Astronaut Scott Kelly is back on Earth following an unprecedented yearlong mission in space for NASA.
Kelly and his Russian roommate for the past year, Mikhail Kornienko, landed in barren, frozen Kazakhstan on Wednesday. They checked out of the International Space Station 3½ hours earlier.
Their Soyuz capsule parachuted onto the central Asian steppes. Also returning to Earth: Russian cosmonaut Sergey Volkov, who piloted the craft.
Kelly and Kornienko spent 340 consecutive days in space. They circled the world 5,440 times on a mission that began last March.
Russia continues to rule, however, when it comes to long-duration spaceflight with the world record of 438 days.
Scientists are hoping for more one-year subjects as NASA looks ahead to Mars trips.
NASA considers it crucial prep work for future Mars explorers who will have to spend much longer in space and won't have the help of a welcoming committee. In fact, this mission — which began with a launch last March — is all about Mars.
"I think we'll learn a lot about longer-duration spaceflight and how that will take us to Mars someday," Kelly said Thursday in his final news conference from orbit. "So I'd like to think that this is another of many steppingstones to us landing on Mars sometime in our future."
Kelly said he misses relationships with people back home and that he can't wait to jump into his pool in Houston, Texas, according to NBC's "Today" show. But if he had to, he said, he could spend another 100 days in space.
What could new arrivals do on Mars, asks Dr. Stevan Gilmore, the lead flight surgeon who was at the landing site to receive Kelly. Could they jump up and down? Could they open a hatch? Could they do an immediate spacewalk?
The tests on Kelly and Kornienko should provide some answers. There will also be blood draws, heart monitoring and other medical exams. The testing will continue for weeks if not months once they're back home in Houston and at cosmonaut headquarters at Star City, Russia.
Checkups will also continue for Kelly's identical twin, retired astronaut Mark Kelly. The 52-year-old brothers joined forces to provide NASA with a potential gold mine of scientific data: one twin studied for a year in orbit — twice the usual space station stay — while his genetic double underwent similar tests on the ground.
While a handful of Russians have spent longer in space, the record being a 438-day flight, those expeditions date back to the 1980s and 1990s aboard the Mir space station, rustic if not rickety compared with the current space station. Medical testing was spotty back then, and the data weren't always widely shared.
As of Thursday — Day 335 — Kelly professed to feeling pretty good.
Kelly's vision has degraded a bit as it did during his last mission, a normal outcome for some astronauts because of increased pressure inside the skull in weightlessness. He anticipates his bones and muscles have weakened as well, despite daily exercise in orbit.
The real question mark — and Kelly's biggest concern — is the possible lingering effects of space radiation.
"Hopefully, I'll never find out what the true effects are of that," Kelly said in a TV interview last week. NASA will need to tackle the problem for Mars trips because of the increased level of exposure.
Johnson Space Center physiologist John Charles puts the psychological side of long-duration spaceflight right up there with radiation, as well as in-flight medical care and even food preservation and packaging for the long haul.
"Just about everything is a big problem for Mars," Charles said in a phone interview.
Mars expeditions planned for the 2030s will last 2½ years; the anticipated crew size will be four to six. The astronauts will almost certainly have to grow some of their own food; that's the reason for an experimental greenhouse aboard the space station.
Kelly and his crewmates grew red romaine lettuce in the mini-hothouse last summer and sampled some of the crop.
Even more impressive, Kelly nursed zinnias back to health in January, displaying a lush orange and yellow bouquet on Valentine's Day. He had to "channel my inner Mark Watney" — the lone astronaut who survives on potatoes in last year's blockbuster movie "The Martian" — to save the zinnias from mold.
Trust me when to add water, Kelly urged Mission Control, not some preflight script. That's how it will need to be when astronauts venture to Mars, he gently reminded everyone.
Charles stresses that Mars travel will be different than a space station stay. No regular phone chats with the husbands, wives and kids back home. No constant whispering in the astronauts' ears from Mission Control. Support would come via email.
"They're going to be highly autonomous," Charles said of the Mars explorers, "and that's something that we're trying to practice on the space station now ... learning how to get Mission Control out of the back pockets of the astronauts."
Kelly points out that crew quarters on Mars-bound craft will be much tighter than the space station — and nothing like the spaceships of science fiction. Between sleeping and working on his laptop, Kelly estimates he's spent almost half his time inside his personal cubicle — about the size of a phone booth.
NASA will need to improve privacy on Mars missions, he said, if it hopes to combat crew stress and fatigue.
The toughest part for Kelly has been the physical isolation from everyone he loves, 250 miles below him. But on a trip to Mars, tens of millions of miles away, astronauts won't be able to even see Earth.
"Obviously going to Mars, there are a lot of other challenges, but none of these we can't overcome," Kelly said.
NASA is discussing doing more one-year flights with the other countries involved in the station program; more subjects are needed for a better understanding of all the challenges. It's a long time, no matter how you cut it. Just ask Kelly, who recently acknowledged, "a year now seems longer than I thought it would be."