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Introduction

NASA has two significant independent classification schemas for software: (1) a software engineering classification as described in NPR 7150.2, NASA Software Engineering Requirements, Appendix E, and (2) a software safety definition as described in NASA-STD-8739.8, Software Assurance Standard, Appendix A. 7.2 - Classification and Safety-Critical Assessment describes the relationship between these classifications. For a given system or subsystem, software is expected to be uniquely defined within a single classification pair (software engineering classification X software safety definition). Knowing this pair determines the minimal set of software requirements from NPR 7150.2 needing to be addressed (via Appendix D of NPR 7150.2) by the project's software team.

The tools found here are aides to those responsible for determining both the software classification and the software safety criticality.

1.1 Safety Criticality

Defining software safety criticality involves the determination of whether the software is performing a safety-critical function, including verification of a safety-critical software, hardware, or operations component, subsystem, or system.

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1.2 Classification Diagrams and Descriptions

Software classification is the determination of NPR 7150.2 requirement applicability for a specific system or sub-system. As stated in NPR 7150.2: "These definitions are based on 1) usage of the software with or within a NASA system, 2) criticality of the system to NASA's major programs and projects, 3) extent to which humans depend upon the system, 4) developmental and operational complexity, and 5) extent of the Agency's investment."

The software classification tool is a question-and-answer-based guide that has been built to help identify the most likely software classification, based on the answers that one provides to each question. This tool is only an additional resource to help determine a system's or sub-system's classification and is not meant to be an authority regarding software classifications. As stated in Appendix E of NPR 7150.2: "Any potential discrepancies in classifying software within Classes A - E are to be resolved using the definitions and the five underlying factors listed in the previous paragraph. Engineering and Safety and Mission Assurance provide dual Technical Authority chains for resolving classification issues, and the NASA Headquarters' Chief Engineer is the ultimate Technical Authority for software classification disputes..."

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Classification Descriptions

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Human Space Flight Software Systems*:
(ground and flight) developed and/or operated by or for NASA that are needed to perform a primary mission objective of human space flight and directly interact with human space flight systems. Limited to software required to perform "vehicle, crew, or primary mission function," as defined by software that is:

1. Required to operate the vehicle or space asset (e.g., spacesuit, rover, or outpost), including commanding of the vehicle or asset, or
2. required to sustain a safe, habitable ¹ environment for the crew, or
3. required to achieve the primary mission objectives, or
4. directly prepares resources (e.g., data, fuel, power) that are consumed by the above functions.

* - Includes software involving launch, onorbit, in space, surface operations, and entry, descent, and landing.

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Examples of Class A software (human rated space flight) include but are not limited to: 

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Exclusions

Class A does not include:

1. Software which happens to fly in space but is superfluous to mission objectives (e.g., software contained in an iPod carried on board by an astronaut for personal use), or
2. software that exclusively supports aeronautics, Research and Technology, and science conducted without spaceflight applications, or
3. systems (e.g., simulators, emulators, stimulators, facilities) used to test Class A systems containing software in a development environment.

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Space Systems*: Flight and ground software that must perform reliably to accomplish primary mission objectives, or major function(s) in Non-Human Space Rated Systems. Limited to software that is:

1. Required to operate the vehicle or space asset (e.g., orbiter, lander, probe, flyby spacecraft, rover, launch vehicle, or primary instrument), such as commanding of the vehicle or asset, or
2. required to achieve the primary mission objectives, or
3. directly prepares resources (data, fuel, power, etc.) that are consumed by the above functions.

Airborne Vehicles: Large-scale¹ aeronautic vehicles that are NASA unique in which the software:

1. Is integral to the control of an airborne vehicle, or 
2. monitors and controls the cabin environment, or 
3. monitors and controls the vehicle's emergency systems. 

This definition includes software for vehicles classified as "test," "experimental," or "demonstration" which meets the above definition for Class B software. Also included are systems in a test or demonstration where the software's known and scheduled intended use is to be part of a Class A or B software system.

* - Includes software involving launch, onorbit, in space, surface operations, and entry, descent, and landing.

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Examples of Class B software [include] but are not limited to:

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Exclusions

Class B does not include:

1. Software that exclusively supports non-primary instruments on Non-Human Space Rated Systems (e.g., low cost, non-primary university supplied instruments) or
2. systems (e.g., simulators emulators, stimulators, facilities) used in testing Class B systems containing software in a development environment.

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Space Systems:

1. Flight or ground software that is necessary for the science return from a single (non-primary) instrument, or 
2. flight or ground software that is used to analyze or process mission data, or 
3. other software for which a defect could adversely impact attainment of some secondary mission objectives or cause operational problems, or 
4. software used for the testing of space assets, or 
5. software used to verify system requirements of space assets by analysis, or 
6. software for space flight operations, that is not covered by Class A or B. 

Airborne Vehicles: Systems for non-large scale aeronautic vehicles in which the software:

1. is integral to the control of an airborne vehicle, or 
2. monitors and controls the cabin environment, or 
3. monitors and controls the vehicle's emergency system. 

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Examples of Class C software include but are not limited to:

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Exclusions

Systems unique to a research, development, test, or evaluation activity in a Major Engineering/Research Facility or Airborne Vehicle where the system is not part of the facility or vehicle and does not impact the operation of the facility or vehicle.

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3. Classification Tool Flowcharts

The following diagrams describe the operation of the classification tool. If you follow the chart below, or print off the diagrams, you can use the mechanics of the tool off-line. To download a PDF of these diagrams, which are appropriate for printing, click here.

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4. Resources