Learning Path: Astronauts & Astronaut Candidates

Who this path is for

For career astronauts, astronaut candidates and people applying to become one, and for professional crew on government or commercial missions. It follows the medical side of a career in order: selection, preparing for flight, living in space, coming home and lifelong follow-up.

Before you start

About 19 steps. Most pages take 10–20 minutes. Pages marked DRAFT have not yet been reviewed.

What to expect, stage by stage

This section summarizes what NASA’s published standards say happens medically across an astronaut career. It describes NASA career astronauts. Other space agencies and commercial companies that employ their own professional crew set their own medical standards; those are not covered here pending verification.

1. Applying and selection

• Basic qualifications. To be considered, NASA lists four requirements: U.S. citizenship; a master’s degree in a science, technology, engineering or math field (or an accepted equivalent, such as a completed medical degree or test pilot school); at least two years of related professional experience or 1,000 hours as pilot-in-command of jet aircraft; and the ability to pass the NASA long-duration flight astronaut physical [1].
• The selection medical. Candidates complete a detailed medical questionnaire, a full aeromedical physical examination, laboratory tests, special tests and imaging (for example ultrasound, a 12-lead heart tracing (electrocardiogram), X-ray and MRI), specialist assessments (eyes, ear-nose-throat, dental, digestive system, heart and lungs, nervous system, behavioral health and, where relevant, gynecology) and a psychiatric evaluation [2]. The goal is to find conditions that could endanger the astronaut, the mission, or be made worse by training such as T-38 jet flying and underwater spacewalk practice [2].
• No waivers at selection. The standard states that no waiver is granted on selection of NASA astronauts [3]. Selection standards also consider a long career, which NASA notes may be reconsidered for non-career astronauts [2].

2. Every year: recertification

• Crewmembers are medically and psychologically selected and then recertified every year under NASA’s astronaut medical standard, OCHMO-STD-100.1A (requirement [V1 3001]) [4][3]. The annual exam checks that no new condition has developed that would make training or flight unsafe [2].
• Unlike selection, a waiver can be requested at recertification. A waiver may set conditions on mission assignment [3].

3. Getting ready for a mission

• NASA requires pre-mission preventive care, including nutrition, vitamin D, a check of medicines needed in flight, bone density imaging every three years, aerobic and strength fitness, flexibility and balance, annual and pre-flight physicals, preventive dental care, recommended vaccinations, behavioral health training, radiation dose monitoring and a pre-launch health stabilization program (a quarantine-like period to avoid catching an infection before launch). It also allows assisted reproductive technology to preserve eggs or sperm before missions with radiation exposure, if the crewmember wants it [4].
• Example timing for a 6-month space station mission: physical exams about 9–6 months, 21–14 days and 2–1 days before launch [3]. NASA labels this schedule as an example; the program tailors it to each mission [3].
• Sleep medicines and space motion sickness medicines are tried on the ground first, any time before 30 days before launch [3].

4. In flight

• Each vehicle has at least two crewmembers trained as crew medical officers (CMOs) [4].
• Crews hold private medical conferences with the flight surgeon during the mission [3], and crew medical officers carry out scheduled health checks on long missions [3].
• The main risks come from NASA’s five hazards: radiation, isolation and confinement, distance from Earth, altered gravity, and a hostile, closed environment [5]. The pages in the reading list below cover each one and the countermeasures (exercise, sleep and workload management, radiation monitoring, and oxygen prebreathe before spacewalks).

5. Coming home

• After landing, a flight surgeon (or designated medical staff) examines crewmembers immediately after landing and periodically after that until they are stable [4].
• Every crewmember gets an individualized reconditioning program that starts at egress from the vehicle and follows guided phases [4].
• Example timing after a 6-month mission: physical exams on landing day and about 3, 7–14 and 60 days after return [3].

6. For life

• Returning crewmembers are monitored long term for health, behavioral health and well-being in a standardized way [4].
• The TREAT Astronauts Act (2017) authorizes NASA to provide medical monitoring, diagnosis and treatment of conditions potentially associated with spaceflight for former astronauts who have flown at least one mission [6].
• NASA limits each astronaut’s career radiation exposure to below 600 mSv [4], mainly because of long-term cancer risk.