The U.S. Air Force is not close to finding a root cause of a recent low-thrust problem in an RL10 upper stage engine made by Pratt & Whitney Rocketdyne, and the service may further delay launch of its Orbital Test Vehicle-3 mission as well as NASA’s Tracking and Data Relay Satellite System K spacecraft, says Air Force Space Command chief Gen. William Shelton.

“I don’t think we are close on the investigation,” he told a small audience during a breakfast here hosted by the Air Force Association. He said the fact that the Boeing GPS IIF-3 satellite made it to orbit was the result of a “bit of a diving save,” owing to a large fuel reserve on the upper stage. “We are hopeful of a smoking gun,” he says, noting work is continuing to narrow down possible causes.

Last week, Shelton delayed the OTV-3 mission, which will orbit the X-37B reusable spaceplane prototype, two weeks to Nov. 27. The second delay of that launch, the slip will allow for more investigation time into the RL10 problem. Today, he indicated a further delay is possible and acknowledged that it will have a domino effect on the manifest of launch provider United Launch Alliance (ULA), owing to a limited number of launch crews and pads.

The RL10 incident occurred during the Oct. 8 launch of a ULA Delta IV (4,2), which uses the RL10B-2 upper stage. Some officials have suggested it was luck that got the satellite into its proper orbit after ULA officials detected what they call an “unexpected data signature” that pointed to underperforming thrust on the upper stage.

OTV-3 and TDRSS are slated for launch on the Atlas V, which also uses the RL10. This booster uses the RL10A version of the upper stage, but it shares common components. The RL10 is a single-point-of-failure for the Atlas V and Delta IV Evolved Expendable Launch Vehicles, underscoring the need to ensure a similar problem cannot happen in the future. “We have to find out what happened and why, because there is no plan B,” Shelton says. “The cost of a launch failure would be staggering,” both in the loss of an expensive satellite and in terms of operational impact because forces have become so dependent on spaceborne services for their work.

The recent RL-10 problem tarnishes ULA’s flawless launch record at a time when the monopoly is fighting to keep its position in the market against such upstarts as SpaceX, which has performed two docking missions to the International Space Station this year. The company is clearly after ULA’s Air Force business, and has submitted a plan to the Air Force to certify its Falcon family for use in government missions.

Shelton says that whether a mission uses a ULA vehicle or a new entrant design, he is unwilling to reduce funding for mission assurance. Because a satellite loss could be so devastating operationally, “maintaining rigor is actually an affordability play for us,” he says. The cost of mission assurance activities is about 3-5% of the total launch price, he adds.