered on one of the red zone target points. The effective whole-body dose equivalent calculation (see Section 6.6) within OLTARIS uses tissue thickness distributions based

upon hundreds of target points that are distributed throughout the body phantom in specific tissues. OLTARIS will add the vehicle thickness distribution closest to each of the zone’s tissue

thickness distributions to get the total shielding around each body point. The user does not have

to use five target points. One target point can be used; therefore, all of the body points are added

to the single vehicle thickness distribution. However, a single target point will be less accurate

than the five target point case, as the local variations in the vehicle shielding may be significant.

2.3 Verification

Users expect to get reliable and accurate results from the tool sets that they use; therefore,

OLTARIS has implemented several levels of verification to ensure consistent and accurate results. The OLTARIS system consists of thousands of lines of code, hundreds of files, and

megabytes of data. All of the source code and data are stored in a version-control repository

that all of the developers can access. This way, all changes are tracked and everyone can have

access to the same code base. The source repository is organized along the lines of Figure 1

and each box has a specific developer who is responsible for, or owns, that module. Before any

new methods or techniques are stored in the repository, the developer must ensure the accuracy

6
Figure 2: Body Phantom Zone Points

of the method and write corresponding test cases that are also entered into the repository. These

test cases are referred to as module tests. Test cases are also developed that test the interaction

between modules or complete runs through the system; these are called functional tests. The

combination of module and functional tests are intended to verify that the code base and data

are generating consistent results. This suite of tests is automatically re-run periodically to make

sure that any changes entered into the repository do not break the system somewhere else. If a

discrepancy is found, the responsible developer is notified and fixes the problem. Once the code

has been sufficiently tested and is ready to be deployed, it is tagged or labeled for reference.

This tagged version is a snapshot of the code base and the tagged version number is noted at the

bottom of every page on OLTARIS.

The web code is maintained under version control, but the testing is manual. There is both a

test website and a production website. The test site has its own server, database, and execution

environment, but it is only used by the developers. Projects can be set up and run on the test

website and compared to runs made without the web code. Several developers test different

paths in order to be sure everything is working properly. Once everything is working properly

on the test system, the codes are deployed to the production site. There is also a change log

7
on OLTARIS so that users can see when changes and updates are made that may change their

results.

3 Material Properties

Material properties are an important part of the transport algorithm. Material dependent cross

sections are used to predict the ways in which neutrons and charged particles will interact with

shielding material. For vehicle thickness distributions, three materials (currently aluminum,

polyethylene, and tissue) are used and their cross sections are pre-calculated. For slab based

calculations, the user can input materials in numerous ways. These materials are then available

for use in a pull-down list when defining slabs. Pre-defined materials important to the space

radiation community already exist in the pull-down menus upon first time use.

A material cross section is the probability of interaction between a particle projectile and the

target nucleus with a particular outcome of that interaction. This probability is represented as

the effective cross sectional area of the target nucleus as a function of the projectile energy and

particle type. The unit is cm2and is usually represented as a barn or 10−24cm2. An example of

an interaction would be:

56Fe + 27Al −→ 12C + A

ZX

where 56Fe is the projectile, 27Al is the target, and X are the leftover projectile and target fragments. The mass number, A, and the atomic number, Z, must add up to 71 and 33, respectively.

3.1 Heavy Ion Nuclear Cross Sections

NUCFRG2 is a classical, geometric model based on the abrasion - ablation concept [21],

whereby a piece of the incoming projectile nucleus is sheared off (abraded) by collision with

the target. The abraded piece is formed in a highly excited state, which subsequently decays

(ablates) by energetic particle emission. The model is geometric in the sense that the entire abrasion - ablation process is determined by considering the relative impact parameter of colliding

spherical nuclei. NUCFRG2 neglects quantum mechanical effects and does not include important shell structure information. Therefore, one of its weaknesses is the inability to account for

the odd - even effect observed in experimental data, where cross sections for fragments with

an even number of nucleons are systematically larger than cross sections for fragments with an

odd number of nucleons. This phenomenon is clearly related to the nuclear pairing interaction.

Efforts are currently underway [22] to upgrade NUCFRG2 to include this effect, as well as to

describe light ion production via coalescence.

3.2 Nucleon and Light Ion Nuclear Cross Sections

Total and differential energy cross sections for nucleon and light ion projectiles are handled

outside of the NUCFRG2 model by a set of subroutines within OLTARIS (previously embedded

8
in HZETRN2005). Processes relevant to the nuclear interactions of nucleons and light ions

are utilized and include elastic scattering, light ion knockout and pickup, light ion projectile

fragmentation, and target fragmentation. The cross sections for these processes are largely

modeled by empirical and semi-empirical parameterizations [4, 9, 23, 24, 25, 26, 27, 28, 29].

3.3 Atomic Cross Sections or Stopping Powers

The transport algorithms solve the Boltzmann equation using the continuous slowing down

approximation (CDSA) with stopping powers and residual ranges calculated using Bethe theory

with corrections [4, 30]. The transport solution uses scaled proton stopping power and ranges

for all ions but directly calculates stopping power individually for each isotope when calculating

some response functions.

4 Radiation Environment or Boundary Conditions

The radiation environments within OLTARIS are computed in a modular fashion, whereby for a

given spacecraft flight condition, the input particle(s) spectrum on the external boundary of the

spacecraft has to be defined to initiate the transport through bulk matter. The input boundaries

can be Galactic Cosmic Rays (GCR) [31, 32], Solar Particle Events (SPE) [4, 33, 34, 35, 36],

trapped protons within the Earth’s geomagnetic field [37, 38], and albedo neutrons from the

Earth’s atmosphere [39, 40, 41]. An energy spectrum for the particle field(s) with individual or

combinations of these spectra is generated following a pre-determined input and output format

to make them compatible with the transport as described in Section 5. There is also a Lunar

Surface boundary condition where directions that point toward the surface are set to zero. The

following sections describe the possible boundary conditions.

4.1 Solar Particle Event Spectra

A solar particle event (SPE) is a large number of protons accelerated by the sun’s magnetic

field. The historical SPE events and their corresponding differential formulas used in OLTARIS

include1:

February 1956 Webber, with 100 MV rigidity [33]:

φ(E) = 1.0 × 107





E + m

q

E(E + 2m)



 exp





239.1 −

q

E(E + 2m)

100





1m is the mass of the proton and is approximately 938 MeV

9
February 1956 LaRC [4]:

φ(E) = 6.0 × 107exp 

10 − E

25 

+ 9.375 × 105exp 

100 − E

320 

November 1960 [4]:

φ(E) = 6.33 × 108exp 

10 − E

12 

+ 4.88 × 106exp 

100 − E

80 

August 1972 King [34]:

φ(E) = 2.98 × 108exp 

30 − E

26.5



August 1972 LaRC [4]:

φ(E) = 2.2 × 107exp 

100 − E

30 

August 1989 [35]:

φ(E) = 8.652 × 1010

59.261

E + m

q

E(E + 2m)

exp





−

q

E(E + 2m)

59.261





September 1989 [35]: 2

φ(E ≤10 MeV) = 1.446 × 108 E + m

q

E(E + 2m)

exp





−

q

E(E + 2m)

102.118





φ(10 MeV<E <30 MeV) =h−0.0015E

2 + 0.07184E + 0.4304i

φ(E ≤10 MeV)

φ(E ≥30 MeV) = 2.034 × 107

r

1 −



m

E+m

2





vuut

E(E + 2m)

30(30 + 2m)





−4.5

2A smoothing function has been added in the 10 to 30 MeV range, and φ(E ≤ 10 MeV) in the smoothed

equation is evaluated at the input energy range between 10 MeV and 30 MeV.

10
October 1989 [35]:

φ(E) = 6.104 × 108





E + m

q

E(E + 2m)



 exp





−

q

E(E + 2m)

92.469





Carrington 1859, with 1989 fit [36]:

φ(E) = 0.877 × 0.3841E

0.3841−1 × 4.79 × 1011 exp (−0.877E0.3841)

Carrington 1859, with 1991 fit [36]:

φ(E) = 0.972 × 0.441E

0.441−1 × 1.47 × 1012 exp (−0.972E0.441)

LaRC stands for Langley Research Center. The boundary condition defines the units used

in the rest of the OLTARIS processes. The units for all of the differential SPE spectra defined

above are protons

cm2−AMeV−event .

4.2 Galactic Cosmic Rays

The model developed by O’Neill [31] is used as GCR input for OLTARIS. This GCR model is

based on fitting the existing balloon and satellite measured energy spectra from 1954 to 1992

and more recent measurements from the Advanced Composition Explorer satellite from 1997 to

2002 with the stationary Fokker-Planck equation. This fit solves the diffusion, convection, and

energy loss boundary value problem and obtains an estimate of the appropriate diffusion coefficient. In addition, correlation of the diffusion coefficient with the Climax neutron monitor data,

which exhibits an odd-even cycle with a 22 year period, enables the estimation of the diffusion

coefficient at times when direct observational data are not available. The implementation of this

GCR model accurately accounts for the solar modulation of hydrogen through nickel by propagating the Local Interplanetary Spectrum of each element through the heliosphere. The model

provides a single value of the deceleration parameter φ(t) describing the level of solar cycle

modulation and determines the GCR differential energy spectrum for elements from hydrogen

to nickel at any given radial distance from the sun.

The earliest date available for input into the system is 01-Jan-1951. The latest date is variable and is controlled by the OLTARIS user interface. Please check the website for the latest

date available. The user has three input methods:

1. Start and end dates from pull-down lists of the day, month, and year.

2. Start date from pull-down lists of the day, month, and year and the mission duration in

days.

3. Preset scenarios with mission duration in days.

11
There are currently eleven preset scenarios available for user selections. Table 1 outlines the

deceleration parameter for each of the scenarios. The boundary condition defines the units used

in the rest of the OLTARIS processes. The units for the GCR environment are particles

cm2−AMeV−day .

Table 1: Deceleration Parameters for Preset OLTARIS GCR Scenarios

Scenario Deceleration Parameter

1956 Solar Min 401

1959 Solar Max 1986

1965 Solar Min 510

1970 Solar Max 1293

1977 Solar Min (DSNE3) 474

1982 Solar Max 1924

1987 Solar Min 467

1991 Solar Max 2525

1997 Solar Min 467

2000 Solar Max 1674

2007 Solar Min (predicted) 490

3DSNE - Constellation Program Design Specification for Natural Environments [32].

4.3 Earth Orbit

The Earth Orbit (EO) boundary condition consists of three components: GCR, omni-directional

trapped protons, and atmospheric albedo neutrons. There are several options for specifying an

EO environment on OLTARIS. The user can input mission dates with altitude and inclination

or select the DSNE environment (Constellation Program Design Specification for Natural Environments [32]), which will fix the dates, altitude, and inclination. The user can also select

which of the three components are to be included.

4.3.1 Galactic Cosmic Rays

The GCR model of Section 4.2 is modulated by a direction averaged geomagnetic transmission

coefficient scaled by global vertical cutoff data using the model in references [42, 43, 44] to

produce charge and energy dependent differential spectra. The acceptable altitude range for

input is 200 to 20,000 km. The units of this boundary condition are in particles

cm2−AMeV−day .

4.3.2 Omni-directional Trapped Protons

The trapped proton model is calculated using AP8MIN and AP8MAX proton flux models based

on the Vette reduction of satellite data [37, 38]. AP8MIN is interpolated on the Jenson and Cain

12
[45] geomagnetic field model and AP8MAX is interpolated on the Cain [46] geomagnetic field

model extrapolated forward in time to 1970. As a side note, within the South Atlantic Anomaly

region, the trapped proton field dips down to about 200 km, which is well within the orbits

of the Space Transportation System (STS) or Shuttle and the International Space Station (ISS)

missions. The acceptable altitude range for input is 200 to 20, 000 km. The units of the omnidirectional trapped proton flux are particles

cm2−AMeV−day .

4.3.3 Atmospheric Albedo Neutrons

Atmospheric albedo neutrons result from the interaction of GCR with the Earth’s atmosphere.

As the GCR intensities are modulated by solar activity so are the atmospheric neutrons modulated with time. The atmospheric neutron model [40] is a parametric fit to data gathered by

NASA Langley Research Center’s studies of the radiations at Supersonic Transport altitudes in

the years 1965 to 1971. It covers the rise and decline of solar cycle 20. Scaling of the data,

with respect to geomagnetic cutoff, altitude, and modulation of the Deep River Neutron Monitor, was found to allow for mapping of the environment to all locations at all times resulting in

an empirically based model for the atmospheric albedo neutrons used in OLTARIS. The units

of the atmospheric albedo neutrons flux are neutrons

cm2−AMeV−day .

4.4 Lunar Surface

The lunar surface environment is currently implemented on OLTARIS in a simplified manner.

The user can select either a lunar SPE or a lunar GCR environment. In each case, the corresponding free-space spectrum is computed and then applied to all of the rays in the vehicle

thickness distribution not pointing toward the lunar surface. The surface pointing rays, which

must be indicated in the thickness distribution, will have a zero boundary applied. At this time,

a lunar neutron albedo spectrum has not been implemented, so this zero-contribution from the

surface is an approximation. The lunar neutron albedo will be added as a future enhancement

to OLTARIS.

5 Particle Transport

The particle transport module in OLTARIS is used to propagate particles of an ambient space

radiation environment (See Section 4) through a combination of vehicle, shielding, and/or tissue. The transport algorithms in HZETRN2005 were developed by Wilson et al. [4, 9, 47] and

Cucinotta [48]. Slaba et al. [17] have since modified the algorithms so that faster and more accurate methods are used. The bi-directional neutron transport algorithms used in the slab calculations were developed by Slaba et al. [16, 49]. In general, the transport algorithms provide an

13
approximate numerical solution to the linearized Boltzmann transport equation with the Continuous Slowing Down Approximation (CSDA) and the straight ahead approximation [4] to yield:

"

∂

∂x −

1

Aj

∂

∂E Sj (E) + σj (E)

#

φj (x, E) = X

k

Z ∞

E

dE

0 σk→j (E0→E)φk(x, E0

) (1)

with the boundary condition

φj (0, E) = fj (E),

where φj (x, E) is the flux or fluence of type j particles at depth x with kinetic energy E. In

equation 1, Ajis the atomic mass number of a type j particle, Sj (E) is the stopping power of

a type j ion with kinetic energy E, σj (E) is the total macroscopic cross section for a type j

particle with kinetic energy E, and σk→j (E

0 → E) is the macroscopic production cross section

for interactions in which a type k particle with kinetic energy E

0 produce a type j particle with

kinetic energy E. The summation limits in equation 1 will be discussed shortly. The boundary

condition spectrum, fj (E), is considered to be a known function over a broad energy spectrum

and has been discussed in Section 4.

The left hand side is known as the Boltzmann operator, and the right hand side is the scattering kernel or collision operator. The Boltzmann operator in equation 1 consists of a streaming

term in one dimension of space and no dimensions of angle, the CSDA term in energy, and the

total interaction probability. The scattering kernel sums and integrates over all particles and energies to represent the source of secondary particles produced through fragmentation and elastic

interactions.

The CSDA is based on the assumption that sufficiently many atomic interactions occur per

unit path length to allow them to be expressed as a continuous process. The straight ahead

approximation is based on the assumption that all primary and secondary particles propagate in

the same direction. This reduces the transport equation to one spatial dimension and no angular

dimensions. The particle source is the boundary condition; therefore, a marching algorithm can

be used to solve the equations in the direction of interest.

Transport solutions for light ions (A≤4) (including neutrons) and heavy ions (A>4) are obtained separately, as demanded by the treatment of the nuclear cross sections and external space

radiation environments. For heavy ions, it is known that prompt projectile fragments have a velocity, or energy per mass unit, very near that of the projectile (the constant velocity approximation), while de-excitation particles from the projectile fragments are produced nearly isotropically with lower energy [5]. The heavy ion projectile produced target fragments are neglected in

the transport procedure due to their low energy and hence range. These approximations greatly

simplify the transport equation (equation 1). If all transported heavy ions are ordered according

to mass, then the heavy ion (A>4 & Z>2) transport equation can be succinctly written as

"

∂

∂x −

1

Aj

∂

∂E Sj (E) + σj (E)

#

φj (x, E) = X

k>j

σk→j (E)φk(x, E), (2)

14
where σk→j (E) is the production cross section for interactions in which a type k particle with

energy E produces a type j particle with energy E. The upper summation limit in equation 2 can

vary, and OLTARIS currently uses 59 ions (See Table 2). For light particles, the equal velocity

approximation is not valid and both the light projectile and the target fragments are included in

the transport procedure. In this case, equation 1 is solved, and the summation is taken over all

light particles: the lightest six particles in Table 2.

Table 2: OLTARIS Transported Isotopes

Isotope A Z Isotope A Z Isotope A Z

Neutron 1 0

1H 1 12H 2 1

3H 3 13He 3 24He 4 2

6Li 6 37Li 7 38Be 8 4

9Be 9 410B 10 511B 11 5

12C 12 613C 13 614N 14 7

15N 15 716O 16 817O 17 8

18F 18 919F 19 920Ne 20 10

21Ne 21 10 22Ne 22 10 23Na 23 11

24Mg 24 12 25Mg 25 12 26Mg 26 12

27Al 27 13 28Si 28 14 29P 29 15

30S 30 16 31S 31 16 32S 32 16

33Cl 33 17 34Ar 34 18 35Cl 35 17

36Ar 36 18 37K 37 19 38Ar 38 18

39K 39 19 40Ca 40 20 41Ca 41 20

42Ca 42 20 43Sc 43 21 44Ti 44 22

45Ti 45 22 46Ti 46 22 47Ti 47 22

48V 48 23 49V 49 23 50Cr 50 24

51Cr 51 24 52Cr 52 24 53Mn 53 25

54Mn 54 25 55Fe 55 26 56Fe 56 26

57Co 57 27 58Ni 58 28

The light ion and heavy ion transport solution methodology is expressed in marching algorithms and have been analytically shown to be accurate to O(h

2

) where h is the step-size in units

of g

cm2 [4]. Slaba et al. [14, 17] have also controlled the energy discretization error through various modifications to the light ion transport algorithm. An extensive review of the verification

and validation efforts associated with the HZETRN2005 marching algorithms can be found in

Wilson et al. [5]. A detailed derivation of the marching algorithms including the recent updates,

can be found in Slaba et al. [17].

In the current OLTARIS implementation, two transport scenarios are used:

15
1. Three material layer database for interpolation currently set to aluminum, polyethylene,

and tissue.

2. Multiple layer slab with coupled bi-directional neutron transport.

Item 1 generates a database of every combination of the three materials from 0.05 g

cm2 for SPE

and EO and 0.1 g

cm2 for GCR to at least 100 gcm2 with a spatial grid created to ensure spatial

convergence of the thickness interpolation algorithms. If rays in the vehicle thickness file are

larger than 100 g

cm2

, the grid is increased in increments of 50 g

cm2

to cover the longest ray up to

1000 g

cm2

. The slab solution, item 2, allows the user to create materials and layer them so that

a response function can be generated at the end of the slab and at each user defined thickness.

The slab solution also utilizes a backward solution for neutrons [49]. Reference [17] has a full

discussion of the coupled spatial step and energy grid size convergence criterion.

6 Response Functions

Once a flux or fluence spectrum as a function of particles and energies is calculated from the

Boltzmann equation, equation 1, then that flux has to be modified to represent the response

wanted by the user. Currently, OLTARIS determines dose (D), dose equivalent (H), thermoluminescence detector (TLD) response, Linear Energy Transfer (LET), Tissue Equivalent Proportional Counter (TPEC) response, and effective whole body dose equivalent (ED). The TEPC

and ED are only calculated for the interpolation transport scheme, but all others are calculated

for the slab and interpolation schemes as explained in Section 5. Therefore, D, H, TLD, and

LET are determined at each of the interpolation edit points and are interpolated over a thickness

file described in Section 2.2 to get the values at a point inside a geometry. For the slab, no interpolation is performed and the values are output at the slab boundary points input by the user.

The TEPC and ED calculations are more complex and need a vehicle description to become

meaningful. Each of these responses is discussed in detail below.

6.1 Dose

While the flux of particles is a detailed quantity describing the environment inside a spacecraft,

it is of little use to inform the user about the damage caused by or the risk resulting from this

particle environment to humans, materials, or electronics. As a first step, the dose is calculated

from the energy deposited along every particle’s track as it traverses the spacecraft. Therefore,

the dose is defined as

D =

X

j

Dj,

where,

Dj =

Z ∞

0

dE Sj (E)φj (E) + d

?

(E)

16
with Sj (E) as the stopping power of a charged particle j at energy E in the material of interest

(usually tissue or silicon) in units of keV

μm

. Of course, the stopping power of neutral particles in

any material is zero; therefore, the integral term is zero. Since heavy target fragments and recoil

nuclei are not transported, their dose is added by the d

?

(E) function [50]. The units of Dose are

mGy. Dose can be reported in tissue or silicon.

The dose is calculated at all interpolation grid points or slab points. This is called the Dose

Table or Dose versus Depth Table. This table can be interpolated over a set of thickness files to

obtain a dose at a point inside a vehicle and/or human.

6.2 Dose Equivalent

While dose gives the energy deposited by a particle in a material, it does not estimate the

probability of stochastic effects in humans such as cancer mortality. For the “complex mixture

of high- and low-LET radiation experienced in LEO,” [51] the National Council on Radiation

Protection and Measurement (NCRP) endorses the use of dose equivalent calculated with the

ICRP-60 [52] quality factor, QICRP−60, for this purpose [51, 53, 54]. As yet, the NCRP has not

made a recommendation for space environments beyond LEO [54], but NASA has adopted the

approach of using dose equivalent for beyond LEO vehicles as well. Dose Equivalent is defined

as

H =

X

j

Hj,

where,

Hj =

Z ∞

0

dE QICRP−60 (Sj (E)) Sj (E)φj (E) + h

?

(E).

The quality factor QICRP−60 is defined as [52]

QICRP−60 (Sj (E)) =







1 for 0 < Sj (E) ≤ 10

0.32Sj (E) − 2.2 for 10 < Sj (E) ≤ 100

√

300

Sj (E)

for 100 > Sj (E)

,

where Sj (E) is the stopping power of a charged particle j at energy E in the material, tissue,

or organ of interest in units of keV

μm

. The stopping power of neutral particles in any materials

is zero; therefore, the integral term is zero. Since heavy target fragments and recoil nuclei are

not transported, their dose equivalent is added by the h

?

(E) function [50]. The units of Dose

Equivalent are mSv.

The dose equivalent is calculated at all interpolation grid points or slab points. This is

called the Dose Equivalent Table or Dose Equivalent versus Depth Table. This table can be

interpolated over a set of thickness files to obtain a dose equivalent value at a point inside a

vehicle and/or human.

17
6.3 TLD-100

For dosimetry measurement purposes, one of the most widely used phosphor based instruments is the Lithium-Fluoride thermo-luminescence detector (TLD-100). These instruments

are routinely flown on ISS and STS missions and were used for validation of OLTARIS. Within

OLTARIS, the flux response function for the TLD-100 sensitivity to an incoming ion of charge

Z and energy E is modeled by the functional fit [55]

FTLD(E, Z) = 0.2418 + 0.8205 exp







−0.002 "

y(Z)

γ(E)

#2







,

where

y(Z) = Z







1 − exp



−125 

γ(E)

Z

!2

3











,

and

γ(E) =

vuuut

1 −

1



1 + E

9322

.

The non-dimensional quantity FTLD(E, Z) then scales the appropriate flux values at a given

depth, energy, and charge. Finally, the scaled fluxes are integrated over energy and summed

over charge to get the TLD-100 response to the particle field.

The TLD-100 response is calculated at all interpolation grid points or slab points. This is

called the TLD-100 Table or TLD-100 versus Depth Table. This table can be interpolated over

a set of thickness files to obtain a TLD-100 value at a point inside a vehicle and/or human.

6.4 Integral and Differential Linear Energy Transfer (LET)

In analyzing charged particle spectra in space due to GCR, SPE, and trapped protons, the conversion or mapping of particle energy spectra into LET distributions is a convenient guide in

assessing biologically significant components of these spectra. The mapping of LET to energy

is a triple valued function and can be defined only on open energy subintervals where the derivative of LET with respect to energy is not zero. OLTARIS uses a well-defined numerical procedure, which allows for the generation of LET spectra on the open energy subintervals that are

integrable in spite of their singular nature [56, 57]. LET can be reported in tissue and silicon.

The differential and integral LET distributions are calculated at all interpolation grid points

or slab points. These are called the LET Distributions or LET versus Depth Distributions. These

distributions can be interpolated over a set of thickness files to obtain a differential and integral

LET distribution at a point inside a vehicle and/or human.

The units of differential LET based flux are particles

cm2 keV

μm

day−or−event

. The units of integral or

cumulative LET based flux are particles

cm2−day−or−event . LET has units of keVμm

.

18
6.5 Tissue Equivalent Proportional Counter (TEPC)

In contrast to the limitations of LET based passive detectors, TEPC detectors simulate a micronsized tissue site and can provide a time resolved spectra in lineal energy. While the mapping of

flux/fluence into LET is a convenient guide in assessing biologically significant components of

these spectra, a feature of ionizing radiation is that it has a discontinuous nature in interacting

with matter. The deposited energy into a medium consists of discrete events with energy partitioning among ionization and excitation processes. This observation led to the suggestion that

the usual LET dependent quality factor (Q) be replaced by a lineal energy dependent Q for use

in radiation protection studies. Furthermore, the usual method of measuring LET is based on

passive plastic track detectors with limited LET range. These detectors can not detect electrons,

their efficiency for detection of secondaries, such as pions or kaons, are not well established, and

they experience detection-resolution limitation above an LET of approximately 250 to 300 keV

μm

.

Finally, because of the passive nature of these detectors, the separation of GCR from trapped

particles for LEO flights is difficult.

Monte Carlo (MC) simulations are the method of choice to model energy deposition by

ions in a micro-volume. MC necessitates a complete model of the important components of

the TEPC device and depending on the uncertainty wanted, can take some time to execute.

In contrast, OLTARIS uses a computationally efficient deterministic method for the numerical

representation of stochastic energy deposition and ionization produced by energetic ions passing

through absorber sites of submicron dimension [58, 59]. The Xapsos methodology and its

extension to obtain the response of a TEPC is an attempt to provide an accurate prediction for

comparison with spacecraft measurements [57].

The units of lineal energy are keV

μm

. The units of differential TEPC response flux/fluence are

particles

cm2sr keV

μm

day−or−event

. The units of integral TEPC response flux/fluence are particles

cm2sr day−or−event .

6.6 Effective and Organ Averaged Dose Equivalent

As is recommended in NCRP-132 and NCRP-142 [51, 53], effective dose equivalent is calculated by first calculating the averaged dose equivalent for the organs and tissues listed in Table 3.

The remainder organs are listed in NCRP-132 as: adrenals, brain, small intestine, large intestine, kidneys, muscle, pancreas, spleen, thymus, and uterus. A weighted average of these organ

or tissue dose equivalent values, as defined in equation 3, is then calculated using the NCRP132 tissue weighting factors given in Table 3.

ED =

X

T

wT H ̄

T , (3)

where wT are the NCRP-132 tissue weighting factors in Table 3 and H ̄

T are the organ or tissue

averaged dose equivalents as calculated by OLTARIS.

Organ or tissue averaged dose equivalent is calculated by first calculating the dose equivalent

at a large enough number of target points in the organ or tissue to accurately characterize that

19
Table 3: NCRP 132 Organs and their weights

Tissue Weights 0.01 0.05 0.12 0.20

Tissue Types Bone Surface Bladder Bone Marrow Gonads

Skin Breast Colon

Liver Lung

Esophagus Stomach

Thyroid

Remainder

organ or tissue and then averaging these point values. Currently, the user can select one of four

human body models (CAM [60], CAF [61, 62], MAX [63], or FAX [64]) for these calculations.

Target point locations for all of the necessary organs and tissues in each of the human body

models have been chosen [15, 65], and body thickness distributions are combined with vehicle

thickness distributions as described in Section 2.2.

There are a few body model specific details that should be noted. First, there are ten remainder organs for the females, but only nine for the males. For this reason, the tissue weighting

factor, wT , for each of the remainder organs is 0.05

10 for females and 0.059

for the males. Second,

in the CAF and CAM models, the colon, large intestine, and small intestine are treated as one

organ. This organ labeled intestine is therefore assigned a tissue weighting factor equivalent to

the sum of the tissue weighting factor specified for the colon, 0.12, and the tissue weighting

factors for two remainder organs. Thus, the intestine weighting factor is 0.12 + 0.05

10 × 2 for

CAF and 0.12 + 0.05

9 × 2 for CAM. Similarly, the colon and the large intestine are treated as

one organ and labeled “colon” in the FAX and MAX models, but the small intestine is treated

as a separate organ in these models. The weighting factor for the colon is therefore 0.12 + 0.05

10

in FAX and 0.12 + 0.05

9

in MAX. Also, the organ averaged dose equivalent is calculated for

several organs not included in the effective dose equivalent calculation. These organs are heart,

hippocampus, lens, and salivary glands for the CAF model; heart, hippocampus, lens, prostate,

and salivary glands for the CAM model; heart, hippocampus, lens, retina, salivary glands, and

trachea for the FAX model; and heart, hippocampus, lens, prostate, retina, salivary glands, and

trachea for the MAX model.

7 Summary and Future Work

The OLTARIS website is a versatile tool in the analysis of vehicles for human space flight that

enables the designers to meet NASA’s requirements for space radiation protection throughout

all stages of vehicle design. The tools within OLTARIS are securely managed, have undergone

a rigorous verification and validation process, and are presented to the user in an easy to follow

20
format. This is achieved with modern tools, a modern understanding of how user’s operate, and

with many people thinking through this problem to get a solution that best fits the tools available

and the user needs. Tools are available for the materials and spacecraft design community

on the OLTARIS website. A user can define their own material and transport any available

space environment through it or through multiple slabs of any reasonable number and thickness.

An example use case is described in the Appendix. This paper has also discussed material

properties, Earth orbit, particle transport and response functions.

OLTARIS can be easily modified to accommodate new user needs and wants. Adding new

features is straightforward because of the nature of the web interface. Adding new calculations

is also straightforward due to the modularity of the computational engine behind the website.

The connection of the website interface to the analysis modules with the Sun Grid Engine

allows external sites to be incorporated, with appropriate security issues resolved, to execute

new models without giving control of those calculations to the OLTARIS team. Interface file

formats are clearly defined and can be used to connect new parts with old parts to create new

calculations. All of these functions are connected through use cases.

For the near future, use cases will be generated for electronic response functions either

within OLTARIS or in conjunction with other sites and new transport algorithms. The near

term transport algorithm addition will be a ray-by-ray transport where the transport algorithm

is executed along each ray in the spacecraft’s thickness file. Each ray will have a complete slab

based transport calculation performed. The results for each ray will then be integrated together

to obtain the response wanted by the user.

Longer term projects could include Monte Carlo solutions for multi-layer slab geometries,

more user control of the existing transport algorithms, new tracked particles in the marching

algorithm like electrons and pions, user specified materials in the interpolation transport algorithm, five or more material layer interpolation transport algorithm, and better and more accurate interaction cross sections to replace NUCFRG2. Of course, as this tool becomes more

mature and gains users, the users will drive future improvements and priorities.

This project develops and maintains an integrated tool set (through the OLTARIS website)

that collects the current best practices, databases, and state-of-the-art methodologies to evaluate and optimize space radiation protection for human systems such as spacecraft, spacesuits,

rovers, and habitats. The modular nature of this development allows for easy verification and

validation of methods employed as well as the ability to provide quick access to improvements

in physics and transport for the radiation community under a configuration managed environment. This tool will increase fidelity by incorporating common spacecraft and user specified

materials into the geometry description with the soon-to-be implemented ray-by-ray transport

algorithm to further minimize uncertainties due to range-scaling of material thicknesses and

material ordering. The ray-by-ray algorithm specifically addresses the limitations associated

with simplified geometry description (equivalent aluminum, three-layer transport interpolation,

random astronaut orientation) and straight ahead transport. The ray-by-ray algorithm will also

establish the basis to calculate the forward/backward neutron transport for vehicle and lunar surface geometries. The back-scattered neutron environment will be calculated from the opposite

21
sides of the vehicle for a crew member’s specific orientation at specific tissue locations. This

will increase NASA’s ability to evaluate the effectiveness of shielding systems.

A Example Use Case

This appendix shows an example use case used to help generate the OLTARIS user interface.

The use case is broken up into sections that show a full description of the job, the job flow, any

alternatives, and status.

UC-P02: Effective Whole-body Dose Equivalent Calculation with oriented astronaut

Summary: Effective dose is a response calculation that requires dose equivalent evaluations

at multiple points throughout the body. Usually, approximations are made to assume a

random orientation of the astronaut within the vehicle. However, it is desired to have the

capability to orient an astronaut at a specific location in the vehicle. This use case describes a technique that utilizes a CAD-geometry phantom astronaut that is used to locate

and orient the astronaut in the users vehicle CAD geometry. This type of calculation is

typically used for short-duration events such as an SPE.

Preconditions: User has account and is logged in.

Direct Actors: All users

Triggers: User creates new project

Main Success Scenario:

1. User inputs a descriptive title of their choosing that will be used to reference the

project

2. User adds a sentence or paragraph giving more details on the project

3. User selects an historic SPE with desired multiplication factor

4. User selects “phantom astronaut” for geometry setup

5. User downloads phantom CAD geometry in desired format (IGES, obj, ...)

6. User saves project and possibly logs out of design tool while orienting phantom in

vehicle geometry

7. User opens project and uploads phantom “reference points” coordinates to the design tool in the vehicle coordinate system

8. User downloads properly oriented ray distribution from design tool

9. User raytraces vehicle at “phantom zone points” using download ray distribution

22
10. User uploads vehicle raytrace

11. User selects desired responses including effective dose

12. User submits job

13. User examines results in the form of numbers, tables, and plots as appropriate

Alternative Scenario Extensions:

• If an error condition results, the user is notified

• User can select different phantoms based on number of zones. More zones increase

the accuracy of the calculation with respect to geometry, but requires more raytracing of the vehicle geometry. In the limit, the user could ray-trace all body points

used in effective dose calculation

Post Conditions: Project is successfully run and returns results to user

Notes and Questions: None

End State: Finished

Once the use case is defined, then Fortran code, perl scripts, data files and whatever else is

needed is assembled in an input, output, and process flowchart. The resultant system is then

module tested and placed in the functional test stream. Ruby scripts that tie the process together

are then generated, and the webpages are modified to incorporate use case into OLTARIS.

23
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29
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Publication

 4. TITLE AND SUBTITLE

OLTARIS: On-Line Tool for the Assessment of Radiation in Space

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Singleterry, Robert C., Jr.; Blattnig, Steve R.; Clowdsley, Martha S.; 

Qualls, Garry D.; Sandridge, Christopher A.; Simonsen, Lisa C.; Norbury, 

John W.; Slaba, Tony C.; Walker, Steven A.; Badavi, Francis F.; Spangler, 

Jan L.; Aumann, Aric R.; Zapp, E. Neal; Rutledge, Robert D.; Lee, Kerry 

T.; Norman, Ryan B. 

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

NASA Langley Research Center

Hampton, VA 23681-2199

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14. ABSTRACT

The On-Line Tool for the Assessment of Radiation In Space (OLTARIS) is a World Wide Web based tool that assesses the 

effects of space radiation on humans and electronics in items such as spacecraft, habitats, rovers, and spacesuits. This 

document explains the basis behind the interface and framework used to input the data, perform the assessment, and output the 

results to the user as well as the physics, engineering, and computer science used to develop OLTARIS. The transport and 

physics is based on the HZETRN and NUCFRG research codes. The OLTARIS website is the successor to the SIREST 

website from the early 2000's. Modifications have been made to the code to enable easy maintenance, additions, and 

configuration management along with a more modern web interface. Overall, the code has been verified, tested, and modified 

to enable faster and more accurate assessments. 

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Space radiation; Design tool; OLTARIS; Radiation effects

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