Guided Missile - positional update routine for a guided missile that tracks a player

GuidedProjectile.cs

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

public class Projectile : MonoBehaviour
{
    [SerializeField] private GameObject target = null;
    
    private const float TURN_RATE = 0.5f;
    private const float CONTACT_DISTANCE = 1;    // explode at distance
    private const float LOCK_DISTANCE = 2;    // stop chasing and lock on last position
    private const float ACCELERATION = 0.01f;
    private const float LAUNCH_VELOCITY = 0.01f;
    private const float MAX_VELOCITY = 2;

    private Vector3 _directionVector;
    private Vector3 _lockPosition;
    private float _currentVelocity = 0;

    void Start()
    {
        _launch();
    }

    private void _launch()
    {
        _lockPosition = target.transform.position;
        _updateDirectionVector(transform.position, _lockPosition);
        _currentVelocity = LAUNCH_VELOCITY;
    }
    
    void FixedUpdate()
    {
        // If the projectile is not locked on keep chasing the target
        if (Vector3.Distance(transform.position, _lockPosition) > LOCK_DISTANCE)
        {
            _lockPosition = target.transform.position;
            _updateDirectionVector(transform.position, _lockPosition);
            transform.rotation = Quaternion.LookRotation(_directionVector);    // look where its going
        }

        // Move based on direction vector
        transform.position += _directionVector * (Time.deltaTime * _currentVelocity);
        _currentVelocity += ACCELERATION * Time.deltaTime;
        _currentVelocity = Math.Max(_currentVelocity, MAX_VELOCITY);
        
        // Explode when in range
        if (isColliding() || Vector3.Distance(transform.position, _lockPosition) < CONTACT_DISTANCE)
        {
            this.gameObject.SetActive(false);
            if (Vector3.Distance(target.transform.position, transform.position) < CONTACT_DISTANCE)
            {
                // TODO: damage based on the distance
                damageTarget();
            }
            // TODO: play FX and SFX
            // TODO: add projectile back into projectile pool
        }
    }

    /// <summary>
    /// Update the direction vector based on player movement.
    /// </summary>
    private void _updateDirectionVector(Vector3 startPosition, Vector3 endPosition)
    {
        var newDirection = endPosition - startPosition;
        _directionVector = Vector3.Lerp(_directionVector, newDirection, Time.deltaTime * TURN_RATE);
        _directionVector.Normalize();
    }

    private bool isColliding()
    {
    }

    private void damageTarget()
    {
    }
}