Work, view of Himalayan lakes kept Scott Kelly 'sane' on ISS

The view of rainbow-hued Himalayan lakes and steady work helped Scott Kelly stay sane during the 340 days he spent aboard the International Space Station (ISS), the NASA astronaut said days after returning to Earth from the record-setting mission.

Kelly and his Russian counterpart, Mikhail Kornienko, spent nearly a year on the ISS studying the effects of radiation, weightlessness and the cramped quarters of spaceflight on humans.

Results from the research will be essential for an eventual mission to Mars, according to NASA.

Kelly said the length of the mission was the biggest challenge, and that he felt significantly more sore on returning to gravity than after shorter trips.

Kelly and his twin brother, Mark, a retired astronaut, have spent the last year taking physical and mental tests. The tests will continue, to help NASA learn about how the body copes with the severe strains of spaceflight.

Describing the striking colours of the waters around the Bahamas and the rainbow hues of lakes that dot the northern Himalayas, Kelly said he would like to visit the region.

However, "predominantly you just notice how thin the atmosphere is, how fragile it looks," Kelly was quoted as saying by The Guardian.

"That combined with these large swaths of pollution is kind of alarming," kelly added.

The astronaut said he could see entire systems of pollution - smoke clouds from wildfires that covered parts of the US, sections of Asia with continuous, visible pollution nearly all year round.

Besides following the news and the beautiful view, Kelly said steady work helped him sane.

"I tried to have milestones that were close, like when is the next crew arriving, the next spacewalk, the next robotics, the next science (experiment). That made a difference to me, keeping my sanity," he said.