Thor DM-21 Ablestar

Thor-Ablestar 1

Mission Profile

Thor DM-21 Ablestar was a two-stage American launch vehicle combining the Thor ballistic missile with the pioneering Ablestar restartable upper stage, which could perform multiple engine burns on orbit to precisely insert payloads into specific trajectories. Standing 27.4 meters tall and weighing 52,600 kg at launch, it generated 758 kN of thrust. Its first flight in April 1960 was a landmark event in space history — it carried Transit 1B, the world's first operational navigation satellite, and demonstrated the first-ever restartable upper stage in space, a technology that became foundational for precision orbital delivery and presaged modern GPS navigation systems.