/// <summary>
/// Traces a space craft orbit by re-centering the world around the parent.
/// </summary>
public static OrbitTrace TraceSpaceCraft(SpaceCraftBase satellite)
{
IMassiveBody parent = satellite.GravitationalParent;
DVector2 initialPosition = satellite.Position - parent.Position;
var shipOffset = new DVector2(Math.Cos(satellite.Rotation) * (satellite.TotalWidth - satellite.Width),
Math.Sin(satellite.Rotation) * (satellite.TotalHeight - satellite.Height)) * 0.5;
initialPosition -= shipOffset;
var proxyParent = new MassiveBodyProxy(DVector2.Zero, DVector2.Zero, parent);
var proxySatellite = new SpaceCraftProxy(initialPosition, satellite.Velocity - parent.Velocity, satellite);
int stepCount;
double targetDt;
double proximityDt;
double orbitalDt = 0;
bool isOrbiting;
double orbitalTerminationRadius = 0;
double altitude = proxyParent.GetRelativeHeight(proxySatellite.Position);
double proximityAltitude = proxyParent.SurfaceRadius * 0.15;
if (altitude < proximityAltitude)
{
stepCount = 1000;
isOrbiting = false;
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = proximityDt;
}
else
{
stepCount = 300;
isOrbiting = true;
orbitalDt = GetOrbitalDt(initialPosition, proxySatellite.Velocity, out orbitalTerminationRadius);
targetDt = orbitalDt;
}
var trace = new OrbitTrace(satellite.Position - shipOffset, altitude);
// Simulate 300 orbital steps, more for proximity
for (int step = 0; step < stepCount; step++)
{
proxySatellite.ResetAccelerations();
proxySatellite.ResolveGravitation(proxyParent);
proxySatellite.ResolveAtmopsherics(proxyParent);
proxySatellite.Update(targetDt);
altitude = proxyParent.GetRelativeHeight(proxySatellite.Position);
// Check if reference frame shifting needs to occur in atmosphere
if (altitude < proxyParent.AtmosphereHeight)
{
double offsetFactor = 1.0 - (altitude / proxyParent.AtmosphereHeight);
DVector2 difference = proxyParent.Position - proxySatellite.Position;
difference.Normalize();
var surfaceNormal = new DVector2(-difference.Y, difference.X);
double altitudeFromCenter = altitude + proxyParent.SurfaceRadius;
// Distance of circumference at this altitude ( c= 2r * pi )
double pathCirumference = 2 * Math.PI * altitudeFromCenter;
double rotationalSpeed = pathCirumference / parent.RotationPeriod;
DVector2 atmopshereVelocity = surfaceNormal * rotationalSpeed;
proxySatellite.ApplyFrameOffset(atmopshereVelocity * offsetFactor * targetDt);
// Return early if the trace goes into a planet
if (altitude <= 0)
{
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
break;
}
}
// Determine the correct change overs from orbital to surface proximity
if (isOrbiting)
{
if (altitude < proximityAltitude)
{
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = MathHelper.Lerp(targetDt, proximityDt, 0.75);
isOrbiting = false;
stepCount = 1000;
}
else
{
targetDt = MathHelper.Lerp(targetDt, orbitalDt, 0.1);
}
}
else
{
if (altitude > proximityAltitude)
{
orbitalDt = GetOrbitalDt(proxySatellite.Position, proxySatellite.Velocity, out orbitalTerminationRadius);
targetDt = MathHelper.Lerp(targetDt, orbitalDt, 0.1);
isOrbiting = true;
stepCount = 300;
}
else
{
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = MathHelper.Lerp(targetDt, proximityDt, 0.75);
}
}
// Check expensive termination conditions after half of the iterations
if (isOrbiting && step > 100)
{
DVector2 offsetVector = proxySatellite.Position - initialPosition;
double distanceFromStart = offsetVector.Length();
// Terminate and add the end point
if (distanceFromStart < orbitalTerminationRadius)
{
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
break;
}
}
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
}
return trace;
}
private void PredictTargetThrottle(SpaceCraftBase spaceCraft)
{
double optimalThrust = _currentThrust;
double optimalLandingSpeed = double.PositiveInfinity;
for (int i = -1; i <= 1; i++)
{
double thrust = 40;
// double thrust = 65;
if (_currentThrust > 0)
{
thrust = _currentThrust;
}
thrust += i * 0.5;
if (thrust < 40 || thrust > 100)
//if (thrust < 60 || thrust > 100)
{
continue;
}
IMassiveBody parent = spaceCraft.GravitationalParent;
DVector2 initialPosition = spaceCraft.Position - parent.Position;
var proxyParent = new MassiveBodyProxy(DVector2.Zero, DVector2.Zero, parent);
var proxySatellite = new SpaceCraftProxy(initialPosition, spaceCraft.Velocity - parent.Velocity, spaceCraft);
foreach (int id in _engineIds)
{
proxySatellite.Engines[id].Startup();
proxySatellite.Engines[id].AdjustThrottle(thrust);
}
proxySatellite.SetGravitationalParent(proxyParent);
// Simulate until the rocket runs out of fuel or touches down
for (int step = 0; step < 1000; step++)
{
proxySatellite.ResetAccelerations();
proxySatellite.ResolveGravitation(proxyParent);
proxySatellite.ResolveAtmopsherics(proxyParent);
if (proxySatellite.PropellantMass <= 0)
{
break;
}
if (proxySatellite.OnGround)
{
double landingSpeed = proxySatellite.RelativeVelocity.Length();
// If the rocket is in motion search for the best speed always
if (_currentThrust > 0)
{
if (landingSpeed < optimalLandingSpeed)
{
optimalLandingSpeed = landingSpeed;
optimalThrust = thrust;
break;
}
}
// Otherwise enforce the landing speed is very good to start
else if (landingSpeed < 5)
{
optimalLandingSpeed = landingSpeed;
optimalThrust = thrust;
break;
}
}
proxySatellite.Update(0.05);
}
}
// Set the target engines to the optimal computed thrust
if (_engineIds != null)
{
// Startup the required landing engines
foreach (int id in _engineIds)
{
IEngine engine = spaceCraft.Engines[id];
engine.AdjustThrottle(optimalThrust);
}
if (optimalThrust > 0)
{
_currentThrust = optimalThrust;
}
}
}