Disabling function of a key

So I need I’m trying to get a gameObject to jump, which I succeeded in, but its 50% of the way there to completion. I can get it to jump once and not get it to go up when I hold “Space”, but if I spam tap space it’ll keep going up. I think I either have a coding error somewhere, or I am just missing a piece of code somewhere. Could I please get someone to point out my error? Thanks!
Here’s my code:
using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class PlayerController : MonoBehaviour
{
    public GameObject Player;
    public float speed;
    public Text countText;
    public Text winText;
    public float jumpHeight = 200f;
    public float bounceHeight = 200f;

    private Rigidbody rb;
    private int count;

    void Start()
    {
        rb = GetComponent<Rigidbody>();
        count = 0;
        SetCountText();
        winText.text = "";
    }

    void Update()
    {
        RaycastHit hit;
        Ray bouncingRay = new Ray(transform.position, Vector3.down);

        if (Physics.Raycast(bouncingRay, out hit, bounceHeight))
        {
            if (hit.collider.tag == "Ground" && Input.GetKeyDown("space"))
                {
                    rb.AddForce(Vector3.up * jumpHeight);
                }
            else
                {
                //need to disable key here
                }
        }
    }

    void FixedUpdate()
    {
        float moveHorizontal = Input.GetAxis("Horizontal");
        float moveVertical = Input.GetAxis("Vertical");

        Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);

        rb.AddForce(movement * speed);

    }

    void OnTriggerEnter(Collider other)
    {
        if (other.gameObject.CompareTag("Pick Up"))
        {
            other.gameObject.SetActive(false);
            count = count + 1;
            SetCountText();
        }
    }

    void SetCountText()
    {
        countText.text = "Count: " + count.ToString();
        if (count >= 8)
        {
            winText.text = "You Win!";
        }
    }
}

@GroveArts Your problem is you are casting the ray down 200 units. You don’t want it to go that far down because even if the player is up in the air it will still allow it to jump as the ray goes farther down. Change your bounceHeight variable to something like 1 or 0.5.

If you set your variable to something like 0 or 0.5, depending on the size of your character you might not be able to jump at all. So remember that your ray is being cast from the center of your player. So if you have a 1 unity high block as your character and you cast a ray 0.1 units down from the center of your character (0.5 units off the ground) it will never touch the ground. So find a value that works well for your character.