Spending almost a year in space means that Kelly will break the record for the longest stint of any U.S. astronaut, passing the entirety of his time on board the International Space Station (ISS) in the company of Russian cosmonaut Mikhail Korienko, writes Craig McCarthy for NJ.com.

N.J. Astronaut To Break Record For Time In Space

Experiment involving Kelly twins

His record-breaking time in the Earth’s orbit is twice as long as any other U.S. astronaut has ever spent there, and is part of an experiment involving Scott Kelly and his twin brother Mark. NASA scientists will observe the twins in order to investigate to what extent life in space affects humans.

Twin brother Mark, who is a former NASA astronaut himself, will stay on Earth as a control in the experiment. Scott is expected to age faster than his twin because of various factors, including radiation, weightlessness, dietary changes and other conditions on the ISS. Researchers want to study how much faster the ageing process becomes in order to prepare astronauts for potential long-haul spaceflights to Mars.

By the time the mission comes to an end, 51-year-old Scott Kelly will have spent 522 days in space throughout his career with NASA, breaking the record previously held by fellow U.S. astronaut Mike Fincke. Kelly has spent over 180 days in space since he started his career at NASA back in 1996.

Russian record-holder also flying today

There are currently three crew members on board the ISS, U.S. astronaut Terry Virts, Russian cosmonaut Anton Shkaplerov and Italian astronaut Samantha Cristoforetti. Kelly and Kornienko will join them later today, along with Gennady Pedalka, who will only stay for six months.

New Jersey boy Kelly was invited to the State of the Union address by Michelle Obama back in January, and he will surely come home to a fine reception after his record-breaking trip.

Although Kelly will take the honor of becoming the NASA astronaut that has spent the longest in space, he will not hold the world record. Padalka has already spent 710 days in space before the upcoming mission, and his six-month deployment will maintain his status as the record-holder for time spent in space by any human being.