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Fix survival chance per timestep calculation #287

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Merged
Capkirk123 merged 1 commit into from
Nov 15, 2025
Merged

Fix survival chance per timestep calculation #287

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23 changes: 7 additions & 16 deletions TestFlightAPI/TestFlightAPI/TestFlightReliability.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,6 @@ public class TestFlightReliabilityBase : PartModule, ITestFlightReliability
public FloatCurve reliabilityCurve;
[KSPField(isPersistant=true)]
public float lastCheck = 0;
[KSPField(isPersistant=true)]
public float lastReliability = 1.0f;


public List<ConfigNode> configs = new List<ConfigNode>();
Expand Down Expand Up @@ -173,6 +171,7 @@ public override void OnUpdate()
if (operatingTime < lastCheck + 1f)
return;

double timestep = operatingTime - lastCheck;
lastCheck = operatingTime;
double baseFailureRate = core.GetBaseFailureRate();
MomentaryFailureRate momentaryFailureRate = core.GetWorstMomentaryFailureRate();
Expand All @@ -183,19 +182,11 @@ public override void OnUpdate()
else
currentFailureRate = baseFailureRate;

// Given we have been operating for a given number of seconds, calculate our chance of survival to that time based on currentFailureRate
// This is *not* an exact science, as the real calculations are much more complex than this, plus technically the momentary rate for
// *each* second should be accounted for, but this is a simplification of the system. It provides decent enough numbers for fun gameplay
// with chance of failure increasing exponentially over time as it approaches the *current* MTBF
// S() is survival chance, f is currentFailureRate
// S(t) = e^(-f*t)

float reliability = Mathf.Exp((float)-currentFailureRate * (float)operatingTime);
// double survivalChance = Mathf.Pow(Mathf.Exp(1), (float)currentFailureRate * (float)operatingTime * -0.693f);
double survivalChance = reliability / lastReliability;
lastReliability = reliability;
// float failureRoll = Mathf.Min(UnityEngine.Random.Range(0f, 1f), UnityEngine.Random.Range(0f, 1f));
// float failureRoll = UnityEngine.Random.Range(0f, 1f);
// The momentary failure rate, as implemented in TF, is more accurately called the 'hazard rate', h(t). This is defined as the
// proportional failure rate of systems still functioning at time t.
// For a working system at time t and a small interval dt, the chance to fail in the next dt seconds is approximately h(t)*dt; this
// approximation is exact in the limit where dt goes to 0.
double survivalChance = 1 - currentFailureRate * timestep;
double failureRoll = core.RandomGenerator.NextDouble();
if (verboseDebugging)
{
Expand All @@ -206,7 +197,7 @@ public override void OnUpdate()
// Debug.Log(String.Format("TestFlightReliability: Survival Chance at Time {0:F2} is {1:f4} -- {2:f4}^({3:f4}*{0:f2}*-1.0)", (float)operatingTime, survivalChance, Mathf.Exp(1), (float)currentFailureRate));
if (verboseDebugging)
{
Log($"Part has failed after {operatingTime:F1} secodns of operation at MET T+{vessel.missionTime:F2} seconds with roll of {failureRoll:F4}");
Log($"Part has failed after {operatingTime:F1} seconds of operation at MET T+{vessel.missionTime:F2} seconds with roll of {failureRoll:F4}");
}
core.TriggerFailure();
}
Expand Down
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