; (B) the Secretary determines that it is in the best interests of the Space Force for the officer to continue to serve in current position and grade; and (C) the officer has not previously opted out of a promotion board under this section. (3) Service in critical skill position If— (A) the officer is serving in a critical skill position that cannot be filled by another Space Force officer serving in the same grade; (B) the Secretary determines that it is in the best interests of the Space Force for the officer to continue to serve in their current position and grade; and (C) the officer has not previously opted out of a promotion board under this section. 20233. Eligibility for consideration for promotion: designation as joint qualified officer required before promotion to brigadier general; exceptions (a) General rule An officer on the Space Force officer list may not be appointed to the grade of brigadier general unless the officer has been designated as a joint qualified officer in accordance with section 661 of this title. (b) Exceptions Subject to subsection (c), the Secretary of Defense may waive subsection (a) in the following circumstances: (1) When necessary for the good of the service. (2) In the case of an officer whose proposed selection for promotion is based primarily upon scientific and technical qualifications for which joint requirements do not exist. (3) In the case of an officer selected by a promotion board for appointment to the grade of brigadier general while serving in a joint duty assignment if— (A) the officer’s total consecutive service in joint duty assignments is not less than two years; and (B) the officer has successfully completed a program of education described in subsections (b) and (c) of section 2155 of this title. (4) In the case of an officer who— (A) is selected by a promotion board for appointment to the grade of brigadier general; (B) is not exempted under subsection (g)