Group-2 unmanned platforms — the category covering systems with maximum takeoff weights between 21 and 55 lbs — represent a large and growing portion of fielded ISR assets. They are also the most SWAP-C-constrained platforms in the DoD inventory. Size, weight, power, and cost limitations are not soft preferences; they are hard physical constraints that determine what fits, what flies, and how long it flies. Adding an edge-AI inference module to a Group-2 payload bay is a systems integration problem first and an AI problem second.
At Kestrelsense, we have worked through this integration on multiple Group-2 platforms in the context of our SBIR program. What follows is a direct account of the constraints we encountered and how the KS-100 was designed to fit within them.
The Weight Budget: Start with the Aircraft's Actual Payload Fraction
A Group-2 aircraft's payload capacity is not the difference between maximum takeoff weight and empty weight. It is the fraction of that difference allocated to mission-specific payload after accounting for fuel, avionics, autopilot electronics, airframe structure, and the weight growth margin that every aircraft carries to accommodate late design changes and qualification weight gains.
In practice, the payload fraction allocated to interchangeable mission modules on Group-2 platforms typically falls between 1.8 and 4.5 kg. Within that allocation, the EO/IR sensor head is usually the largest single weight item — a capable multi-spectral gimbal weighs 600g to 1.4 kg depending on aperture and stabilization capability. The remaining weight budget for compute, comms, and supporting electronics can be as low as 800g on constrained platforms.
The KS-100 module weighs 95 grams including connectors and conformal coating. In the context of an 800g remaining weight budget, that 95g represents approximately 12% of the available margin. It is not a trivial number — any 12% budget item must be justified by proportional mission value — but it is physically accommodable in nearly all Group-2 configurations we have evaluated. The modules that are not accommodable are those that weigh 250g or more: once you add a heat spreader, connector bracket, and cable harness, a component that starts at 200g on the datasheet frequently exceeds 350g in the installed configuration.
The Power Interface: Know What the Aircraft Actually Delivers
Most Group-2 ISR platforms expose payload power through a regulated 28V DC bus per MIL-STD-704 or an unregulated aircraft bus that varies between 20V and 32V depending on battery state and generator load. The KS-100 accepts 5–28V input and includes an onboard DC/DC converter that maintains regulated 5V and 3.3V rails for internal use regardless of bus voltage variation.
What program engineers sometimes discover mid-integration is that the aircraft's payload power controller has current limits that are stricter than the raw bus would suggest. A 28V aircraft bus that could theoretically deliver 30A continuous is often current-limited at the payload bay connector to 1.0A or 1.5A — 28W or 42W respectively — by the power controller's overcurrent protection settings. At 7.8W peak draw, the KS-100 is well within these limits. An edge-AI module drawing 18W peak is not.
The second power interface detail that matters is connector pinout compatibility. The MIL-DTL-38999 Series III connector has become a de facto standard for power and signal in UAV payload bays, but pin assignments vary significantly between platforms. We design the KS-100 with a configurable connector harness that can be adapted to the pin assignment of a specific aircraft without requiring PCB modifications. The harness configuration is documented in the module's Interface Control Document and takes approximately 30 minutes to configure for a new platform type.
The Avionics Bus Interface: MIL-STD-1553 vs. Serial Ethernet
Group-2 platforms fall into two broad avionics architectures: legacy 1553-bus aircraft designed in the 1990s and 2000s, and newer platforms built around Ethernet-based architectures using ARINC-818 or simple UDP/IP for payload data interfaces.
The KS-100 supports both. The 1553 interface operates as a Remote Terminal and can receive task orders (sensor cueing commands, classification threshold adjustments, model profile selection) and transmit target track data over the bus at standard 1553 rates. The Ethernet interface provides higher throughput for track data volume — useful when the target density is high and each track requires a full MISB metadata bundle — and supports firmware update delivery over the avionics network.
In practice, most Group-2 integrations we have executed use the Ethernet interface for track data output and the 1553 interface for C2 commands, mirroring the architecture of the host aircraft's avionics. The two interfaces can operate concurrently; the module arbitrates between them based on a configurable priority policy stored in the module's configuration partition.
Physical Integration: The Payload Bay Geometry Problem
The KS-100 measures 68mm x 40mm x 12mm — approximately the footprint of a standard EO payload control board. This was a deliberate design choice: matching the PCB footprint of common payload controllers means integrators can mount the KS-100 in an existing board slot or stackable carrier without designing a custom mechanical interface.
Real payload bay geometry is messier than CAD models suggest. Cables run in unexpected directions, cooling fins intrude on the available volume, and the connector placement on adjacent boards was designed by someone who did not anticipate a third board in the stack. In our integration experience, the most common physical fit issue is cable routing — specifically, the cable from the KS-100's sensor input connector to the EO/IR gimbal's data output connector. On some platforms, the gimbal's data cable exits from the base of the gimbal housing and must route through the bay before reaching the inference module; on others, it exits from the top and requires a different harness length and routing path.
We maintain a platform-specific integration note for each Group-2 aircraft we have qualified the KS-100 on, documenting cable routing, mounting orientation, and any chassis modifications required. Integrators working with a new platform type should request the relevant integration note before beginning installation — it typically reduces integration time by 4–6 hours compared to working from the Interface Control Document alone.
Payload Swap and Mission Profile Adaptation
One operational advantage of the KS-100's architecture is the ability to swap inference model profiles between sorties without replacing or reflashing the hardware. The module stores up to four independent inference graphs in a secured model partition. A mission planner can select the active model profile via the avionics bus before takeoff — switching, for example, from a vehicle classification profile to a personnel detection profile, or from a standard daylight model to a LWIR-optimized nighttime model.
Model swap takes less than 45 seconds and does not require a module reboot. The aircraft can power up, load the appropriate mission profile, and be ready for launch within the standard pre-flight sequence. For operators running multiple mission types from the same platform with the same payload, this eliminates the need to maintain separate hardware configurations for each mission type — a significant logistics and cost advantage for small unit operations.
Group-2 UAV payload integration is a discipline where the difference between a successful integration and a failed one often comes down to the details that are not in the spec sheet: the power controller's overcurrent threshold, the cable routing geometry in a specific aircraft model, the connector pinout table that conflicts with the avionics ICD. At Kestrelsense, we have worked through these details in the context of real aircraft integrations, and we document them systematically because we know the next integrator will encounter the same issues. That institutional knowledge — not just the module specifications — is part of what we offer to programs evaluating the KS-100.
