The Boeing Starliner is designed to be compatible with four launch vehicles: Atlas V, Delta IV, Falcon 9, and Vulcan.

The test flight was launched on an Atlas V, so it can be assumed that more launches will be using it.

What about the others?

  • Delta IV doesn't seem human rated yet, but they did propose to make it human-rated at some point. But would they bother using it when the Atlas V is already shown to work properly for Starliner?

  • Vulcan is intended to undergo human-rating certification to launch the Starliner, but will that include launches to the ISS?

  • Falcon 9 isn't associated with Boeing or ULA. Would Spacex even let a competitor fly on their launcher? Are there any plans for this?


1 Answer 1


When this kind of compatibility is required, they mostly mean mechanically, vibrations and things like that. The software isn't written, nor the conops, and other tests haven't likely been done. In theory, however, this allows one to, in the event of a major issue, launch on another rocket, with some work. I strongly suspect Crew Dragon is rated for at least Atlas, for instance.

I'm quite sure it will never be flown from a Delta IV. There are no new missions planned for that rocket, soon Vulcan will completely take over there.

Vulcan is another question entirely. I'm quite sure that once it is available, ULA would like to launch using the Vulcan. This will take some time, but I expect that in 10 years or less, Vulcan will become the primary launch vehicle for Starliner.

As to Falcon 9, SpaceX would actually have to allow it to be used, if requested, for a number of reasons. I'm sure at least a basic level test has been done, but most likely this is not complete. Cygnus at least for a time considered flying on Falcon 9 when the Antares rocket blew up. The only reason why this would actually be done, however, is if the Atlas rocket had a serious issue. I can't imagine this to be the case, but it is good to at least make sure that the payload is comparable with the rocket in the event of a major emergency.

  • 1
    $\begingroup$ "As to Falcon 9, SpaceX would actually have to allow it to be used, if requested, for a number of reasons." Reference? $\endgroup$ Commented Jul 31, 2020 at 15:08
  • $\begingroup$ I would assume anti-trust laws, but maybe I'm flat wrong in that assumption. They can't seem to block Starlink competitors from using them as a launch service, for instance... $\endgroup$
    – PearsonArtPhoto
    Commented Jul 31, 2020 at 15:25
  • $\begingroup$ Nice answer, but the second sentence has some awkward grammar. $\endgroup$
    – DrSheldon
    Commented Jul 31, 2020 at 16:49
  • 1
    $\begingroup$ @DrSheldon I edited the order, I think it's less awkward now $\endgroup$ Commented Jul 31, 2020 at 20:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.