How to add a gravity vector/force to my playerShip's current velocity?

I’m pretty sure I’m making this way more complicated than it needs to be. I’m trying to add a vector3 to another vector3, just like the question says, but I want to vary the additive vector by a planet’s mass. The object being that the gravity of a planet bends the trajectory of a ship. If the ship is close enough and going at the right speed it will go into an orbit. Anyway, here’s what I have. I think my trig is wrong. My ship’s code is pretty simple, it accelerates along the positive x axis until it reaches it’s max speed. I know this is kinda a newb question, but hey, that’s what I am. New to both coding and Unity. Cheers y’all.

sing UnityEngine;
using System.Collections;

public class GravitateTo : MonoBehaviour {

//public float grav = new Vector3;
public GameObject player;
public float mass;

private Rigidbody playerRB;
private Rigidbody RB;
private float grav;

// Use this for initialization
void Start () {

	Rigidbody RB = GetComponent<Rigidbody> ();
	Rigidbody playerRB = player.GetComponent<Rigidbody>();
}

// Update is called once per frame
void Update () {

	float dist = Vector3.Distance (playerRB.position, RB.position); //distance from the planet

	float angle = Vector3.Angle(playerRB.position, RB.position); //direction the gravity force will be exerted

	if (dist > 0) {
		grav = mass / (dist * dist); //gravity magnitude
	}

	//Figure out the vector for gravity
	float xVal = grav * Mathf.Tan (angle);
	float zVal = grav * Mathf.Cos (angle);

	//playerRB.AddForce (xVal, 0f, zVal, ForceMode.Acceleration);
	//playerRB.rotation = Quaternion.Euler (0.0f, angle, 0.0f);

	Vector3 gravMag = new Vector3 (xVal, 0, zVal);
	Vector3 shipPos = new Vector3 (playerRB.transform.position.x, playerRB.transform.position.y, playerRB.transform.position.z);

	shipPos += gravMag;
	playerRB.transform.position = shipPos;

	//Debug.Log (playerRB.transform.position.x + " " + xVal);
}

}

That won’t quite work, since Angle always returns a positive number (if the planet is 90 degrees to your left or right, Angle says 90.) Not sure what else might be wrong or right, since there’s a standard easier way for any sort of pull or push:

Vector toPlanet=(target.position - player.position).normalized();
...
shipPos+=toPlanet*gravMag*Time.deltaTime;

Using normalized direction vectors is just a standard math trick. Time.deltaTime is a usual Unity frame-rate fix (accounts for gravity being added 60 times.sec.)