Shielding design on large human-rated systems allows minimization of radiation impact on electronic systems. Shielding design tools require adequate methods for evaluation of design layouts, guiding qualification testing, and adequate follow-up on final design evaluation

Boeder, P.

Koontz, Steven L.

O'Neill, P. J.

Pandolf, J. E.

Pankop, C.

Reddell, B.

Tripathi, R. K.

Wilson, J. W.

Zang, T. A.

NASA Technical Reports Server

Wilson                                                                                                     IEEE NSREC 2007 1 
Reliability-based Electronics Shielding Design Tools 
 
J.W. Wilson1, P.M. O’Neill2, T.A. Zang1, J.E. Pandolf1, R.K. Tripathi1, 
Steven L. Koontz2, P. Boeder3, B. Reddell3, C. Pankop3 
1NASA Langley Research Center, Hampton, Virginia 23681 
2NASA Johnson Space Center, Houston, Texas 77058 
3The Boeing Company, Houston, Texas 77058 
POC: john.w.wilson@nasa.gov 
 
 
Abstract 
 
Shielding design on large human-rated systems allows minimization of 
radiation impact on electronic systems. Shielding design tools require 
adequate methods for evaluation of design layouts, guiding qualification 
testing, and adequate follow-up on final design evaluation.  
https://ntrs.nasa.gov/search.jsp?R=20070030934 2019-08-30T01:32:35+00:00Z
Wilson                                                                                                     IEEE NSREC 2007 2 
Introduction 
It is well established that space radiation shielding provided by large-scale human-rated 
spacecraft is an important consideration for single event upsets (SEU) in avionics systems (Shinn 
et al. 1995, 1998).    Furthermore, provision of appropriate design methods is critical to the use of 
low-cost commercial-off-the-shelf (COTS) electronic devices with their, often, high-radiation 
sensitivity and manufacture variability.  A similar shield design tool development activity for 
human protection under the Constellation Program already includes evaluation of the natural and 
induced environments mapped throughout the modeled vehicle to assure astronaut safety, thus 
providing most of the software framework required for electronics shield design and evaluation.  
The present project would prepare modified software tools for use in electronics shield design 
with appropriate National Aeronautical and Space Administration (NASA) mandated verification 
and validation processes using the Space Shuttle and the International Space Station (ISS) flight 
data (Wilson et al. 2006a).  This development provides a well-validated tool for use in the Crew 
Exploration Vehicle (CEV) design with first design validation in low Earth orbit (LEO).  User-
friendly design engineering interfaces to follow preliminary design concepts to final engineering 
design are being developed (Wilson et al 2004). Provision for multidisciplinary optimization 
(MDO) processes (Qualls et al. 2003) and reliability design methods (Wilson et al. 2004) 
supported by high-speed computational procedures will be discussed. Currently, only the NASA-
developed HZETRN code has been identified for this purpose within the NASA design standard 
STD-3000.  As a result, Wilson et al. (2005) have prepared a review of past HZETRN code 
development, verification, and validation activity.  This design tool is of utmost importance for 
electronics placement in future large-scale human rated systems. 
Design Tool Development 
A schematic overview of the design tool functionality being developed under NASA’s 
Constellation Program is shown in Fig. 1.  Spacecraft shield geometry specification is a central 
part of model development but the response of sensitive systems (such as human tissue, materials, 
or electronics) is an integral part of the design process as indicated in the top tier of the figure.  
The analysis/interface tools imply interaction with other non-radiation related tools shown on the 
bottom tier of the figure.  Current interest is integration of flight data as shown on the middle tier 
of the figure. This requires interfacing with ISS models and detector response functions, and 
comparing with flight measurements to validate the galactic cosmic ray (GCR) and South 
Atlantic Anomaly (SAA) tool functionality.  Present application focus is on web-based analysis 
tools with on-the-fly model 
building for Constellation 
development teams. 
Enabling Technology 
The development of 
such a tool is enabled by high-
performance computational 
methods based on direct 
solution of the Boltzmann 
transport equation.  This multi-
dimensional system of partial-
differential-integral equations 
defined over three position 
variables x and three motion 
variables Ω ,E describe all of 
the processes by which 
ionizing radiation interacts 
with bulk materials including 
 
Fig. 1. Schematic overview of radiation analysis and design tools.  Current 
focus denoted by *. 
 
Wilson                                                                                                     IEEE NSREC 2007 3 
molecular, atomic, and nuclear processes.  The Boltzmann equation describes the radiation flux of 
type j particles φj(x,Ω ,E) (including photons) as 
         Ω•∇φj(x,Ω ,E) =  ∑k∫ σjk(Ω ,Ω′ ,E,E′) φk(x,Ω′ ,E′) dΩ′  dE′  - σj(E) φj(x,Ω ,E) 
where σj(E) and σjk(Ω ,Ω′ ,E,E′) are the 
shield media macroscopic cross sections, 
and incoming flux is specified at the 
material boundary.  The σjk(Ω ,Ω′ ,E,E′) 
represent all those processes by which type 
k particles moving in direction Ω′  with 
energy  E′ produce type j particles in 
direction Ω  with energy E (including decay 
processes).  The solution methods are 
based on combinations of physical 
perturbation, asymptotic expansions, and 
numerical procedures (Wilson et 2005).  
Monte Carlo codes (HETC and TIGER) 
have played an important role in 
verification of the combination of 
analytical and numerical procedures as 
shown in Figs. 2 and 3.  
Validation follows two tracks.  The 
first track is the validation of basic 
computational procedures and databases 
(molecular/atomic and nuclear) using well-
defined particle beams and detailed 
experimental characterization of the 
resulting fields produced in materials 
(Wilson et al. 2005, 2006b).  The second 
validation method is through flight 
measurements involving specific flight 
platforms.  Unlike the laboratory validation 
where the radiation source and material 
geometry is simple and well understood, 
flight validation is often limited by 
uncertainty in environmental models, 
uncertainty in material arrangement, and 
properties of complicated spacecraft.  
Otherwise, flight validation represents 
more accurately the engineering design 
problem.  An example flight validation using the Liulin-094 detector system in the forward 
compartment of the US Laboratory of ISS during 27 June-4 July 2001 (Dachev et al. 2006) is 
shown as a single pass through the SAA along a descending phase trajectory in Fig. 4 in 
comparison to the current modeled values (Wilson et al. 2007).  Improved definition of the SAA 
is required. 
Electronic Response Models 
 The computational models with verification and validation processes discussed to this 
point are common to any shield design problem whether it is for protection astronauts, various 
materials, or electronic devices.  Specific shield design applications is through the specification of  
 
Fig. 2.  Verification using dose equivalent evaluation with 
HZETRN and HETC in 30-cm water shielded by iron at 20 
g/cm2 from the Webber model solar particle event. 
 Fig. 3.  Verification using dose in water for incident 
electrons according to LaRC ELTRN and the Air Force 
TIGER code. 
Wilson                                                                                                     IEEE NSREC 2007 4 
responses and mission design require-
ments.  Similar to the case of human 
protection, response functions are 
driven by basic physical processes 
through which energy is transferred to 
sensitive materials or tissues.  There 
are two main processes by which 
energy is transferred to sensitive 
materials.  The first process is the 
transfer to the orbital electrons leading 
to direct ionization, and the second 
process is the displacement of atoms 
from well ordered lattice sites on which 
the device function depends.  The 
transfer of energy from a passing 
energetic ion to orbital electrons 
provides a local electron flux 
propagating from the ion path into the 
material producing additional 
ionization and excitation.  Aside from the addition of dose to the bulk material, these electrons 
produce a current (if local electric fields are present) and additionally initiate chemical change in 
materials through ionization and excitation processes.  The high-energy density in electronic 
devices provide high electron-hole pair densities near the central track of the ion path resulting in 
Auger recombination effects limiting the response of electronic devices depending on the exact 
nature of the energy deposit and the charge collection time of the device.   
 Auger recombination effects for low-energy target fragments within electronic devices is 
demonstrated in the Shuttle computers (Shinn et al. 1995) with results of SEU rate 
(SEU/computer-day) for STS-51 at low orbit inclination and STS-56 at high inclination shown in 
Table 1.  The SEU from target fragments produced 
mainly by protons and neutrons colliding with the 
Si nuclei of the memory chips is grossly over-
estimated if the Auger processes are ignored (Shinn 
et al. 1995, 1998).  With Auger recombination, 
reasonable agreement is obtained with computa-
tional models as seen in the table. 
Spacecraft Analysis Method 
It is instructive to go through a specific design process to see how the above tool 
elements are integrated to accomplish an end design product.  The SAGE-III instrument (Fig. 5) 
samples light from the Earth’s atmosphere and passes it down an optical bench to a quartz grating 
which is focused on a charged-coupled device (CCD) array to quantify the optical frequency 
distribution.  The CCD is sensitive to displacement damage in its active layers.  It was anticipated 
that energetic trapped electrons would be a major limiting factor in the performance of the device, 
and a tantalum shield was planned because of the efficient multiple scattering limiting electron 
penetration.  A detailed shielding model was developed as shown in Fig. 5 for the analysis.  
Although the electron induced displacements were indeed the major contributor to CCD 
degradation as expected, neutrons produced in the tantalum shield that also contributed to driving 
the CCD beyond requirements.  An aluminum detector shield was designed to adequately limit 
electron penetration and reduce the neutron component as shown in Fig. 6. 
Table 1. Shuttle shield and memory SEU 
model validation (SEU/computer-day). 
Mission Flight data Model 
STS-51 2.13 1.52 
STS-56 6.05 5.85 
 
0
50
100
150
200
0 5 10 15 20
Time from Start of Crossing, min.
D
o
s
e
 R
a
te
, 
m
ic
ro
-G
y
/h
r
Meas.
Calc.
 
Fig. 4.   Dose rate measured on a single descending passage 
through the heart of the SAA compared to computational 
model results. 
Wilson                                                                                                     IEEE NSREC 2007 5 
Concluding Remarks 
The Constellation Program requires 
verified/validated/standardized analysis, 
design, and testing procedures for quality 
assurance of future hardware.  This involves 
the improvement and validation of 
environmental models and computational 
procedures for Constellation design teams.  
From a hardware perspective, environment 
and shielding design tools will be coupled to 
hardware specific damage functions of which 
the first level is evaluation of basic physics 
models for total ionization, displacement 
damage, and linear energy transfer spectra.  
These basic quantities then couple to specific 
device response models with shielding 
analysis and shield materials optimization.  
The output of such analysis would include 
design specific testing protocols for 
qualification that assures the proper mix of 
basic physical processes (dose, dose rate, 
displacement damage, and LET spectral 
contributions) to be matched to available 
accelerator capabilities (electrons, protons, 
high energy heavy ions).  The design tool 
software can then be run in a design 
validation to qualify with test-flight data in 
low Earth orbit for design prediction 
validation mode for Lunar and Mars mission 
design validation.  Developing design tools plays a central role in the above processes and at 
minimum added costs when leveraged out of the human protection program. 
References 
Dachev, T., et al., ISS Observations of SAA radiation distribution by Liulin-E094 instrument. Adv. Space 
Res. 37: 1672-1677; 2006. 
Qualls, G.D., et al., International Space Station radiation shield augmentation optimization. Space 2003 
Conference AIAA 2003-6222, 2003. 
Shinn, J. L., et al., Effects of target fragmentation on evaluation of LET spectra from space radiation in 
low-Earth orbit (LEO) environment:  Impact on SEU predictions.  IEEE Trans. Nucl. Sci., 42(6): 2017-
2025; 1995. 
Shinn, J. L., et al., Validation of a comprehensive space radiation transport code.  IEEE Trans. Nucl. Sci. 
45(6): 2711-2719; 1998. 
Wilson, J.W., et al.,  Emerging radiation health-risk mitigation technologies. Space Technology 
Applications & Information Forum, STAIF-2004, AIP Conference Publications, 2004. 
Wilson, J.W., et al., Verification and validation: High charge and energy (HZE) transport codes and future 
development. NASA/TP-213784, 2005. 
Wilson, J.W., et al., International Space Station: A testbed for experimental and computational dosimetry. 
Adv. Space Res. 37: 1656-1663; 2006a. 
Wilson, J.W., et al., Standardized radiation shield design method: 2005 HZETRN. ICES 2006-01-2109, 
2006b. 
Wilson, et al., Time serial analysis of the induced LEO environments within the ISS 6A.  Adv. Space Res. 
In press, 2007. 
 
Fig. 5.  SAGE-III shielding model used in CCD 
shield design. 
 
 
Fig. 6.  Final SAGE-III detector shield with 
aluminum alloy. 
 


Reliability-Based Electronics Shielding Design Tools

Reliability-Based Electronics Shielding Design Tools

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server