Astronauts are exposed to various health issues during extended space missions, such as loss of muscle and bone, radiation exposure, and vision issues. These complications become more pronounced as humans venture deeper into space to destinations like Mars.

Two US astronauts, Butch Wilmore and Sunita Williams, are on the verge of their return from their nine-month-long stay at the International Space Station (ISS). Although some of the health challenges they endured are known and well-managed, others are shrouded in mystery.

Exercise is very important in maintaining the health of astronauts in space. Nine-month missions on the ISS are becoming routine, according to Rihana Bokhari, assistant professor at Baylor College's Center for Space Medicine. Most missions on the ISS are around six months long, but some have lasted almost a year.

On Earth, gravity acts naturally to make muscles and bones stronger from use. But in space, with no gravity, astronauts must supplement with exercise to maintain a healthy state. The ISS features three exercise machines, such as a resistance device added in 2009 that employs vacuum tubes and flywheel cables to mimic weightlifting.

Astronauts exercise for two hours a day to keep muscles and bones strong.  "The best results that we have to show that we're being very effective is that we don't really have a fracture problem in astronauts when they return to the ground," Bokhari told AFP. However, bone loss is still visible in scans.

How does microgravity affect the body?

Balance disorders are another widespread problem for astronauts. Emmanuel Urquieta, the vice chair of Aerospace Medicine at the University of Central Florida, described how microgravity impacts the inner ear, which manages balance. "This happens to every single astronaut, even those who go into space just for a few days," he said.

Astronauts must re-develop their balance with NASA's 45-day post-mission rehabilitation program.

Another issue is "fluid shift," in which fluids in the body shift towards the head during microgravity. It has the potential to increase calcium content in urine, making individuals more prone to kidney stones. It also increases intracranial pressure, which can alter the shape of the eyeball and result in vision impairment. It is referred to as spaceflight-associated neuro-ocular syndrome (SANS).

Jessica Meir, an astronaut with NASA, spoke of her experience with SANS. "When I launched, I wore glasses and contacts, but due to globe flattening, I now have 20/15 vision -- most expensive corrective surgery possible. Thank you, taxpayers," she said.

How dangerous is radiation in space?

Radiation exposure is another serious risk. The ISS passes through the Van Allen radiation belt, but Earth’s magnetic field provides some protection. However, future missions to the Moon and Mars will expose astronauts to even higher radiation levels.

Siegfried Eggl, an astrophysicist at the University of Illinois Urbana-Champaign, said that protecting astronauts from radiation is difficult. "Shielding is best done with heavy materials like lead or water, but you need vast quantities of it," he explained.

NASA aims to limit astronauts’ increased lifetime cancer risk to within three percent. Future space probes could warn astronauts about high-radiation events like coronal mass ejections from the Sun, but cosmic radiation remains hard to predict.

Can artificial gravity help?

Artificial gravity could help astronauts adjust to long space missions. Rotating spacecraft frames could simulate gravity, making it easier for astronauts to function when they reach Mars.

Another option is using spacecraft that accelerate and decelerate at speeds matching Earth’s gravity. This would shorten travel time and reduce radiation exposure, but it would require advanced nuclear propulsion technology that doesn’t yet exist.

How do astronauts cope with mental stress?

The psychological strain of being in space for extended durations is also a major challenge. Joseph Keebler, a psychologist at Embry-Riddle Aeronautical University, likened it to being trapped in a confined space with the same individuals for years.

"Imagine being stuck in a van with anybody for three years: these vessels aren't that big, there's no privacy, there's no backyard to go to," he said. "I really commend astronauts that commit to this. It's an unfathomable job."

With longer and more complicated space missions on the horizon, staying physically and mentally healthy will be essential to the success of future exploration.

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