United Launch Alliance a year ago was projecting a 2021 debut for Vulcan Centaur, a heavy-lift rocket powered by the BE-4 engine made by Jeff Bezos’ Blue Origin.

But meeting that goal was hugely dependent on Blue Origin completing engine development and delivering two flight-ready BE-4s.

Those engines have not yet been delivered, and Vulcan’s first flight timetable continues to shift to the right. A recent SpaceNews.com article says ULA now projects receiving engines in mid-2022 and flying Vulcan by year’s end.

Meanwhile, ULA’s margin for schedule slippage keeps shrinking as Vulcan must complete two successful launches — for commercial customers Astrobotic and Sierra Space — before it can be certified by the U.S. Space Force to fly national security missions.

ULA so far has been assigned four missions under its National Security Space Launch Phase 2 contract. ULA got the top score in the NSSL competition, edging out SpaceX to claim a 60 percent share of the up to 35 missions covered under the contract.

Due to Vulcan delays, ULA’s first Phase 2 mission has already been reassigned to the company’s legacy rocket Atlas 5. ULA’s CEO Tory Bruno said Vulcan will be ready for NSSL missions in 2023. If that doesn’t happen, using the Atlas 5 would no longer provide a backup option. ULA sold its remaining Atlas 5 inventory to Amazon to launch the Project Kuiper internet constellation.

If Vulcan is not ready for NSSL launches by 2023, the next option for the Space Force would be to reassign ULA’s missions to SpaceX. “The reason to have two launch providers is that if something happens to one, and you’ve got another one to rely on,” noted Kendall, the U.S. Air Force secretary.