Scott Kelly's one year in space to end with bumpy ride home

In closing out his fourth, and likely last, mission to space, 51-year-old American astronaut Scott Kelly told reporters Thursday that he feels good physically, he is ready to be reunited with his family, and that he will always try to stay involved with the space program.

“It’s my life’s work, I feel very strongly about it,” Mr. Kelly said.

He reflected on his time in space and on the future of space exploration during his final live webcast from the International Space Station, a football-field-size lab orbiting 240 miles above Earth. Sending humans to Mars, as NASA hopes to do in the 2030s, is within reach, said the astronaut, if the United States wants it badly enough.

“I think there is nothing we can’t accomplish if we put our minds and resources behind it,” said Kelly in the video stream. “If we can dream it, we can do it,” he said.

Kelly is set to travel back to Earth on March 1 with Russian cosmonauts Mikhail Kornienko and Sergey Volkov in a cramped capsule inside the Russian Soyuz spacecraft. They will undock it from the space station, and drift away for a few minutes before firing their engines. This technique protects the station’s solar panels from Soyuz's exhaust fuel.

Once the engines are on, the travelers will spend three-and-a-half hours descending to Earth, most of that time at a speed of 17,500 miles per hour.

Doug Wheelock, a NASA astronaut who spent 178 days in space over the course of two missions, told ABC News that the ride felt like "going over Niagara falls in a barrel, but the barrel is on fire."

The hardest part likely will be the final hour, which is when the astronauts start to decelerate the spacecraft as they “tumble” to Earth in a spinning motion, slowed by the drag from the atmosphere.

During this time, parts of the spacecraft will blast away from the capsule to burn up in the atmosphere.

As the astronauts fall closer to Earth, they’ll experience g-forces 3.8 times that of Earth's gravity, “which is crushing,” according to Canadian astronaut Chris Hadfield, especially compared to the microgravity environment the astronauts will have experienced during their many months on the space station. Col. Hadfield wrote about the reentry experience in his 2013 book, An Astronaut's Guide to Life on Earth. 

“That feels more or less like 15 explosions followed by a car crash,” he wrote of the fiery tumble to Earth.

Several parachutes will release from the capsule in the final 10 minutes of descent to float it down to the grassy plains smack in the middle of Kazakhstan. Touchdown is scheduled for 10:30 a.m. local time.

A small crew – including a NASA surgeon and nurse – will be on hand to help the astronauts out of the capsule and to test their reflexes in several tasks, such as getting up from lying down, bending over, and walking with their eyes closed and open, Blake Chamberlain, lead surgeon for the space station, explains to the The Christian Science Monitor.

“They used to be really weak when they came out, but their strength is good now,” says Dr. Chamberlain in a phone interview.

This is because in recent years astronauts on the space station have been required to exercise daily to mitigate the muscle and bone loss associated with microgravity. Aboard the space station is a treadmill – named COLBERT, after comedian Stephen Colbert – and a bicycle. Astronauts have to strap themselves into the exercise equipment to stay attached to it.

There is also a 'weight-lifting' machine on the space station. It provides resistance in microgravity as astronauts pull levers against the suction of a vacuum chamber.

"We have done much better job of getting them back on their feet because of the exercise machines," Chamberlain says.

After the battery of tests at the landing site, Kelly will board a jet and fly with a surgeon to the Johnson Space Center in Houston, where he will finally be reunited with his family. And where he’ll be subjected to more tests.

“And then I’m going to go home and jump in my pool,” said Kelly, though that won’t happen for at least another day or two, as he will have to camp at the space center for observation.

Kelly’s first days and weeks will be full of physical and psychological testing and of conditioning to help get him back to normal. After spending so much time in so little gravity, and amid such high radiation, researchers suspect that his bones could be weaker, and his motor skills and vision could be impaired.

Tracking these changes will help scientists understand how the body reacts to a long mission to space, which is instrumental to the future of human space travel, particularly for long missions to Mars. Kelly has spent a year aboard the space station, longer than any American astronaut.

He is a particularly valuable test subject because scientists can compare him to his Earth-based identical twin brother, retired astronaut Mark Kelly. Both are part of a NASA twin study that has given the agency an unprecedented opportunity to observe the effects of long-term spaceflight on a genetic level by comparing the brothers – one having spent a year in space, and the other on Earth.