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My Brother Scott Just Hit the Halfway Point of His #YearInSpace

This week, my twin brother Scott Kelly reached a milestone: the halfway point in his nearly year-long mission aboard the International Space Station.

This week, my twin brother Scott Kelly reached a milestone: the halfway point in his nearly year-long mission aboard the International Space Station.

For 173 days (as of my writing), Scott has served our country in zero gravity, floating inside the International Space Station as it orbits 250 miles above our planet at 17,500 miles per hour, far away from his family and friends. On this flight alone, he has already traveled 72 million miles around Earth.

For 173 days, Scott has lived in a tough, unforgiving, and unchanging environment. The lighting hasn’t changed. The temperature and humidity haven’t changed. The humming and whirring of the Space Station hasn’t changed.

For 173 days, there has been no warm sunshine, no cooling breeze, no thunderstorm, no patter of a rain shower, no sound of waves hitting the shore. Nothing.

Read More: Scott Kelly Tweets Picture of Manhattan from International Space Station

Because every day aboard the Space Station, you wake up to an environment that is exactly is the same as the day before it. Imagine being stuck in your office for 173 days with no way to go outside, and with no up and no down and nothing ever changing, and know you’ve got nearly six months to go before you can leave. And it’s not like you can get a pizza delivered.

Fortunately for Scott and his crewmates, being stuck at the Space Station includes some incredible views. And fortunately for all of us, Scott has heeded President Obama’s order at February’s State of the Union to Instagram -- and tweet -- photos of his mission. He has not disappointed.

But more important than Scott’s stunning photos of space and our planet is how his service aboard the Space Station is providing data that will help us better understand how spending a long time in space impacts the human body, what kind of problems it creates, and what we need to do if we are going to send Americans beyond low-earth orbit to places like Mars on a journey that could take three years.

There are a lot of exciting destinations in the universe, and some of them are not too far away. Scott’s mission is another step toward them.

As Scott reaches the six-month mark of his mission, we are headed into unknown but exciting territory -- because we have never had an American in space for such a long period of time. Sure, in the late 1980s and early 1990s the Soviets had cosmonauts at the Mir Space Station for more than a year, but the technology available then couldn’t provide nearly the amount of data that today’s can. We simply don’t know a lot about what happens to astronauts in space after six months. Scott’s mission is effectively doubling the amount of data we have.

Read More: Mark Kelly: My Twin Brother Scott Just Blasted Off for a Year in Space

To maximize the knowledge we gain from Scott’s mission, NASA is studying both of us in its “Twins Study.” Since we’re identical twins, researchers have a first-of-a-kind chance to understand how the human body changes in space. Think of it this way: Scott’s the test subject, and I’m the control.

What has my participation in the so-called “Twins Study” been like up to this halfway point in his mission? Compared to Scott, I’ve had the easy (and less fun) part, staying here on Earth and providing a ton of data for NASA researchers. I’ve given a lot of blood -- at my house, at clinics, and even in a tucked-away corner of a hotel lobby, where NASA researchers came to meet me. I’ve spent time at my home in Tucson on a NASA laptop, using software designed to test and compare Scott's and my cognitive abilities. (I’m optimistic the tests will definitively show I’m the smart one.) I’ve also already traveled a few times to NASA’s Johnson Space Center in Houston, where I worked for 15 years, to undergo MRIs, ultrasounds, and exams. I’m headed back there in October for another round of tests.

And even after Scott returns from his mission, NASA researchers will continue to study us.

For now, even though one of us is off the planet and the other one is on it, Scott and I get to talk a lot -- sometimes more than when we’re both on Earth. We trade emails several times a day. We give each other a hard time on Twitter -- proving that brothers’ innate drive to make fun of each other knows no earthly bounds. And we talk on the phone about every other day. There’s a phone at the Space Station that Scott can use during certain times of the day, so while I can’t call up to him, he can call down to me. Thanks to my daughter Claire, who programmed the Space Station’s Houston-area number into my iPhone’s contacts, when Scott calls, my phone just says “SPACE” is calling -- along with two emojis: a rocket and an alien.

Read More: NASA Astronaut Scott Kelly's Year on Space Station Blazes Trail to Mars

When Scott returns to our planet in March on a Russian Soyuz capsule, which will land out in the desert steppes of Kazakhstan, no other American will have spent more time in space during a single flight. He’ll have orbited the Earth 5,472 times, traveling more than 141 million statute miles. He’ll have put himself at tremendous risk for science, for America’s space program, and for our country.

And there is no doubt he’ll be happy to be home -- and that all of us Americans who believe it is in the DNA of our great country to explore will be grateful to Scott for his service.