This version of SWEHB is associated with NPR 7150.2B. Click for the latest version of the SWEHB based on NPR7150.2D

SWE-070 - Models, Simulations, Tools

1. Requirements

4.5.7 The project manager  shall use validated and accredited software models, simulations, and analysis tools required to perform qualification of flight software or flight equipment.

1.1 Notes

Information regarding specific verification and validation techniques and the analysis of models and simulations can be found in NASA-STD-7009 272 and NASA-HDBK-7009.

1.2 Applicability Across Classes























Key:    - Applicable | - Not Applicable
A & B = Always Safety-Critical; C & D = Not Safety-Critical; CSC & DSC = Safety-Critical; E - H = Never Safety-Critical.

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:

  1. The question(s) to be answered and the particular aspects of the problem that the M&S will be used to help address.
  2. The decisions that will be made based on the M&S results.
  3. The consequences resulting from erroneous M&S outputs. 175

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 Verification and Validation (V&V) 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

5.1 Tools

Tools to aid in compliance with this SWE, if any, may be found in the Tools Library in the NASA Engineering Network (NEN).

NASA users find this in the Tools Library in the Software Processes Across NASA (SPAN) site of the Software Engineering Community in NEN.

The list is informational only and does not represent an “approved tool list”, nor does it represent an endorsement of any particular tool. The purpose is to provide examples of tools being used across the Agency and to help projects and centers decide what tools to consider.

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.

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