Two Denver region aerospace companies won’t take off together as soon as expected.

Tory Bruno, the CEO and president of United Launch Alliance — headquartered in Centennial — announced Wednesday in a media conference that the next launch of its Vulcan rocket won’t carry Sierra Space’s highly-anticipated Dream Chaser and will use a backup payload instead.

Louisville-based Sierra Space couldn’t make ULA’s deadline without “significant risk” for the Vulcan’s second certification launch required by the U.S. Space Force, Bruno said. ULA has two government missions set after the certification launch scheduled for September.

“They told us that they will step aside in order to support our critical national security space missions that come afterwards,” Bruno said.

Sierra Space’s Dream Chaser — the reusable commercial space plane reminiscent of NASA’s former space shuttle — is still on track to fly by the end of 2024, spokesperson Alex Walker said in an emailed statement.

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“As a defense-tech prime, we understand how important ULA’s Cert-2 mission is to the criticality of national security and our launch partner’s schedule.” Walker stated. “We are working closely with ULA to identify the next available launch date.”

The backup package onboard will be a mass simulator, a device mimicking extra weight the rocket may carry on future missions.

ULA has been ready for a second launch for the midyear but was willing to hold off until the Dream Chaser, Bruno said.

“We waited as long as we really could,” Bruno said.

The Vulcan rocket is a key part of shaping ULA into a solid competitor against Elon Musk’s SpaceX.

ULA recently launched an Atlas V rocket carrying a crewed Boeing’s Starliner for a test to begin the long-awaited commercial flights to the International Space Station. While ULA’s job of launching the crew into space is completed, Boeing is facing delays on returning the astronauts back to Earth.  

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In the conference call, Bruno explained how the Centennial aerospace company is positioning itself against SpaceX by providing longer-range and more cost-effective rockets.

“It’s a less complicated rocket and it is able to effectively fly its booster back because it doesn’t fly very high,” Bruno said about the Falcon and Starship rockets from SpaceX.

It’s useful for commercial spaceflights, Bruno said, but makes it harder for winning government contracts that require longer missions and ULA’s rockets cost less because it doesn’t burn as much fuel to get further into space. It’s one of the reasons ULA won Amazon’s lucrative Project Kuiper project, he said.

“We’re running about 34% cheaper for those missions because we were designed for those missions and they were designed for different ones,” he explained. “It’s just literally as simple.”