https://phys.org/news/2018-08-trump-space-pentagon-idea.html

The administration intends to announce next week the results of a Pentagon study that is expected to call for creating a new military command—U.S. Space Command—to consolidate space warfighting forces and making other organizational changes short of establishing a separate service, which only Congress can do. Any legislative proposal to create a separate service would likely not be put on the table until next year.

Mattis, who said prior to Trump's "Space Force" announcement in June that he opposes creating a new branch of the military for space, said afterward that this would require "a lot of detailed planning."