; or (2) if there is a vacancy in the office of the Vice Chief of Staff or the Vice Chief of Staff is absent or disabled, unless the President directs otherwise, the most senior officer of the Space Force in the Space Staff who is not absent or disabled and who is not restricted in performance of duty shall perform the duties of the Chief of Staff until a successor to the Chief of Staff or the Vice Chief of Staff is appointed or until the absence or disability of the Chief of Staff or Vice Chief of Staff ceases, whichever occurs first. . 1702. Under Secretary of the Air Force for Space (a) Establishment Section 9015 of title 10, United States Code, is amended— (1) in the heading, by striking Under Secretary and inserting Under Secretaries ; (2) in subsection (a), by striking is an Under Secretary of the Air Force and inserting are two Under Secretaries of the Air Force