finished refactoring to have a distinct part for the balloon and the case ; when cutting the rope the balloon becomes an independent vessel ; the balloon can be destroyed by a collision or over heating

Parts/HeliumBalloon/heliumBalloon.cfg

@@ -4,24 +4,17 @@ PART
 	module = Part
 	author = Youen
 	mesh = model.mu
-	scale = 0.1
-	rescaleFactor = 1
-	node_stack_bottom = 0.0, -0.020649, 0.0, 0.0, -1.0, 0.0, 1
-	node_attach = 0.0, -0.020649, 0.0, 0.0, -1.0, 0.0
-	sound_parachute_open = activate
-	TechRequired = advLanding
-	entryCost = 3500
-	cost = 5000
-	category = Utility
+	TechRequired = Unresearcheable
+	entryCost = 0
+	cost = 0
+	category = none
 	subcategory = 0
 	title = Balloon
-	description = A big balloon that can be inflated with helium (sold separately).
-	attachRules = 1,0,0,1,0
-	mass = 0.2
+	mass = 0.050
 	dragModelType = default
-	angularDrag = 3
+	angularDrag = 10
 	crashTolerance = 12
-	maxTemp = 2000 // = 3100
+	maxTemp = 1000
 	breakingForce = 100
 	breakingTorque = 50
 	bodyLiftMultiplier = 0
@@ -29,6 +22,6 @@ PART
 	bulkheadProfiles = size1, srf
 	MODULE
 	{
-		name = ModuleBalloonCase
+		name = ModuleBalloon
 	}
 }

Parts/HeliumBalloonCase/heliumBalloonCase.cfg

@@ -0,0 +1,34 @@
+PART
+{
+	name = heliumBalloonCase
+	module = Part
+	author = Youen
+	mesh = model.mu
+	scale = 0.1
+	rescaleFactor = 1
+	node_stack_bottom = 0.0, -0.020649, 0.0, 0.0, -1.0, 0.0, 1
+	node_attach = 0.0, -0.020649, 0.0, 0.0, -1.0, 0.0
+	sound_parachute_open = activate
+	TechRequired = advLanding
+	entryCost = 3500
+	cost = 5000
+	category = Utility
+	subcategory = 0
+	title = Balloon
+	description = A big balloon that can be inflated with helium (sold separately).
+	attachRules = 1,0,0,1,0
+	mass = 0.2
+	dragModelType = default
+	angularDrag = 3
+	crashTolerance = 12
+	maxTemp = 2000 // = 3100
+	breakingForce = 100
+	breakingTorque = 50
+	bodyLiftMultiplier = 0
+	stageOffset = -1
+	bulkheadProfiles = size1, srf
+	MODULE
+	{
+		name = ModuleBalloonCase
+	}
+}

Plugin/ModuleBalloon.cs

@@ -8,14 +8,29 @@ namespace Aerostats
 {
     public class ModuleBalloon : PartModule
     {
-        public float MaxBalloonVolume { get; private set; }
-        public float GasDensity { get; private set; }
-        public float BalloonDragCoeff { get; private set; }
-        public float BalloonEmptyMass { get; private set; }
+        /// <summary>
+        /// Volume at which the balloon is full. Trying to add more gas, or simply having already stored gas expand due to lower exterior pressure or increased temperature, will cause gas to be vented through the security valve.
+        /// Air density at sea level is about 1.2kg/m^3, which means a 1000m^3 balloon will be able to lift about 1 ton at sea level (after substracting the balloon gas weight)
+        /// </summary>
+        [KSPField(isPersistant = false, guiActive = false)]
+        public float MaxVolume = 15000;
+
+        /// <summary>
+        /// Drag coefficient of the balloon
+        /// </summary>
+        [KSPField(isPersistant = false, guiActive = false)]
+        public float DragCoeff = 0.3f;
+
+        public float GasMolarMass { get; private set; }
+
+        /// <summary>
+        /// Mass of the empty balloon, in kg
+        /// </summary>
+        public float EmptyMass { get; private set; }
 
         public float LiftingGasQuantity { get; private set; }
         public float CurrentVolume { get; private set; }
-        public float BalloonLift { get; private set; }
+        public float Lift { get; private set; }
         public bool IsVenting { get; private set; }
 
         /// <summary>
@@ -25,22 +40,47 @@ namespace Aerostats
 
         public float Radius { get; private set; }
 
+        public ModuleBalloonCase AttachedCase { get; private set; }
+
         /// <summary>
         /// Must be called right after creating a balloon
         /// </summary>
-        public void Initialize(float emptyMass, Vector3 initialVelocity, float maxVolume, float gasDensity, float dragCoeff)
+        public void Initialize(ModuleBalloonCase attachedCase, Vector3 initialVelocity, float gasDensity, float initialGasQuantity)
         {
-            MaxBalloonVolume = maxVolume;
-            GasDensity = gasDensity;
-            BalloonDragCoeff = dragCoeff;
-            BalloonEmptyMass = emptyMass;
+            AttachedCase = attachedCase;
+            GasMolarMass = gasDensity / GasUtilities.StpVolumeToMoles;
+            EmptyMass = part.mass * 1000.0f;
+
+            // replace mesh and collider by a sphere (hack until proper assets are created)
+            var sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);
+            gameObject.GetComponentInChildren<MeshFilter>().mesh = sphere.GetComponent<MeshFilter>().mesh;
+            Destroy(gameObject.collider);
+            var collider = gameObject.AddComponent<SphereCollider>();
+            collider.radius = 0.67f; // don't ask me, I don't know why
+            Destroy(sphere);
 
             gameObject.AddComponent<Rigidbody>();
-            rigidbody.mass = BalloonEmptyMass;
+            rigidbody.mass = EmptyMass * 0.001f;
             rigidbody.velocity = initialVelocity; // start with the same velocity or everything explodes when deploying from a moving vessel
             rigidbody.angularDrag = 10.0f;
+            rigidbody.position = transform.position;
 
-            InjectGas(0.0001f);
+            InjectGas(initialGasQuantity);
+
+            part.OnJustAboutToBeDestroyed += OnPartDestroyed;
+        }
+
+        public void OnDetached()
+        {
+            AttachedCase = null;
+        }
+
+        private void OnPartDestroyed()
+        {
+            if(AttachedCase != null)
+                AttachedCase.Cut();
+
+            part.OnJustAboutToBeDestroyed -= OnPartDestroyed;
         }
 
         /// <summary>
@@ -56,7 +96,7 @@ namespace Aerostats
             if (LiftingGasQuantity > currentMaxQuantity)
             {
                 IsVenting = true;
-                Util.PostSingleScreenMessage("security valve", "Some gas has been vented by the balloon security valve");
+                Util.PostDebugSingleScreenMessage("security valve", "Some gas has been vented by the balloon security valve");
                 LiftingGasQuantity = currentMaxQuantity;
             }
             else
@@ -73,21 +113,20 @@ namespace Aerostats
 
             float currentGasMoles = GasUtilities.StpVolumeToMoles * LiftingGasQuantity;
             CurrentVolume = currentGasMoles * GasUtilities.R * balloonInternalTemperature / externalPressure;
-            Inflation = CurrentVolume / MaxBalloonVolume;
+            Inflation = CurrentVolume / MaxVolume;
 
-            Util.PostSingleScreenMessage("inflation", "Inflation = " + (Inflation * 100.0f).ToString("0.00") + "%");
+            Util.PostDebugSingleScreenMessage("inflation", "Inflation = " + (Inflation * 100.0f).ToString("0.00") + "%");
 
             float airDensity = (float)FlightGlobals.getAtmDensity(externalPressure / 1000.0f, externalTemperature, body);
-            float currentGasDensity = GasDensity * balloonInternalTemperature / GasUtilities.ZeroCelsius / externalPressure * GasUtilities.StandardPressure;
-            BalloonLift = CurrentVolume * airDensity;
-            float balloonGasMass = currentGasDensity * CurrentVolume;
-            Util.PostSingleScreenMessage("lift", "Air density = " + airDensity + "kg/m^3, Lift = " + (BalloonLift - balloonGasMass) + "kg");
+            Lift = CurrentVolume * airDensity;
+            float balloonGasMass = GasMolarMass * currentGasMoles;
+            Util.PostDebugSingleScreenMessage("lift", "Air density = " + airDensity + "kg/m^3, Lift = " + (Lift - balloonGasMass) + "kg");
 
             // V = 4/3*pi*r^3
             Radius = Mathf.Pow(CurrentVolume * 0.75f / Mathf.PI, 0.333f);
-            float scale = Radius * 2.0f + 0.1f;
+            float scale = Radius + 0.1f;
             transform.localScale = new Vector3(scale, scale, scale);
-            rigidbody.mass = (BalloonEmptyMass + balloonGasMass) * 0.001f;
+            rigidbody.mass = (EmptyMass + balloonGasMass) * 0.001f;
 
             return LiftingGasQuantity;
         }
@@ -103,9 +142,9 @@ namespace Aerostats
             float externalTemperature = (float)FlightGlobals.getExternalTemperature(worldPos, body);
             float balloonInternalTemperature = externalTemperature;
             float externalPressure = Math.Max((float)FlightGlobals.getStaticPressure(worldPos, body) * 1000.0f, 0.00001f);
-            Util.PostSingleScreenMessage("external atmo", "Temperature = " + externalTemperature + "K, Pressure=" + externalPressure + "Pa");
+            Util.PostDebugSingleScreenMessage("external atmo", "Temperature = " + externalTemperature + "K, Pressure=" + externalPressure + "Pa");
 
-            float currentMaxQuantity = MaxBalloonVolume / GasUtilities.R / balloonInternalTemperature * externalPressure / GasUtilities.StpVolumeToMoles;
+            float currentMaxQuantity = MaxVolume / GasUtilities.R / balloonInternalTemperature * externalPressure / GasUtilities.StpVolumeToMoles;
 
             return currentMaxQuantity;
         }
@@ -115,6 +154,8 @@ namespace Aerostats
             Vector3d worldPos = vessel.GetWorldPos3D();
             CelestialBody body = vessel.mainBody;
 
+            rigidbody.WakeUp();
+
             InjectGas(0); // update security valve venting
 
             var gravityAccel = FlightGlobals.getGeeForceAtPosition(worldPos);
@@ -125,14 +166,14 @@ namespace Aerostats
             float externalPressure = Math.Max((float)FlightGlobals.getStaticPressure(worldPos, body) * 1000.0f, 0.00001f);
             float airDensity = (float)FlightGlobals.getAtmDensity(externalPressure / 1000.0f, externalTemperature, body);
 
-            rigidbody.AddForce(-gravityAccel * BalloonLift / 1000.0f, ForceMode.Force);
+            rigidbody.AddForce(-gravityAccel * Lift / 1000.0f, ForceMode.Force);
 
             // balloon drag
             var airVelocity = rigidbody.velocity + Krakensbane.GetFrameVelocity() /*- vessel.mainBody.getRFrmVel(vessel.GetWorldPos3D())*/;
             float sqVel = (float)airVelocity.magnitude;
             sqVel *= sqVel;
-            float dragForce = 0.5f * airDensity * sqVel * BalloonDragCoeff * (Mathf.PI * Radius * Radius);
-            Util.PostSingleScreenMessage("balloon drag", "Drag = " + dragForce + "N");
+            float dragForce = 0.5f * airDensity * sqVel * DragCoeff * (Mathf.PI * Radius * Radius);
+            Util.PostDebugSingleScreenMessage("balloon drag", "Drag = " + dragForce + "N");
             rigidbody.AddForce(-airVelocity.normalized * dragForce / 1000.0f, ForceMode.Force);
         }
     }

Plugin/ModuleBalloonCase.cs

@@ -20,13 +20,6 @@ namespace Aerostats
         [KSPField(isPersistant = false, guiActive = false)]
         public float MaxGasVentRate = 500;
 
-        /// <summary>
-        /// Volume at which the balloon is full. Trying to add more gas, or simply having already stored gas expand due to lower exterior pressure or increased temperature, will cause gas to be vented through the security valve.
-        /// Air density at sea level is about 1.2kg/m^3, which means a 1000m^3 balloon will be able to lift about 1 ton at sea level (after substracting the balloon gas weight)
-        /// </summary>
-        [KSPField(isPersistant = false, guiActive = false)]
-        public float MaxBalloonVolume = 15000;
-
         /// <summary>
         /// Weight, in kilograms, of 1m^3 of gas at 100kPa and 0°C
         /// Helium is 179g/m^3
@@ -43,24 +36,12 @@ namespace Aerostats
         [UI_FloatRange(minValue = 0, maxValue = 20000.0f, stepIncrement = 100.0f)]
         public float LiftingGasTargetQuantity = 100.0f;
 
-        /// <summary>
-        /// Mass of the empty balloon, in kg
-        /// </summary>
-        [KSPField(isPersistant = false, guiActive = false)]
-        public float BalloonEmptyMass = 50.0f;
-
         /// <summary>
         /// Minimum amount of gas that will be used to inflate the balloon at the beginning. The balloon can not be deflated below this amount.
         /// </summary>
         [KSPField(isPersistant = false, guiActive = false)]
         public float MinimumFillQuantity = 10.0f;
 
-        /// <summary>
-        /// Drag coefficient of the balloon
-        /// </summary>
-        [KSPField(isPersistant = false, guiActive = false)]
-        public float BalloonDragCoeff = 0.3f;
-
         /// <summary>
         /// Length of spring that can not be extended (no force applied under this length)
         /// </summary>
@@ -80,6 +61,8 @@ namespace Aerostats
 
         private bool Destroyed;
 
+        private Vector3 EstimatedNextFramePosition;
+
         /// <summary>
         /// Gas quantity currently inside the balloon
         /// </summary>
@@ -92,26 +75,60 @@ namespace Aerostats
         private ModuleBalloon Balloon;
         private LineRenderer Spring;
 
-        private Vector3 EstimatedNextFramePosition;
+        public static void RemoveAttachJointBetween(Part part1, Part part2)
+        {
+            if (part1.attachJoint && ((part1.attachJoint.Host == part1 && part1.attachJoint.Target == part2) || (part1.attachJoint.Host == part2 && part1.attachJoint.Target == part1)))
+            {
+                part1.attachJoint.DestroyJoint();
+            }
+            if (part2.attachJoint && ((part2.attachJoint.Host == part2 && part2.attachJoint.Target == part1) || (part2.attachJoint.Host == part1 && part2.attachJoint.Target == part2)))
+            {
+                part2.attachJoint.DestroyJoint();
+            }
+        }
 
-        [KSPEvent(guiActive = true, active = true, externalToEVAOnly = false, guiActiveUnfocused = true, guiName = "Deploy balloon", unfocusedRange = 5)]
-        public void Deploy()
-        {
+        [KSPEvent(guiActive = true, active = true, externalToEVAOnly = false, guiActiveUnfocused = true, guiName = "Deploy balloon", unfocusedRange = 5)]
+        public void Deploy()
+        {
             if (Destroyed || Deployed)
                 return;
 
             Deployed = true;
 
             UnityEngine.Debug.Log("Aerostats: staged");
-            Util.PostScreenMessage("staged");
+            Util.PostDebugScreenMessage("staged");
 
-            var balloonObject = GameObject.CreatePrimitive(PrimitiveType.Sphere);
+            /*var balloonObject = GameObject.CreatePrimitive(PrimitiveType.Sphere);
+            balloonObject.SetActive(false);
             balloonObject.transform.position = part.Rigidbody.position + part.Rigidbody.transform.up;
-            Balloon = balloonObject.AddComponent<ModuleBalloon>();
-            Balloon.part = part; // TODO: remove this hack and properly instantiate a new vessel?
-            Balloon.Initialize(BalloonEmptyMass, part.rigidbody.velocity, MaxBalloonVolume, GasDensity, BalloonDragCoeff);
-
-            LiftingGasQuantity = Balloon.InjectGas(part.RequestResource("Helium", MinimumFillQuantity));
+            var balloonPart = balloonObject.AddComponent<Part>();
+            balloonPart.children = new List<Part>();
+            balloonPart.partTransform = balloonObject.transform;
+            balloonPart.name = "heliumBalloon";
+            new GameObject("model").transform.parent = balloonPart.partTransform;
+            balloonPart.SetHierarchyRoot(balloonPart);
+            balloonPart.vessel = vessel;
+            balloonPart.setParent(part);*/
+
+            AvailablePart avPart = PartLoader.Instance.parts.Single(p => p.name == "heliumBalloon");
+            var balloonPart = (Part)UnityEngine.Object.Instantiate(avPart.partPrefab);
+            var balloonObject = balloonPart.gameObject;
+            balloonObject.transform.position = part.Rigidbody.position + part.Rigidbody.transform.up * 3.0f;
+            //balloonObject.transform.rotation = part.Rigidbody.rotation;
+            balloonPart.SetHierarchyRoot(balloonPart);
+            balloonPart.vessel = vessel;
+            balloonPart.setParent(part);
+
+            Balloon = balloonObject.GetComponent<ModuleBalloon>();
+            Balloon.part = balloonPart;
+            float initialGasQuantity = Mathf.Min(0.1f, part.RequestResource("Helium", MinimumFillQuantity));
+
+            balloonObject.SetActive(true);
+            GameEvents.onVesselWasModified.Fire(vessel);
+
+            Balloon.Initialize(this, part.rigidbody.velocity, GasDensity, initialGasQuantity);
+
+            LiftingGasQuantity = Balloon.LiftingGasQuantity;
 
             Spring = part.gameObject.AddComponent<LineRenderer>();
             Spring.useWorldSpace = true;
@@ -122,27 +139,33 @@ namespace Aerostats
 
             part.OnJustAboutToBeDestroyed += OnPartDestroyed;
 
-            EstimatedNextFramePosition = part.Rigidbody.position;
+            EstimatedNextFramePosition = part.Rigidbody.position;
         }
 
-        [KSPEvent(guiActive = true, active = true, externalToEVAOnly = false, guiActiveUnfocused = true, guiName = "Cut rope", unfocusedRange = 5)]
-        public void Cut()
-        {
-            if (Destroyed || !Deployed)
+        [KSPEvent(guiActive = true, active = true, externalToEVAOnly = false, guiActiveUnfocused = true, guiName = "Cut rope", unfocusedRange = 5)]
+        public void Cut()
+        {
+            if (Destroyed || !Deployed)
                 return;
 
-            Balloon = null;
+            if (Balloon != null)
+            {
+                Balloon.OnDetached();
+                Balloon.part.decouple(); // after that, the balloon becomes an independent vessel
+                Balloon.part.vessel.vesselName = vessel.vesselName + " balloon";
+                Balloon = null;
+            }
             Destroy(Spring);
             Spring = null;
             part.OnJustAboutToBeDestroyed -= OnPartDestroyed;
-            Destroyed = true;
+            Destroyed = true;
         }
 
         public override void OnStart(PartModule.StartState state)
         {
             if (!HighLogic.LoadedSceneIsEditor && !HighLogic.LoadedSceneIsFlight) { return; }
 
-            Util.PostScreenMessage("Aerostat loaded");
+            Util.PostDebugScreenMessage("Aerostat loaded");
             part.stagingIcon = "PARACHUTES";
         }
 
@@ -151,6 +174,19 @@ namespace Aerostats
             Cut();
         }
 
+        private void CheckKrakensbane()
+        {
+            // detect Krakensbane teleportation, and fix up the balloon position (otherwise it results in instant ship disintegration due to extreme forces on the spring)
+            if ((part.Rigidbody.position - EstimatedNextFramePosition).magnitude > 1000.0f)
+            {
+                Util.PostDebugScreenMessage("Krakensbane teleportation detected! (dist=" + (part.Rigidbody.position - EstimatedNextFramePosition).magnitude + ")");
+                var offset = part.rigidbody.position - EstimatedNextFramePosition;
+                Balloon.rigidbody.position += offset;
+                Balloon.transform.position = Balloon.rigidbody.position;
+            }
+            EstimatedNextFramePosition = part.rigidbody.position + part.rigidbody.velocity * Time.fixedDeltaTime;
+        }
+
         private void FixedUpdate()
         {
             if (Destroyed)
@@ -167,15 +203,10 @@ namespace Aerostats
 
             if (Deployed)
             {
-                // detect Krakensbane teleportation, and fix up the balloon position (otherwise it results in instant ship disintegration due to extreme forces on the spring)
-                if ((part.Rigidbody.position - EstimatedNextFramePosition).magnitude > 1000.0f)
-                {
-                    Util.PostScreenMessage("Krakensbane teleportation detected! (dist=" + (part.Rigidbody.position - EstimatedNextFramePosition).magnitude+")");
-                    var offset = part.rigidbody.position - EstimatedNextFramePosition;
-                    Balloon.rigidbody.position += offset;
-                    Balloon.transform.position = Balloon.rigidbody.position;
-                }
-                EstimatedNextFramePosition = part.rigidbody.position + part.rigidbody.velocity * Time.fixedDeltaTime;
+                // makes sure the balloon can move freely relatively to the vessel (apparently, KSP creates a joint when attaching a part)
+                RemoveAttachJointBetween(Balloon.part, part);
+
+                CheckKrakensbane();
 
                 float currentMaxQuantity = Balloon.GetCurrentMaxQuantity();
 
@@ -209,7 +240,7 @@ namespace Aerostats
                     Status = "full (venting)";
                 }
                 
-                VolumeStatus = Mathf.Round(Balloon.CurrentVolume) + " / " + Mathf.Round(MaxBalloonVolume);
+                VolumeStatus = Mathf.Round(Balloon.CurrentVolume) + " / " + Mathf.Round(Balloon.MaxVolume);
 
                 // spring between balloon and base
                 float restLength = SpringRestLength + Balloon.Radius;
@@ -225,7 +256,7 @@ namespace Aerostats
                     part.rigidbody.AddForce(springForce, ForceMode.Force);
                     Balloon.rigidbody.AddForceAtPosition(-springForce, balloonAttachPoint, ForceMode.Force);
                 }
-                Util.PostSingleScreenMessage("spring force", "Spring force = " + springForceMag + "N");
+                Util.PostDebugSingleScreenMessage("spring force", "Spring force = " + springForceMag + "N");
             }
             else
             {
@@ -241,11 +272,23 @@ namespace Aerostats
 
             if (Deployed)
             {
+                CheckKrakensbane();
                 var balloonAttachPoint = Balloon.rigidbody.position - Balloon.transform.up.normalized * Balloon.Radius;
 
                 Spring.SetPosition(0, part.transform.position);
                 Spring.SetPosition(1, balloonAttachPoint);
             }
         }
+
+        private void Update()
+        {
+            if (Destroyed)
+                return;
+
+            if (Deployed)
+            {
+                CheckKrakensbane();
+            }
+        }
     }
 }

Plugin/Util.cs

@@ -13,7 +13,7 @@ namespace Aerostats
     {
         private static Dictionary<string, ScreenMessage> messages = new Dictionary<string, ScreenMessage>();
 
-        public static void PostSingleScreenMessage(string id, string message)
+        public static void PostDebugSingleScreenMessage(string id, string message)
         {
             #if ENABLE_ONSCREEN_DEBUG
             if (messages.ContainsKey(id))
@@ -22,7 +22,7 @@ namespace Aerostats
             #endif
         }
 
-        public static void PostScreenMessage(string message)
+        public static void PostDebugScreenMessage(string message)
         {
             #if ENABLE_ONSCREEN_DEBUG
             ScreenMessages.PostScreenMessage(message);

todo.txt

@@ -1,4 +1,4 @@
 save/load balloon state
 test in orbit
-button to deploy
-button to cut the rope
+test reentry (before and after deploying the balloon)
+test with RSS / RO