Vulcan launch plans in doubt as Dream Chaser faces further delays.

Sierra Space's Dream Chaser spacecraft has been delayed again and is now scheduled to dock with the International Space Station no earlier than December 17, 2023. This delay raises questions about the launch manifest of United Launch Alliance's Vulcan rocket, which was supposed to fly Dream Chaser on its "Cert. 2" mission in August. The delay also means that the US segment of the space station will be reliant on the Falcon 9 rocket alone for cargo supply missions. United Launch Alliance remains committed to flying a national security mission in 2023, but it is highly improbable that Vulcan completes two certification flights this summer and fall and is able to also launch a national security mission before the end of the year.