How to make a planet orbit a star?

[anonymous_user_c3e69a5a]

So what you are doing now is performing a translation in 2D space according to some constant force aka the resulting velocity, am I right? (Btw, maybe rename Direction into Velocity, thats more physically accurate )

So you update the position like

p2 = p1 + T

with T being the translation vector T = (T.x, T.z) = velocity * time = (v.x, v.z) * dt (delta time)

And what you need now is adding also a Rotational component:

p2 = R * p1 + T

with R being the 2D rotation matrix around an angle a, then we get

p2.x = p1.x cos(a) - p1.z sin(a) + t.x

p2.z = p1.x sin(a) + p1.z cos(a) + t.z

Now the next question: how to we get the angle a? its by using Angular velocity

w = a / dt = v / r

a = v / r * dt

w is the angular velocity (radians per seconds), v is the velocity magnitude and r is the radius (=distance) magnitude

So lets modify your code a little - No garantee it´s working, I did not test it.

  float XZVector2Magnitude(FVector v) {
     return sqrt(pow(v.X, 2) + pow(v.Z, 2));
}

void ARotating_sphere::Tick(float DeltaTime)
 {
     Super::Tick(DeltaTime);
     
     time += DeltaTime;
 
     OldLocation = GetActorLocation();
     FVector Distance = FVector((OldLocation.X - StarLocation.X), 0, (OldLocation.Z - StarLocation.Z));
 
     // I would calculate the force first 
     Force.X = ((Mass1 * Mass2) / pow(Distance.X,2));
     Force.Z = ((Mass1 * Mass2) / pow(Distance.Z,2));

     Velocity.X += ((Force.X) / mass1) * DeltaTime;
     Velocity.Z += ((Force.Z) / mass1) * DeltaTime;
     float Angle = XZVector2Magnitude(Velocity) / XZVector2Magnitude(Distance) * DeltaTime;
     
     NewLocation.X = OldLocation.X * cos(Angle) - OldLocation.Y * sin( Angle) + Velocity.X * DeltaTime;
     NewLocation.Z = OldLocation.X * sin(Angle) + OldLocation.Y * cos(Angle) + Velocity.Z * DeltaTime;

     
     SetActorLocationAndRotation(NewLocation, NewRotation, false, 0, ETeleportType::None);
 
 }

Another Point - if you really want to simulate accuratly, you should add the Gravitational constant to your force calculation.