However, as of last month, Air Force Space Command chief Gen. William Shelton was skeptical any cause could be found soon. “I don't think we are close on this investigation,” he said, adding that the satellite's flight to the right orbit was the result of a “bit of a diving save” owing to a large fuel reserve on the upper stage. Though the satellite reached orbit, this incident is more than just a blot on ULA's track record. “We have to find out what happened and why, because there is no Plan B,” Shelton says. “The cost of launch failure would be staggering.”
The RL10 is the sole upper stage for EELV boosters While the variants used for the Atlas V and Delta IV are slightly different, the upper stage is a potential single-point-of-failure for the entire military space program.