how to make player fly

i am making a character that i want to fly when you double click space and keep flying until you make contact with ground. can it be implemented in this script? using UnityEngine;

 [RequireComponent(typeof(CharacterController))]
 
 public class SC_CharacterController : MonoBehaviour
 {
     public float speed = 7.5f;
     public float jumpSpeed = 8.0f;
     public float gravity = 20.0f;
     public Camera playerCamera;
     public float lookSpeed = 2.0f;
     public float lookXLimit = 45.0f;
 
     CharacterController characterController;
     Vector3 moveDirection = Vector3.zero;
     Vector2 rotation = Vector2.zero;
 
     [HideInInspector]
     public bool canMove = true;
 
     void Start()
     {
         characterController = GetComponent<CharacterController>();
         rotation.y = transform.eulerAngles.y;
     }
 
     void Update()
     {
         if (characterController.isGrounded)
         {
             // We are grounded, so recalculate move direction based on axes
             Vector3 forward = transform.TransformDirection(Vector3.forward);
             Vector3 right = transform.TransformDirection(Vector3.right);
             float curSpeedX = canMove ? speed * Input.GetAxis("Vertical") : 0;
             float curSpeedY = canMove ? speed * Input.GetAxis("Horizontal") : 0;
             moveDirection = (forward * curSpeedX) + (right * curSpeedY);
 
             if (Input.GetButton("Jump") && canMove)
             {
                 moveDirection.y = jumpSpeed;
             }
         }
 
         // Apply gravity. Gravity is multiplied by deltaTime twice (once here, and once below
         // when the moveDirection is multiplied by deltaTime). This is because gravity should be applied
         // as an acceleration (ms^-2)
         moveDirection.y -= gravity * Time.deltaTime;
 
         // Move the controller
         characterController.Move(moveDirection * Time.deltaTime);
 
         // Player and Camera rotation
         if (canMove)
         {
             rotation.y += Input.GetAxis("Mouse X") * lookSpeed;
             rotation.x += -Input.GetAxis("Mouse Y") * lookSpeed;
             rotation.x = Mathf.Clamp(rotation.x, -lookXLimit, lookXLimit);
             playerCamera.transform.localRotation = Quaternion.Euler(rotation.x, 0, 0);
             transform.eulerAngles = new Vector2(0, rotation.y);
         }
     }
 }