NASA astronauts Sunita Williams and Barry 'Butch' Wilmore are enduring seriously harmful levels of radiation in space than they would have if Starliner was working fine.

Estimates suggest that the two astronauts who were supposed to spend just eight days aboard the International Space Station (ISS) will receive high doses of radition until February 2025. Their stay was extended until next year due to the Starliner spacecraft which turned out to be faulty before their return after June 5 launch.

Now the spacecraft is returning empty on September 7.

According to NASA, astronauts are exposed to ionising radiation with effective doses in the range from 50 to 2,000 mSv depending on the duration of their stay. The Milli-Sievert or mSv is the unit to measure radiation levels.

One mSv is equivalent to about three chest x-rays - making the doses of radiation in space as high as getting 150 to 6,000 x-rays continuously.

Since there is no protection of the atmosphere and the magnetosphere, humans in space get bombarded with ionised particles emerging from the Sun and other high energy sources in deep space.

According to NASA, Williams and Wilmore have already been exposed to roughly 40-80 mSv of radiation since early June - equivalent to about 120-240 X-rays. By 2025, they are likely to endure more than double of this amount. In comparison, humans on Earth receive just 2mSv of radiation each year thanks to the atmospheric protection.

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There is evidence to support the fact that astronauts are more prone to risk for cancer, central nervous system effects, and degenerative diseases. Currently, the Sun is also more active owing to the solar maximum phase and is expelling higher amounts of radiation.

"Butch and Suni, since they are on the ISS, will not be exposed to enough radiation to seriously cause large impacts on body systems but the long duration exposure to greater radiation than on Earth could lead to an increase in the risk of cancer, said Dr. Rihana Bokhari to ABC News. She is the acting chief scientific officer at Baylor College of Medicine's Translational Research Institute for Space Health.

Williams and Wilmore are forced to spend eight months aboard the ISS instead of eight days as Starliner is no longer safe for a return journey. NASA has given the job of rescuing them to SpaceX via the Crew-9 mission which is currently scheduled to launch on September 24.

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(Image: NASA)