Quality is key to success in U.S. space and missile defense programs, but quality problems exist that have endangered entire missions along with less-visible problems leading to unnecessary repair, scrap, rework, and stoppage; long delays; and millions in cost growth. For space and missile defense acquisitions, GAO was asked to examine quality problems related to parts and manufacturing processes and materials across DOD and NASA. GAO assessed (1) the extent to which parts quality problems affect those agencies space and missile defense programs; (2) causes of any problems; and (3) initiatives to prevent, detect, and mitigate parts quality problems. To accomplish this, GAO reviewed all 21 systems with mature designs and projected high costs: 5 DOD satellite systems, 4 DOD missile defense systems, and 12 NASA systems. GAO reviewed existing and planned efforts for preventing, detecting, and mitigating parts quality problems. Further, GAO reviewed regulations, directives, instructions, policies, and several studies, and interviewed senior headquarters and contractor officials. DOD and NASA should implement a mechanism for periodic assessment of the condition of parts quality problems in major space and missile defense programs with periodic reporting to Congress. DOD partially agreed with the recommendation and NASA agreed. DOD agreed to annually address all quality issues, to include parts quality.