Most people who apply to become a NASA astronaut are disqualified before they ever reach a medical exam or interview. The biggest filters are straightforward: you need U.S. citizenship, a master’s degree in a STEM field, and at least two years of related professional experience. Beyond those baseline requirements, a range of physical, medical, and psychological factors can knock you out of the running.
Citizenship and Education Requirements
You must be a U.S. citizen to apply. Green card holders, dual citizens of other countries without U.S. citizenship, and foreign nationals are not eligible, with extremely rare exceptions. This single requirement eliminates the vast majority of the world’s population from consideration.
On the education side, NASA requires a master’s degree in a STEM field: engineering, biological science, physical science, computer science, or mathematics. A bachelor’s degree alone won’t qualify you, no matter how impressive your work experience. However, there are a few alternate paths that satisfy the master’s requirement. Two years of work toward a STEM doctoral program counts, as does a completed Doctor of Medicine or Doctor of Osteopathic Medicine degree. Completing a nationally recognized test pilot school program also meets the standard. If your degree is in a non-STEM field like business, law, political science, or the humanities, you’re disqualified regardless of degree level.
Height and Body Size Limits
Spacecraft have fixed dimensions, and your body has to fit inside them. NASA’s anthropometric limits for astronaut candidates currently range from 58 inches (4 feet 10 inches) to 77 inches (6 feet 5 inches) in height, with a weight range of 95 to 243 pounds. These limits exist primarily because of spacesuit sizing and the physical constraints of crew vehicles and the International Space Station. If you fall outside this range, there’s no waiver or workaround.
Vision Standards
Poor eyesight used to be one of the most common disqualifiers, but the rules have loosened significantly. In the early shuttle era, uncorrected distance vision had to meet strict minimums. Today, NASA allows astronauts to wear soft contact lenses in space, and since 2007, candidates have been permitted to correct their vision with LASIK or PRK laser eye surgery. So needing glasses or contacts alone won’t disqualify you.
That said, certain eye conditions still pose problems. Cataracts, chorioretinopathy (damage to the retina’s light-sensing layer), and severely defective distance visual acuity that can’t be adequately corrected may still be disqualifying. The key shift is that correctable vision problems are no longer a barrier, while structural eye diseases can be.
Medical Disqualifiers
NASA puts astronaut candidates through one of the most thorough medical evaluations in any profession. The agency doesn’t publish a complete public list of every disqualifying condition, but the screening covers cardiovascular health, neurological function, musculoskeletal fitness, and organ function in detail. Conditions that could become emergencies in microgravity, where medical care is extremely limited, are taken the most seriously.
Heart conditions are a major area of scrutiny. Uncontrolled high blood pressure, significant arrhythmias, and coronary artery disease can all disqualify a candidate. The logic is simple: a cardiac event on the International Space Station, where the nearest hospital is a several-hour Soyuz ride and reentry away, could be fatal. Kidney stones are another well-known concern, since microgravity increases the risk of developing them, and passing a stone in space with no surgical options is a serious medical scenario.
Conditions requiring ongoing medication management can also be problematic, particularly if missing doses or supply interruptions could cause rapid deterioration. Any history of certain cancers may require extended periods of remission before an applicant would be considered. Bone density issues matter too, since astronauts lose bone mass in space at roughly 1 to 2 percent per month in weight-bearing bones, and starting from an already weakened baseline would be risky.
Psychological and Psychiatric Screening
NASA’s selection process uses psychological evaluation in two distinct ways. The first is “select-out” screening, which looks for diagnosable psychiatric conditions that would disqualify a candidate. Active psychotic disorders, severe untreated mood disorders, personality disorders that impair interpersonal functioning, and substance abuse disorders all fall into this category. The goal is to identify pathological conditions that could compromise crew safety or mission success.
The second layer is “select-in” evaluation, which is less about disqualification and more about identifying candidates who are particularly well-suited to the work. Astronauts live and work in a confined space with a small team for months at a time, often under high stress with minimal privacy. Evaluators look for emotional stability, adaptability, the ability to function well in a group, and tolerance for isolation. You could be psychiatrically healthy and still lose out to candidates who score better on these traits. As missions grow longer, with eventual Mars trips lasting two to three years, these psychological “select-in” criteria are becoming increasingly important.
Professional Experience
A degree alone isn’t enough. NASA requires at least two years of related, progressively responsible professional experience in your STEM field after completing your degree. Alternatively, at least 1,000 hours of pilot-in-command time in jet aircraft satisfies this requirement. Having no professional track record, or experience in an unrelated field, effectively disqualifies you at the application stage.
The experience requirement filters for people who have actually applied their training in demanding, real-world environments. NASA’s most recent astronaut classes have included military test pilots, physicians, geologists, engineers, and research scientists, all with substantial careers behind them. The typical selectee has far more than the minimum two years, often bringing a decade or more of professional accomplishment.
Age, Criminal History, and Other Factors
NASA does not set an official age limit for astronaut candidates. In practice, the education and experience requirements mean most applicants are in their late 20s at the youngest, and the average age of selection tends to fall in the mid-30s. Being older doesn’t automatically disqualify you, but the physical demands of training and spaceflight favor candidates in strong overall health.
Criminal history is handled under federal hiring rules. The Fair Chance to Compete for Jobs Act prohibits NASA from asking about criminal records before making a conditional job offer. So a criminal record doesn’t disqualify you at the application stage, though it would come up during the background investigation that follows a conditional offer. Felony convictions or patterns of serious offenses could ultimately prevent final selection, particularly given the security clearances involved in the role.
Military applicants follow a slightly different path, applying first through their branch of service rather than directly through NASA’s civilian process. The underlying requirements remain the same, but the chain of application differs.