Sunita Williams, Butch Wilmore: Toughest task is to learn walking again

AFTER nine months in space, Nasa astronauts Sunita Williams and Butch Wilmore have finally returned to Earth.

It brings to an end a mission that was supposed to last for just eight days, but got stretched to a much longer duration.

After the SpaceX capsule made a gentle splashdown off the Florida coast and brought ashore, the astronauts were helped onto a stretcher, as they returned to the world of gravity.

They will spend time at the Johnson Space Centre in Houston, Texas, where they will be examined by medical experts.

Long-duration missions in space take a toll on the body, astronauts lose bone density and suffer muscle loss.

Blood circulation is also affected, and fluid shifts can also impact eyesight.

It can take a long time for the body to return to normal, so the pair will be given an extensive exercise regime as their bodies re-adapt to living with gravity.

Even basic movement on Earth like walking resists gravity, an element missing while in space.

To counteract this, astronauts use three exercise machines on the International Space Station (ISS), including a 2009-installed resistance device that simulates free weights using vacuum tubes and flywheel cables.

A two-hour daily workout keeps them in shape.

"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," though bone loss is still detectable on scans, said Rihana Bokhari, an assistant professor at the Center for Space Medicine at Baylor College of Medicine.

Balance disruption

Balance disruption is another issue that affects every astronaut.

According to Emmanuel Urquieta, vice chair of Aerospace Medicine at the University of Central Florida, "This happens to every single astronaut, even those who go into space just for a few days."

After returning to Earth, they need to work to rebuild trust in their inner ear.

Astronauts must retrain their bodies during NASA's 45-day post-mission rehabilitation program.

Another challenge is "fluid shift" - the redistribution of bodily fluids toward the head in microgravity. This can increase calcium levels in urine, raising the risk of kidney stones.

Fluid shifts might also contribute to increased intracranial pressure, altering the shape of the eyeball and causing spaceflight-associated neuro-ocular syndrome (SANS), causing mild-to-moderate vision impairment.

Managing radiation

Radiation levels aboard the International Space Station (ISS) are higher than on the ground, as it passes through the Van Allen radiation belt, but Earth's magnetic field still provides significant protection.

The shielding is crucial, as NASA aims to limit astronauts' increased lifetime cancer risk to within three per cent.

A lot of research is currently being done to develop drugs and gene therapies to enhance the body's defences against space radiation. (Agencies)