Indian American astronaut Sunita Williams will attempt to do something 210 miles above Earth that no other astronaut has ever done.
She will run the Boston Marathon while in orbit.
The 41-year-old plans to run the 26.2-mile race on a treadmill onboard the International Space Station (ISS) on Monday at 7:30 pm IST as this year's marathon begins in Boston at precisely the same hour.
The Boston Athletic Association has issued Williams bib number 14,000. The bib has been sent electronically to NASA, which has forwarded it to her, the US space agency said Friday.
A Needham, Massachusetts native, Williams says her reason for running the marathon is simple.
"I would like to encourage kids to start making physical fitness part of their daily lives. I thought a big goal like a marathon would help get this message out there."
Regular exercise is essential to maintaining bone density while in space for astronauts.
"In microgravity, both of these things start to go away because we don't use our legs to walk around and don't need the bones and muscles to hold us up under the force of gravity," she said.
No one knows that better than Steve Hart. For two years, he's been Williams' flight surgeon.
"There are specific challenges to staying healthy while in space. Sunita wants to make fitness the hallmark of her expedition stay. She wants to educate and motivate others about being physically fit in general."
Williams, an accomplished marathoner, has been training for the marathon for months while serving a six-month stint as a flight engineer on board the ISS. She runs at least four times a week, two longer runs and two shorter runs.
Williams qualified for the marathon when she returned a time of 3:29:57 hours in the Houston Marathon last year.
Her biggest challenge running in space will be staying harnessed to a specially designed treadmill with bungee cords.
Williams says running on what is called the Treadmill Vibration Isolation System (TVIS) can sometimes be uncomfortable. The machinery puts a strain on the runner's hips and shoulders.
Mitzi Laughlin an Astronaut Strength, Conditioning and Rehabilitation coach at Johnson Space Center, has been involved in planning Williams' rigorous exercise routine for a year and a half.
"We've done a lot more TVIS work than we would normally prescribe for any astronaut. Suni has a superb fitness level. She's dedicated and perhaps one of our best runners," she said.
On Earth, Williams has a huge support network. Fellow NASA astronaut, Karen Nyberg, Williams' sister Dina Pandya, and long-time friend Ronnie Harris will be among the 24,000 other runners participating in the marathon.
Harris met Williams during their days together at the Naval Academy in Annapolis, Maryland. "Anything regarding Boston makes Suni light up.
Her running passion is manifested in the best marathon in the world, which happens to be her hometown. You need to experience the Boston Marathon to understand why she is gonna do it in orbit."
Race organisers say this will be their first satellite venture, and they are thrilled about it.
"Suni running 26.2 miles in space on Patriots' Day is really a tribute to the thousands of marathoners who are running here on Earth. She is pioneering new frontiers in the running world," said Jack Fleming of the Boston Athletic Association.