The California firm behind the first 3D-printed rocket launched safely on Wednesday, but it failed to reach orbit.
At 11:25 p.m., Cape Canaveral fired the dummy Terran 1 rocket. Relativity Space captured a "anomaly" during second-stage separation in low Earth orbit.
Wednesday's flight showed that the rocket, 85% 3D-printed, could survive liftoff.
The third launch succeeded. Launch was delayed due to fuel temperature issues on March 8.
Relativity claims Terran 1 was the first privately funded methane-fueled rocket to reach low Earth orbit on its first try.
Terran 1's first flight carried no cargo, but the rocket can ultimately launch 1,250 pounds into low Earth orbit.
Nine Aeon 1 engines and one Aeon Vacuum engine make up 85% of its mass.
The Long Beach-based firm claims it is the world's biggest 3D-printed item.
The firm said Terran 1's motors use liquid oxygen and liquid natural gas, "propellants of the future," to power a Mars mission.