Enlarge / A happy Elon Musk on the night after the Falcon Heavy launched. (credit: Trevor Mahlmann for Ars Technica)

Flush with the success of the Falcon Heavy rocket launch last week, SpaceX CEO Elon Musk began discussing the performance of the booster Monday on Twitter. He was evidently miffed about comparisons between the Delta IV Heavy rocket—manufactured by SpaceX competitor United Launch Alliance—and the Falcon Heavy rocket.

Last week on Twitter, Doug Ellison, a Jet Propulsion Laboratory visualization producer, did some back-of-the-envelope calculations to demonstrate that in some cases, the Delta IV Heavy rocket could match the performance of the Falcon Heavy for certain missions to the outer Solar System.

Musk responded that Ellison’s numbers were based on flawed underlying data and that even if they weren’t, the Falcon Heavy cost substantially less than the competition. Then Tory Bruno, the chief executive of United Launch Alliance, joined the discussion.