An Ility Calculation for Satellite Software Validation

Systems engineering uses quality attributes known as “ilities” to validate a target architecture. Space agencies call for software development methodologies (SDM) to be unified, customized, and updated. Affiliated primes have documented conflicting ilities across multiple standards. Ilities can be used to derive and verify selected mission constraints. Satellites have been prone to software failures since manual validation in the 1960s. Software verification techniques have evolved past static validation. In 2015 NASA independent verification and validation (IV & V) department found that a common practice for small satellites is the late acceptance of risk due to failed validation, creating orbital debris. In 2016, the NASA Software Architecture Review Board (SARB) justified developing a quality attribute tool. The SARB table aimed to quantify desired ilities of systems. The SARB proposed quantifying the desired ilities of systems, prioritizing reliability, scalability, and adaptability, and called for further research to identify inputs for these calculations. Identified desired ilities inputs improve functional design. A systematic qualitative review collated previous ility classification articles. Current literature presents guidelines, tables, and the conflicting definition of ilities but rarely moves past high-level definitions, and inputs are uncollated. The article applied grounded theory to develop a collection of 345 ilities as a unified taxonomy based on prior classification literature and operational standards. The taxonomy used ten leading civilian space agencies and five public companies with launch and satellite capabilities to identify active ilities. A taxonomy visualizes desired ilities and the definition of such ilities. Standards from leading civilian space agencies and prime space companies are listed. Researchers applied quantitative text analysis to the taxonomy to compare literature and agency ilities. Early ility decisions influence the validation of software. It is critical to realize inputs at the beginning of the private space race. Designing for ilities is a solution for optimizing cost, time, effort, and risk across smallsat design. Reliability, scalability, and adaptability are within the top 10% of 161 unique ility classes. In total, the classes contain 668 total ilities. Ilities are split between small satellite systems and smallsat software architecture-an aggregate review identified inputs for the desired ilities. A conceptual schema is presented for each ility to show inputs for the development of future calculations.