精灵随机停止绘制XNA 4.0

我正在制作一款简单的2人飞船射击游戏。

当我按住空格键射击时，投射物的精灵就会被绘制出来，但当我松开空格键并再次射击时，第一个精灵根本就没有被绘制出来。

但它仍然在游戏中并按其本意运行，是代码有问题还是有解决方案?

protected override void Draw(GameTime gameTime)
{
    //Loading and Drawing the background through XNA spriteBatch
    spriteBatch.Begin(0, BlendState.AlphaBlend);
    spriteBatch.Draw(backgroundTexture, GraphicsDevice.Viewport.Bounds, Color.White);
    //Drawing the spaceship on the screen
    spriteBatch.Draw(spaceship.sprite, spaceship.position, null, Color.White);
    //Drawing the alienship
    spriteBatch.Draw(alienship.sprite2, alienship.position2, null, Color.White);
    spriteBatch.End();
    //Drawing the projectile
    spriteBatch.Begin(0, BlendState.AlphaBlend);
    if (projectile.alive == true)
    {
        spriteBatch.Draw(projectile.sprite, projectile.position, Color.White);
    }
    //Drawing the 3rd Projectile
    if(projectile3.alive == true)
    {
        spriteBatch.Draw(projectile3.sprite, projectile3.position, Color.Red);
    }
    //Drawing the 4th Projectile
    if (projectile4.alive == true)
    {
        spriteBatch.Draw(projectile4.sprite, projectile4.position, Color.Green);
    }
    //Drawing the Special Projectile
    if (projectile2.alive)
    {
        spriteBatch.Draw(projectile2.sprite, projectile2.position, Color.White);
    }
    spriteBatch.End();
    // TODO: Add your drawing code here
    base.Draw(gameTime);
}