President Trump said Tuesday that he would nominate Barbara Barrett, a former diplomat and aerospace research executive, to be the next Air Force secretary, a move that came as Mr. Trump ratchets up plans to increase the military’s focus on threats in space.

Mr. Trump announced his plans on Twitter, more than two months after the current Air Force secretary, Heather A. Wilson, said she would resign. Ms. Wilson had spent two years reining in plans for the United States Space Force, successfully working to ensure that the Space Force would be a part of the Air Force instead of a separate military branch amid concerns over cost and bureaucracy.

Mr. Trump provided few details on Tuesday about why he had selected Ms. Barrett. The White House did not return an email request for comment, and Ms. Barrett could not immediately be reached.