Becoming an astronaut is one of the most competitive career paths on Earth. When NASA last accepted applications in 2024, more than 8,000 people applied and only 10 were selected, an acceptance rate of about 0.1%. That’s roughly five times harder to get into than Harvard Medical School. And getting selected is just the beginning: years of grueling training, physical demands, and long-term health risks follow.
The Odds of Getting Selected
NASA doesn’t recruit on a regular schedule. The agency opens applications only when it needs new astronaut candidates, which has historically happened every four to six years. When the window does open, thousands of highly qualified people compete for a handful of spots. The 2024 class picked 10 candidates from over 8,000 applicants. Previous cycles have been similarly brutal. In 2017, NASA received more than 18,000 applications and chose 12.
What makes this especially daunting is that the applicant pool isn’t random. Most people who apply already hold advanced STEM degrees, have years of professional experience, and meet strict medical standards. You’re not competing against the general public. You’re competing against fighter pilots, surgeons, physicists, and engineers who are all near the top of their fields.
What You Need Before You Apply
NASA requires a master’s degree (or higher) in a STEM field: engineering, biological science, physical science, computer science, or mathematics. A medical degree (M.D. or D.O.) also qualifies, as does completing two years of a doctoral program in a related field. A bachelor’s degree alone won’t cut it.
Beyond the degree, you need at least two years of related professional experience or at least 1,000 hours of pilot-in-command time in jet aircraft. Many successful candidates far exceed these minimums. Selected astronauts typically bring a combination of operational experience (military test piloting, submarine service, field research in extreme environments) and deep technical expertise. Having both makes you stand out in a pool where nearly everyone already meets the baseline requirements.
You also need to pass NASA’s long-duration spaceflight physical, which evaluates vision, cardiovascular health, and a range of other medical benchmarks. Certain conditions are automatic disqualifiers. The medical screening is thorough enough that it eliminates candidates who look perfect on paper.
Two Years of Training Before You’re Official
Getting selected doesn’t make you an astronaut. It makes you an astronaut candidate, and you still have roughly two years of training and evaluation ahead before you earn the title. The training takes place primarily at Johnson Space Center and covers a wide range of skills, many of which will be completely new even to experienced pilots and scientists.
Candidates must complete training in five core areas to graduate:
- International Space Station systems: Learning to operate and troubleshoot the station’s complex hardware, life support, and experiments.
- Extravehicular activity (spacewalking): This starts with military water survival training and SCUBA certification, then moves to underwater practice in NASA’s massive Neutral Buoyancy Laboratory, a 40-foot-deep pool that simulates weightlessness.
- Robotics: Operating the station’s robotic arm, which is used to capture visiting spacecraft and support spacewalks.
- Russian language: Because international crews share the station, working proficiency in Russian is mandatory.
- Aircraft flight readiness: All candidates learn to fly T-38 jet trainers. Pilot astronauts must log 15 hours per month in the T-38 to maintain proficiency. Non-pilots fly a minimum of 4 hours per month. The jets expose astronauts to g-forces similar to those during launch, helping their bodies adapt to the flight environment.
Failing any of these areas can end your candidacy. And completing the program still doesn’t guarantee you’ll fly. Some astronauts wait years after graduating before being assigned to a mission.
What Spaceflight Does to Your Body
The difficulty doesn’t stop once you reach orbit. Long-duration spaceflight takes a measurable toll on human health, and astronauts accept these risks as part of the job.
Without Earth’s gravity, weight-bearing bones lose an average of 1% to 1.5% of their mineral density per month. On a six-month space station mission, that’s roughly the same bone loss a postmenopausal woman experiences over an entire year on Earth. Astronauts follow rigorous exercise regimens in space (about two hours daily) to slow this loss, but recovery after landing can take months.
Radiation exposure is another serious concern. Outside the protection of Earth’s atmosphere and magnetic field, astronauts absorb far more radiation than people on the ground. This increases the long-term risk of cancer, heart disease, and cataracts. NASA monitors radiation doses carefully and is developing better shielding and detection tools, but the risk cannot be eliminated entirely, especially for future missions to the Moon or Mars that would last much longer than current station stays.
Vision changes are common too. Many astronauts return from long missions with measurable shifts in eyesight caused by increased pressure inside the skull in microgravity. Some of these changes are permanent.
The Psychological Toll
Living in a confined space the size of a small apartment, with the same handful of people, for six months or more creates psychological pressures that are hard to simulate on the ground. The more restricted the environment and the less contact with the outside world, the higher the risk of behavioral issues, cognitive changes, or even psychiatric conditions.
Crew morale can shift over the course of a mission. Longing for family, feeling helpless during emergencies back home, and the monotony of routine all take a toll. Sleep quality often suffers because of noise, tight quarters, unusual light and dark cycles, and the stress of prolonged isolation. On Mars missions, communication delays of up to 20 minutes each way would make real-time conversations with loved ones or mission control impossible, adding another layer of psychological strain.
How to Improve Your Chances
Even with a 0.1% selection rate, there are concrete steps that make you a stronger candidate. The people NASA picks tend to share a few characteristics beyond the minimum requirements.
First, pursue operational experience in high-stress, team-based environments. Military test pilots, submarine officers, flight surgeons, and researchers who’ve done fieldwork in Antarctica or other remote locations show up disproportionately in astronaut classes. NASA values people who’ve proven they can perform under pressure, work in small teams, and adapt when things go wrong.
Second, go beyond the master’s degree if you can. A Ph.D. or M.D. with hands-on research or clinical experience demonstrates deep expertise and perseverance. Many selected candidates hold multiple advanced degrees.
Third, stay in peak physical condition. The medical screening is comprehensive, and some conditions that develop over time (high blood pressure, certain vision problems) can disqualify you even if you meet every other requirement.
Finally, apply more than once. Several current and former astronauts were rejected on their first or even second application before eventually being selected. Persistence matters, and gaining additional experience between application cycles can make a real difference.