A Modular Open Systems Approach (MOSA) for an unmanned aircraft system means designing replaceable hardware and software around defined interfaces, while arranging the documentation, rights, and supplier access needed to change those components over time. The practical goal is to replace a payload, processor, or mission application without redesigning everything connected to it.
The federal MOSA overview treats this as both an engineering and a business strategy. For a UAS team, a useful starting question is specific: can another qualified supplier replace the intended module using the delivered interface information, and can the resulting aircraft system still meet its requirements?
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- Choose the UAS boundary that needs to change
- Specify more than the connector
- Use standards for their actual scope
- Follow a payload command through the system
- Find the failure hidden behind a successful connection
- Balance replaceability against aircraft constraints
- Connect the architecture to real upgrade work
- Define the replacement demonstration
Choose the UAS boundary that needs to change
Scope the architecture across the aircraft, control station, communications, and support elements needed for the intended operation. A removable aircraft payload is one possible module; a ground-station application or onboard processing service can be another.
Start with an intended change. Examples include replacing an obsolete mission computer, fitting a different inspection camera, or updating image-processing software independently of flight-control software. Select a boundary that makes that change manageable, then identify everything crossing it.
The Army's MOSA explanation emphasizes program-specific modularity and openness decisions. There is no universal MOSA box or single standard. A useful claim of conformance must identify what was evaluated and the criteria used.
In architecture terms, a module should contain closely related functions and depend on neighboring modules through controlled interfaces. For an illustrative inspection UAS, one design might place image processing in a mission computer and route permitted requests through a defined flight-controller interface. That boundary needs to specify the authority of those requests, not merely their message format.
The broader guide to open architecture in unmanned systems explains the underlying distinctions. Here, the additional MOSA question is whether the proposed UAS component can actually be competed, integrated, maintained, and replaced.
Specify more than the connector
An interface control document (ICD) records the agreement between connected components. The 2025 MOSA implementation guidebook calls for physical, message-structure, meaning, behavioral, and timing parameters at module boundaries.
For the inspection-camera example, turn those categories into questions a replacement supplier can answer:
| Interface concern | What the UAS team should define | Replacement question |
|---|---|---|
| Mechanical and electrical | Mounting, permitted mass, power demand, startup behavior, cooling | Can this payload operate within the aircraft's allocated resources? |
| Data meaning | Image format, coordinate frame, units, timestamps, calibration identity | Does the receiver interpret the observation correctly? |
| Timing and loading | Required update behavior, permitted delay, competing traffic | Is the observation still useful when processing is busy? |
| Control and recovery | Command ownership, response meaning, restart and disconnect behavior | Who controls the payload after an interruption? |
These are proposed engineering questions, informed by the guidebook and the MAVLink examples below. They are not a universal UAS interface profile.
A camera can send readable images while supplying unusable orientation or capture-time information. When imagery feeds a navigation or perception function, review the related sensor-fusion timing and calibration requirements. Successful transport is only one part of a usable observation.
Use standards for their actual scope
MOSA is the approach; individual standards define particular interfaces. Record the chosen edition, profile, options, and extensions. A list of standard names does not identify the exact combination a replacement must implement.
Hardware Open Systems Technologies (HOST) illustrates the scope distinction. NAVAIR's HOST FAQ describes its focus on hardware modules, including electronic and mechanical interfaces and minimum performance requirements. The supplier's implementation remains its intellectual property.
That is useful for a rugged mission-computer boundary, but it does not by itself specify every mission message or aircraft behavior. NAVAIR explicitly distinguishes HOST's hardware scope from standards addressing software and communications architectures. Choose complementary interfaces where the system needs them.
Likewise, a documented protocol can help define a payload interface without establishing that an entire aircraft follows a particular program's MOSA. Ask for the component's actual interface specification and test scope. Separate three questions: does it implement the specified interface, does it work with the intended neighboring components, and does the integrated UAS meet its operational requirements?
Follow a payload command through the system
The MAVLink Gimbal Protocol v2 provides a concrete example of an interface with defined roles. A gimbal manager handles higher-level control, while the gimbal device receives the associated manager's lower-level messages. Applications request control through the manager rather than independently steering the device.
The protocol defines primary and secondary controlling components and identifies which gimbal is being addressed. In an inspection scenario, a mission application and an operator station might both want camera control. The integration must implement the intended transfer of authority between them.
Follow the whole chain: the operator requests a view, the manager interprets the request, the device moves, and status returns. Confirm which software hosts the manager and how messages reach it. Record the device's supported capabilities as well: discovering a manager does not establish that it supports every requested camera function.
Response semantics matter too. The MAVLink command protocol distinguishes command acceptance from completion. An accepted response means the command is valid and the flight stack will attempt it; it does not establish that the requested action has finished.
For a replacement test, therefore, record both the command response and the resulting status or observation. A positive acknowledgment alone cannot demonstrate that the camera reached the requested attitude. This is an illustration of interface testing, not a claim that every UAS uses MAVLink or that protocol support establishes MOSA conformance.
Find the failure hidden behind a successful connection
Use the following proposed checks to separate failures that can otherwise appear as a generic payload problem. They apply the ICD categories and MAVLink role and response distinctions discussed above.
| Observed symptom | Possible mismatch | Controlled check |
|---|---|---|
| Payload starts, then resets during use | Power or thermal assumptions differ | Exercise the intended operating load while recording supply and temperature behavior. |
| Images arrive, but pointing or geolocation is wrong | Frame, calibration, or timestamp disagreement | Use a known scene and compare the associated metadata at both endpoints. |
| Command is accepted, but the requested action is absent | Acceptance was treated as completion | Inspect the subsequent device state and failure response. |
| Manual pointing conflicts with an automated task | Control ownership is unclear | Transfer control between the operator and mission application and observe manager status. |
| Replacement works until software is updated | Interface edition or extension has changed | Repeat the exchange against the recorded supported versions. |
Run fault cases in an appropriate bench or simulation environment before flight. Test payload restart separately from loss of the ground link; the two events need not have the same response. Define expected recovery, including whether control must be explicitly reacquired, and distinguish mission degradation from failures requiring an aircraft protective response.
For a change that affects flight-related functions, review the associated UAS design assurance and continued-safety work. An interface test does not answer every aircraft-safety question.
Balance replaceability against aircraft constraints
The federal guidebook warns that increasing modularity can carry price or technical-performance costs. More separable components are not automatically a better design.
For a small UAS, compare the proposed module boundary against its mass, power, cooling, and timing allocations. A separate processor may make an application easier to replace, but it also needs accommodation in the aircraft. For a larger platform, reserving resources for later payloads may be more practical. Treat these as design choices to evaluate, rather than universal prescriptions.
The lifecycle case also needs evidence. In its 2025 MOSA acquisition review, GAO found that none of the 20 selected programs supplied documentation of a cost-benefit analysis supporting whether, and how extensively, to adopt MOSA. Its sample covered several weapon-system categories; it was not a UAS savings study.
Compare the initial interface-development and integration effort with specific future changes. Include replacement engineering, regression testing, documentation maintenance, and supplier support. A savings percentage without a stated baseline and change scenario does little to inform that choice.
Connect the architecture to real upgrade work
An October 2024 Army account of future UAS acquisition describes using separate contractual relationships with aircraft manufacturers and technology suppliers. It also describes FTUAS MOSA use cases covering operations, training, maintenance, spares, and hardware and software changes.
That dated account illustrates how supplier access and architecture can support the same objective. It does not establish present program status, universal interchangeability, or achieved savings.
Representative UAS applications include exchanging an inspection payload, refreshing onboard computing, updating a mission application, and maintaining common ground-control functions. For each, name the component to be changed and the delivered information another supplier would need. An aircraft with removable boxes can remain difficult to sustain if essential interface details or integration tools are unavailable.
Keep responsibility explicit: who maintains the interface baseline, authorizes changes to it, resolves incompatibilities, and supports the system after the original component is replaced? The MOSA overview's business dimension belongs alongside the technical design from the beginning.
Turn a demonstration into reusable evidence
Keep a replacement demonstration useful after the demonstration team leaves. The following proposed acceptance record extends the interface-documentation and verification approach in the federal guidebook. For each tested exchange, record the initiating component, receiving component, interface edition, starting configuration, expected response, observed response, and evidence location. Include the configuration of neighboring modules that remained unchanged. This makes it possible to distinguish a reproducible interface result from a successful integration that depended on an undocumented setting.
For the camera-control example, separate three records: a request reached the intended manager, the manager accepted or rejected it, and the device reported the resulting state. The MAVLink command documentation supports that distinction between acceptance and completion. As a proposed test procedure, repeat the exchange after the relevant restart or control transfer defined in the ICD. Record an absent response as an observation to investigate, rather than inferring that the camera completed the action because no error appeared at the operator station.
Also record what the replacement supplier needed from the original supplier. A phone call explaining an undocumented field, a private configuration utility, or a corrected interface file may be necessary during integration. Documenting that assistance is useful evidence about the delivered interface package; it is not proof that the replacement was impossible or that a supplier acted improperly. Resolve whether the missing information belongs in the maintained baseline before treating the same replacement as repeatable.
Finally, give each discrepancy an owner and a disposition. Distinguish a corrected implementation defect from a changed requirement or an accepted operating limitation. Retain the failed observation alongside the successful retest. This proposed recordkeeping approach supports the article's bounded replacement question: another team should be able to see exactly which configuration was demonstrated, which conditions were exercised, and which conclusions remain outside the test scope.
Define the replacement demonstration
Before accepting a broad MOSA claim, ask the supplier to demonstrate a bounded change against a recorded baseline:
- Identify the module, its interfaces, and the functions expected to remain unchanged.
- Supply the applicable documentation, permitted use rights, versions, and necessary integration tools.
- Integrate the replacement using those delivered materials and record any undocumented assistance.
- Exercise normal operation, resource loading, interruption, restart, and control transfer where relevant.
- Record the affected regression and safety work, remaining limitations, and configuration to be supported.
This proposed demonstration turns a general architecture promise into a concrete engineering question. The useful result is a documented account of what changed, what remained compatible, and what work the replacement still required.
Sources
- Federal MOSA overview: government explanation of modular design, verified interfaces, and the accompanying business strategy.
- Army: Demystifying MOSA: program-specific modularity, openness, and conformance criteria.
- MOSA Implementation Guidebook, February 2025: government engineering guidance on interface documentation, verification, and modularity tradeoffs.
- NAVAIR HOST FAQ: hardware-interface scope and supplier intellectual property.
- MAVLink Gimbal Protocol v2: manager/device roles and control ownership.
- MAVLink command protocol: acknowledgment and completion semantics.
- GAO-25-106931: independent government audit of MOSA investment planning across selected acquisition programs.
- Army future UAS account, October 2024: historical FTUAS contracting and upgrade use cases.
Last checked: September 10, 2026.
