Add fuel tank leak parameter

docs/source/Support/bskReleaseNotes.rst

@@ -68,6 +68,8 @@ Version |release|
 - ``ConfigureStopTime`` now supports specifying the stop condition as ``<=`` (default, prior behavior) or ``>=`` (new).
   The new option is useful when the user wants to ensure that the simulation runs for at least the specified time,
   instead of at most the specified time.
+- Add the ``fuelLeakRate`` parameter to the :ref:`FuelTank` module to simulate fuel leaks that cause a loss of fuel mass
+  without imparting momentum.
 
 
 Version 2.8.0 (August 30, 2025)

src/simulation/dynamics/FuelTank/_UnitTest/test_mass_depletion.py

@@ -194,5 +194,52 @@ def test_massDepletionTest(show_plots, thrusterConstructor):
                                err_msg="Thruster mass depletion not ramped up")
     np.testing.assert_allclose(fuelMassDot[-1],0, rtol=1e-12, err_msg="Thruster mass depletion not ramped down")
 
+def test_leakyTank():
+    """Module Unit Test"""
+    scObject = spacecraft.Spacecraft()
+    scObject.ModelTag = "spacecraftBody"
+    unitTaskName = "unitTask"
+    unitProcessName = "TestProcess"
+
+    #   Create a sim module as an empty container
+    unitTestSim = SimulationBaseClass.SimBaseClass()
+
+    # Create test thread
+    testProcessRate = macros.sec2nano(0.1)
+    testProc = unitTestSim.CreateNewProcess(unitProcessName)
+    testProc.addTask(unitTestSim.CreateNewTask(unitTaskName, testProcessRate))
+
+    # Make Fuel Tank
+    unitTestSim.fuelTankStateEffector = fuelTank.FuelTank()
+    tankModel = fuelTank.FuelTankModelConstantVolume()
+    unitTestSim.fuelTankStateEffector.setTankModel(tankModel)
+    tankModel.propMassInit = 40.0
+
+    # Add tank
+    scObject.addStateEffector(unitTestSim.fuelTankStateEffector)
+
+    # Make the tank leaky
+    leakRate = 1e-5  # kg/s
+    unitTestSim.fuelTankStateEffector.fuelLeakRate = leakRate # kg/s
+
+    # Add test module to runtime call list
+    unitTestSim.AddModelToTask(unitTaskName, unitTestSim.fuelTankStateEffector)
+    unitTestSim.AddModelToTask(unitTaskName, scObject)
+
+    fuelLog = unitTestSim.fuelTankStateEffector.fuelTankOutMsg.recorder()
+    unitTestSim.AddModelToTask(unitTaskName, fuelLog)
+    unitTestSim.InitializeSimulation()
+
+    stopTime = 1000.0
+    unitTestSim.ConfigureStopTime(macros.sec2nano(stopTime))
+    unitTestSim.ExecuteSimulation()
+
+    fuelMass = fuelLog.fuelMass
+    fuelMassDot = fuelLog.fuelMassDot
+
+    assert np.allclose(fuelMassDot, -leakRate, rtol=1e-6)
+    assert np.isclose(fuelMass[-1], 40.0 - stopTime * leakRate, rtol=1e-6)
+
+
 if __name__ == "__main__":
     test_massDepletionTest(True, thrusterDynamicEffector.ThrusterDynamicEffector)

src/simulation/dynamics/FuelTank/fuelTank.cpp

@@ -106,6 +106,7 @@ void FuelTank::updateEffectorMassProps(double integTime) {
 
     // Mass depletion (call thrusters attached to this tank to get their mDot, and contributions)
     this->fuelConsumption = 0.0;
+    this->fuelConsumption += this->fuelLeakRate;
     for (auto &dynEffector: this->thrDynEffectors) {
         dynEffector->computeStateContribution(integTime);
         this->fuelConsumption += dynEffector->stateDerivContribution(0);

src/simulation/dynamics/FuelTank/fuelTank.h

@@ -270,6 +270,7 @@ class FuelTank :
     bool updateOnly = true;                             //!< -- Sets whether to use update only mass depletion
     Message<FuelTankMsgPayload> fuelTankOutMsg{};       //!< -- fuel tank output message name
     FuelTankMsgPayload fuelTankMassPropMsg{};           //!< instance of messaging system message struct
+    double fuelLeakRate{};                              //!< [kg/s] rate of fuel leaking from tank; does not produce force
 
 private:
     StateData *omegaState{};                            //!< -- state data for omega_BN of the hub