Of the 24,000 runners taking part in the Boston Marathon this year, one woman is planning to join from more than 300 km above the actual venue.
Sunita Williams, an Indian-American astronaut in the middle of a six-month stint in orbit on the International Space Station, is an official entrant in the April 16 race.
A Massachusetts native, Williams plans to run the 42 km on the space station's treadmill as the first person to participate in a marathon from space. She even has a so-called bib number, 14,000, forwarded to her electronically by the Boston Athletic Association.
Williams, 41, qualified for the race by finishing among the top 100 women in last year's Houston Marathon, with a time of three hours, 29 minutes and 57 seconds, and has been working up her stamina in space over the last few months.
"I think it's going as well as it can go," Williams said in interviews from the ISS broadcast on NASA TV, noting that she had already completed a 16-mile (25.6-km) run in preparation. "I think I'm almost there."
The conditions are not quite the same. There is no way of simulating the Boston race's most infamous stretch, known to runners as Heartbreak Hill: "Thank God, we can't," said Williams.
But for anyone who thinks being in orbit gives an advantage, running on a treadmill in nearly gravity-less space carries its own challenges.
"The treadmill itself isn't the easiest thing to run on," Williams said in a televised interview from the station with The Boston Globe. "It's going to be a little bit of a pain."
The hip and shoulders of Williams will be strapped into a harness, connected to the treadmill by bungee chords.
Williams has had to work extra to keep up her stamina and strength, as bone density and muscles easily weaken in the weightless environment.
"This will be a challenging event in a completely different way," said US astronaut Michael Lopez-Alegria, who will be cheering on his fellow crewmember aboard the ISS. "The fact that she'll be able to do it and finish it will be quite an achievement."
Williams will likely have five spectators to cheer on her marathon run, as a Russian Soyuz craft is set to dock Monday with the ISS. "Make the first steps of the race as difficult as possible," Lopez-Alegria quipped.
NASA hopes that Williams can run the race at the same time as the actual marathon, but sleeping schedules and work requirements mean it might be delayed or postponed.
"This is a working spaceship," Williams said. "Hopefully, we will actually get to do it. ... We don't want to interrupt all the other stuff that's going on."