; and (B) if sufficient Space Force officers are not available pursuant to subparagraph (A), Air Force officers who hold a grade higher than the grade of the officers under consideration by the board and who are retired officers, but only if the Air Force officer to be appointed to the board has served in a space-related career field of the Air Force for sufficient time such that the Secretary of the Air Force determines that the retired Air Force officer has adequate knowledge concerning the standards of performance and conduct required of an officer of the Space Force. (4) Exclusion of retired general officers on active duty to serve on a board from numeric general officer active-duty limitations A retired general officer who is on active duty for the purpose of serving on a selection board shall not, while so serving, be counted against any limitation on the number of general and flag officers who may be on active duty. (b) Limitation on membership on consecutive boards (1) General rule Except as provided in paragraph (2), no officer may be a member of two successive selection boards convened under section 20211 of this title for the consideration of officers of the same grade. (2) Exception for general officer boards Paragraph (1) does not apply with respect to selection boards convened under section 20211 of this title for the consideration of officers in the grade of colonel or brigadier general. (c) Joint qualified officers (1) Each selection board convened under section 20211 of this title that will consider an officer described in paragraph (2) shall include at least one officer designated by the Chairman of the Joint Chiefs of Staff who is a joint qualified officer. (2) Paragraph (1) applies with respect to an officer who— (A) is serving on, or has served on, the Joint Staff