Slerper.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Slerper : MonoBehaviour {

    public Transform startPos;
    public Transform endPos;
    public float journeyTime = 1.0f;
    public float speed;
    public bool repeatable;

    float startTime;
    Vector3 centerPoint;
    Vector3 startRelCenter;
    Vector3 endRelCenter;	
	
	// Update is called once per frame
	void Update () {
		GetCenter(Vector3.up);
        if(!repeatable) {
            float fracComplete = (Time.time - startTime) / journeyTime * speed;
            transform.position = Vector3.Slerp(startRelCenter, endRelCenter, fracComplete * speed);
            transform.position += centerPoint;
        }
        if (repeatable) {
            float fracComplete = Mathf.PingPong(Time.time - startTime, journeyTime / speed);
            transform.position = Vector3.Slerp(startRelCenter, endRelCenter, fracComplete * speed);
            transform.position += centerPoint;
            if (fracComplete >= 1) {
                startTime = Time.time;
            }
        }
	}

    public void GetCenter(Vector3 direction) {
        centerPoint = (startPos.position + endPos.position) * .5f;
        centerPoint -= direction;
        startRelCenter = startPos.position - centerPoint;
        endRelCenter = endPos.position - centerPoint;
    }
}