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Book A.
Introduction

Book B.
7150 Requirements Guidance

Book C.
Topics

Tools,
References, & Terms

SPAN
(NASA Only)

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{alias:SWE-133} {tabsetup:1. The Requirement|2. Rationale|3. Guidance|4. Small Projects|5. Resources|6. Lessons Learned} {div3:id=tabs-1} h1. 1. Requirements
Wiki Markup
Tabsetup
1. The Requirement
1. The Requirement
12. Rationale
23. Guidance
34. Small Projects
45. Resources
56. Lessons Learned


Div
idtabs-1

1. Requirements

2.2.8.3

The

project,

in

conjunction

with

the

Safety

and

Mission

Assurance

organization,

shall

determine

the

software

safety

criticality

in

accordance

with

NASA-STD-8739.8.

h2. {color:#003366}{*}

1.1

Notes{*}{color} Software safety criticality is initially determined in the formulation phase using the NASA Software Assurance Standard,

Notes

Software safety criticality is initially determined in the formulation phase using the NASA Software Assurance Standard, NASA-STD-8739.8

{sweref:278}. As the software is developed or changed and the computer software configuration items

.

sweref
278
278
As the software is developed or changed and the computer software configuration items (CSCI),

models,

and

simulations

are

identified,

the

safety-critical

software

determination

can

be

reassessed

and

applied

at

lower

levels.

The

software

safety

assessment

and

planning

are

performed

for

each

software

acquisition,

development,

and

maintenance

activity,

and

for

changes

to

legacy\heritage

systems.

When

software

in

a

system

or

subsystem

is

found

to

be

safety

critical,

additional

requirements

in

the

NASA

Software

Safety

Standard

{sweref:271} will augment those associated with the software class requirements found in this document. The software assurance organization is required by NASA Software Assurance Standard,

sweref
271
271
will augment those associated with the software class requirements found in this document. The software assurance organization is required by NASA Software Assurance Standard, NASA-STD-8739.8

{sweref:278}, to perform an independent software safety criticality assessment and work with the project to resolve any differences. Engineering and software assurance must reach agreement on safety-critical determination of software. Disagreements are elevated via both the Engineering Technical Authority and Safety and Mission Assurance Technical Authority chains. h2. 1.2 Applicability Across Classes {applicable:asc=1|ansc=1|bsc=1|bnsc=1|csc=1|cnsc=1|dsc=1|dnsc=1|esc=1|ensc=1|f=1|g=1|h=1} {div3} {div3:id=tabs-2} h1. 2. Rationale Each project, with the responsible Software Assurance organization, evaluates the project software to determine if the software is safety-critical.  If the software is determined to be safety-critical, the software safety requirements within this NPR and NASA-STD-8719.13 {sweref:271} are applied to the safety critical project software. {div3} {div3:id=tabs-3} h1. 3. Guidance The project can use the NASA Software Assurance Standard, NASA-STD-8739.8 {sweref:278}, to perform it's determination of the software safety criticality. The software safety litmus test in appendix A.1 of the standard is applicable to all projects. The software is considered safety critical if it meets any of the three major criteria listed in the appendix. If the project is determined to be safety critical, then the project must adhere to the applicable statements in the NASA Software Safety Standard, NASA-STD-8719.13 {sweref:271}. As noted in NASA-STD-8719.13 {sweref:271}, non-safety critical software residing with safety critical software is a concern because it may fail in a way that it disables or impairs the functioning of the safety critical software. When methods to separate the code, such as partitioning, can't be used to limit the software defined as safety critical, care must be exercised to assure safety for a block of software (multiple CSCI) where only a portion are safety critical, and or for individual safety critical CSC's within a larger CSCI. The NASA Software Safety Standard, NASA-STD-8719.13 {sweref:271}, requires the software safety criticality to be re-assessed periodically -- typically at each major milestone review---by the project's responsible software assurance engineer.  This individual evaluates the project software for determination of safety criticality utilizing the Software Safety Litmus Test within NASA-STD-8719.13 {sweref:271}.  This allows the software safety requirements to be refined and applied to the required areas (preventing a possibly costly over-application or a non-compliant and risky under application).  It also assures that requirements are met and/or changes to the software are addressed and checked for safety criticality. The software safety criticality assessment process and the location of the assessment results are documented within the Software Safety Plan (or equivalent).  Most projects document the software safety criticality with the software classification.  The project's system safety documentation also addresses it. A best practice is to document the software safety criticality assessment results with the software classification assessment, with local S&MA and the Engineering Technical Authority both approving the results.  An example form is provided in NASA-STD-8719.13 NASA Software Safety Standard {sweref:271}. {div3} {div3:id=tabs-4} h1. 4. Small Projects This requirement does not have any special guidance relative to small projects. {div3} {div3:id=tabs-5} h1. 5. Resources # NASA Technical Standard, "[NASA Software Safety Standard|https://standards.nasa.gov/documents/detail/3314914]", NASA-STD-8719.13B, 2004. Includes the Software Safety Litmus Test and an example form.  # NASA Technical Standard, "[NASA Software Safety Guidebook|https://standards.nasa.gov/documents/detail/3315126]", NASA-GB-8719.13, 2004. # STEP Level 2 Overview of Software Safety course, SMA-SA-WBT-230, [SATERN|https://saterninfo.nasa.gov/] (need user account to access SATERN courses). # STEP Level 3 Software Safety for Practitioners course, SMA-SOFT-NSC-1005, [SATERN|https://saterninfo.nasa.gov/] (need user account to access SATERN courses). \\ {refstable} {toolstable} {div3} {div3:id=tabs-6} h2. 6. Lessons Learned A documented lesson from the NASA Lessons Learned database notes the following:  *Mars Global Surveyor (MGS) Spacecraft Loss of Contact. Lesson Number 1805:*  Contact was lost with the Mars Global Surveyor (MGS) spacecraft in November 2006 during its 4th extended mission. A routine memory load command sent to an incorrect address 5 months earlier corrupted positioning parameters, and their subsequent activation placed MGS in an attitude that fatally overheated a battery and depleted spacecraft power. The report by the independent MGS Operations Review Board listed 10 key recommendations to strengthen operational procedures and processes, correct spacecraft design weaknesses, and assure that economies implemented late in the course of long-lived missions do not impose excessive risks.  ([http://www.nasa.gov/offices/oce/llis/imported_content/lesson_1805.html]) {div3} {tabclose}

,

sweref
278
278
to perform an independent software safety criticality assessment and work with the project to resolve any differences. Engineering and software assurance must reach agreement on safety-critical determination of software. Disagreements are elevated via both the Engineering Technical Authority and Safety and Mission Assurance Technical Authority chains.

1.2 Applicability Across Classes


applicable
f1
g1
h1
ansc1
asc1
bnsc1
csc1
bsc1
esc1
cnsc1
dnsc1
dsc1
ensc1



Div
idtabs-2

2. Rationale

Each project, with the responsible Software Assurance organization, evaluates the project software to determine if the software is safety-critical.  If the software is determined to be safety critical, the software safety requirements within NPR 7150.2, NASA Software Engineering Requirements, and NASA-STD-8719.13, NASA Software Safety Standard,

sweref
271
271
are applied to the safety-critical project software.


Div
idtabs-3

3. Guidance

The project can use NASA-STD-8739.8

sweref
278
278
to perform its determination of the software safety criticality. The software safety litmus test in Appendix A.1 of the Standard is applicable to all projects. The software is considered safety critical if it meets any of the three major criteria listed in the appendix. If the project is determined to be safety critical, then the project must adhere to the applicable statements in NASA-STD-8719.13. 
sweref
271
271

As noted in NASA-STD-8719.13,
sweref
271
271
non safety-critical software residing with safety-critical software is a concern because it may fail in a way that it disables or impairs the functioning of the safety-critical software. When methods to separate the code, such as partitioning, can't be used to limit the software defined as safety critical, care must be exercised to assure safety for a block of software (multiple CSCI) where only a portion are safety critical, and or for individual safety critical CSC's within a larger CSCI.

NASA-STD-8719.13

sweref
271
271
requires the software safety criticality to be re-assessed periodically (typically at each major milestone review) by the project's responsible software assurance engineer. This individual evaluates the project software for determination of safety criticality utilizing the Software Safety Litmus Test within NASA-STD-8719.13.
sweref
271
271
This allows the software safety requirements to be refined and applied to the required areas (preventing a possibly costly over-application or a non-compliant and risky under application). It also assures that requirements are met and/or changes to the software are addressed and checked for safety criticality.

The software safety criticality assessment process and the location of the assessment results are documented within the Software Safety Plan (or equivalent). Most projects document the software safety criticality with the software classification. The project's system safety documentation also addresses it.

A best practice is to document the software safety criticality assessment results with the software classification assessment, with local S&MA and the Engineering TA both approving the results.  An example form is provided in NASA-STD-8719.13.

sweref
271
271


Div
idtabs-4

4. Small Projects

No additional guidance is available for small projects. The community of practice is encouraged to submit guidance candidates for this paragraph.


Div
idtabs-5

5. Resources


refstable

toolstable


Div
idtabs-6

6. Lessons Learned

A documented lesson from the NASA Lessons Learned database notes the following: 

Mars Global Surveyor (MGS) Spacecraft Loss of Contact. Lesson Number 1805:  "Contact was lost with the Mars Global Surveyor (MGS) spacecraft in November 2006 during its 4th extended mission. A routine memory load command sent to an incorrect address 5 months earlier corrupted positioning parameters, and their subsequent activation placed MGS in an attitude that fatally overheated a battery and depleted spacecraft power. The report by the independent MGS Operations Review Board listed 10 key recommendations to strengthen operational procedures and processes, correct spacecraft design weaknesses, and assure that economies implemented late in the course of long-lived missions do not impose excessive risks." 

sweref
569
569