Object appearing as sattelite with amazing speed stops and maneuvers in many ways.I was watching for satellites in the direction of Las Vegas, which is also in the direction of Nellis Air Force Base, when I saw what I thought was a satellite going north at what I thought was normal speed for a satellite. All at once it sped up and appeared to be going twice the speed that it started at for about three to four seconds, and then slowed to its previous speed and in a mind blowing it just stopped. I watched it for about 10 to 15 seconds when it started moving again in a northeast direction and made an arching turn to the left and I lost sight of it. It made no noise whatsoever, and appeared to be in the same territory that satellites travel. Then it dissapeared out of my sight.