Modular Open Systems Approach (MOSA)
A modular open systems approach (MOSA) is the integrated business and technical strategy 10 U.S.C. 4401 requires of major defense acquisition programs: modular designs with interfaces built to widely supported, consensus-based standards so components can be added, removed, or replaced across the life cycle.
The statute applies to MDAPs receiving Milestone A or B approval after January 1, 2019, which must be designed and developed with a MOSA to the maximum extent practicable. 10 U.S.C. 4401 also defines the terms of art, including the modular system interface: a shared boundary defined by physical, logical, and functional characteristics, at which major system components are meant to be severable as technology and threats change.
DoDI 5000.88 carries the requirement into engineering practice. The systems engineering plan must incorporate MOSA, lead systems engineers use consensus-based interface standards unless none is available or suitable, and a program manager who forgoes MOSA owes the decision authority a justification. The FY 2025 NDAA added disclosure requirements for the interface standards a program relies on.
The failure mode is MOSA on paper: an architecture labeled open while the interface technical data stays proprietary. DoDI 5000.88 directs programs to acquire rights to interface data for this reason; without them, every component swap runs through the incumbent.
Regulatory Reference
10 U.S.C. 4401; DoDI 5000.88
RFO Status
MOSA sits in title 10 and DoD engineering policy, which the FAR Overhaul's model deviations do not rewrite; the recent statutory movement came from the FY 2025 NDAA, which added interface-standard disclosure requirements to 10 U.S.C. 4401.
Category
Processes & Methods
How AcqBot Helps
AcqBot reviews a draft SEP and RFP language for what DoDI 5000.88 expects of a MOSA program, including severable major system components, consensus-based interface standards, and rights to interface data, and flags where the data rights ask fails to match the openness claim.
Related glossary entries
Sources Sought Notice
A Sources Sought Notice is a pre-solicitation announcement, typically posted to SAM.gov, asking companies to identify their interest and capability to perform a prospective requirement — primarily used as market research to shape competition and set-aside decisions.
Request for Information (RFI)
A Request for Information (RFI) is a formal market research instrument used to gather industry input on capabilities, approaches, pricing structures, or draft requirements when the government is not yet ready to solicit — responses are voluntary and non-binding.
Lowest Price Technically Acceptable (LPTA)
Lowest Price Technically Acceptable (LPTA) is a source selection process that awards to the lowest-priced offeror whose proposal meets minimum acceptability standards — no credit is given for exceeding requirements, and tradeoffs between price and quality are not permitted.
Best-Value Tradeoff
The best-value tradeoff process permits award to other than the lowest-priced or highest-rated offeror when the source selection authority documents that the superior proposal's benefits are worth its price premium, or that a cheaper proposal's savings outweigh its weaknesses.