14 CFR §1203a.103

1. (a)Only those NASA employees, NASA contractor employees, and visitors who have a need for such access and who meet the following criteria may enter a security area:
   1. (1)Controlled area. Be authorized to enter the area alone or be escorted by or under the supervision of a NASA employee or NASA contractor employee who is authorized to enter the area.
   2. (2)Limited area. Possess a security clearance equal to the level of the classified information or material held, discussed, or disseminated on site or is the holder of a positive national agency check if classified material or information is not involved. Personnel who do not meet the requirements for unescorted access may be escorted by a NASA employee or NASA contractor employee who meets the access requirements and has been authorized to enter the area.
   3. (3)Exclusion area. Possess a security clearance equal to the classified information or material involved.
2. (b)The Center Directors, including Component Facilities and Technical and Service Support Centers, and the Executive Director for Headquarters Operations, NASA Headquarters, may rescind previously granted authorizations to enter a security area when an individual's access is no longer required, threatens the security of the property, or is disruptive of Government operations.