1. Requirements

3.4.6 The project shall verify, validate, and accredit software models, simulations, and analysis tools required to perform qualification of flight software or flight equipment.

1.1 Notes

Center processes address issues such as numerical accuracy, uncertainty analysis, and sensitivity analysis, as well as verification and validation for software implementations of models and simulations. Information regarding specific verification and validation techniques and the analysis of models and simulations can be found in the NASA standard NASA-STD-7009.

1.2 Applicability Across Classes

This requirement applies when software models, simulations, and analysis tools are used to perform qualification of flight software or flight equipment for Classes C through E and Safety Critical, Class C Not Safety Critical, and Class D Not Safety Critical.

Class G is labeled with "P (Center)." This means that an approved Center-defined process which meets a non-empty subset of the full requirement can be used to achieve this requirement.

2. Rationale

Performing verification and validation (V&V) to accredit software models, simulations, and analysis tools is important to ensure the credibility of the results produced by those tools. Critical decisions may be made, at least in part, based upon the results produced by models, simulations, and analysis tools. Reducing the risk associated with these decisions is one reason to use accredited tools that have been properly verified and validated.

3. Guidance

The processes of V&V are key activities for accrediting all types of models and simulations. With the goal of providing a basis to determine if the models, simulations, and analysis tools are acceptable for use for a specific purpose, there are three pieces of information to capture and address from the modeling and simulation (M&S) characterizations as part of this process:

Information for the V&V of models, simulations and tools used to develop software code can be found in NASA-STD-7009, Standard for Models and Simulations, ²⁷²  and in NPR 7150.2. Center requirements and associated processes flowed down from these two documents address numerical accuracy, uncertainty analysis, sensitivity analysis and V&V of models and simulations.

The use of NASA-STD-7009 in fulfilling the requirements of NPR 7150.2 is described in Topic 7.15 - Relationship Between NPR 7150.2 and NASA-STD-7009. The Topic also provides a list of additional resources for V&V of models and simulations used in the software development life cycle.

Per section 4.4 of NASA-STD-7009, ²⁷² the following basic activities are to be performed for verification of models and simulations:

• Document verification techniques and the conditions under which the verification was conducted.
• Document any numerical error estimates for the results of the computational model.
• Document the verification status.

Per section 4.4 of NASA-STD-7009, ²⁷²  the following basic activities are to be performed for validation of models and simulations:

• Document techniques used to validate the models and simulations for their intended use.
• Document the conditions under which the validation was conducted.
• Document any validation metrics and any validation data sets used.
• Document any studies conducted.
• Document validation results.

To better understand the uncertainties affecting the results of the models and simulations, follow the required steps in section 4.4 of NASA-STD-7009 and the steps for assessing and reporting the credibility of model and simulation results found in sections 4.7 and 4.8 of NASA-STD-7009. ²⁷²

4. Small Projects

Small projects may choose to lighten their V&V (Verification and Validation) and accreditation requirements through the use of software models, simulations, and analysis tools verified, validated, and accredited by other NASA projects that used these tools in a similar manner and purpose as the small project. To determine the relevance and usefulness of this option, small projects need to be aware of differences between the projects and the prior project's V&V and accreditation activities as well as the versions of the models, simulations, and analysis tools on which the V&V and accreditation activities were performed.

5. Resources

6. Lessons Learned

Topic 7.15 - Relationship Between NPR 7150.2 and NASA-STD-7009 ²⁷² includes lessons learned for the verification and validation of models and simulations.