How to rotate a ship based on gravity around a planet?

Hey everyone, here's a youtube link to my problem. I'm trying to get my ship to rotate with the gravity pull so that it can go into a more orbit-like motion. If I need to supply more info please let me know. Here are a couple of the scripts on my ship with a couple of my ideas commented out.

 using UnityEngine;
 using System.Collections;
 
 public class PlayerControllerForce : MonoBehaviour {
 
     public float speed;
     public float maxSpeed;
     //public static float angleFacing;
     //public Vector3[] positions = new Vector3[2];
 
     //private Vector3 lastPosition;
     private Rigidbody playerRB;
     //private int frameNumber = 0;
     //private  positions : LinkedList.<Vector3> = new LinkedList.<Vector3>();
 
     // Use this for initialization
     void Start () {
         playerRB = GetComponent<Rigidbody> ();
     }
     
     // Update is called once per frame
     void FixedUpdate () {
 
 
         //forward movement and limiting top speed
         playerRB.AddForce (transform.forward * speed);
 
         if (playerRB.velocity.magnitude > maxSpeed) {
             playerRB.velocity = playerRB.velocity.normalized * maxSpeed;//returning a vector with the value of 1 and multiplying by maxSpeed
         }
 
         //Vector3 currentPosition = playerRB.transform.position;
 
         //if (frameNumber % 2 == 0) {
         //    lastPosition = playerRB.transform.position;
         //}
 
         //for (int i = 0; i <= 1; i++) {
         //    positions[i] = playerRB.transform.position;
         //}
 
         //Debug.Log ("lp is " + lastPosition);
         //Debug.Log ("p is " + playerRB.transform.position);
 
 
         //frameNumber ++;
         //angleFacing = Mathf.Atan2 ((playerRB.transform.position.z - lastPosition.z), playerRB.transform.position.x - lastPosition.x);
 
         //if (angleFacing != 0) {
         //    playerRB.rotation = Quaternion.Euler (0.0f, angleFacing + 90, 0.0f);
         //}
 
         //Debug.Log ("angle is " + angleFacing);
     }
 }

AND this one for all of my user input and rotation.

 using UnityEngine;
 using System.Collections;
 
 public static class ExtensionMethods {
     public static float Remap (this float value, float from1, float to1, float from2, float to2) {
         return (value - from1) / (to1 - from1) * (to2 - from2) + from2;
     }
 }
 
 public class Rotate_Script : MonoBehaviour {
 
     public static float direction = 90.0f;
     public float countdown = 3.0f;
 
     public GameObject scaleGUI; //rotation cube GUI
 
     private Rigidbody playerRB;
     private float scaleRot = 1.0f; //value holder for scale ratio
     private bool empty = false;
 
 
 
     // Use this for initialization
     void Start () {
         playerRB = GetComponent<Rigidbody> ();
     }
     
     // Update is called once per frame
     void FixedUpdate () {
 
         if (scaleRot > 0 && empty == false){
             //Angle adjustments
             if (Input.GetKey ("up") && countdown > 0.0f) {
                 direction -= 2.0f;
                 countdown -= Time.deltaTime;
                 scaleRot = countdown.Remap (0.0f, 3.0f, 0.0f, 1.0f);
                 scaleGUI.transform.localScale = new Vector3 (1.0f, scaleRot, 1.0f);
             
             } else if (Input.GetKey ("down") && countdown > 0.0f) {
                 direction += 2.0f;
                 countdown -= Time.deltaTime;
                 scaleRot = countdown.Remap (0.0f, 3.0f, 0.0f, 1.0f);
                 scaleGUI.transform.localScale = new Vector3 (1.0f, scaleRot, 1.0f);
             }
         } else {
             empty = true;
             scaleRot += 0.1f * Time.deltaTime;
             scaleGUI.transform.localScale = new Vector3 (1.0f, scaleRot, 1.0f);
         }
 
 
         //GUI Code maybe move this later
         if (scaleRot >= 1.0f) {
             countdown = 3.0f;
             empty = false;
         }
         
         playerRB.rotation = Quaternion.Euler (0.0f, direction, 0.0f);
 
 
 
         //Debug.Log (oldPosition.x);
         //Debug.Log (playerRB.position.x);
     }
 }