The Artemis II crew are closing in on Earth after a record-breaking mission to the far side of the moon, where they travelled further from their home planet than anyone in history.

Astronauts Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen reached a distance of 252,756 miles from Earth on a mission which NASA hopes will pave the way for longer lunar visits and eventually, trips to Mars.

Humans have been through millions of years of evolution to become perfectly adapted to life on Earth, so spending time in space - with no gravity, no sunlight and different levels of radiation - poses a real challenge physically.

So what are the main health concerns space travel presents and how does NASA contend with them?

Space radiation

Astronauts are exposed to high-energy radiation in space, unlike on Earth, where the atmosphere and planetary magnetic field provide a shield against it.

This can lead to DNA damage, increased cancer risk, neurodegenerative effects, cardiovascular issues and immune system dysregulation, experts say.

The International Space Station (ISS), where astronauts spend much of their time, is somewhat protected from radiation by Earth's magnetosphere, as it's around 250 miles away.

But the further you go into space, the more radiation you get exposed to, says Dr Haig Aintablian, director of space medicine at UCLA.

"Once you go beyond low Earth orbit, you lose much of the protection of Earth's magnetic field," he tells Sky News, adding radiation is one of the "real challenges" deep space poses.

Effects of microgravity

Floating around in space may look like a lot of fun, but gravity plays a critical role in regulating bodily functions, and its absence has negative impacts on human health, according to experts.

"The body is built to live and work in gravity. When that gravity signal is removed, the inner ear has to recalibrate, muscles and bones are used differently, and fluids shift upward toward the head," Dr Aintablian says.

"That is why we can see changes in balance, strength and, in some cases, vision."

You'll have seen the astronauts using specialist exercise equipment during their journey, and that's to contend with the fact that their bodies are not being engaged by the same forces they are used to on Earth.

Vitally, they are known to lose bone density, meaning bones get weaker and more brittle.

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For every month in space, astronauts' weight-bearing bones become roughly 1% less dense if precautions aren't taken, according to NASA.

They can also experience muscle atrophy, the wasting or thinning of muscle tissue, during their time in space.

Headaches are also widely reported for people in space. A study published in 2024 found 22 out of 24 surveyed astronauts who travelled in space for up to 26 weeks experienced them frequently while away from Earth.

Dr Aintablian says other common health concerns include motion sickness, dizziness, cardiovascular conditioning and sleep disruption.

He adds many of the health effects of space travel are temporary and improve once astronauts are back - though some have difficulty readjusting to gravity.

"Some changes can take longer to recover from, and a few, particularly involving vision or bone, can persist beyond the mission," he says.

How does NASA deal with health concerns?

The space agency monitors the health of the crew very closely before, during and after the flight.

It has flight surgeons, who act as personal doctors to the astronauts.

"On a mission like Artemis II, doctors are tracking not just how the crew feels, but how their bodies are responding in real time," Dr Aintablian says.

He says that while deep space travel always presents risks, he's confident they are understood well enough to be managed carefully.

The mission has included radiation monitoring, sleep and activity tracking, exercise countermeasures, and a structured post-landing medical recovery plan, he adds.

"There are a broad set of checks, including blood and other biological samples, balance and vestibular testing, strength and cardiovascular assessments, sleep monitoring, and behavioural health evaluations."

These checks not only help the astronauts now, but data collected throughout the mission will also prove vital for future missions.

"Artemis II is a critical step because it gives us human data from beyond low Earth orbit. That is essential if we are going to prepare crews safely for longer lunar missions and, eventually, Mars," Dr Aintablian explains.

The four astronauts are set to land in the Pacific Ocean at about 1am UK time.

(c) Sky News 2026: What 10 days of space travel could mean for Artemis astronauts' health