 The failure was described as "especially disappointing" since it was the final launch in the Able probe series as its successor, the Ranger program, was in the works.In the end, the US space program would not see a completely successful lunar probe until Ranger 7 four years later.It also marked the final launch in the first generation of lunar probes, which used direct ascent trajectories and would give way to the second generation probes which had parking orbits.