In space, everyone grows. This astronaut shot up 3½ inches

By Alex Horton / The Washington Post

In space, everyone can see you grow.

Japanese astronaut Norishige Kanai said on Twitter that he is 3½ inches taller since arriving at the International Space Station on Dec. 19. Weightlessness has that effect: Without gravitational force compressing the spine, vertebrae relax and temporarily expand, like a coiled spring unspooled from the top.

“Good morning, everyone. Today I share some serious news. Since coming to space, I have grown 9 centimeters. This is the most I’ve grown in three weeks since junior high school,” Kanai wrote Monday.

But even 3½ inches is a remarkable height difference. NASA has said about two inches of growth is typical and expected in space.

“Nine centimeters is a lot, but it is possible, knowing that every human body is different,” said Libby Jackson, a program manager for the United Kingdom Space Agency, the BBC reported.

While it is temporary, and astronauts return to their normal height when they slip the bonds of space and return home, the height difference has an immediate effect on the dimensions of space suits, stations and vehicles.

Space is a premium in, well, space, with each inch scrutinized to pack in instruments, tools, plants and insects for experiments and other essentials like food and water. That means living and working quarters are tight. On the Russian Soyuz TMA spacecraft station, the vehicle used to get astronauts to and from the ISS, personnel are limited to 6 feet 3 so they can fit inside the seats. That means anyone at that limit on Earth would be restricted from ISS operations.

“I am a little worried I won’t fit in my seat on the return trip on Soyuz,” Kanai said, though he was probably joking. Each seat liner on the vehicle is customized and molded to the body of each astronaut and taken to the Soyuz to ensure a tight fit during the violent reintroduction to gravity. “To help absorb the shock of landing, explosive charges fired and instantly pushed our seats forward so that our faces were very close to the instrument panel,” wrote astronaut Ron Garan in October 2011, describing re-entry from the Soyuz vehicle.

Once the vehicle re-enters Earth’s atmosphere, astronauts are once again compressed to their normal height, said Stephanie L. Schierholz, a NASA spokeswoman.

Taller spacewalking hopefuls had their dreams dashed in earlier decades. The country’s first astronauts, the legendary Mercury Seven crew including John Glenn and Alan Shepard, were all under 6 feet — any more would be too much inside the claustrophobic Mercury capsule. But later recruits could exceed that limit in the space shuttle program, though some flirted with the restriction among the celestial bodies.

“According to my quick calculations here, I seem to have grown about an inch or so. So I’m now too tall to fly in space,” said the 6-3 Columbia payload Cmdr. Richard Hieb in July 1994, after measuring himself as part of a medical experiment. “And that’s without slipper-socks.”

While height differences are fleeting, NASA scientists and researchers have yet to understand some of the longer-term effects of zero gravity on the human body, a vital lesson if humans reach beyond the moon and colonize Mars and other planets. The agency received a rare opportunity in 2015 when astronaut Scott Kelly spent a year on the ISS, a record, to provide researchers a wealth of metrics. His twin brother, Mark, a retired astronaut, was studied so scientists could compare notes on terrestrial and extraterrestrial effects on the mind and body.

There are a host of concerns, from plaque buildup in arteries and how shifts in bodily fluids affect eyesight. Vision problems are a common issue among astronauts — gravity on Earth tends to draw fluids downward, but that does not occur in space, and scientists believe those fluids fluctuate and build in the skull and behind eyes.

An exam of John Phillips, an astronaut on the ISS in 2005, determined that the backs of his eyes were flatter and pushed his retinas forward. In six months, his eyesight went from 20/20 to 20/100. His vision later improved to 20/50 but remained there, even years later.

But few dangers pose more risk than radiation exposure. A radiation detector aboard the Mars Curiosity Rover concluded that a human would be bombarded with a minimum of 0.66 sieverts during a round-trip excursion to Mars, or the equivalent of receiving a CT body scan every five to six days. That would bolster the risk of cancer and other ailments.

Earth’s magnetic field helps protect humans from the sun’s radiation, with the average person enjoying a perfectly tolerable 10 microsieverts (0.00001 sievert). But that isn’t true for space, or for Mars. Plan accordingly.