/// <summary>
/// Calculates the fuel units required for the transfer.
/// </summary>
public float CalculateFuelUnits()
{
// Fuel required is cached at launch, so just return the cached value
if (Status != DeliveryStatus.PreLaunch)
{
return(_fuelUnits);
}
CelestialBody mainBody = Origin.mainBody;
var sourceProtoVessel = Origin.protoVessel;
var targetProtoVessel = Destination.protoVessel;
var sourceSituation = sourceProtoVessel.situation;
var targetSituation = targetProtoVessel.situation;
double fuelUnits = double.PositiveInfinity;
// Calculate fuel requirements based on source/target situation (i.e. landed or orbiting)
// Both vessels on the ground
if (sourceSituation == (sourceSituation & SURFACE) && targetSituation == (targetSituation & SURFACE))
{
// Determine central angle between the vessels' coordinates
double centralAngle = GetCentralAngle(
sourceProtoVessel.latitude, sourceProtoVessel.longitude,
targetProtoVessel.latitude, targetProtoVessel.longitude
);
// Determine the percentage of 360 degrees the central angle represents
double anglePercent = centralAngle / 360;
// Determine the velocity of a low, circular orbit around the body
double orbitV = OrbitalLogisticsExtensions.OrbitalVelocity(mainBody, mainBody.minOrbitalDistance + mainBody.Radius);
// Determine dV required to reach the target (i.e. a percentage of the dV required to achieve full orbit)
double dV = orbitV * anglePercent * GRAV_LOSS_MODIFIER;
fuelUnits = CalculateFuelNeededFromDeltaV(dV, mainBody.atmosphere);
}
// One or both vessels in orbit
else
{
// One vessel on the ground, one in orbit
if ((sourceSituation == (sourceSituation & SURFACE) && targetSituation == Vessel.Situations.ORBITING) ||
(sourceSituation == Vessel.Situations.ORBITING && targetSituation == (targetSituation & SURFACE))
)
{
// Determine average orbital velocity
double velocity = sourceSituation == Vessel.Situations.ORBITING
? Origin.AverageOrbitalVelocity()
: Destination.AverageOrbitalVelocity();
// Determine dV required to land/launch
double dV = velocity * INC_CHANGE_MODIFIER * GRAV_LOSS_MODIFIER;
fuelUnits = CalculateFuelNeededFromDeltaV(dV, mainBody.atmosphere);
}
// Both vessels in orbit
else if (sourceSituation == Vessel.Situations.ORBITING && targetSituation == Vessel.Situations.ORBITING)
{
// Determine which vessel has the higher semi major axis and which is lower
double highOrbitSMA;
double lowOrbitSMA;
if (sourceProtoVessel.orbitSnapShot.semiMajorAxis >= targetProtoVessel.orbitSnapShot.semiMajorAxis)
{
highOrbitSMA = sourceProtoVessel.orbitSnapShot.semiMajorAxis;
lowOrbitSMA = targetProtoVessel.orbitSnapShot.semiMajorAxis;
}
else
{
highOrbitSMA = targetProtoVessel.orbitSnapShot.semiMajorAxis;
lowOrbitSMA = sourceProtoVessel.orbitSnapShot.semiMajorAxis;
}
// Determine orbit velocity of origin and destination vessels
double highOrbitV = OrbitalLogisticsExtensions.OrbitalVelocity(mainBody, highOrbitSMA);
double lowOrbitV = OrbitalLogisticsExtensions.OrbitalVelocity(mainBody, lowOrbitSMA);
// Determine difference in sma
double dSMA = highOrbitSMA - lowOrbitSMA;
// If the orbits are similar, we need to spend some extra fuel to get into a transfer orbit
double transferV = 0;
if (dSMA < 10000)
{
// Determine the dV needed to get into a higher orbit
transferV = highOrbitV - OrbitalLogisticsExtensions.OrbitalVelocity(mainBody, highOrbitSMA + 30000);
}
// Total dV is the difference between the orbital velocities plus any transfer dV needed
// Note: Remember, the lower orbit has the higher velocity!
double dV = lowOrbitV - highOrbitV + transferV;
// Factor in potential inclination changes to calculate the total cost
fuelUnits = CalculateFuelNeededFromDeltaV(dV * INC_CHANGE_MODIFIER);
}
}
return((float)fuelUnits * FUEL_MULTIPLIER);
}
