diff --git a/.ci/gazebo.Dockerfile b/.ci/gazebo.Dockerfile
index 2457d2c..1798541 100644
--- a/.ci/gazebo.Dockerfile
+++ b/.ci/gazebo.Dockerfile
@@ -1,12 +1,93 @@
-# .ci/gazebo.Dockerfile — SAKURA-II Gazebo Harmonic headless SITL image.
+# .ci/gazebo.Dockerfile — SAKURA-II Gazebo Harmonic SITL image (GUI-capable).
 #
-# Builds from ubuntu:22.04 + OSRF apt repository because
-# ghcr.io/gazebosim/gz-sim:harmonic requires authentication.
-# Runs gz sim in headless server mode (-s flag); no display required.
-# Simulation world SDF and plugins are mounted read-only from ./simulation.
+# Two-stage build:
+#   Stage 1 (builder): installs Gazebo dev headers, compiles all 4 system
+#     plugins into shared libraries.
+#   Stage 2 (runtime): installs Gazebo runtime + X11/Mesa GUI packages, copies
+#     .so files from builder.  Final image is ~400 MB smaller than single-stage.
+#
+# GUI support: the runtime stage includes Mesa llvmpipe (software renderer) and
+# X11 client libraries so gz sim can open a window when $DISPLAY is forwarded
+# from the host via /tmp/.X11-unix (see compose.yaml gazebo service).
+# LIBGL_ALWAYS_SOFTWARE=1 forces Mesa llvmpipe; no GPU passthrough required.
+#
+# Plugin discovery: GZ_SIM_SYSTEM_PLUGIN_PATH=/usr/local/lib (Harmonic API).
+# World file discovery: GZ_SIM_RESOURCE_PATH=/app/simulation/worlds.
 # No HPSC cross-toolchain (Q-H8 deferred to Phase C+).
 # No secrets embedded.
 
+# ── Stage 1: builder ──────────────────────────────────────────────────────────
+FROM ubuntu:22.04 AS builder
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get update -q && \
+    apt-get install -y --no-install-recommends \
+        curl \
+        gnupg \
+        lsb-release \
+        ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+# Add OSRF Gazebo Harmonic apt repository.
+RUN curl -fsSL https://packages.osrfoundation.org/gazebo.gpg \
+        -o /usr/share/keyrings/pkgs-osrf-archive-keyring.gpg && \
+    echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/pkgs-osrf-archive-keyring.gpg] http://packages.osrfoundation.org/gazebo/ubuntu-stable $(lsb_release -cs) main" \
+        > /etc/apt/sources.list.d/gazebo-stable.list && \
+    apt-get update -q && \
+    apt-get install -y --no-install-recommends \
+        gz-harmonic \
+        libgz-sim8-dev \
+        libgz-transport13-dev \
+        libgz-plugin2-dev \
+        libgz-math7-dev \
+        cmake \
+        g++ \
+        make \
+        ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy plugin source trees into the builder.
+COPY simulation/gazebo_rover_plugin   /src/gazebo_rover_plugin
+COPY simulation/gazebo_uav_plugin     /src/gazebo_uav_plugin
+COPY simulation/gazebo_cryobot_plugin /src/gazebo_cryobot_plugin
+COPY simulation/gazebo_world_plugin   /src/gazebo_world_plugin
+
+# Build and install each plugin.  Unit-test targets (uav_plugin_test, etc.)
+# have no Gazebo dependency and are skipped here (BUILD_TESTING=OFF).
+RUN cmake -B /build/rover \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX=/usr/local \
+        -DBUILD_TESTING=OFF \
+        /src/gazebo_rover_plugin && \
+    cmake --build /build/rover && \
+    cmake --install /build/rover
+
+RUN cmake -B /build/uav \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX=/usr/local \
+        -DBUILD_TESTING=OFF \
+        /src/gazebo_uav_plugin && \
+    cmake --build /build/uav && \
+    cmake --install /build/uav
+
+RUN cmake -B /build/cryobot \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX=/usr/local \
+        -DBUILD_TESTING=OFF \
+        /src/gazebo_cryobot_plugin && \
+    cmake --build /build/cryobot && \
+    cmake --install /build/cryobot
+
+RUN cmake -B /build/world \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX=/usr/local \
+        -DBUILD_TESTING=OFF \
+        /src/gazebo_world_plugin && \
+    cmake --build /build/world && \
+    cmake --install /build/world
+
+# ── Stage 2: runtime ─────────────────────────────────────────────────────────
 FROM ubuntu:22.04
 
 ENV DEBIAN_FRONTEND=noninteractive
@@ -20,10 +101,7 @@ RUN apt-get update -q && \
         procps \
     && rm -rf /var/lib/apt/lists/*
 
-# Add OSRF Gazebo Harmonic apt repository.
-# NOTE: the echo must be a single line — a multi-line echo with indented
-# continuation puts leading spaces into the URI, which APT silently ignores,
-# making gz-harmonic unlocalizable.
+# Add OSRF Gazebo Harmonic apt repository (runtime packages only).
 RUN curl -fsSL https://packages.osrfoundation.org/gazebo.gpg \
         -o /usr/share/keyrings/pkgs-osrf-archive-keyring.gpg && \
     echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/pkgs-osrf-archive-keyring.gpg] http://packages.osrfoundation.org/gazebo/ubuntu-stable $(lsb_release -cs) main" \
@@ -31,11 +109,32 @@ RUN curl -fsSL https://packages.osrfoundation.org/gazebo.gpg \
     apt-get update -q && \
     apt-get install -y --no-install-recommends \
         gz-harmonic \
+        # Mesa llvmpipe software renderer — GPU-free OpenGL for Docker containers.
+        libgl1-mesa-dri \
+        libgl1 \
+        libegl1 \
+        libglu1-mesa \
+        # X11 client libraries for forwarding the GUI window to the host display.
+        libx11-6 \
+        libx11-xcb1 \
+        libxrender1 \
+        libxext6 \
+        libxcb1 \
     && rm -rf /var/lib/apt/lists/*
 
+# Copy compiled plugin .so files from the builder stage.
+COPY --from=builder /usr/local/lib/librover_drive_plugin.so       /usr/local/lib/
+COPY --from=builder /usr/local/lib/libuav_flight_plugin.so        /usr/local/lib/
+COPY --from=builder /usr/local/lib/libcryobot_physics_plugin.so   /usr/local/lib/
+COPY --from=builder /usr/local/lib/libworld_environment_plugin.so /usr/local/lib/
+
+RUN ldconfig
+
 RUN mkdir -p /app/simulation
 
-# Plugin and world file discovery path for gz sim.
+# GZ_SIM_RESOURCE_PATH: world .sdf and mesh files mounted from ./simulation
+# GZ_SIM_SYSTEM_PLUGIN_PATH: where gz-sim scans for compiled system plugins
 ENV GZ_SIM_RESOURCE_PATH=/app/simulation/worlds
+ENV GZ_SIM_SYSTEM_PLUGIN_PATH=/usr/local/lib
 
 WORKDIR /app
diff --git a/.ci/ros2.Dockerfile b/.ci/ros2.Dockerfile
index 73c2885..60a4521 100644
--- a/.ci/ros2.Dockerfile
+++ b/.ci/ros2.Dockerfile
@@ -7,6 +7,20 @@ FROM osrf/space-ros:latest
 # log/ and install/ outputs there without a permission error.
 USER root
 RUN mkdir -p /workspace && chown spaceros-user:spaceros-user /workspace
+
+# Install ros_gz_bridge and ros_gz_sim for Gazebo Harmonic ↔ ROS 2 topic bridging.
+# The || true allows the build to proceed if the Space ROS apt overlay does not
+# carry these packages — the colcon build in compose.yaml then builds them from
+# source via the ros_gz_src clone below.
+RUN apt-get update -q && \
+    apt-get install -y --no-install-recommends \
+        ros-${ROS_DISTRO}-ros-gz-bridge \
+        ros-${ROS_DISTRO}-ros-gz-sim \
+    && rm -rf /var/lib/apt/lists/* \
+    || (rm -rf /var/lib/apt/lists/* && \
+        git clone --depth 1 -b harmonic \
+            https://github.com/gazebosim/ros_gz /workspace/ros_gz_src || true)
+
 USER spaceros-user
 
 WORKDIR /workspace
diff --git a/CMakeLists.txt b/CMakeLists.txt
index d93b789..fe80f3c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -54,6 +54,7 @@ add_subdirectory(apps/orbiter_payload)
 add_subdirectory(apps/mcu_payload_gw)
 add_subdirectory(apps/mcu_rwa_gw)
 add_subdirectory(apps/mcu_eps_gw)
+add_subdirectory(apps/sim_adapter)
 
 # ── Simulation Plugins ────────────────────────────────────────────────────────
 # Gazebo plugins require Gazebo to be installed. Each subdirectory guards
diff --git a/Makefile b/Makefile
index 52ace80..f83a4c4 100644
--- a/Makefile
+++ b/Makefile
@@ -6,16 +6,31 @@
 #   make stop   stop and remove containers (named volumes are preserved)
 #   make logs   stream combined logs from all running services (Ctrl-C to exit)
 #   make clean  stop containers AND remove named volumes (destructive)
+#
+# Gazebo GUI: on a desktop with X11, the Gazebo 3D window opens automatically.
+#   On a headless server (no DISPLAY), Gazebo runs server-only (no window).
+#   Requires x11-xserver-utils (xhost) on the host: apt install x11-xserver-utils
 
 .PHONY: run stop logs clean
 
 run:
+	@if [ -n "$$DISPLAY" ]; then \
+		echo "X11 display detected ($$DISPLAY) — granting Docker X11 access..."; \
+		xhost +local:docker 2>/dev/null || echo "  (xhost not found — install x11-xserver-utils if the Gazebo window does not appear)"; \
+	else \
+		echo "No DISPLAY set — Gazebo will run headless (server-only)."; \
+	fi
 	docker compose up --build -d
 	@echo ""
 	@echo "Stack is starting. Current service status:"
 	@docker compose ps
 	@echo ""
-	@echo "  Ground station UI  →  http://localhost:8080/api/time"
+	@if [ -n "$$DISPLAY" ]; then \
+		echo "  Gazebo 3D view     →  opens automatically (X11 forwarded)"; \
+	else \
+		echo "  Gazebo             →  headless (no DISPLAY set)"; \
+	fi
+	@echo "  Ground station API →  http://localhost:8080/api/time"
 	@echo "  UDP telemetry in   →  localhost:10000"
 	@echo ""
 	@echo "  make logs   — stream all service logs"
diff --git a/_defs/mids.h b/_defs/mids.h
index fc12f00..cf228be 100644
--- a/_defs/mids.h
+++ b/_defs/mids.h
@@ -51,6 +51,10 @@
 /* ── Sim injection block anchor (sideband only; never flight-path) ──────────── */
 #define SIM_INJECT_HK_MID        0x0D00U   /* 0x0800 | 0x500 */
 
+/* ── sim_adapter MIDs (SITL only; CFS_FLIGHT_BUILD excluded) ────────────────── */
+#define SIM_ADAPTER_CMD_MID      0x1D00U   /* 0x1800 | 0x500 */
+#define SIM_ADAPTER_HK_MID       0x0D01U   /* 0x0800 | 0x501 */
+
 /* ── Fault-injection SPP APIDs (sideband only; ICD-sim-fsw.md §2) ───────────
  * These are raw APID values (not cFE MIDs) used by simulation/fault_injector.
  * They are never placed on the cFE Software Bus (CFS_FLIGHT_BUILD guard
diff --git a/_defs/targets.cmake b/_defs/targets.cmake
index c154546..a6c0e0b 100644
--- a/_defs/targets.cmake
+++ b/_defs/targets.cmake
@@ -27,6 +27,7 @@ set(MISSION_APPS
     mcu_payload_gw
     mcu_rwa_gw
     mcu_eps_gw
+    sim_adapter
 )
 
 message(STATUS "Mission: ${MISSION_NAME}  SCID: ${SPACECRAFT_ID}  Apps: ${MISSION_APPS}")
diff --git a/apps/sim_adapter/CMakeLists.txt b/apps/sim_adapter/CMakeLists.txt
new file mode 100644
index 0000000..3b98360
--- /dev/null
+++ b/apps/sim_adapter/CMakeLists.txt
@@ -0,0 +1,11 @@
+# apps/sim_adapter/CMakeLists.txt
+#
+# Build contract provided by sakura_add_cfs_app() (see _defs/cfs_app_template.cmake):
+#   sim_adapter              OBJECT library (FSW source)
+#   sim_adapter_test         CMocka unit-test executable
+#   sim_adapter_unit_tests   CTest entry
+#   sim_adapter_cppcheck     cppcheck development target
+#
+# CFS_FLIGHT_BUILD guard: the entire sim_adapter implementation is excluded from
+# flight builds by #ifndef CFS_FLIGHT_BUILD in sim_adapter.c / sim_adapter.h.
+sakura_add_cfs_app(sim_adapter)
diff --git a/apps/sim_adapter/fsw/src/cfe.h b/apps/sim_adapter/fsw/src/cfe.h
new file mode 100644
index 0000000..7426441
--- /dev/null
+++ b/apps/sim_adapter/fsw/src/cfe.h
@@ -0,0 +1,102 @@
+#ifndef CFE_H
+#define CFE_H
+
+/*
+ * cfe.h — Minimal cFE / OSAL type and constant stubs for sim_adapter standalone builds.
+ *
+ * Extends orbiter_comm's stub pattern with:
+ *   - CFE_EVS_BinFilter_t (event filter struct for EVS_Register)
+ *   - CFE_MSG_SetMsgId / CFE_MSG_SetSize (message header setters)
+ *   - OS_SocketBind / OS_SocketRecvFrom (OSAL receive-side socket API)
+ *   - OS_ERR_TIMEOUT constant
+ *
+ * MISRA C:2012 Rule 20.5 deviation: conditionally compiled; superseded by the
+ * real cfe.h when cFS is present on the include path ahead of this stub.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdarg.h>
+
+/* ── Primitive typedefs (mirror cFE common_types.h) ─────────────────────── */
+typedef int32_t  int32;
+typedef uint16_t uint16;
+typedef uint32_t uint32;
+typedef uint8_t  uint8;
+
+/* ── Software Bus types ──────────────────────────────────────────────────── */
+typedef uintptr_t           CFE_SB_PipeId_t;
+typedef uint32_t            CFE_SB_MsgId_Atom_t;
+typedef CFE_SB_MsgId_Atom_t CFE_SB_MsgId_t;
+
+/* CCSDS primary-header minimum (6 bytes) plus secondary-header stub (10 bytes) */
+typedef struct { uint8 Byte[16]; } CFE_MSG_Message_t;
+typedef struct { CFE_MSG_Message_t Msg; } CFE_SB_Buffer_t;
+typedef uint16_t CFE_MSG_FcnCode_t;
+
+/* ── Event Services types ────────────────────────────────────────────────── */
+typedef struct {
+    uint16 EventID;
+    uint16 Mask;
+} CFE_EVS_BinFilter_t;
+
+/* ── Status codes ────────────────────────────────────────────────────────── */
+#define CFE_SUCCESS                  ((int32) 0)
+#define CFE_SB_BAD_ARGUMENT          ((int32)-1)
+#define CFE_SB_PIPE_RD_ERR           ((int32)-2)
+#define CFE_SB_MAX_MSGS_MET          ((int32)-3)
+#define CFE_ES_ERR_APP_REGISTER      ((int32)-4)
+#define CFE_EVS_APP_FILTER_OVERLOAD  ((int32)-5)
+
+/* ── Executive Services constants ───────────────────────────────────────── */
+#define CFE_ES_RunStatus_APP_RUN    1U
+#define CFE_ES_RunStatus_APP_ERROR  2U
+#define CFE_ES_RunStatus_APP_EXIT   3U
+
+/* ── Software Bus constants ─────────────────────────────────────────────── */
+#define CFE_SB_PEND_FOREVER         ((int32)-1)
+#define CFE_SB_INVALID_MSG_ID       ((CFE_SB_MsgId_t)0xFFFFU)
+
+/* ── Event Services constants ────────────────────────────────────────────── */
+#define CFE_EVS_EventFilter_BINARY    1U
+#define CFE_EVS_EventType_INFORMATION 1U
+#define CFE_EVS_EventType_ERROR       4U
+
+/* ── API declarations (implemented by cFE or by UNIT_TEST stubs) ─────────── */
+int32 CFE_ES_RegisterApp(void);
+bool  CFE_ES_RunLoop(uint32 *RunStatus);
+void  CFE_ES_ExitApp(uint32 ExitStatus);
+
+int32 CFE_EVS_Register(const void *Filters, uint16 NumFilters, uint16 FilterScheme);
+void  CFE_EVS_SendEvent(uint16 EventID, uint16 EventType, const char *Spec, ...);
+
+int32 CFE_SB_CreatePipe(CFE_SB_PipeId_t *PipeIdPtr, uint16 Depth, const char *PipeName);
+int32 CFE_SB_Subscribe(CFE_SB_MsgId_t MsgId, CFE_SB_PipeId_t PipeId);
+int32 CFE_SB_ReceiveBuffer(CFE_SB_Buffer_t **BufPtr, CFE_SB_PipeId_t PipeId, int32 TimeOut);
+int32 CFE_SB_TransmitMsg(CFE_MSG_Message_t *MsgPtr, bool IncrementSequenceCount);
+CFE_SB_MsgId_Atom_t CFE_SB_MsgIdToValue(CFE_SB_MsgId_t MsgId);
+CFE_SB_MsgId_t      CFE_SB_ValueToMsgId(CFE_SB_MsgId_Atom_t MsgIdValue);
+
+int32 CFE_MSG_GetMsgId(const CFE_MSG_Message_t *MsgPtr, CFE_SB_MsgId_t *MsgId);
+int32 CFE_MSG_GetFcnCode(const CFE_MSG_Message_t *MsgPtr, CFE_MSG_FcnCode_t *FcnCode);
+int32 CFE_MSG_SetMsgId(CFE_MSG_Message_t *MsgPtr, CFE_SB_MsgId_t MsgId);
+int32 CFE_MSG_SetSize(CFE_MSG_Message_t *MsgPtr, uint32 TotalMsgSize);
+
+/* ── OSAL network types ──────────────────────────────────────────────────── */
+typedef uint32_t osal_id_t;
+typedef struct { uint8_t AddrData[28]; } OS_SockAddr_t;
+typedef enum { OS_SocketDomain_INET = 2 } OS_SocketDomain_t;
+typedef enum { OS_SocketType_DATAGRAM = 2 } OS_SocketType_t;
+
+#define OS_SUCCESS       ((int32) 0)
+#define OS_ERR_TIMEOUT   ((int32)-10)
+
+int32 OS_SocketOpen(osal_id_t *sock_id, OS_SocketDomain_t Domain, OS_SocketType_t Type);
+int32 OS_SocketAddrInit(OS_SockAddr_t *Addr, OS_SocketDomain_t Domain);
+int32 OS_SocketAddrSetPort(OS_SockAddr_t *Addr, uint16 PortNum);
+int32 OS_SocketBind(osal_id_t sock_id, const OS_SockAddr_t *Addr);
+int32 OS_SocketRecvFrom(osal_id_t sock_id, void *buffer, uint32 buflen,
+                        OS_SockAddr_t *RemoteAddr, int32 timeout_ms);
+
+#endif /* CFE_H */
diff --git a/apps/sim_adapter/fsw/src/sim_adapter.c b/apps/sim_adapter/fsw/src/sim_adapter.c
new file mode 100644
index 0000000..6e27cf0
--- /dev/null
+++ b/apps/sim_adapter/fsw/src/sim_adapter.c
@@ -0,0 +1,301 @@
+/*
+ * sim_adapter.c — SAKURA-II cFS SITL UDP–to–Software-Bus adapter.
+ *
+ * Polls a UDP socket on port 5700 for CCSDS Space Packets from the
+ * fault_injector, validates APID (ICD-sim-fsw.md §4.1) and
+ * CRC-16/CCITT-FALSE (poly 0x1021, init 0xFFFF), then routes valid
+ * packets to the cFE Software Bus via SIM_INJECT_HK_MID.
+ *
+ * Entire body guarded by #ifndef CFS_FLIGHT_BUILD — zero symbols in
+ * flight image (ICD-sim-fsw.md §5.2).
+ *
+ * MISRA C:2012 compliance target. No dynamic memory allocation.
+ * Stack depth statically bounded.
+ */
+
+#ifndef CFS_FLIGHT_BUILD
+
+#include "sim_adapter.h"
+#include <string.h>
+
+/* ── File-scope state ────────────────────────────────────────────────────── */
+#ifdef UNIT_TEST
+/* Non-static so unit tests can inspect counters directly. */
+SIM_ADAPTER_AppData_t SIM_ADAPTER_Data;
+#else
+static SIM_ADAPTER_AppData_t SIM_ADAPTER_Data;
+#endif /* UNIT_TEST */
+
+/* MISRA Rule 18.8: fixed-size; not a VLA. */
+static uint8 frame_buf[SIM_ADAPTER_FRAME_BUF_SIZE];
+
+/* ── Forward declarations ─────────────────────────────────────────────────── */
+static int32 SIM_ADAPTER_Init(void);
+static void  SIM_ADAPTER_RouteToSB(uint16 apid, const uint8 *payload,
+                                    uint32 payload_len);
+
+#ifndef UNIT_TEST
+static int32  SIM_ADAPTER_ProcessUdp(const uint8 *buf, uint32 len);
+static uint16 SIM_ADAPTER_Crc16(const uint8 *data, uint16 len);
+#endif /* !UNIT_TEST */
+
+/* ---------------------------------------------------------------------------
+ * SIM_ADAPTER_AppMain — Application entry point
+ * --------------------------------------------------------------------------- */
+void SIM_ADAPTER_AppMain(void)
+{
+    int32 status;
+
+    SIM_ADAPTER_Data.RunStatus = CFE_ES_RunStatus_APP_RUN;
+
+    status = SIM_ADAPTER_Init();
+    if (status != CFE_SUCCESS)
+    {
+        SIM_ADAPTER_Data.RunStatus = CFE_ES_RunStatus_APP_ERROR;
+    }
+
+    while (CFE_ES_RunLoop(&SIM_ADAPTER_Data.RunStatus) == true)
+    {
+        /* Non-blocking poll: returns byte count (>0) or negative error code. */
+        int32 bytes_recv = OS_SocketRecvFrom(SIM_ADAPTER_Data.UdpSockId,
+                                       frame_buf, SIM_ADAPTER_FRAME_BUF_SIZE,
+                                       NULL, 0);
+        if (bytes_recv > 0)
+        {
+            (void)SIM_ADAPTER_ProcessUdp(frame_buf, (uint32)bytes_recv);
+        }
+
+        SIM_ADAPTER_Data.UptimeSeconds++;
+    }
+
+    CFE_ES_ExitApp(SIM_ADAPTER_Data.RunStatus);
+}
+
+/* ---------------------------------------------------------------------------
+ * SIM_ADAPTER_Init — One-time application initialization
+ * --------------------------------------------------------------------------- */
+static int32 SIM_ADAPTER_Init(void)
+{
+    int32 status;
+
+    status = CFE_ES_RegisterApp();
+    if (status != CFE_SUCCESS)
+    {
+        return status;
+    }
+
+    status = CFE_EVS_Register(SIM_ADAPTER_Data.EventFilters,
+                               (uint16)SIM_ADAPTER_EVT_COUNT,
+                               (uint16)CFE_EVS_EventFilter_BINARY);
+    if (status != CFE_SUCCESS)
+    {
+        return status;
+    }
+
+    status = CFE_SB_CreatePipe(&SIM_ADAPTER_Data.CmdPipe,
+                                (uint16)SIM_ADAPTER_PIPE_DEPTH,
+                                "SIM_ADAPTER_CMD");
+    if (status != CFE_SUCCESS)
+    {
+        return status;
+    }
+
+    status = CFE_SB_Subscribe(CFE_SB_ValueToMsgId(SIM_ADAPTER_CMD_MID),
+                               SIM_ADAPTER_Data.CmdPipe);
+    if (status != CFE_SUCCESS)
+    {
+        return status;
+    }
+
+    status = OS_SocketOpen(&SIM_ADAPTER_Data.UdpSockId,
+                            OS_SocketDomain_INET, OS_SocketType_DATAGRAM);
+    if (status != OS_SUCCESS)
+    {
+        CFE_EVS_SendEvent(SIM_ADAPTER_EID_INIT_SOCKET_ERR,
+                          CFE_EVS_EventType_ERROR,
+                          "SIM_ADAPTER: UDP socket open failed 0x%08X",
+                          (unsigned int)status);
+        return status;
+    }
+
+    status = OS_SocketAddrInit(&SIM_ADAPTER_Data.UdpBindAddr,
+                                OS_SocketDomain_INET);
+    if (status != OS_SUCCESS)
+    {
+        return status;
+    }
+
+    status = OS_SocketAddrSetPort(&SIM_ADAPTER_Data.UdpBindAddr,
+                                   (uint16)SIM_ADAPTER_UDP_PORT);
+    if (status != OS_SUCCESS)
+    {
+        return status;
+    }
+
+    status = OS_SocketBind(SIM_ADAPTER_Data.UdpSockId,
+                            &SIM_ADAPTER_Data.UdpBindAddr);
+    if (status != OS_SUCCESS)
+    {
+        return status;
+    }
+
+    SIM_ADAPTER_Data.PacketsRouted  = 0U;
+    SIM_ADAPTER_Data.CrcMismatches  = 0U;
+    SIM_ADAPTER_Data.ApidRejects    = 0U;
+    SIM_ADAPTER_Data.UptimeSeconds  = 0U;
+
+    CFE_EVS_SendEvent(SIM_ADAPTER_STARTUP_INF_EID,
+                      CFE_EVS_EventType_INFORMATION,
+                      "SIM_ADAPTER initialized v%d.%d.%d (UDP port %u)",
+                      SIM_ADAPTER_MAJOR_VERSION,
+                      SIM_ADAPTER_MINOR_VERSION,
+                      SIM_ADAPTER_REVISION,
+                      (unsigned int)SIM_ADAPTER_UDP_PORT);
+
+    return CFE_SUCCESS;
+}
+
+/* ---------------------------------------------------------------------------
+ * SIM_ADAPTER_Crc16 — CRC-16/CCITT-FALSE (poly 0x1021, init 0xFFFF, no reflect)
+ *
+ * Identical algorithm to MCU_EPS_GW_Crc16 and spp_crc16() in fault_injector.
+ * Canonical check: Crc16("123456789", 9) == 0x29B1.
+ * Per ICD-sim-fsw.md §4.1 and Q-C9.
+ * --------------------------------------------------------------------------- */
+#ifdef UNIT_TEST
+uint16 SIM_ADAPTER_Crc16(const uint8 *data, uint16 len)
+#else
+static uint16 SIM_ADAPTER_Crc16(const uint8 *data, uint16 len)
+#endif /* UNIT_TEST */
+{
+    uint16 crc = SIM_ADAPTER_CRC16_INIT;
+    uint16 i;
+    uint8  bit;
+
+    for (i = 0U; i < len; i++)
+    {
+        crc ^= (uint16)((uint16)data[i] << 8U);
+        for (bit = 0U; bit < 8U; bit++)
+        {
+            if ((crc & 0x8000U) != 0U)
+            {
+                crc = (uint16)((uint16)(crc << 1U) ^ SIM_ADAPTER_CRC16_POLY);
+            }
+            else
+            {
+                crc = (uint16)(crc << 1U);
+            }
+        }
+    }
+    return crc;
+}
+
+/* ---------------------------------------------------------------------------
+ * SIM_ADAPTER_ProcessUdp — Validate and dispatch one UDP datagram.
+ *
+ * Validation order per ICD-sim-fsw.md §4.1:
+ *   1. Length gate (< 18 bytes → reject)
+ *   2. APID extraction (big-endian, bytes 0–1)
+ *   3. APID range gate (0x500–0x57F)
+ *   4. CRC-16/CCITT-FALSE over payload bytes (buf[16..len-3])
+ *   5. Route valid packet to SB
+ * --------------------------------------------------------------------------- */
+#ifdef UNIT_TEST
+int32 SIM_ADAPTER_ProcessUdp(const uint8 *buf, uint32 len)
+#else
+static int32 SIM_ADAPTER_ProcessUdp(const uint8 *buf, uint32 len)
+#endif /* UNIT_TEST */
+{
+    uint16 apid;
+    uint16 crc_computed;
+    uint16 crc_stored;
+
+    /* 1. Length gate: need at least 16-byte header + 2-byte CRC = 18 bytes. */
+    if (len < 18U)
+    {
+        CFE_EVS_SendEvent(SIM_ADAPTER_EID_PACKET_TOO_SHORT,
+                          CFE_EVS_EventType_ERROR,
+                          "SIM_ADAPTER: datagram too short (%u bytes)",
+                          (unsigned int)len);
+        SIM_ADAPTER_Data.ApidRejects++;
+        return CFE_SB_BAD_ARGUMENT;
+    }
+
+    /* 2. APID from CCSDS primary header bytes 0–1 (big-endian, 11-bit field). */
+    apid = (uint16)(((uint16)(buf[0U] & 0x07U) << 8U) | (uint16)buf[1U]);
+
+    /* 3. APID range gate: sim sideband block 0x500–0x57F only. */
+    if ((apid < SIM_ADAPTER_APID_MIN) || (apid > SIM_ADAPTER_APID_MAX))
+    {
+        CFE_EVS_SendEvent(SIM_ADAPTER_EID_APID_OUT_OF_RANGE,
+                          CFE_EVS_EventType_ERROR,
+                          "SIM_ADAPTER: APID 0x%03X out of range [0x%03X–0x%03X]",
+                          (unsigned int)apid,
+                          (unsigned int)SIM_ADAPTER_APID_MIN,
+                          (unsigned int)SIM_ADAPTER_APID_MAX);
+        SIM_ADAPTER_Data.ApidRejects++;
+        return CFE_SB_BAD_ARGUMENT;
+    }
+
+    /* 4. CRC-16/CCITT-FALSE over payload bytes (buf[16..len-3]).
+     * Payload length = len - 18 (16-byte header + 2-byte CRC trailer).
+     * Stored CRC is big-endian at buf[len-2..len-1]. */
+    crc_computed = SIM_ADAPTER_Crc16(buf + 16U, (uint16)(len - 18U));
+    crc_stored   = (uint16)(((uint16)buf[len - 2U] << 8U) | (uint16)buf[len - 1U]);
+
+    if (crc_computed != crc_stored)
+    {
+        CFE_EVS_SendEvent(SIM_ADAPTER_EID_CRC_MISMATCH,
+                          CFE_EVS_EventType_ERROR,
+                          "SIM_ADAPTER: CRC mismatch APID 0x%03X (got 0x%04X, expected 0x%04X)",
+                          (unsigned int)apid,
+                          (unsigned int)crc_stored,
+                          (unsigned int)crc_computed);
+        SIM_ADAPTER_Data.CrcMismatches++;
+        return CFE_SB_BAD_ARGUMENT;
+    }
+
+    /* 5. Route valid payload to SB. */
+    SIM_ADAPTER_RouteToSB(apid, buf + 16U, len - 18U);
+
+    return CFE_SUCCESS;
+}
+
+/* ---------------------------------------------------------------------------
+ * SIM_ADAPTER_RouteToSB — Publish a validated fault SPP to the cFE Software Bus.
+ *
+ * Stub routing target is SIM_INJECT_HK_MID; a future phase maps each APID to
+ * its own MID once the full fault-injection table is wired (ICD-sim-fsw.md §5).
+ * --------------------------------------------------------------------------- */
+static void SIM_ADAPTER_RouteToSB(uint16 apid, const uint8 *payload,
+                                   uint32 payload_len)
+{
+    static CFE_SB_Buffer_t tlm_buf;
+    int32 status;
+
+    (void)payload;
+    (void)payload_len;
+
+    (void)CFE_MSG_SetMsgId(&tlm_buf.Msg, CFE_SB_ValueToMsgId(SIM_INJECT_HK_MID));
+    (void)CFE_MSG_SetSize(&tlm_buf.Msg, (uint32)sizeof(CFE_SB_Buffer_t));
+
+    status = CFE_SB_TransmitMsg(&tlm_buf.Msg, true);
+    if (status != CFE_SUCCESS)
+    {
+        CFE_EVS_SendEvent(SIM_ADAPTER_EID_SB_TRANSMIT_ERR,
+                          CFE_EVS_EventType_ERROR,
+                          "SIM_ADAPTER: SB transmit failed 0x%08X APID 0x%03X",
+                          (unsigned int)status,
+                          (unsigned int)apid);
+        return;
+    }
+
+    SIM_ADAPTER_Data.PacketsRouted++;
+    CFE_EVS_SendEvent(SIM_ADAPTER_EID_FAULT_APPLIED_INF_EID,
+                      CFE_EVS_EventType_INFORMATION,
+                      "SIM_ADAPTER: fault SPP routed APID 0x%03X total %u",
+                      (unsigned int)apid,
+                      (unsigned int)SIM_ADAPTER_Data.PacketsRouted);
+}
+
+#endif /* !CFS_FLIGHT_BUILD */
diff --git a/apps/sim_adapter/fsw/src/sim_adapter.h b/apps/sim_adapter/fsw/src/sim_adapter.h
new file mode 100644
index 0000000..c7dda00
--- /dev/null
+++ b/apps/sim_adapter/fsw/src/sim_adapter.h
@@ -0,0 +1,56 @@
+#ifndef SIM_ADAPTER_H
+#define SIM_ADAPTER_H
+
+/*
+ * sim_adapter.h — SITL-only cFS application: UDP fault-SPP → Software Bus adapter.
+ *
+ * Receives CCSDS Space Packets from the fault_injector via UDP port 5700,
+ * validates APID (0x500–0x57F) and CRC-16/CCITT-FALSE, then routes valid
+ * packets onto the cFE Software Bus as SIM_INJECT_HK_MID messages.
+ *
+ * Entire implementation is excluded from flight builds by the
+ * CFS_FLIGHT_BUILD compile-time guard (ICD-sim-fsw.md §5.2).
+ */
+
+#ifndef CFS_FLIGHT_BUILD
+
+#include "cfe.h"
+#include "sim_adapter_events.h"
+#include "sim_adapter_version.h"
+#include "mids.h"
+
+/* ── Constants ───────────────────────────────────────────────────────────── */
+#define SIM_ADAPTER_PIPE_DEPTH      10U
+#define SIM_ADAPTER_UDP_PORT        5700U
+#define SIM_ADAPTER_FRAME_BUF_SIZE  1024U   /* max UDP datagram; no VLA (MISRA Rule 18.8) */
+#define SIM_ADAPTER_APID_MIN        0x500U
+#define SIM_ADAPTER_APID_MAX        0x57FU
+#define SIM_ADAPTER_CRC16_POLY      0x1021U /* CRC-16/CCITT-FALSE polynomial */
+#define SIM_ADAPTER_CRC16_INIT      0xFFFFU /* CRC-16/CCITT-FALSE initial value */
+
+/* ── Application state ───────────────────────────────────────────────────── */
+typedef struct {
+    CFE_EVS_BinFilter_t EventFilters[SIM_ADAPTER_EVT_COUNT];
+    CFE_SB_PipeId_t     CmdPipe;
+    osal_id_t           UdpSockId;
+    OS_SockAddr_t       UdpBindAddr;
+    uint32              PacketsRouted;
+    uint32              CrcMismatches;
+    uint32              ApidRejects;
+    uint32              RunStatus;
+    uint32              UptimeSeconds;
+} SIM_ADAPTER_AppData_t;
+
+/* ── Entry point ─────────────────────────────────────────────────────────── */
+void SIM_ADAPTER_AppMain(void);
+
+/* ── Unit-test surface (non-static under UNIT_TEST) ─────────────────────── */
+#ifdef UNIT_TEST
+extern SIM_ADAPTER_AppData_t SIM_ADAPTER_Data;
+int32  SIM_ADAPTER_ProcessUdp(const uint8 *buf, uint32 len);
+uint16 SIM_ADAPTER_Crc16(const uint8 *data, uint16 len);
+#endif /* UNIT_TEST */
+
+#endif /* !CFS_FLIGHT_BUILD */
+
+#endif /* SIM_ADAPTER_H */
diff --git a/apps/sim_adapter/fsw/src/sim_adapter_events.h b/apps/sim_adapter/fsw/src/sim_adapter_events.h
new file mode 100644
index 0000000..1f98811
--- /dev/null
+++ b/apps/sim_adapter/fsw/src/sim_adapter_events.h
@@ -0,0 +1,19 @@
+#ifndef SIM_ADAPTER_EVENTS_H
+#define SIM_ADAPTER_EVENTS_H
+
+/* Event ID constants for sim_adapter.
+ * Source of truth: ICD-sim-fsw.md §6. */
+
+#define SIM_ADAPTER_STARTUP_INF_EID         1U   /* Initialization complete */
+#define SIM_ADAPTER_EID_PACKET_TOO_SHORT    2U   /* UDP datagram < 18 bytes */
+#define SIM_ADAPTER_EID_BAD_HEADER          3U   /* Primary header version error */
+#define SIM_ADAPTER_EID_APID_OUT_OF_RANGE   4U   /* APID outside 0x500–0x57F */
+#define SIM_ADAPTER_EID_CRC_MISMATCH        5U   /* CRC-16/CCITT-FALSE mismatch */
+#define SIM_ADAPTER_EID_FAULT_APPLIED_INF_EID 6U /* Fault SPP routed to SB */
+#define SIM_ADAPTER_EID_UNKNOWN_APID        7U   /* APID in range but unregistered */
+#define SIM_ADAPTER_EID_INIT_SOCKET_ERR     8U   /* OSAL UDP socket init failure */
+#define SIM_ADAPTER_EID_SB_TRANSMIT_ERR     9U   /* CFE_SB_TransmitMsg failure */
+
+#define SIM_ADAPTER_EVT_COUNT               9U
+
+#endif /* SIM_ADAPTER_EVENTS_H */
diff --git a/apps/sim_adapter/fsw/src/sim_adapter_version.h b/apps/sim_adapter/fsw/src/sim_adapter_version.h
new file mode 100644
index 0000000..6adad89
--- /dev/null
+++ b/apps/sim_adapter/fsw/src/sim_adapter_version.h
@@ -0,0 +1,8 @@
+#ifndef SIM_ADAPTER_VERSION_H
+#define SIM_ADAPTER_VERSION_H
+
+#define SIM_ADAPTER_MAJOR_VERSION  1
+#define SIM_ADAPTER_MINOR_VERSION  0
+#define SIM_ADAPTER_REVISION       0
+
+#endif /* SIM_ADAPTER_VERSION_H */
diff --git a/apps/sim_adapter/fsw/unit-test/sim_adapter_test.c b/apps/sim_adapter/fsw/unit-test/sim_adapter_test.c
new file mode 100644
index 0000000..b5be08c
--- /dev/null
+++ b/apps/sim_adapter/fsw/unit-test/sim_adapter_test.c
@@ -0,0 +1,312 @@
+/*
+ * sim_adapter_test.c — CMocka unit tests for sim_adapter.
+ *
+ * CFE and OSAL API calls are intercepted via UNIT_TEST guards; no real cFE
+ * library is linked. SIM_ADAPTER_ProcessUdp and SIM_ADAPTER_Crc16 are exposed
+ * as non-static under UNIT_TEST so tests can call them directly.
+ *
+ * Coverage target: 100% branch coverage of sim_adapter.c.
+ */
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+#include <string.h>
+
+#include "sim_adapter.h"
+
+/* ---------------------------------------------------------------------------
+ * CFE / OSAL stub implementations (UNIT_TEST only)
+ * --------------------------------------------------------------------------- */
+#ifdef UNIT_TEST
+
+int32 CFE_ES_RegisterApp(void) { return (int32)mock(); }
+
+int32 CFE_EVS_Register(const void *F, uint16 N, uint16 S)
+{
+    (void)F; (void)N; (void)S;
+    return (int32)mock();
+}
+
+int32 CFE_SB_CreatePipe(CFE_SB_PipeId_t *P, uint16 D, const char *N)
+{
+    (void)D; (void)N;
+    *P = (CFE_SB_PipeId_t)mock();
+    return (int32)mock();
+}
+
+int32 CFE_SB_Subscribe(CFE_SB_MsgId_t MsgId, CFE_SB_PipeId_t PipeId)
+{
+    (void)MsgId; (void)PipeId;
+    return (int32)mock();
+}
+
+void CFE_EVS_SendEvent(uint16 EventID, uint16 EventType, const char *Spec, ...)
+{
+    (void)EventID; (void)EventType; (void)Spec;
+    function_called();
+}
+
+bool CFE_ES_RunLoop(uint32 *RunStatus)
+{
+    (void)RunStatus;
+    return (bool)mock();
+}
+
+int32 CFE_SB_ReceiveBuffer(CFE_SB_Buffer_t **BufPtr, CFE_SB_PipeId_t PipeId, int32 TimeOut)
+{
+    (void)PipeId; (void)TimeOut;
+    *BufPtr = (CFE_SB_Buffer_t *)mock();
+    return (int32)mock();
+}
+
+int32 CFE_SB_TransmitMsg(CFE_MSG_Message_t *MsgPtr, bool Inc)
+{
+    (void)MsgPtr; (void)Inc;
+    function_called();
+    return (int32)mock();
+}
+
+void CFE_ES_ExitApp(uint32 ExitStatus) { (void)ExitStatus; }
+
+int32 CFE_MSG_GetMsgId(const CFE_MSG_Message_t *M, CFE_SB_MsgId_t *Id)
+{
+    (void)M;
+    *Id = (CFE_SB_MsgId_t)mock();
+    return CFE_SUCCESS;
+}
+
+int32 CFE_MSG_GetFcnCode(const CFE_MSG_Message_t *M, CFE_MSG_FcnCode_t *C)
+{
+    (void)M;
+    *C = (CFE_MSG_FcnCode_t)mock();
+    return CFE_SUCCESS;
+}
+
+int32 CFE_MSG_SetMsgId(CFE_MSG_Message_t *MsgPtr, CFE_SB_MsgId_t MsgId)
+{
+    (void)MsgPtr; (void)MsgId;
+    return CFE_SUCCESS;
+}
+
+int32 CFE_MSG_SetSize(CFE_MSG_Message_t *MsgPtr, uint32 TotalMsgSize)
+{
+    (void)MsgPtr; (void)TotalMsgSize;
+    return CFE_SUCCESS;
+}
+
+CFE_SB_MsgId_Atom_t CFE_SB_MsgIdToValue(CFE_SB_MsgId_t MsgId)
+{
+    return (CFE_SB_MsgId_Atom_t)MsgId;
+}
+
+CFE_SB_MsgId_t CFE_SB_ValueToMsgId(CFE_SB_MsgId_Atom_t MsgIdValue)
+{
+    return (CFE_SB_MsgId_t)MsgIdValue;
+}
+
+int32 OS_SocketOpen(osal_id_t *sock_id, OS_SocketDomain_t Domain, OS_SocketType_t Type)
+{
+    (void)Domain; (void)Type;
+    *sock_id = (osal_id_t)mock();
+    return (int32)mock();
+}
+
+int32 OS_SocketAddrInit(OS_SockAddr_t *Addr, OS_SocketDomain_t Domain)
+{
+    (void)Addr; (void)Domain;
+    return (int32)mock();
+}
+
+int32 OS_SocketAddrSetPort(OS_SockAddr_t *Addr, uint16 PortNum)
+{
+    (void)Addr; (void)PortNum;
+    return (int32)mock();
+}
+
+int32 OS_SocketBind(osal_id_t sock_id, const OS_SockAddr_t *Addr)
+{
+    (void)sock_id; (void)Addr;
+    return (int32)mock();
+}
+
+int32 OS_SocketRecvFrom(osal_id_t sock_id, void *buf, uint32 buflen,
+                        OS_SockAddr_t *RemoteAddr, int32 timeout_ms)
+{
+    (void)sock_id; (void)buf; (void)buflen; (void)RemoteAddr; (void)timeout_ms;
+    return (int32)mock();
+}
+
+#endif /* UNIT_TEST */
+
+/* ---------------------------------------------------------------------------
+ * Helpers
+ * --------------------------------------------------------------------------- */
+
+/* CRC-16/CCITT-FALSE canonical check vector (ASCII "123456789"). */
+static const uint8 CRC_VECTOR[] = {
+    0x31U, 0x32U, 0x33U, 0x34U, 0x35U, 0x36U, 0x37U, 0x38U, 0x39U
+};
+#define CRC_VECTOR_LEN  ((uint16)9U)
+#define CRC_VECTOR_EXPECTED  ((uint16)0x29B1U)
+
+/* Minimal valid datagram: 16-byte header (APID=0x540) + 0-byte payload + 2-byte CRC.
+ * APID 0x540: buf[0]=0x05, buf[1]=0x40.
+ * CRC of 0 bytes = init = 0xFFFF → buf[16]=0xFF, buf[17]=0xFF. */
+static const uint8 VALID_PKT[] = {
+    0x05U, 0x40U,                               /* APID = 0x540 */
+    0x00U, 0x00U, 0x00U, 0x00U,                 /* primary header bytes 2–5 */
+    0x00U, 0x00U, 0x00U, 0x00U, 0x00U, 0x00U,   /* secondary header bytes 0–5 */
+    0x00U, 0x00U, 0x00U, 0x00U,                 /* secondary header bytes 6–9 */
+    0xFFU, 0xFFU                                 /* CRC of 0 payload bytes = 0xFFFF */
+};
+#define VALID_PKT_LEN  ((uint32)18U)
+
+/* Same as VALID_PKT but with incorrect CRC bytes. */
+static const uint8 BAD_CRC_PKT[] = {
+    0x05U, 0x40U,
+    0x00U, 0x00U, 0x00U, 0x00U,
+    0x00U, 0x00U, 0x00U, 0x00U, 0x00U, 0x00U,
+    0x00U, 0x00U, 0x00U, 0x00U,
+    0x00U, 0x00U   /* wrong CRC — correct would be 0xFFFF */
+};
+#define BAD_CRC_PKT_LEN  ((uint32)18U)
+
+/* 18-byte datagram with APID 0x600 (out of range: 0x06 | 0x00). */
+static const uint8 OOR_APID_PKT[] = {
+    0x06U, 0x00U,   /* APID = 0x600 — outside [0x500, 0x57F] */
+    0x00U, 0x00U, 0x00U, 0x00U,
+    0x00U, 0x00U, 0x00U, 0x00U, 0x00U, 0x00U,
+    0x00U, 0x00U, 0x00U, 0x00U,
+    0xFFU, 0xFFU
+};
+#define OOR_APID_PKT_LEN  ((uint32)18U)
+
+/* 10-byte datagram — too short to pass the length gate. */
+static const uint8 SHORT_PKT[] = {
+    0x05U, 0x40U, 0x00U, 0x00U, 0x00U,
+    0x00U, 0x00U, 0x00U, 0x00U, 0x00U
+};
+#define SHORT_PKT_LEN  ((uint32)10U)
+
+/* Reset SIM_ADAPTER_Data before tests that inspect counters. */
+static int reset_data(void **state)
+{
+    (void)state;
+    memset(&SIM_ADAPTER_Data, 0, sizeof(SIM_ADAPTER_Data));
+    return 0;
+}
+
+/* ---------------------------------------------------------------------------
+ * Test 1: CRC-16/CCITT-FALSE known vector
+ *
+ * Crc16("123456789", 9) must equal 0x29B1.
+ * This exercises the entire CRC loop and verifies polynomial / init constants.
+ * --------------------------------------------------------------------------- */
+static void test_crc_known_vector(void **state)
+{
+    (void)state;
+    uint16 result = SIM_ADAPTER_Crc16(CRC_VECTOR, CRC_VECTOR_LEN);
+    assert_int_equal((int)result, (int)CRC_VECTOR_EXPECTED);
+}
+
+/* ---------------------------------------------------------------------------
+ * Test 2: Short datagram rejected before APID extraction
+ *
+ * Given:  10-byte datagram (< 18)
+ * When:   SIM_ADAPTER_ProcessUdp called
+ * Then:   EID_PACKET_TOO_SHORT event; ApidRejects incremented; no SB transmit
+ * --------------------------------------------------------------------------- */
+static void test_short_packet_rejected(void **state)
+{
+    (void)state;
+    expect_function_call(CFE_EVS_SendEvent);  /* EID_PACKET_TOO_SHORT */
+    (void)SIM_ADAPTER_ProcessUdp(SHORT_PKT, SHORT_PKT_LEN);
+    assert_int_equal((int)SIM_ADAPTER_Data.ApidRejects, 1);
+}
+
+/* ---------------------------------------------------------------------------
+ * Test 3: APID outside sideband block rejected
+ *
+ * Given:  18-byte datagram, APID=0x600 (outside 0x500–0x57F)
+ * When:   SIM_ADAPTER_ProcessUdp called
+ * Then:   EID_APID_OUT_OF_RANGE event; ApidRejects incremented; no SB transmit
+ * --------------------------------------------------------------------------- */
+static void test_apid_out_of_range_rejected(void **state)
+{
+    (void)state;
+    expect_function_call(CFE_EVS_SendEvent);  /* EID_APID_OUT_OF_RANGE */
+    (void)SIM_ADAPTER_ProcessUdp(OOR_APID_PKT, OOR_APID_PKT_LEN);
+    assert_int_equal((int)SIM_ADAPTER_Data.ApidRejects, 1);
+}
+
+/* ---------------------------------------------------------------------------
+ * Test 4: CRC mismatch causes packet to be dropped
+ *
+ * Given:  18-byte datagram, APID=0x540, stored CRC=0x0000 (wrong)
+ * When:   SIM_ADAPTER_ProcessUdp called
+ * Then:   EID_CRC_MISMATCH event; CrcMismatches incremented; no SB transmit
+ * --------------------------------------------------------------------------- */
+static void test_crc_mismatch_rejected(void **state)
+{
+    (void)state;
+    expect_function_call(CFE_EVS_SendEvent);  /* EID_CRC_MISMATCH */
+    (void)SIM_ADAPTER_ProcessUdp(BAD_CRC_PKT, BAD_CRC_PKT_LEN);
+    assert_int_equal((int)SIM_ADAPTER_Data.CrcMismatches, 1);
+}
+
+/* ---------------------------------------------------------------------------
+ * Test 5: Valid packet is routed to the Software Bus
+ *
+ * Given:  18-byte datagram, APID=0x540, CRC=0xFFFF (correct for 0 payload bytes)
+ * When:   SIM_ADAPTER_ProcessUdp called
+ * Then:   CFE_SB_TransmitMsg called once; PacketsRouted == 1
+ * --------------------------------------------------------------------------- */
+static void test_valid_packet_routed(void **state)
+{
+    (void)state;
+    expect_function_call(CFE_SB_TransmitMsg);
+    will_return(CFE_SB_TransmitMsg, CFE_SUCCESS);
+    expect_function_call(CFE_EVS_SendEvent);  /* EID_FAULT_APPLIED_INF_EID */
+    (void)SIM_ADAPTER_ProcessUdp(VALID_PKT, VALID_PKT_LEN);
+    assert_int_equal((int)SIM_ADAPTER_Data.PacketsRouted, 1);
+}
+
+/* ---------------------------------------------------------------------------
+ * Test 6: OS_SocketOpen failure causes Init to return an error
+ *
+ * Given:  OS_SocketOpen returns a negative error code
+ * When:   SIM_ADAPTER_AppMain called
+ * Then:   EID_INIT_SOCKET_ERR event; RunLoop entered with APP_ERROR → exits immediately
+ * --------------------------------------------------------------------------- */
+static void test_init_socket_failure(void **state)
+{
+    (void)state;
+    will_return(CFE_ES_RegisterApp, CFE_SUCCESS);
+    will_return(CFE_EVS_Register,   CFE_SUCCESS);
+    will_return(CFE_SB_CreatePipe,  1);
+    will_return(CFE_SB_CreatePipe,  CFE_SUCCESS);
+    will_return(CFE_SB_Subscribe,   CFE_SUCCESS);
+    will_return(OS_SocketOpen,      0);          /* socket id (unused on failure) */
+    will_return(OS_SocketOpen,      (int32)-1);  /* OS_ERR_SOCKET_CLOSED */
+    expect_function_call(CFE_EVS_SendEvent);  /* EID_INIT_SOCKET_ERR */
+    will_return(CFE_ES_RunLoop, false);
+    SIM_ADAPTER_AppMain();
+}
+
+/* ---------------------------------------------------------------------------
+ * Test runner
+ * --------------------------------------------------------------------------- */
+int main(void)
+{
+    const struct CMUnitTest tests[] = {
+        cmocka_unit_test(test_crc_known_vector),
+        cmocka_unit_test_setup(test_short_packet_rejected,        reset_data),
+        cmocka_unit_test_setup(test_apid_out_of_range_rejected,   reset_data),
+        cmocka_unit_test_setup(test_crc_mismatch_rejected,        reset_data),
+        cmocka_unit_test_setup(test_valid_packet_routed,          reset_data),
+        cmocka_unit_test(test_init_socket_failure),
+    };
+    return cmocka_run_group_tests(tests, NULL, NULL);
+}
diff --git a/compose.yaml b/compose.yaml
index 9c2d454..532e9ff 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -44,11 +44,18 @@ services:
       retries: 10
       start_period: 10s
 
-  # ── Gazebo Harmonic (headless) ────────────────────────────────────────────────
-  # Runs gz sim server with mars_surrogate.sdf (Mars gravity, flat terrain,
-  # rover/UAV/cryobot models).  Plugin .so files are not compiled in this
-  # image so Gazebo emits "plugin not found" warnings and continues without
-  # rover dynamics — full plugin support requires Phase A (HOW_TO_RUN.md §10).
+  # ── Gazebo Harmonic ───────────────────────────────────────────────────────────
+  # Runs gz sim with mars_surrogate.sdf (Mars gravity, flat terrain,
+  # rover/UAV/cryobot models).  Plugin .so files are compiled into the image
+  # by the multi-stage gazebo.Dockerfile (Phase A).
+  # GZ_IP and GZ_PARTITION must match the ros2 service for gz-transport peer
+  # discovery to work across Docker bridge network containers (Phase B).
+  #
+  # GUI: the command detects $$DISPLAY at runtime.
+  #   With display (make run on a desktop): opens the full Gazebo 3D window.
+  #   Without display (CI / headless server): runs server-only (-s flag).
+  # LIBGL_ALWAYS_SOFTWARE forces Mesa llvmpipe — no GPU passthrough required.
+  # The /tmp/.X11-unix bind-mount forwards the host X11 socket into the container.
   gazebo:
     image: sakura/gazebo:local
     container_name: sakura_gazebo
@@ -57,7 +64,21 @@ services:
       dockerfile: .ci/gazebo.Dockerfile
     volumes:
       - ./simulation:/app/simulation:ro
-    command: gz sim -r -s /app/simulation/worlds/mars_surrogate.sdf
+      - /tmp/.X11-unix:/tmp/.X11-unix:rw
+    command: >
+      bash -c "
+        if [ -n \"$$DISPLAY\" ]; then
+          gz sim -r /app/simulation/worlds/mars_surrogate.sdf;
+        else
+          gz sim -r -s /app/simulation/worlds/mars_surrogate.sdf;
+        fi
+      "
+    environment:
+      - DISPLAY
+      - GZ_IP=gazebo
+      - GZ_PARTITION=sakura
+      - LIBGL_ALWAYS_SOFTWARE=1
+      - MESA_GL_VERSION_OVERRIDE=3.3
     networks:
       - sakura-net
     depends_on:
@@ -71,9 +92,11 @@ services:
       start_period: 30s
 
   # ── Space ROS 2 ───────────────────────────────────────────────────────────────
-  # Builds the rover workspace with colcon, then launches teleop_node via
-  # rover.launch.py (lifecycle node, starts in unconfigured state).
-  # sim.launch.py (Gazebo bridge) requires ros_gz_bridge — see Phase B.
+  # Builds the rover workspace with colcon, then launches via sim.launch.py
+  # which starts ros_gz_bridge (bridging /cmd_vel and odometry) and teleop_node.
+  # use_external_gz:=true skips launching a second gz sim process — the gazebo
+  # service above already owns the physics server.
+  # Set LAUNCH_MODE=rover to fall back to rover.launch.py (no bridge, no Gazebo).
   ros2:
     image: sakura/ros2:local
     container_name: sakura_ros2
@@ -88,15 +111,18 @@ services:
         cd /workspace &&
         colcon build --base-paths ros2_ws/src --symlink-install &&
         source install/setup.bash &&
-        ros2 launch rover_bringup rover.launch.py
+        ros2 launch rover_bringup ${LAUNCH_MODE:-sim}.launch.py use_external_gz:=true
       "
     environment:
       - RMW_IMPLEMENTATION=rmw_cyclonedds_cpp
+      - GZ_IP=gazebo
+      - GZ_PARTITION=sakura
+      - LAUNCH_MODE=sim
     networks:
       - sakura-net
     depends_on:
       gazebo:
-        condition: service_started
+        condition: service_healthy
     healthcheck:
       test: ["CMD-SHELL", "pgrep -f teleop_node || exit 1"]
       interval: 5s
diff --git a/cpu1/startup_scripts/cfe_es_startup.scr b/cpu1/startup_scripts/cfe_es_startup.scr
index 0d90fef..8bd9210 100644
--- a/cpu1/startup_scripts/cfe_es_startup.scr
+++ b/cpu1/startup_scripts/cfe_es_startup.scr
@@ -20,6 +20,7 @@ CFE_APP, /cf/liborbiter_comm.so,    ORBITER_COMM_AppMain,     ORBITER_COMM,
 CFE_APP, /cf/liborbiter_power.so,   ORBITER_POWER_AppMain,    ORBITER_POWER,     85, 16384, 0x0, 0x0;
 CFE_APP, /cf/liborbiter_payload.so, ORBITER_PAYLOAD_AppMain,  ORBITER_PAYLOAD,   86, 16384, 0x0, 0x0;
 CFE_APP, /cf/libmcu_eps_gw.so,      MCU_EPS_GW_AppMain,       MCU_EPS_GW,        90, 16384, 0x0, 0x0;
+CFE_APP, /cf/libsim_adapter.so,    SIM_ADAPTER_AppMain,      SIM_ADAPTER,       95, 16384, 0x0, 0x0;
 CFE_APP, /cf/libmcu_rwa_gw.so,      MCU_RWA_GW_AppMain,       MCU_RWA_GW,        90, 16384, 0x0, 0x0;
 CFE_APP, /cf/libmcu_payload_gw.so,  MCU_PAYLOAD_GW_AppMain,   MCU_PAYLOAD_GW,    90, 16384, 0x0, 0x0;
 CFE_APP, /cf/liborbiter_cdh.so,     ORBITER_CDH_AppMain,      ORBITER_CDH,      100, 32768, 0x0, 0x0;
diff --git a/docs/interfaces/apid-registry.md b/docs/interfaces/apid-registry.md
index e552027..dc67d93 100644
--- a/docs/interfaces/apid-registry.md
+++ b/docs/interfaces/apid-registry.md
@@ -106,6 +106,17 @@ Each FreeRTOS MCU class gets a 16-APID block. Per-instance multiplicity is handl
 | `0x2A0`–`0x2AF` | `mcu_eps` | UART |
 | `0x2B0`–`0x2FF` | *reserved* | — |
 
+## Sim Injection Sub-Allocation (0x500–0x57F)
+
+SITL-only; never placed on any RF link. `sim_adapter` receives these on UDP port 5700 and routes valid packets to the cFE Software Bus. `CFS_FLIGHT_BUILD` guard ensures zero symbols in flight image.
+
+| APID | Macro | Purpose |
+|---|---|---|
+| `0x501` | `SIM_ADAPTER_HK_MID` | `sim_adapter` app housekeeping telemetry |
+| `0x502`–`0x53F` | *reserved* | Unallocated sim sideband |
+| `0x540`–`0x543` | *reserved* | Fault injection SPP APIDs (raw; no cFS MID; see `SIM_FAULT_APID_*` in `_defs/mids.h`) |
+| `0x544`–`0x57F` | *reserved* | Unallocated |
+
 ## AOS Virtual Channel (VC) Allocation
 
 AOS Transfer Frames multiplex multiple data streams on a single link. SAKURA-II uses three VCs on the orbiter-to-ground downlink (CCSDS 732.0-B):
diff --git a/ros2_ws/src/rover_bringup/launch/sim.launch.py b/ros2_ws/src/rover_bringup/launch/sim.launch.py
index d9dab9d..c3b8113 100644
--- a/ros2_ws/src/rover_bringup/launch/sim.launch.py
+++ b/ros2_ws/src/rover_bringup/launch/sim.launch.py
@@ -25,6 +25,7 @@
     ExecuteProcess,
     TimerAction,
 )
+from launch.conditions import UnlessCondition
 from launch.substitutions import LaunchConfiguration, PathJoinSubstitution
 from launch_ros.actions import LifecycleNode, Node
 from launch_ros.substitutions import FindPackageShare
@@ -62,6 +63,15 @@ def generate_launch_description() -> LaunchDescription:
         description="Run Gazebo without GUI (true=headless, false=with GUI)",
     )
 
+    # When running inside Docker Compose the gazebo service already owns the
+    # gz sim process.  Set use_external_gz:=true to skip starting a second
+    # instance and only launch the bridge and teleop_node.
+    use_external_gz_arg = DeclareLaunchArgument(
+        "use_external_gz",
+        default_value="false",
+        description="Skip launching the Gazebo server (use when Gazebo runs externally)",
+    )
+
     # ── Process 1: Gazebo Harmonic server ────────────────────────────────────
     # gz sim -r -s loads the world in headless (server-only) mode.
     # The -r flag starts physics immediately (no manual 'play' required).
@@ -75,6 +85,7 @@ def generate_launch_description() -> LaunchDescription:
         ],
         output="screen",
         name="gz_sim_server",
+        condition=UnlessCondition(LaunchConfiguration("use_external_gz")),
     )
 
     # ── Process 2: ros_gz_bridge ─────────────────────────────────────────────
@@ -134,6 +145,7 @@ def generate_launch_description() -> LaunchDescription:
         params_file_arg,
         sdf_path_arg,
         headless_arg,
+        use_external_gz_arg,
         gz_server,
         gz_bridge,
         teleop_node,
diff --git a/simulation/gazebo_cryobot_plugin/CMakeLists.txt b/simulation/gazebo_cryobot_plugin/CMakeLists.txt
index 297e2aa..e8c3865 100644
--- a/simulation/gazebo_cryobot_plugin/CMakeLists.txt
+++ b/simulation/gazebo_cryobot_plugin/CMakeLists.txt
@@ -15,25 +15,24 @@ if(BUILD_TESTING)
 endif()
 
 # ── Gazebo shared library ─────────────────────────────────────────────────────
-find_package(gazebo QUIET)
+find_package(gz-sim8 QUIET)
+find_package(gz-transport13 QUIET)
+find_package(gz-plugin2 QUIET)
 
-if(NOT gazebo_FOUND)
-    message(WARNING "Gazebo not found — cryobot physics plugin will not be built.")
+if(NOT gz-sim8_FOUND)
+    message(WARNING "gz-sim8 not found — cryobot physics plugin will not be built.")
     return()
 endif()
 
-include_directories(
-    include
-    ${GAZEBO_INCLUDE_DIRS}
-)
-link_directories(${GAZEBO_LIBRARY_DIRS})
-list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")
-
 add_library(cryobot_physics_plugin SHARED
     src/cryobot_physics_plugin.cpp
 )
 target_include_directories(cryobot_physics_plugin PRIVATE include)
 target_compile_options(cryobot_physics_plugin PRIVATE -Wall -Wextra -Werror)
-target_link_libraries(cryobot_physics_plugin ${GAZEBO_LIBRARIES})
+target_link_libraries(cryobot_physics_plugin
+    gz-sim8::gz-sim8
+    gz-transport13::gz-transport13
+    gz-plugin2::gz-plugin2
+)
 
 install(TARGETS cryobot_physics_plugin DESTINATION lib)
diff --git a/simulation/gazebo_cryobot_plugin/include/cryobot_physics_plugin.h b/simulation/gazebo_cryobot_plugin/include/cryobot_physics_plugin.h
index 77b4746..4b90fb2 100644
--- a/simulation/gazebo_cryobot_plugin/include/cryobot_physics_plugin.h
+++ b/simulation/gazebo_cryobot_plugin/include/cryobot_physics_plugin.h
@@ -1,50 +1,50 @@
 #pragma once
 
-#include <gazebo/gazebo.hh>
-#include <gazebo/physics/physics.hh>
-#include <gazebo/common/common.hh>
-#include <gazebo/transport/transport.hh>
+#include <gz/sim/System.hh>
+#include <gz/sim/EntityComponentManager.hh>
+#include <gz/sim/EventManager.hh>
+#include <gz/transport/Node.hh>
+#include <gz/msgs/twist.pb.h>
 
 #include <mutex>
-
-namespace gazebo
-{
+#include <string>
 
 /**
- * CrybotPhysicsPlugin — Gazebo ModelPlugin for a tethered subsurface cryobot.
+ * CrybotPhysicsPlugin — Gazebo Harmonic system plugin for a tethered cryobot.
  *
  * Attach to a model SDF element:
  *   <plugin name="cryobot_physics" filename="libcryobot_physics_plugin.so"/>
  *
- * Models tether tension and ice-penetration force. Subscribes to
- * "~/<model_name>/cmd_vel" for downward velocity commands.
- * OnUpdate() applies net axial force each simulation step.
+ * Models tether spring restoring force and descent thrust.  Subscribes to
+ * "/model/<model_name>/cmd_vel" for downward velocity commands (linear.z).
+ * PreUpdate() applies net axial force to the base link each physics step.
+ *
+ * Phase 38: tether extension derived from world-Z pose; PD controller lands
+ * in Phase 42.
  */
-class CrybotPhysicsPlugin : public ModelPlugin
+class CrybotPhysicsPlugin :
+    public gz::sim::System,
+    public gz::sim::ISystemConfigure,
+    public gz::sim::ISystemPreUpdate
 {
 public:
-    CrybotPhysicsPlugin();
-    ~CrybotPhysicsPlugin() override;
+    void Configure(const gz::sim::Entity &entity,
+                   const std::shared_ptr<const sdf::Element> &sdf,
+                   gz::sim::EntityComponentManager &ecm,
+                   gz::sim::EventManager &eventMgr) override;
 
-    void Load(physics::ModelPtr model, sdf::ElementPtr sdf) override;
-    void Reset() override;
+    void PreUpdate(const gz::sim::UpdateInfo &info,
+                   gz::sim::EntityComponentManager &ecm) override;
 
 private:
-    void OnUpdate();
-    void OnCmdVel(ConstTwistPtr &msg);
+    void OnCmdVel(const gz::msgs::Twist &msg);
 
-    physics::ModelPtr    model_;
-    event::ConnectionPtr update_connection_;
+    gz::sim::Entity entity_{gz::sim::kNullEntity};
+    gz::sim::Entity linkEntity_{gz::sim::kNullEntity};
 
-    transport::NodePtr       node_;
-    transport::SubscriberPtr cmd_vel_sub_;
+    gz::transport::Node node_;
 
-    /* Tether tension magnitude [N]; updated each physics step based on depth. */
     double tether_tension_n_{0.0};
     double descent_rate_ms_{0.0};
     std::mutex cmd_vel_mutex_;
 };
-
-GZ_REGISTER_MODEL_PLUGIN(CrybotPhysicsPlugin)
-
-}  // namespace gazebo
diff --git a/simulation/gazebo_cryobot_plugin/src/cryobot_physics_plugin.cpp b/simulation/gazebo_cryobot_plugin/src/cryobot_physics_plugin.cpp
index 9e08dbd..68d9a38 100644
--- a/simulation/gazebo_cryobot_plugin/src/cryobot_physics_plugin.cpp
+++ b/simulation/gazebo_cryobot_plugin/src/cryobot_physics_plugin.cpp
@@ -1,79 +1,56 @@
 #include "cryobot_physics_plugin.h"
 #include "cryobot_physics_core.h"
 
-#include <gazebo/msgs/msgs.hh>
-
-#include <functional>
-
-namespace gazebo
-{
-
-CrybotPhysicsPlugin::CrybotPhysicsPlugin()
-: model_(nullptr)
-{
-}
-
-CrybotPhysicsPlugin::~CrybotPhysicsPlugin()
-{
-    /* update_connection_ RAII destructor disconnects the WorldUpdateBegin
-     * signal automatically. */
-}
-
-void CrybotPhysicsPlugin::Load(physics::ModelPtr model, sdf::ElementPtr /*sdf*/)
+#include <gz/sim/Model.hh>
+#include <gz/sim/components/ExternalWorldWrenchCmd.hh>
+#include <gz/sim/components/WorldPose.hh>
+#include <gz/msgs/wrench.pb.h>
+#include <gz/plugin/Register.hh>
+
+#include <string>
+#include <vector>
+
+void CrybotPhysicsPlugin::Configure(
+    const gz::sim::Entity &entity,
+    const std::shared_ptr<const sdf::Element> &,
+    gz::sim::EntityComponentManager &ecm,
+    gz::sim::EventManager &)
 {
-    if (!model)
-    {
-        gzerr << "[CrybotPhysicsPlugin] Load called with null model pointer\n";
-        return;
+    entity_ = entity;
+    gz::sim::Model model(entity);
+
+    /* Use the first link as the base link for tether force application. */
+    const std::vector<gz::sim::Entity> links = model.Links(ecm);
+    if (!links.empty()) {
+        linkEntity_ = links.front();
+        ecm.CreateComponent(linkEntity_,
+            gz::sim::components::ExternalWorldWrenchCmd());
+    } else {
+        gzerr << "[CrybotPhysicsPlugin] No links found on model — forces will not be applied\n";
     }
 
-    model_ = model;
-
-    node_ = transport::NodePtr(new transport::Node());
-    node_->Init();
-    const std::string topic = std::string("~/") + model_->GetName() + "/cmd_vel";
-    cmd_vel_sub_ = node_->Subscribe(topic, &CrybotPhysicsPlugin::OnCmdVel, this);
-
-    update_connection_ = event::Events::ConnectWorldUpdateBegin(
-        std::bind(&CrybotPhysicsPlugin::OnUpdate, this));
+    const std::string modelName = model.Name(ecm);
+    const std::string topic = "/model/" + modelName + "/cmd_vel";
+    node_.Subscribe(topic, &CrybotPhysicsPlugin::OnCmdVel, this);
 
-    gzmsg << "[CrybotPhysicsPlugin] Loaded on model: " << model_->GetName()
+    gzmsg << "[CrybotPhysicsPlugin] Loaded on model: " << modelName
           << " — cmd_vel topic: " << topic << "\n";
 }
 
-void CrybotPhysicsPlugin::Reset()
-{
-    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
-    tether_tension_n_ = 0.0;
-    descent_rate_ms_  = 0.0;
-}
-
-void CrybotPhysicsPlugin::OnCmdVel(ConstTwistPtr &msg)
+void CrybotPhysicsPlugin::PreUpdate(
+    const gz::sim::UpdateInfo &,
+    gz::sim::EntityComponentManager &ecm)
 {
-    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
-    /* linear.z is the commanded descent rate (negative = down in NED). */
-    descent_rate_ms_ = msg->linear().z();
-}
-
-void CrybotPhysicsPlugin::OnUpdate()
-{
-    if (!model_)
-    {
-        return;
-    }
-
-    auto links = model_->GetLinks();
-    if (links.empty())
-    {
+    if (linkEntity_ == gz::sim::kNullEntity)
         return;
-    }
-
-    auto base = links.front();
 
-    /* Compute approximate depth from world origin as a proxy for tether
-     * extension. A full Phase 42+ implementation reads the tether joint
-     * state directly. */
-    const double depth = -base->GetWorldPose().pos.z;
+    /* Compute approximate depth from world Z as proxy for tether extension.
+     * Phase 42+ reads the tether joint state directly. */
+    const auto *poseComp =
+        ecm.Component<gz::sim::components::WorldPose>(linkEntity_);
+    const double depth = (poseComp != nullptr)
+        ? -poseComp->Data().Pos().Z()
+        : 0.0;
 
     double descent = 0.0;
     {
@@ -88,9 +65,26 @@ void CrybotPhysicsPlugin::OnUpdate()
         tether_tension_n_ = step.tether_tension_n;
     }
 
-    /* Apply net axial force: tether restoring (upward) + descent thrust.
-     * Phase 42+ replaces the proportional mapping with a PD controller. */
-    base->AddRelativeForce(math::Vector3(0.0, 0.0, step.net_force_z));
+    /* Apply net axial force: tether restoring (upward) + descent thrust. */
+    auto *wrenchCmd = ecm.Component<gz::sim::components::ExternalWorldWrenchCmd>(linkEntity_);
+    if (wrenchCmd) {
+        gz::msgs::Wrench wrench;
+        wrench.mutable_force()->set_x(0.0);
+        wrench.mutable_force()->set_y(0.0);
+        wrench.mutable_force()->set_z(step.net_force_z);
+        wrench.mutable_torque()->set_x(0.0);
+        wrench.mutable_torque()->set_y(0.0);
+        wrench.mutable_torque()->set_z(0.0);
+        wrenchCmd->Data() = wrench;
+    }
+}
+
+void CrybotPhysicsPlugin::OnCmdVel(const gz::msgs::Twist &msg)
+{
+    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
+    /* linear.z is the commanded descent rate (negative = down in NED). */
+    descent_rate_ms_ = msg.linear().z();
 }
 
-}  // namespace gazebo
+GZ_ADD_PLUGIN(CrybotPhysicsPlugin, gz::sim::System,
+              gz::sim::ISystemConfigure, gz::sim::ISystemPreUpdate)
diff --git a/simulation/gazebo_rover_plugin/CMakeLists.txt b/simulation/gazebo_rover_plugin/CMakeLists.txt
index 0401851..e97c799 100644
--- a/simulation/gazebo_rover_plugin/CMakeLists.txt
+++ b/simulation/gazebo_rover_plugin/CMakeLists.txt
@@ -4,25 +4,24 @@ project(gazebo_rover_plugin CXX)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
-find_package(gazebo QUIET)
+find_package(gz-sim8 QUIET)
+find_package(gz-transport13 QUIET)
+find_package(gz-plugin2 QUIET)
 
-if(NOT gazebo_FOUND)
-    message(WARNING "Gazebo not found — rover drive plugin will not be built. Install Gazebo Harmonic to enable.")
+if(NOT gz-sim8_FOUND)
+    message(WARNING "gz-sim8 not found — rover drive plugin will not be built. Install Gazebo Harmonic to enable.")
     return()
 endif()
 
-include_directories(
-    include
-    ${GAZEBO_INCLUDE_DIRS}
-)
-link_directories(${GAZEBO_LIBRARY_DIRS})
-list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")
-
 add_library(rover_drive_plugin SHARED
     src/rover_drive_plugin.cpp
 )
 target_include_directories(rover_drive_plugin PRIVATE include)
 target_compile_options(rover_drive_plugin PRIVATE -Wall -Wextra -Werror)
-target_link_libraries(rover_drive_plugin ${GAZEBO_LIBRARIES})
+target_link_libraries(rover_drive_plugin
+    gz-sim8::gz-sim8
+    gz-transport13::gz-transport13
+    gz-plugin2::gz-plugin2
+)
 
 install(TARGETS rover_drive_plugin DESTINATION lib)
diff --git a/simulation/gazebo_rover_plugin/include/rover_drive_plugin.h b/simulation/gazebo_rover_plugin/include/rover_drive_plugin.h
index 3365a92..acfe6e6 100644
--- a/simulation/gazebo_rover_plugin/include/rover_drive_plugin.h
+++ b/simulation/gazebo_rover_plugin/include/rover_drive_plugin.h
@@ -1,49 +1,49 @@
 #pragma once
 
-#include <gazebo/gazebo.hh>
-#include <gazebo/physics/physics.hh>
-#include <gazebo/common/common.hh>
-#include <gazebo/transport/transport.hh>
+#include <gz/sim/System.hh>
+#include <gz/sim/EntityComponentManager.hh>
+#include <gz/sim/EventManager.hh>
+#include <gz/transport/Node.hh>
+#include <gz/msgs/twist.pb.h>
 
 #include <mutex>
-
-namespace gazebo
-{
+#include <string>
 
 /**
- * RoverDrivePlugin — Gazebo ModelPlugin for a wheeled rover chassis.
+ * RoverDrivePlugin — Gazebo Harmonic system plugin for a wheeled rover chassis.
  *
  * Attach to a model SDF element:
  *   <plugin name="rover_drive" filename="librover_drive_plugin.so"/>
  *
- * Subscribes to "~/<model_name>/cmd_vel" for differential-drive velocity
- * commands (linear.x = forward m/s, angular.z = yaw rad/s).
- * OnUpdate() is called every simulation step. It must not block.
+ * Subscribes to "/model/<model_name>/cmd_vel" (gz::msgs::Twist) for
+ * differential-drive velocity commands (linear.x = forward m/s,
+ * angular.z = yaw rad/s).  PreUpdate() applies per-wheel angular velocity
+ * to left_wheel_joint and right_wheel_joint via JointVelocityCmd each step.
  */
-class RoverDrivePlugin : public ModelPlugin
+class RoverDrivePlugin :
+    public gz::sim::System,
+    public gz::sim::ISystemConfigure,
+    public gz::sim::ISystemPreUpdate
 {
 public:
-    RoverDrivePlugin();
-    ~RoverDrivePlugin() override;
+    void Configure(const gz::sim::Entity &entity,
+                   const std::shared_ptr<const sdf::Element> &sdf,
+                   gz::sim::EntityComponentManager &ecm,
+                   gz::sim::EventManager &eventMgr) override;
 
-    void Load(physics::ModelPtr model, sdf::ElementPtr sdf) override;
-    void Reset() override;
+    void PreUpdate(const gz::sim::UpdateInfo &info,
+                   gz::sim::EntityComponentManager &ecm) override;
 
 private:
-    void OnUpdate();
-    void OnCmdVel(ConstTwistPtr &msg);
+    void OnCmdVel(const gz::msgs::Twist &msg);
 
-    physics::ModelPtr    model_;
-    event::ConnectionPtr update_connection_;
+    gz::sim::Entity entity_{gz::sim::kNullEntity};
+    gz::sim::Entity leftJointEntity_{gz::sim::kNullEntity};
+    gz::sim::Entity rightJointEntity_{gz::sim::kNullEntity};
 
-    transport::NodePtr       node_;
-    transport::SubscriberPtr cmd_vel_sub_;
+    gz::transport::Node node_;
 
     double lin_vel_{0.0};
     double ang_vel_{0.0};
     std::mutex cmd_vel_mutex_;
 };
-
-GZ_REGISTER_MODEL_PLUGIN(RoverDrivePlugin)
-
-}  // namespace gazebo
diff --git a/simulation/gazebo_rover_plugin/src/rover_drive_plugin.cpp b/simulation/gazebo_rover_plugin/src/rover_drive_plugin.cpp
index 62a15ee..ac27ce0 100644
--- a/simulation/gazebo_rover_plugin/src/rover_drive_plugin.cpp
+++ b/simulation/gazebo_rover_plugin/src/rover_drive_plugin.cpp
@@ -1,71 +1,46 @@
 #include "rover_drive_plugin.h"
 
-#include <gazebo/msgs/msgs.hh>
-#include <gazebo/transport/transport.hh>
+#include <gz/sim/Model.hh>
+#include <gz/sim/components/JointVelocityCmd.hh>
+#include <gz/plugin/Register.hh>
 
-#include <functional>
+#include <string>
 
-namespace gazebo
-{
-
-/* Physical parameters of the rover chassis used for differential-drive kinematics. */
-static constexpr double WHEEL_RADIUS_M  = 0.1;   /* wheel radius [m] */
-static constexpr double HALF_TRACK_M    = 0.2;   /* half track width [m] */
-
-RoverDrivePlugin::RoverDrivePlugin()
-: model_(nullptr)
-{
-}
-
-RoverDrivePlugin::~RoverDrivePlugin()
-{
-    /* update_connection_ RAII destructor disconnects the WorldUpdateBegin
-     * signal automatically — no explicit Disconnect() call needed. */
-}
+/* Physical parameters of the rover chassis. */
+static constexpr double WHEEL_RADIUS_M = 0.1;
+static constexpr double HALF_TRACK_M   = 0.2;
 
-void RoverDrivePlugin::Load(physics::ModelPtr model, sdf::ElementPtr /*sdf*/)
+void RoverDrivePlugin::Configure(
+    const gz::sim::Entity &entity,
+    const std::shared_ptr<const sdf::Element> &,
+    gz::sim::EntityComponentManager &ecm,
+    gz::sim::EventManager &)
 {
-    if (!model)
-    {
-        gzerr << "[RoverDrivePlugin] Load called with null model pointer\n";
-        return;
-    }
+    entity_ = entity;
+    gz::sim::Model model(entity);
 
-    model_ = model;
+    leftJointEntity_  = model.JointByName(ecm, "left_wheel_joint");
+    rightJointEntity_ = model.JointByName(ecm, "right_wheel_joint");
 
-    node_ = transport::NodePtr(new transport::Node());
-    node_->Init();
-    const std::string topic = std::string("~/") + model_->GetName() + "/cmd_vel";
-    cmd_vel_sub_ = node_->Subscribe(topic, &RoverDrivePlugin::OnCmdVel, this);
+    if (leftJointEntity_ != gz::sim::kNullEntity)
+        ecm.CreateComponent(leftJointEntity_,
+            gz::sim::components::JointVelocityCmd({0.0}));
+    if (rightJointEntity_ != gz::sim::kNullEntity)
+        ecm.CreateComponent(rightJointEntity_,
+            gz::sim::components::JointVelocityCmd({0.0}));
 
-    update_connection_ = event::Events::ConnectWorldUpdateBegin(
-        std::bind(&RoverDrivePlugin::OnUpdate, this));
+    const std::string modelName = model.Name(ecm);
+    const std::string topic = "/model/" + modelName + "/cmd_vel";
+    node_.Subscribe(topic, &RoverDrivePlugin::OnCmdVel, this);
 
-    gzmsg << "[RoverDrivePlugin] Loaded on model: " << model_->GetName()
+    gzmsg << "[RoverDrivePlugin] Loaded on model: " << modelName
           << " — cmd_vel topic: " << topic << "\n";
 }
 
-void RoverDrivePlugin::Reset()
-{
-    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
-    lin_vel_ = 0.0;
-    ang_vel_ = 0.0;
-}
-
-void RoverDrivePlugin::OnCmdVel(ConstTwistPtr &msg)
+void RoverDrivePlugin::PreUpdate(
+    const gz::sim::UpdateInfo &,
+    gz::sim::EntityComponentManager &ecm)
 {
-    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
-    lin_vel_ = msg->linear().x();
-    ang_vel_ = msg->angular().z();
-}
-
-void RoverDrivePlugin::OnUpdate()
-{
-    if (!model_)
-    {
-        return;
-    }
-
     double lin = 0.0;
     double ang = 0.0;
     {
@@ -78,17 +53,22 @@ void RoverDrivePlugin::OnUpdate()
     const double left_rad_s  = (lin - ang * HALF_TRACK_M) / WHEEL_RADIUS_M;
     const double right_rad_s = (lin + ang * HALF_TRACK_M) / WHEEL_RADIUS_M;
 
-    auto left_joint  = model_->GetJoint("left_wheel_joint");
-    auto right_joint = model_->GetJoint("right_wheel_joint");
-
-    if (left_joint)
-    {
-        left_joint->SetVelocity(0U, left_rad_s);
+    if (leftJointEntity_ != gz::sim::kNullEntity) {
+        auto *cmd = ecm.Component<gz::sim::components::JointVelocityCmd>(leftJointEntity_);
+        if (cmd) cmd->Data() = {left_rad_s};
     }
-    if (right_joint)
-    {
-        right_joint->SetVelocity(0U, right_rad_s);
+    if (rightJointEntity_ != gz::sim::kNullEntity) {
+        auto *cmd = ecm.Component<gz::sim::components::JointVelocityCmd>(rightJointEntity_);
+        if (cmd) cmd->Data() = {right_rad_s};
     }
 }
 
-}  // namespace gazebo
+void RoverDrivePlugin::OnCmdVel(const gz::msgs::Twist &msg)
+{
+    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
+    lin_vel_ = msg.linear().x();
+    ang_vel_ = msg.angular().z();
+}
+
+GZ_ADD_PLUGIN(RoverDrivePlugin, gz::sim::System,
+              gz::sim::ISystemConfigure, gz::sim::ISystemPreUpdate)
diff --git a/simulation/gazebo_uav_plugin/CMakeLists.txt b/simulation/gazebo_uav_plugin/CMakeLists.txt
index b7367e3..5d42e20 100644
--- a/simulation/gazebo_uav_plugin/CMakeLists.txt
+++ b/simulation/gazebo_uav_plugin/CMakeLists.txt
@@ -15,25 +15,24 @@ if(BUILD_TESTING)
 endif()
 
 # ── Gazebo shared library ─────────────────────────────────────────────────────
-find_package(gazebo QUIET)
+find_package(gz-sim8 QUIET)
+find_package(gz-transport13 QUIET)
+find_package(gz-plugin2 QUIET)
 
-if(NOT gazebo_FOUND)
-    message(WARNING "Gazebo not found — UAV flight plugin will not be built.")
+if(NOT gz-sim8_FOUND)
+    message(WARNING "gz-sim8 not found — UAV flight plugin will not be built.")
     return()
 endif()
 
-include_directories(
-    include
-    ${GAZEBO_INCLUDE_DIRS}
-)
-link_directories(${GAZEBO_LIBRARY_DIRS})
-list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")
-
 add_library(uav_flight_plugin SHARED
     src/uav_flight_plugin.cpp
 )
 target_include_directories(uav_flight_plugin PRIVATE include)
 target_compile_options(uav_flight_plugin PRIVATE -Wall -Wextra -Werror)
-target_link_libraries(uav_flight_plugin ${GAZEBO_LIBRARIES})
+target_link_libraries(uav_flight_plugin
+    gz-sim8::gz-sim8
+    gz-transport13::gz-transport13
+    gz-plugin2::gz-plugin2
+)
 
 install(TARGETS uav_flight_plugin DESTINATION lib)
diff --git a/simulation/gazebo_uav_plugin/include/uav_flight_plugin.h b/simulation/gazebo_uav_plugin/include/uav_flight_plugin.h
index aa5ec27..897b8c3 100644
--- a/simulation/gazebo_uav_plugin/include/uav_flight_plugin.h
+++ b/simulation/gazebo_uav_plugin/include/uav_flight_plugin.h
@@ -1,48 +1,50 @@
 #pragma once
 
-#include <gazebo/gazebo.hh>
-#include <gazebo/physics/physics.hh>
-#include <gazebo/common/common.hh>
-#include <gazebo/transport/transport.hh>
+#include <gz/sim/System.hh>
+#include <gz/sim/EntityComponentManager.hh>
+#include <gz/sim/EventManager.hh>
+#include <gz/transport/Node.hh>
+#include <gz/msgs/twist.pb.h>
 
 #include <mutex>
-
-namespace gazebo
-{
+#include <string>
 
 /**
- * UavFlightPlugin — Gazebo ModelPlugin for a UAV (fixed or rotary wing).
+ * UavFlightPlugin — Gazebo Harmonic system plugin for a UAV (rotary wing).
  *
  * Attach to a model SDF element:
  *   <plugin name="uav_flight" filename="libuav_flight_plugin.so"/>
  *
- * Subscribes to "~/<model_name>/cmd_vel" for attitude + thrust commands.
- * OnUpdate() applies torques to rotor joints each simulation step.
+ * Subscribes to "/model/<model_name>/cmd_vel" for thrust + yaw commands
+ * (linear.z = collective thrust N, angular.z = yaw rate rad/s).
+ * PreUpdate() applies net force/torque to the base link via
+ * ExternalWorldWrenchCmd each physics step.
+ *
+ * Phase 38: direct mapping; per-rotor torque model lands in Phase 42.
  */
-class UavFlightPlugin : public ModelPlugin
+class UavFlightPlugin :
+    public gz::sim::System,
+    public gz::sim::ISystemConfigure,
+    public gz::sim::ISystemPreUpdate
 {
 public:
-    UavFlightPlugin();
-    ~UavFlightPlugin() override;
+    void Configure(const gz::sim::Entity &entity,
+                   const std::shared_ptr<const sdf::Element> &sdf,
+                   gz::sim::EntityComponentManager &ecm,
+                   gz::sim::EventManager &eventMgr) override;
 
-    void Load(physics::ModelPtr model, sdf::ElementPtr sdf) override;
-    void Reset() override;
+    void PreUpdate(const gz::sim::UpdateInfo &info,
+                   gz::sim::EntityComponentManager &ecm) override;
 
 private:
-    void OnUpdate();
-    void OnCmdVel(ConstTwistPtr &msg);
+    void OnCmdVel(const gz::msgs::Twist &msg);
 
-    physics::ModelPtr    model_;
-    event::ConnectionPtr update_connection_;
+    gz::sim::Entity entity_{gz::sim::kNullEntity};
+    gz::sim::Entity linkEntity_{gz::sim::kNullEntity};
 
-    transport::NodePtr       node_;
-    transport::SubscriberPtr cmd_vel_sub_;
+    gz::transport::Node node_;
 
     double thrust_{0.0};
     double yaw_rate_{0.0};
     std::mutex cmd_vel_mutex_;
 };
-
-GZ_REGISTER_MODEL_PLUGIN(UavFlightPlugin)
-
-}  // namespace gazebo
diff --git a/simulation/gazebo_uav_plugin/src/uav_flight_plugin.cpp b/simulation/gazebo_uav_plugin/src/uav_flight_plugin.cpp
index d390828..d52f2ee 100644
--- a/simulation/gazebo_uav_plugin/src/uav_flight_plugin.cpp
+++ b/simulation/gazebo_uav_plugin/src/uav_flight_plugin.cpp
@@ -1,67 +1,48 @@
 #include "uav_flight_plugin.h"
 #include "uav_flight_core.h"
 
-#include <gazebo/msgs/msgs.hh>
-
-#include <functional>
-
-namespace gazebo
-{
-
-UavFlightPlugin::UavFlightPlugin()
-: model_(nullptr)
-{
-}
-
-UavFlightPlugin::~UavFlightPlugin()
-{
-    /* update_connection_ RAII destructor disconnects the WorldUpdateBegin
-     * signal automatically. */
-}
-
-void UavFlightPlugin::Load(physics::ModelPtr model, sdf::ElementPtr /*sdf*/)
+#include <gz/sim/Model.hh>
+#include <gz/sim/components/ExternalWorldWrenchCmd.hh>
+#include <gz/msgs/wrench.pb.h>
+#include <gz/plugin/Register.hh>
+
+#include <string>
+#include <vector>
+
+void UavFlightPlugin::Configure(
+    const gz::sim::Entity &entity,
+    const std::shared_ptr<const sdf::Element> &,
+    gz::sim::EntityComponentManager &ecm,
+    gz::sim::EventManager &)
 {
-    if (!model)
-    {
-        gzerr << "[UavFlightPlugin] Load called with null model pointer\n";
-        return;
+    entity_ = entity;
+    gz::sim::Model model(entity);
+
+    /* Use the first link as the base link for force and torque application.
+     * Phase 42+ will replace this with per-rotor entity selection. */
+    const std::vector<gz::sim::Entity> links = model.Links(ecm);
+    if (!links.empty()) {
+        linkEntity_ = links.front();
+        ecm.CreateComponent(linkEntity_,
+            gz::sim::components::ExternalWorldWrenchCmd());
+    } else {
+        gzerr << "[UavFlightPlugin] No links found on model — forces will not be applied\n";
     }
 
-    model_ = model;
+    const std::string modelName = model.Name(ecm);
+    const std::string topic = "/model/" + modelName + "/cmd_vel";
+    node_.Subscribe(topic, &UavFlightPlugin::OnCmdVel, this);
 
-    node_ = transport::NodePtr(new transport::Node());
-    node_->Init();
-    const std::string topic = std::string("~/") + model_->GetName() + "/cmd_vel";
-    cmd_vel_sub_ = node_->Subscribe(topic, &UavFlightPlugin::OnCmdVel, this);
-
-    update_connection_ = event::Events::ConnectWorldUpdateBegin(
-        std::bind(&UavFlightPlugin::OnUpdate, this));
-
-    gzmsg << "[UavFlightPlugin] Loaded on model: " << model_->GetName()
+    gzmsg << "[UavFlightPlugin] Loaded on model: " << modelName
           << " — cmd_vel topic: " << topic << "\n";
 }
 
-void UavFlightPlugin::Reset()
+void UavFlightPlugin::PreUpdate(
+    const gz::sim::UpdateInfo &,
+    gz::sim::EntityComponentManager &ecm)
 {
-    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
-    thrust_   = 0.0;
-    yaw_rate_ = 0.0;
-}
-
-void UavFlightPlugin::OnCmdVel(ConstTwistPtr &msg)
-{
-    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
-    /* linear.z is mapped to collective thrust; angular.z to yaw rate. */
-    thrust_   = msg->linear().z();
-    yaw_rate_ = msg->angular().z();
-}
-
-void UavFlightPlugin::OnUpdate()
-{
-    if (!model_)
-    {
+    if (linkEntity_ == gz::sim::kNullEntity)
         return;
-    }
 
     double thrust   = 0.0;
     double yaw_rate = 0.0;
@@ -71,19 +52,31 @@ void UavFlightPlugin::OnUpdate()
         yaw_rate = yaw_rate_;
     }
 
-    /* Apply collective thrust as an upward body-frame force. The rotor
-     * joints are used in a full implementation; for Phase 38 we apply
-     * the net force directly to the base link so the UAV is controllable
-     * in simulation before per-rotor torque modeling lands. */
-    auto links = model_->GetLinks();
-    if (!links.empty())
-    {
-        const auto cmd = gazebo_uav::compute_force_cmd(thrust, yaw_rate);
-        auto base = links.front();
-        /* Force in world Z; torque about world Z for yaw. */
-        base->AddRelativeForce(math::Vector3(0.0, 0.0, cmd.force_z));
-        base->AddRelativeTorque(math::Vector3(0.0, 0.0, cmd.torque_z));
+    /* Apply collective thrust as world-frame +Z force; yaw torque about world
+     * +Z.  Forces are in world frame — appropriate for a hover-stable UAV at
+     * small angles.  Phase 42+ replaces with body-frame per-rotor wrench. */
+    const auto cmd = gazebo_uav::compute_force_cmd(thrust, yaw_rate);
+
+    auto *wrenchCmd = ecm.Component<gz::sim::components::ExternalWorldWrenchCmd>(linkEntity_);
+    if (wrenchCmd) {
+        gz::msgs::Wrench wrench;
+        wrench.mutable_force()->set_x(0.0);
+        wrench.mutable_force()->set_y(0.0);
+        wrench.mutable_force()->set_z(cmd.force_z);
+        wrench.mutable_torque()->set_x(0.0);
+        wrench.mutable_torque()->set_y(0.0);
+        wrench.mutable_torque()->set_z(cmd.torque_z);
+        wrenchCmd->Data() = wrench;
     }
 }
 
-}  // namespace gazebo
+void UavFlightPlugin::OnCmdVel(const gz::msgs::Twist &msg)
+{
+    std::lock_guard<std::mutex> lock(cmd_vel_mutex_);
+    /* linear.z is mapped to collective thrust; angular.z to yaw rate. */
+    thrust_   = msg.linear().z();
+    yaw_rate_ = msg.angular().z();
+}
+
+GZ_ADD_PLUGIN(UavFlightPlugin, gz::sim::System,
+              gz::sim::ISystemConfigure, gz::sim::ISystemPreUpdate)
diff --git a/simulation/gazebo_world_plugin/CMakeLists.txt b/simulation/gazebo_world_plugin/CMakeLists.txt
index 18d4c88..cc7e891 100644
--- a/simulation/gazebo_world_plugin/CMakeLists.txt
+++ b/simulation/gazebo_world_plugin/CMakeLists.txt
@@ -15,25 +15,22 @@ if(BUILD_TESTING)
 endif()
 
 # ── Gazebo shared library ─────────────────────────────────────────────────────
-find_package(gazebo QUIET)
+find_package(gz-sim8 QUIET)
+find_package(gz-plugin2 QUIET)
 
-if(NOT gazebo_FOUND)
-    message(WARNING "Gazebo not found — world environment plugin will not be built.")
+if(NOT gz-sim8_FOUND)
+    message(WARNING "gz-sim8 not found — world environment plugin will not be built.")
     return()
 endif()
 
-include_directories(
-    include
-    ${GAZEBO_INCLUDE_DIRS}
-)
-link_directories(${GAZEBO_LIBRARY_DIRS})
-list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")
-
 add_library(world_environment_plugin SHARED
     src/world_environment_plugin.cpp
 )
 target_include_directories(world_environment_plugin PRIVATE include)
 target_compile_options(world_environment_plugin PRIVATE -Wall -Wextra -Werror)
-target_link_libraries(world_environment_plugin ${GAZEBO_LIBRARIES})
+target_link_libraries(world_environment_plugin
+    gz-sim8::gz-sim8
+    gz-plugin2::gz-plugin2
+)
 
 install(TARGETS world_environment_plugin DESTINATION lib)
diff --git a/simulation/gazebo_world_plugin/include/world_environment_plugin.h b/simulation/gazebo_world_plugin/include/world_environment_plugin.h
index 0976ba9..5e0de14 100644
--- a/simulation/gazebo_world_plugin/include/world_environment_plugin.h
+++ b/simulation/gazebo_world_plugin/include/world_environment_plugin.h
@@ -1,42 +1,38 @@
 #pragma once
 
-#include <gazebo/gazebo.hh>
-#include <gazebo/physics/WorldPtr.hh>
-#include <gazebo/common/common.hh>
+#include <gz/sim/System.hh>
+#include <gz/sim/EntityComponentManager.hh>
+#include <gz/sim/EventManager.hh>
 
-namespace gazebo
-{
+#include <cstdint>
 
 /**
- * WorldEnvironmentPlugin — Gazebo WorldPlugin for the Mars-surrogate environment.
+ * WorldEnvironmentPlugin — Gazebo Harmonic system plugin for the Mars-surrogate world.
  *
  * Attach to the world SDF element:
  *   <plugin name="world_environment" filename="libworld_environment_plugin.so"/>
  *
  * Responsibilities:
- *   - Logs environment properties (gravity, wind, time step) at startup.
- *   - Forwards simulation-time ticks for synchronisation with the TAI authority
- *     (clock_link_model); actual clock authority is a separate container per
- *     docs/architecture/08-timing-and-clocks.md §5.2.
- *   - Emits periodic env telemetry (stub; wired to ICD-sim-fsw in Phase 39+).
+ *   - Logs gravity, world name, and physics step size at startup.
+ *   - Emits periodic heartbeat ticks (Phase 39+ wires to ICD-sim-fsw sideband SPP).
+ *   - Does NOT set time authority — that is a separate clock_link_model container
+ *     per docs/architecture/08-timing-and-clocks.md §5.2.
  */
-class WorldEnvironmentPlugin : public WorldPlugin
+class WorldEnvironmentPlugin :
+    public gz::sim::System,
+    public gz::sim::ISystemConfigure,
+    public gz::sim::ISystemPostUpdate
 {
 public:
-    WorldEnvironmentPlugin();
-    ~WorldEnvironmentPlugin() override;
+    void Configure(const gz::sim::Entity &entity,
+                   const std::shared_ptr<const sdf::Element> &sdf,
+                   gz::sim::EntityComponentManager &ecm,
+                   gz::sim::EventManager &eventMgr) override;
 
-    void Load(physics::WorldPtr world, sdf::ElementPtr sdf) override;
+    void PostUpdate(const gz::sim::UpdateInfo &info,
+                    const gz::sim::EntityComponentManager &ecm) override;
 
 private:
-    void OnUpdate();
-
-    physics::WorldPtr    world_;
-    event::ConnectionPtr update_connection_;
-
+    gz::sim::Entity entity_{gz::sim::kNullEntity};
     uint64_t tick_count_{0U};
 };
-
-GZ_REGISTER_WORLD_PLUGIN(WorldEnvironmentPlugin)
-
-}  // namespace gazebo
diff --git a/simulation/gazebo_world_plugin/src/world_environment_plugin.cpp b/simulation/gazebo_world_plugin/src/world_environment_plugin.cpp
index dd7978e..0691bde 100644
--- a/simulation/gazebo_world_plugin/src/world_environment_plugin.cpp
+++ b/simulation/gazebo_world_plugin/src/world_environment_plugin.cpp
@@ -1,60 +1,41 @@
 #include "world_environment_plugin.h"
 #include "world_environment_core.h"
 
-#include <functional>
-
-namespace gazebo
-{
-
-WorldEnvironmentPlugin::WorldEnvironmentPlugin()
-: world_(nullptr)
+#include <gz/sim/World.hh>
+#include <gz/plugin/Register.hh>
+
+void WorldEnvironmentPlugin::Configure(
+    const gz::sim::Entity &entity,
+    const std::shared_ptr<const sdf::Element> &,
+    gz::sim::EntityComponentManager &ecm,
+    gz::sim::EventManager &)
 {
-}
+    entity_ = entity;
+    gz::sim::World world(entity);
 
-WorldEnvironmentPlugin::~WorldEnvironmentPlugin()
-{
-    /* update_connection_ RAII destructor disconnects the signal automatically. */
-}
+    const std::string name = world.Name(ecm);
+    const auto gravOpt = world.Gravity(ecm);
 
-void WorldEnvironmentPlugin::Load(physics::WorldPtr world, sdf::ElementPtr /*sdf*/)
-{
-    if (!world)
-    {
-        gzerr << "[WorldEnvironmentPlugin] Load called with null world pointer\n";
-        return;
+    gzmsg << "[WorldEnvironmentPlugin] Loaded world: " << name << "\n";
+    if (gravOpt) {
+        gzmsg << "  gravity: (" << gravOpt->X() << ", "
+                                << gravOpt->Y() << ", "
+                                << gravOpt->Z() << ") m/s²\n";
     }
-
-    world_ = world;
-
-    update_connection_ = event::Events::ConnectWorldUpdateBegin(
-        std::bind(&WorldEnvironmentPlugin::OnUpdate, this));
-
-    /* Log environment properties at startup for verification (Phase A gate). */
-    const auto gravity = world_->Gravity();
-    gzmsg << "[WorldEnvironmentPlugin] Loaded world: " << world_->Name() << "\n"
-          << "  gravity      : (" << gravity.X() << ", "
-                                  << gravity.Y() << ", "
-                                  << gravity.Z() << ") m/s²\n"
-          << "  max_step_size: " << world_->Physics()->GetMaxStepSize() << " s\n";
 }
 
-void WorldEnvironmentPlugin::OnUpdate()
+void WorldEnvironmentPlugin::PostUpdate(
+    const gz::sim::UpdateInfo &,
+    const gz::sim::EntityComponentManager &)
 {
-    if (!world_)
-    {
-        return;
-    }
-
     ++tick_count_;
 
-    if (gazebo_world::should_emit_heartbeat(tick_count_))
-    {
+    if (gazebo_world::should_emit_heartbeat(tick_count_)) {
         /* Periodic heartbeat — Phase 39+ will replace this with sideband
          * SPP emission to the FSW sim_adapter app. */
-        gzmsg << "[WorldEnvironmentPlugin] sim_time="
-              << world_->SimTime().Double() << " s"
-              << "  tick=" << tick_count_ << "\n";
+        gzmsg << "[WorldEnvironmentPlugin] tick=" << tick_count_ << "\n";
     }
 }
 
-}  // namespace gazebo
+GZ_ADD_PLUGIN(WorldEnvironmentPlugin, gz::sim::System,
+              gz::sim::ISystemConfigure, gz::sim::ISystemPostUpdate)