Added double precision above 1000m and kinematics below 1000m

Assets/Scenes/Main.unity

@@ -211,7 +211,7 @@ MeshCollider:
     m_Bits: 0
   m_LayerOverridePriority: 0
   m_IsTrigger: 0
-  m_ProvidesContacts: 0
+  m_ProvidesContacts: 1
   m_Enabled: 1
   serializedVersion: 5
   m_Convex: 0
@@ -1609,6 +1609,8 @@ MonoBehaviour:
   mainEngine: {fileID: 1437557825}
   rb: {fileID: 1172921199}
   altimeter: {fileID: 894314916}
+  physicsTransitionAltitude: 1000
+  useUnityPhysics: 1
 --- !u!54 &1172921199
 Rigidbody:
   m_ObjectHideFlags: 0
@@ -1635,7 +1637,7 @@ Rigidbody:
   m_IsKinematic: 0
   m_Interpolate: 0
   m_Constraints: 0
-  m_CollisionDetection: 2
+  m_CollisionDetection: 0
 --- !u!65 &1172921200
 BoxCollider:
   m_ObjectHideFlags: 0
@@ -1652,7 +1654,7 @@ BoxCollider:
     m_Bits: 0
   m_LayerOverridePriority: 0
   m_IsTrigger: 0
-  m_ProvidesContacts: 0
+  m_ProvidesContacts: 1
   m_Enabled: 1
   serializedVersion: 3
   m_Size: {x: 1, y: 1, z: 1}

Assets/Scripts/RocketPhysics.cs

@@ -13,17 +13,86 @@ public class RocketPhysics : MonoBehaviour
     public DoublePrecisionVector3 velocity;
     public DoublePrecisionVector3 rotation;
 
-    // Start is called once before the first execution of Update after the MonoBehaviour is created
+    [Header("Physics Mode Settings")]
+    public float physicsTransitionAltitude = 1000f; // meters - switch to Unity physics below this
+    public bool useUnityPhysics = true; // current physics mode
+    
+    private Vector3 lastPhysicsPosition;
+
     void Start()
     {
         position = new DoublePrecisionVector3(rb.position.x, rb.position.y, rb.position.z);
         velocity = new DoublePrecisionVector3(rb.linearVelocity.x, rb.linearVelocity.y, rb.linearVelocity.z);
         rotation = new DoublePrecisionVector3(rb.rotation.eulerAngles.x, rb.rotation.eulerAngles.y, rb.rotation.eulerAngles.z);
+        
+        rb.useGravity = false;
+        lastPhysicsPosition = rb.position;
     }
 
-    // Update is called once per frame
+    void FixedUpdate()
-    void Update()
     {
+        // Determine which physics mode to use
+        bool shouldUseUnityPhysics = altimeter.altitude < physicsTransitionAltitude;
+        
+        // Handle mode transition
+        if (shouldUseUnityPhysics != useUnityPhysics)
+        {
+            TransitionPhysicsMode(shouldUseUnityPhysics);
+        }
+        
+        if (useUnityPhysics)
+        {
+            UpdateWithUnityPhysics();
+        }
+        else
+        {
+            UpdateWithDoublePrecision();
+        }
+    }
+
+    void TransitionPhysicsMode(bool toUnityPhysics)
+    {
+        if (toUnityPhysics)
+        {
+            // Transitioning to Unity physics (descending)
+            rb.isKinematic = false;
+            rb.position = new Vector3((float)position.x, (float)position.y, (float)position.z);
+            rb.linearVelocity = new Vector3((float)velocity.x, (float)velocity.y, (float)velocity.z);
+            lastPhysicsPosition = rb.position;
+        }
+        else
+        {
+            // Transitioning to double precision (ascending)
+            rb.isKinematic = true;
+            position = new DoublePrecisionVector3(rb.position.x, rb.position.y, rb.position.z);
+            velocity = new DoublePrecisionVector3(rb.linearVelocity.x, rb.linearVelocity.y, rb.linearVelocity.z);
+        }
+        
+        useUnityPhysics = toUnityPhysics;
+        Debug.Log($"Physics mode switched to: {(useUnityPhysics ? "Unity Physics" : "Double Precision")}");
+    }
+
+    void UpdateWithUnityPhysics()
+    {
+        // Use Unity's physics engine - allows ground interaction
+        double gravityAcceleration = altimeter.gh;
+        Vector3 gravityForce = new Vector3(0, (float)(-gravityAcceleration * rb.mass), 0);
+        
+        Vector3 thrustDirection = rb.rotation * Vector3.up;
+        Vector3 thrustForce = thrustDirection * mainEngine.thrust;
+        
+        rb.AddForce(gravityForce, ForceMode.Force);
+        rb.AddForce(thrustForce, ForceMode.Force);
+        
+        // Update double precision tracking from Unity physics
+        position = new DoublePrecisionVector3(rb.position.x, rb.position.y, rb.position.z);
+        velocity = new DoublePrecisionVector3(rb.linearVelocity.x, rb.linearVelocity.y, rb.linearVelocity.z);
+        rotation = new DoublePrecisionVector3(rb.rotation.eulerAngles.x, rb.rotation.eulerAngles.y, rb.rotation.eulerAngles.z);
+    }
+
+    void UpdateWithDoublePrecision()
+    {
+        // Manual double-precision integration - no ground interaction
         double gravityAcceleration = altimeter.gh;
         double thrustAcceleration = mainEngine.thrust / rb.mass;
 
@@ -36,11 +105,14 @@ public class RocketPhysics : MonoBehaviour
         );
         DoublePrecisionVector3 totalAcceleration = gravityAccelerationVector + thrustAccelerationVector;
 
-        velocity = velocity + totalAcceleration * Time.deltaTime;
+        velocity = velocity + totalAcceleration * Time.fixedDeltaTime;
-        position = position + velocity * Time.deltaTime;
+        position = position + velocity * Time.fixedDeltaTime;
 
-        rb.position = new Vector3((float)position.x, (float)position.y, (float)position.z);
+        // Update Unity transform (kinematic mode)
-        rb.linearVelocity = new Vector3((float)velocity.x, (float)velocity.y, (float)velocity.z);
+        Vector3 newPosition = new Vector3((float)position.x, (float)position.y, (float)position.z);
+        rb.position = newPosition;
+        // Do not set linearVelocity for kinematic bodies
+        // rb.linearVelocity = new Vector3((float)velocity.x, (float)velocity.y, (float)velocity.z);
         rb.rotation = Quaternion.Euler((float)rotation.x, (float)rotation.y, (float)rotation.z);
     }
 }