diff --git a/core/src/net/sf/openrocket/simulation/RK4SimulationStatus.java b/core/src/net/sf/openrocket/simulation/RK4SimulationStatus.java
index 67465e16d..d42d951fa 100644
--- a/core/src/net/sf/openrocket/simulation/RK4SimulationStatus.java
+++ b/core/src/net/sf/openrocket/simulation/RK4SimulationStatus.java
@@ -8,7 +8,6 @@ public class RK4SimulationStatus extends SimulationStatus implements Cloneable {
 	private Coordinate launchRodDirection;
 	
 	private double previousAcceleration = 0;
-	private AtmosphericConditions previousAtmosphericConditions;
 	
 	// Used for determining when to store aerodynamic computation warnings:
 	private double maxZVelocity = 0;
@@ -26,7 +25,6 @@ public class RK4SimulationStatus extends SimulationStatus implements Cloneable {
 			this.previousAcceleration = ((RK4SimulationStatus) other).previousAcceleration;
 			this.maxZVelocity = ((RK4SimulationStatus) other).maxZVelocity;
 			this.startWarningTime = ((RK4SimulationStatus) other).startWarningTime;
-			this.previousAtmosphericConditions = ((RK4SimulationStatus) other).previousAtmosphericConditions;
 		}
 	}
 	public void setLaunchRodDirection(Coordinate launchRodDirection) {
@@ -49,18 +47,6 @@ public class RK4SimulationStatus extends SimulationStatus implements Cloneable {
 		this.previousAcceleration = previousAcceleration;
 	}
 	
-	
-	public AtmosphericConditions getPreviousAtmosphericConditions() {
-		return previousAtmosphericConditions;
-	}
-	
-	
-	public void setPreviousAtmosphericConditions(
-			AtmosphericConditions previousAtmosphericConditions) {
-		this.previousAtmosphericConditions = previousAtmosphericConditions;
-	}
-	
-	
 	public double getMaxZVelocity() {
 		return maxZVelocity;
 	}
diff --git a/core/src/net/sf/openrocket/simulation/RK4SimulationStepper.java b/core/src/net/sf/openrocket/simulation/RK4SimulationStepper.java
index 5c3934a0a..0f32bb142 100644
--- a/core/src/net/sf/openrocket/simulation/RK4SimulationStepper.java
+++ b/core/src/net/sf/openrocket/simulation/RK4SimulationStepper.java
@@ -59,9 +59,7 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 	private static final double MAX_PITCH_CHANGE = 4 * Math.PI / 180;
 	
 	private Random random;
-	
-	
-	
+	DataStore store = new DataStore();
 	
 	@Override
 	public RK4SimulationStatus initialize(SimulationStatus original) {
@@ -90,28 +88,32 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 	public void step(SimulationStatus simulationStatus, double maxTimeStep) throws SimulationException {
 		
 		RK4SimulationStatus status = (RK4SimulationStatus) simulationStatus;
-		DataStore store = new DataStore();
 		
 		////////  Perform RK4 integration:  ////////
 		
 		RK4SimulationStatus status2;
 		RK4Parameters k1, k2, k3, k4;
 		
+		
 		/*
 		 * Start with previous time step which is used to compute the initial thrust estimate.
 		 * Don't make it longer than maxTimeStep, but at least MIN_TIME_STEP.
 		 */
-		store.timestep = status.getPreviousTimeStep();
 		store.timestep = MathUtil.max(MathUtil.min(store.timestep, maxTimeStep), MIN_TIME_STEP);
 		checkNaN(store.timestep);
-		
+
+		/*
+		 * Get the current atmospheric conditions
+		 */
+		calculateFlightConditions(status, store);
+		store.atmosphericConditions = store.flightConditions.getAtmosphericConditions();
+
 		/*
 		 * Compute the initial thrust estimate.  This is used for the first time step computation.
 		 */
-		store.thrustForce = calculateAverageThrust(status, store.timestep, status.getPreviousAcceleration(),
-				status.getPreviousAtmosphericConditions(), false);
+		store.thrustForce = calculateAverageThrust(status, store.timestep, store.longitudinalAcceleration,
+												   store.atmosphericConditions, false);
 		
-
 		/*
 		 * Perform RK4 integration.  Decide the time step length after the first step.
 		 */
@@ -150,7 +152,7 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 			dt[0] /= 5.0;
 			dt[6] = status.getSimulationConditions().getLaunchRodLength() / k1.v.length() / 10;
 		}
-		dt[7] = 1.5 * status.getPreviousTimeStep();
+		dt[7] = 1.5 * store.timestep;
 		
 		store.timestep = Double.MAX_VALUE;
 		int limitingValue = -1;
@@ -261,8 +263,6 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 		}
 		status.setSimulationTime(status.getSimulationTime() + store.timestep);
 		
-		status.setPreviousTimeStep(store.timestep);
-		
 		// Store data
 		// TODO: MEDIUM: Store acceleration etc of entire RK4 step, store should be cloned or something...
 		storeData(status, store);
@@ -283,11 +283,17 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 			throws SimulationException {
 		RK4Parameters params = new RK4Parameters();
 		
-		//		if (dataStore == null) {
-		//			dataStore = new DataStore();
-		//		}
+		// Call pre-listeners
+		store.accelerationData = SimulationListenerHelper.firePreAccelerationCalculation(status);
+
+		// Calculate acceleration (if not overridden by pre-listeners)
+		if (store.accelerationData == null) {
+			store.accelerationData = calculateAcceleration(status, dataStore);
+		}
+		
+		// Call post-listeners
+		store.accelerationData = SimulationListenerHelper.firePostAccelerationCalculation(status, store.accelerationData);
 		
-		calculateAcceleration(status, dataStore);
 		params.a = dataStore.linearAcceleration;
 		params.ra = dataStore.angularAcceleration;
 		params.v = status.getRocketVelocity();
@@ -312,13 +318,7 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 	 * @param status   the status of the rocket.
 	 * @throws SimulationException 
 	 */
-	private void calculateAcceleration(RK4SimulationStatus status, DataStore store) throws SimulationException {
-		
-		// Call pre-listeners
-		store.accelerationData = SimulationListenerHelper.firePreAccelerationCalculation(status);
-		if (store.accelerationData != null) {
-			return;
-		}
+	private AccelerationData calculateAcceleration(RK4SimulationStatus status, DataStore store) throws SimulationException {
 		
 		// Compute the forces affecting the rocket
 		calculateForces(status, store);
@@ -403,9 +403,8 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 			store.angularAcceleration = status.getRocketOrientationQuaternion().rotate(store.angularAcceleration);
 			
 		}
-		
-		// Call post-listeners
-		store.accelerationData = SimulationListenerHelper.firePostAccelerationCalculation(status, store.accelerationData);
+
+		return new AccelerationData(null, null, store.linearAcceleration, store.angularAcceleration, status.getRocketOrientationQuaternion());
 	}