 The main difference is that the four propulsion rockets were not located in the forward fairing, but in a boost skirt located at the bottom of the test vehicle.
<fluency>  The main difference is that the four propulsion rockets were not located in the forward fairing, but in a boost skirt located at the bottom of the test vehicle.
 The main difference was that the four propulsion rockets were not located in the forward fairing, but in a boost skirt located at the bottom of the test vehicle.