As if going to space wasn't dangerous enough already, it turns out that astronauts face a problem with squashed eyeballs that can seriously impact their vision when they return to Earth.
That's led scientists to develop a new sleeping bag to help alleviate the issue caused by zero gravity.
In space, fluid floats in the body and head, and this can cause the eyeball to be squashed over extended periods of time. It's called spaceflight-associated neuro-ocular syndrome (SANS).
As well as flattening at the back of the eyeball, it can also lead to optic nerve swelling and further vision impairment.
Astronaut John Phillips was particularly unlucky. When he flew to the International Space Station in 2005 he had perfect, 20/20 vision, the BBC reported.
On return six months later he had much deteriorated 20/100 vision - meaning he must be 20 feet away to see what a person with perfect vision can see at 100 feet.
The sleeping bag was developed by a team led by Dr Benjamin Levine, a professor at University of Texas (UT) Southwestern Medical Center in Dallas. It works like a vacuum cleaner, with a pressure difference 'sucking' fluid out of the head and towards the feet.
This could stop SANS developing and means one of the bigger health risks to astronauts could be mitigated.
According to the BBC, NASA has experienced vision problems in more than half of those who have served for six months or more on the ISS. That has the potential to cause huge issues, particularly with extended space missions on the horizon.
"We don't know how bad the effects might be on a longer flight, like a two-year Mars operation," Levine told the BBC.
"It would be a disaster if astronauts had such severe impairments that they couldn't see what they're doing and it compromised the mission."
Levine is hoping that he will be able to get the new invention to the ISS as further research on how long and when the bag should be used needs to be carried out.
"This is perhaps one of the most mission-critical medical issues that has been discovered in the last decade for the space program," Levine said.
SANS was identified by Levine while working with cancer survivors in conditions that simulated zero gravity.
The scientists were able to measure the volunteers' brain pressure due to the port in their heads that delivered chemotherapy drugs.
