What is MOSA?
A Modular Open Systems Approach (MOSA) is not itself a technical standard. Rather, MOSA is an acquisition and design strategy that prioritizes the use of open standards-based technology for, as the Defense Standardization Program states, "designing an affordable and adaptable system."
A mandate for all new defense acquisition programs to be designed and developed using MOSA was actually codified into law (Title 10 U.S.C. 2446a.(b), Sec 805); however, the major push toward MOSA took place in 2019 when the U.S. DoD issued a memorandum with the subject "Modular Open Systems Approaches for our Weapon Systems is a Warfighting Imperative." The memo states that the Secretaries of the Air Force, Army, and Navy have reviewed the open standards that have been developed, demonstrated, and validated in their respective branches for the past several years. Deeming the continued use of such open standards "vital to our success," the memo mandates that MOSA supporting standards should be included in requirements for all weapons systems going forward.