WASHINGTON — The U.S. Air Force expects a replacement for the Delta 4 Heavy rocket will be ready by 2023, with one of several vehicles under development able to take its place, Gen. Jay Raymond, head of Air Force Space Command, told a House committee May 19.

Testifying before the House Armed Services Committee’s strategic forces subcommittee, Raymond said that the Air Force expects to have uninterrupted access to heavy launch for national security missions.

Several companies have heavy-lift vehicles in development, including SpaceX’s Falcon Heavy and Blue Origin’s New Glenn, that could replace the Delta 4 Heavy built by United Launch Alliance.

The Air Force has purchased launches on seven more Delta 4 Heavy rockets, Raymond said, though one launch will be a NASA mission. The final launch is scheduled for 2023.

“We’re comfortable that we will have a new capability online that will be able to support the requirements going forward,” Raymond said.

The Air Force also has three more Delta 4 Medium rockets left, with the last launch scheduled for 2019.

National Reconnaissance Office Director Betty Sapp told members of Congress that heavy launch is “essential to my mission” of launching spy satellites and other intelligence assets.

There is still time, Sapp said, to see how replacements develop before the U.S. needs to make a definitive decision on retiring the Delta 4.

“I believe we have time to see how the new programs mature before we cannot go back on the Delta 4 Heavy,” she said. “We’ve got it funded for launch through 2023, so we have some time to make the right decisions.”

Engine trouble

The Air Force is also looking for a replacement for ULA’s other rocket, the Atlas 5. The vehicle has been at the center of criticism on Capitol Hill because it uses the Russian-made RD-180 engine.

Purchases of RD-180 engines were one of the few exceptions granted when the U.S. imposed sanctions on Russia following that nation’s invasion of Crimea in 2014.

Ensuring that the Air Force had reliable access to space by using the RD-180 was considered the paramount need, but both the Air Force and ULA have been looking for a replacement, with plans to phase out use of the engine.

Raymond said that the Air Force is monitoring commercial development of launch systems, including reusable rockets, but that it does not change the service’s ultimate goals.

“Our strategy remains three things: assured access to space, competition, and to get off the RD-180 engine,” he said.

ULA is currently searching for an engine for its Vulcan rocket, which is intended to succeed the Atlas 5 and Delta 4. The company has said the leading candidate is the BE-4 liquid methane engine under development by Jeff Bezos’ Blue Origin. That engine will also be used on Blue Origin’s New Glenn heavy launch vehicle.

However, the company reported that, on May 13, testing of the engine went awry and it lost a set of powerpack testing hardware.

Raymond said the incident is “regrettable, but isn’t uncommon in development efforts.”

“I think this adds credibility to our strategy to make sure there’s multiple engines being developed…I think we have visibility, pretty significant visibility, into all these processes, although it’s Blue Origin’s final ultimate decision” on when the rocket might be ready, he said.

The general added that when ULA makes a decision on what engine to use for its Vulcan rocket, “obviously the Air Force is a significant customer of that launch service.”