Spin like “Google Earth” in Unity

#pragma strict
 
var numberAverages : int = 3;
private var originalRotation : Quaternion;
private var offsetRotation : Quaternion;
 
// Make sure there are always SphereCollider and Rigidbody
@script RequireComponent (SphereCollider)
@script RequireComponent (Rigidbody)
 
function Awake () {
    numberAverages = Mathf.Clamp (numberAverages, 1, numberAverages);
}
 
function OnMouseDown () {
    var hit : RaycastHit;
    var dir : Vector3;
 
    // Stop spinning
    rigidbody.angularVelocity = Vector3.zero;
 
    // Record initial variables 
    if (Physics.Raycast (Camera.main.ScreenPointToRay(Input.mousePosition), hit)) {
        originalRotation = transform.rotation;
        dir = hit.point - transform.position;
        offsetRotation = Quaternion.Inverse (Quaternion.LookRotation (dir));
        Spin (dir);
    }
}
 
function Spin (dir : Vector3) {
    var hit : RaycastHit;
    var privDirList : Array = new Array ();
    var currentDir : Vector3;
 
    // Initialize previous direction list
    for (var i : int = 0; i < numberAverages; i++) {
        privDirList.Add (currentDir);
    }
 
    currentDir = dir;
 
    // Make the object rotate with the cursor while we are grabbing it
    while (Input.GetButton ("Fire1") && Physics.Raycast (camera.main.ScreenPointToRay(Input.mousePosition), hit)) {
        // Remove first element of the array
        privDirList.RemoveAt (0);
 
        // Add current direction to the end
        privDirList.Add (currentDir);
        currentDir = hit.point - transform.position;
        transform.rotation =  Quaternion.LookRotation (currentDir) * offsetRotation * originalRotation;
        yield;
    }
 
    // User let go of the mouse so make the object spin on its own
    var avgPrevDir : Vector3 = Vector3.zero;
    var newPDirList : Vector3[] = privDirList.ToBuiltin(Vector3);
    for (dir in newPDirList) {
        avgPrevDir += dir;
    }
 
    // Keep spinning with the direction when you end touching
    avgPrevDir /= numberAverages;
    MoveAcceleration (currentDir, avgPrevDir); 
}
 
function MoveAcceleration (r2 : Vector3, r1 : Vector3) {
    var linearVelocity : Vector3;
    var angVelocity : Vector3;
 
    // Calculate the angular velocity:  Omega = r x v / r^2
    linearVelocity = (r2 - r1) / Time.deltaTime;
    rigidbody.angularVelocity = Vector3.Cross (r2, linearVelocity) / r2.sqrMagnitude;
}