Rotate sample component

RotateTest.cs

using UnityEngine;
using System.Collections;

public class RotateTest : MonoBehaviour
{
	public GameObject target;
	public Vector3 additional;
	Quaternion _rot;
	Quaternion _initRot;
	Vector3 _vec;
	// Use this for initialization
	void Start ()
	{
		_initRot = transform.rotation;
		_rot = Quaternion.identity;
		_vec = transform.position - target.transform.position;
	}
	
	// Update is called once per frame
	void Update ()
	{
		_rot *= Quaternion.AngleAxis (180f * Time.deltaTime, Vector3.up);
		var r = _rot * Quaternion.Euler (additional);
		transform.position = r * _vec + target.transform.position;
		transform.rotation = r * _initRot;
	}
}