14 CFR 1214.1101 – Announcement
(a) Astronaut candidate opportunities Will be announced nationwide and publicized periodically unless specifically canceled by NASA.
(b) Civilian applicants may apply at any time.
(c) Military personnel on active duty must apply through and be nominated by the military service with which they are affiliated. Military nominees will not be part of the continuing pool of applicants. The military services will convene their internal selection boards and provide nominees to NASA. The military nominees will be evaluated by NASA and the military services will be notified promptly of those nominees who are finalists.
(d) The Assistant Administrator for Equal Opportunity Programs, NASA Headquarters, will provide assistance in the recruiting process.