I don't remember what I did but it was probably important

Assets/Scripts/FuelTank.cs

@@ -3,19 +3,32 @@ using UnityEngine;
 public class FuelTank : MonoBehaviour
 {
     public float fuelAmount = 1000f; // kg of fuel available in the tank
+    public float rcsFuelAmount = 200f; // kg of monopropellant available for RCS
     public bool isEmpty => fuelAmount <= 0f;
+    public bool isRcsEmpty => rcsFuelAmount <= 0f;
     public float RequestFuel(float amount)
     {
         float fuelGiven = Mathf.Min(amount, fuelAmount);
         fuelAmount -= fuelGiven;
         return fuelGiven;
     }
+    public float RequestRcsFuel(float amount)
+    {
+        float fuelGiven = Mathf.Min(amount, rcsFuelAmount);
+        rcsFuelAmount -= fuelGiven;
+        return fuelGiven;
+    }
     public float GetFuelAmount() => fuelAmount;
+    public float GetRcsFuelAmount() => rcsFuelAmount;
     void Update()
     {
         if (fuelAmount <= 0f)
         {
             fuelAmount = 0f;
         }
+        if (rcsFuelAmount <= 0f)
+        {
+            rcsFuelAmount = 0f;
+        }
     }
 }