JERG-2-144

GeneralDESIGN STANDARD
Micro-debris Impact Survivability
Assessment Procedure

May 10, 2012

Japan Aerospace Exploration Agency

JERG-2-144

This is an English translation of JERG-2-144. Whenever there is anything ambiguous in thisdocument, the original document (the Japanese version) shall be used to clarify the intent of therequirement.

Disclaimer
The information contained herein is for general informational purposes only. JAXA makes nowarranty, express or implied, including as to the accuracy, usefulness or timeliness of any
information herein.
JAXA will not be liable for any losses relating to the use of the information.

Published by
Japan Aerospace Exploration Agency
Safety and Mission Assurance Department
2-1-1 Sengen Tsukuba-shi, Ibaraki 305-8505, Japani

JERG-2-144

Contents

1. Scope ...................................................................................................................... 1
2. Related documents ................................................................................................ 1
2.1 Applicable documents......................................................................................... 1
2.2 References ........................................................................................................... 1
3. Terminology, Definition and Abbreviation ........................................................... 1
3.1 Terms and Definitions ......................................................................................... 1
3.2 Abbreviation......................................................................................................... 14. Condition for assessment ..................................................................................... 15. Impact survivability assessment guidelines ........................................................ 25.1 Standard requirement.......................................................................................... 25.2 Impact survivability assessment procedure ...................................................... 25.3 Confirmation of spacecraft design architecture and operational parameters. 25.3.1 Operational parameters..................................................................................... 25.3.2 Spacecraft design data...................................................................................... 25.4 Setting of requirements for resistance to debris impact .................................. 25.5 Identification of components to be assessed and their failure modes ............ 3
5.6 Identification of ballistic limit.............................................................................. 3
5.7 Impact probability analysis ................................................................................. 3
5.8 Calculation of failure probability and non-failure probability ........................... 4
5.9 Assessment ......................................................................................................... 45.9.1 The non-failure probability is larger than requirement ................................... 4
5.9.2 The non-failure probability is smaller than the requirement .......................... 4ii

JERG-2-144

1. Scope
This standard describes the assessment procedure for verifying the validity of the protection designof satellites and probes (hereinafter referred to as spacecraft) against risks of impact withmicro-debris and meteoroid (hereinafter referred to as debris) which are 1 mm or less in size and whose
impact probability and impact damage is not negligible.
2. Related documents
2.1 Applicable documents
N/A

2.2 References
Related references shall be as follows:(1) IADC-04-03 Protection Manual (April 2011).
3. Terminology, Definition and Abbreviation
3.1 Terms and Definitions
The terms are defined as followings:(1) Impact conditions: Characteristics of the impacting object (mass, dimensions, impact speed,material characteristics, impact angle) and characteristics of the impacted object(2) Ballistic limit: The limit leading to harmful damage represented by the diameter of the debris foreach subject to be assessed.
(3) Failure probability: Expected probability of harmful damages (defined in Paragraph (6)) caused
by debris impact per unit of time. This value can be defied considering the debris impact
probability causing harmful damage and the redundancy of portions vulnerable to impact. Whenthe impact probability is a function of time, this is also a function of time.
(4) Ballistic limit equation: Used as a meaning of "impact damage equation" to represent theballistic limit defined by the diameter of debris(5) Debris impact survivability requirement: Definition of allowable probability of harmful damage
incidence represented by PNF min (minimum non-failure probability)(6) Harmful damage: Damage caused by debris impact which disables the functions of thecomponents to be assessed. Depending on the characteristics of the component, the harmful
damage mode covers damages such as perforation, craters larger than a predetermined size anddamages on the cable shielding. Thus, it shall be determined in accordance with thecharacteristics of the component to be assessed.
3.2 Abbreviation(1) IADC: Inter-Agency Space Debris Coordination Committee(2) PNF: Probability of Non Failure
4. Condition for assessment
To ensure the spacecraft mission in the environment of the micro-debris and meteoroid, thefollowing points including the system design must be coordinated with JAXA during the progress ofthe development of the system from the Mission Requirements Definition Phase.
(1) Consideration of debris density when determine the operational orbit altitude(2) Consideration of the distribution of debris impact probability when determine the shape ofspacecraft(3) Setting the policy concerning the allowable limit of impact risk (mission importance,relationship with other redundant elements, etc.)(4) Assessment in view of system design including the influence of loss of mass and layout changeof components associated with impact protection measures (including allocation of resources)(5) Setting a contingency plan including impact detection, damage monitoring, recovering,reconstruction and isolation
This standard serves as guidance for impact protection design on the condition that the spacecraft
has been defined in shape, dimensions, operational orbital characteristics and operational period
considering above conditions.

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5. Impact survivability assessment guidelines
5.1 Standard requirement
In the spacecraft design phase, impact survivability shall be assessed to decide the necessity ofmeasures against risks of debris impact potentially preventing successful disposal after the completionof spacecraft operation. How the mission equipment to be protected shall be determined depending on
the characteristics of project.
5.2 Impact survivability assessment procedure
The assessment flow shall be as follows: (See the assessment flow diagram in the appendix.)(1) Preparation of information for spacecraft design architecture and operational parameters(2) Identification of requirements for debris impact survivability(3) Identification of components to be assessed and their failure modes(4) Identification of ballistic limit(5) Impact probability analysis(6) Calculation of failure probability and non-failure probability(7) Assessment of impact survivability
5.3 Confirmation of spacecraft design architecture and operational parameters
The debris impact probability differs depending on the altitude and inclination of operation orbit,operation period, shape of the spacecraft, and location of components in the spacecraft to be assessed.
In this sub-clause, such information needed for analysis shall be collected as analysis conditions.
5.3.1 Operational parameters

The spacecraft’s operational parameters including orbital characteristics (altitude, orbital
inclination, etc.), attitude respected to travelling direction, and operation period, shall be identified.
5.3.2 Spacecraft design data

Geometric information including the shape and dimensions necessary for creating a spacecraft
structural model, and design data necessary for definition of the damage modes shall be prepared.
5.4 Setting of requirements for resistance to debris impact
The spacecraft's system minimum non-failure probability (PNF min) against debris impact shall bedefined as a requirement for impact survivability.
The basic idea of the impact survivability assessment is to confirm that the relation between thesystem minimum non-failure probability (PNF min) and the system non-failure probability (PNF S/C)
obtained by the analysis satisfies the following equation.

PNFS / C ≥ PNFmin
Generally the non-failure probability (PNF) is obtained by the following equation using theoperation period (t) and the failure probability p(t) calculated from the debris impact probability whichcauses damages exceeding the ballistic limit. In this process, if there were the redundant elements anadequate consideration shall be paid as in the case of the reliability analysis.

 t
PNF = exp − ∫ p (t )dt  0

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If the failure rate (λ) during the operation period is assumed to be constant, the equation would be
simplified as follows:

PNF = e − λt
5.5 Identification of components to be assessed and their failure modes
Vulnerable components subject to harmful damage due to debris impact shall be identified forassessment. At least the vulnerable components necessary for disposal operation shall be identified.
Failure modes leading to harmful damage shall be identified using reliability analysis technology suchas FMEA.
(Reference: The failure modes to be identified should include the damage of shielding for power
cable leading to short circuit, and perforation in the propellant tank leading to blowout, etc. Details
shall be determined according to the design concept of the spacecraft.)
5.6 Identification of ballistic limit
For the assessment of components identified in sub-clause 5.5, the minimum diameter of debris
causing damage exceeding the ballistic limit shall be identified by collecting the design information(structural wall facing to the direction of debris impact, shielding materials, satellite structure panels
and stand-off distance with them), identifying the adequate existing ballistic limit equation, andassuming the impact characteristics (including debris material, impact speed, and impact angle).
If an available ballistic limit equation cannot be obtained, it shall be coordinated with JAXA toapply the existing equation or derive a new equation by conducting a hypervelocity impact test andsimulation analysis.
5.7 Impact probability analysis
The spacecraft structural shape shall be modeled based on the design information obtained in
sub-clause 5.3. The impact probability of each surface of the spacecraft shall be understood from theoperational parameters and operational period.
The impact probability of the entire spacecraft system shall be detailed to the impact probability
with debris whose diameter exceeds the ballistic limit for each component to be assessed. The impact
probability during the entire operation period shall be calculated by integrating the impact probability
per unit period along the operation period with the projected area in the impact direction of thecomponents to be assessed.

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5.8 Calculation of failure probability and non-failure probability
For each component to be assessed or for the system including the component, the non-failure
probability during the operational period shall be calculated from the failure rate obtained by the impact
probability. In case that the redundant elements would be exist, the same method as the reliability
analysis would be considered.
For all the components to be assessed, the non-failure probability shall be calculated and compiled
to the system non-failure probability (PNF S/C).
5.9 Assessment
5.9.1 The non-failure probability is larger than requirement
If the following relation can be confired, then analysis can be completed.

PNFS / C ≥ PNFmin

5.9.2 The non-failure probability is smaller than the requirement

If the following relation is obtained, measures must be taken.

PNFS / C < PNFmin
Proper measures shall be taken as follows:(1) If the assessment process has any room for reviewing, it shall be performed.
a) It shall be required to re-confirm whether the assumptions and conditions for analysis would
be proper and whether the requirements would not be too excessive.
b) If a large uncertainty of the ballistic limit equation would cause the problems, coordination
shall be made with JAXA to improve the assessment accuracy by conducting impact test orsimulation analysis.
(2) It shall be required to take measures for adding shielding materials, bumper installation,
relocation of the component layout, and providing redundant design.

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AppendixStart

5.4 Setting of requirements forresistance to debris collision

5.3 Preparation of space craft designand operational parameter

Reviewing ofimpact survivabilityrequirements

Design information

5.3.1 Operational parameter(1) Orbital characteristics of space
craft,(2) Position in travelling direction,(3) Operational period

5.5 Extraction of components to beevaluated and identification of failuremode⇒

5.3.2 Space craft design data
(1) Geometric information including
the shape and dimensions(2) Design data

Design information ⇒Design information, operational information⇒

5.6 Identification of ballistic
limit

Confirmationof ballistic
limit
equation
Reviewing ofassumptions
andconditions

5.7 Impact probability
analysis

5.8 Calculation of failure
probability andnon-failure probability

Conformance (PNF S/C≥PNF min)

Design change

5.9 Assessment(1) Provision ofprotective material(2) Reviewing of layout(3) Providing of
redundant system

Nonconforming(PNF S/C<PNF min) Necessary

Consideration ofmeasures
Correspond with design change

Assessment flow diagram

5Completion

Correspond by reviewing the assessment process