After two days back on Earth, astronaut Scott Kelly has lost the inch-and-a-half of height that he gained during his American-record-setting 340 days aboard the International Space Station.

Microgravity uncompressed his spinal discs, but now that he’s returned “he’s been squished back to normal height,” his twin brother Mark Kelly, a retired astronaut, joked to reporters at a news conference on Friday. Or, as Scott put it, “gravity pushes you back down to size.”

Scientists are just beginning to analyze the blood samples, cognitive assessments, ultrasounds, and other measurements that Kelly performed on himself during his mission, and will continue to test him for months. He has already, since his landing on Tuesday, undergone tests of muscle strength, as well as MRIs aimed at assessing how the redistribution of bodily fluids in his skull and brain might have affected his eyes and optic nerve.

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Those and other results will show whether the bone loss, muscle atrophy, and other well-documented effects of microgravity bottom out after a few months in space or continue for the duration of the mission. That information will be crucial to understanding what a crew might experience during a mission to Mars, which would take 30 months, as well as whether “countermeasures” that NASA has implemented — exercise equipment to minimize bone loss, for instance — worked.

Revealing the effects of space

In advance of the formal scientific results, however, Kelly revealed some of the effects of his space odyssey — some of them unexpected.

His skin is surprisingly sensitive, he told reporters: “Any significant contact is almost like a burning sensation whenever I sit or walk.” He’s managing that with special, extra cushiony shoes. He’s also experiencing more muscle soreness and joint pain than he expected. “I figured [the effect of a year in space] would be a little bit different [from shorter flights], but it’s more than a little bit different,” he said.

Kelly is still adjusting mentally to being back in an environment where gravity pulls things down. “The first thing I tried to throw on a table I missed,” he admitted. “But I don’t seem to have a tendency to drop things” as he did after his first, eight-day space mission in 1999.

Vision changes in space have been a key target of NASA’s biological studies, since many astronauts become farsighted during their flights. Kelly said his vision changes were “very consistent with my last flight,” and that “in the beginning you notice some changes but then it levels off,” suggesting that 12 months in space does not have twice the effect on vision as six months do.

The psychological impact was stronger, however. In a six-month mission “you can see the end” from the very beginning. “But when you launch in March and you think of coming back the next March it’s not something you can really comprehend,” Kelly said. Facing nine more months on the ISS is “kind of hard to get your head around.”

NASA officials said at the news briefing that it’ll likely be a year or even two before their full medical analysis on Scott Kelly is completed. 

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