A good starting point is NASA Software Engineering Requirements NPR 7150.2B
3.6 Software Assurance and Software IV&V
3.6.1 The project manager shall plan and implement software assurance per NASA-STD-8739.8. [SWE-022]
Note: Software assurance activities occur throughout the life of the project. Some of the actual analyses and activities may be performed by engineering or the project.
3.6.2 For projects reaching Key Decision Point (KDP) A after the effective date of this directive's revision, the program manager shall ensure that software IV&V is performed on the following categories of projects: [SWE-141]
a. Category 1 projects as defined in NPR 7120.5.
b. Category 2 projects as defined in NPR 7120.5 that have Class A or Class B payload risk classification per NPR NPR 7150.2B -- Chapter3
c. Projects specifically selected by the NASA CSMA to have software IV&V.
3.6.3 If software IV&V is performed on a project, the project manager shall ensure that an IV&V Project Execution Plan (IPEP) is developed. [SWE-131]
Note: The scope of IV&V services is determined by the project and the IV&V provider, and is documented in the IPEP. The IPEP is developed by the IV&V provider and serves as the operational document that will be shared with the project receiving IV&V support. In accordance with the responsibilities defined in NPD 7120.4, section 5.J.(5), projects ensure that software providers allow access to software and associated artifacts to enable implementation of IV&V. A template and instructions for an IPEP may be found in the NASA IV&V Management System, accessible at http://www.nasa.gov/centers/ivv/ims/home/index.html
3.7.1 When a project is determined to have safety-critical software, the project manager shall implement the requirements of NASA-STD-8719.13. [SWE-023]
SLS would fall in class A (human-rated).
More on the flight control system for SLS:
The fundamental design paradigms that shaped the development of the architecture are as follows:
1. Rely on simple, proven, flight-tested algorithms and processes. Based on a heritage of more than fifty years of successful NASA flight controls development for large boosters, the use of classical PID control, multi-station rate gyro blending, linear optimal bending filters, and gain scheduling is retained.
2. Enhance algorithm capability when warranted with compact and verifiable methods. The use of optimal reconfigurable linear control allocation has been employed to maximize control authority and enhance fault tolerance, and a novel mechanization of classical load relief has been applied. In addition, robustness enhancement is obtained through the use of a simple model reference adaptive control scheme.
3. Maximize robustness to failures. As a program requirement, tolerance of at least one engine failure at any point in the flight regime with negligible impact to flight control performance is supported by the architecture. Robustness to sensor failures and severe off-nominal conditions has been demonstrated through rigorous simulation analysis.
4. Seamlessly integrate with the SLS program to facilitate flight certification. In support of concise communication of the design margin from the flight controls element, new metrics, such as the flight control Technical Performance Metric (TPM), are used to facilitate straightforward assessment of the design’s merit and the vehicle capability at the system engineering level.
This presentation gives a high-level overview of the development process.