It will be the greatest game of "capture the flag" ever played.
When Nasa astronauts Doug Hurley and Bob Behnken set foot on the International Space Station they will collect a small US flag that has acquired mythical status in space lore.
The 12 inch by 8 inch banner will be brought back to Earth and presented to SpaceX as the prize for being the first commercial company to launch humans into orbit, winning a decade-long race with rivals including Boeing.
Hurley, 53 and Behnken,49, are due to blast off from Florida's Kennedy Space Center on Wednesday, watched by President Donald Trump.
A SpaceX Falcon 9 rocket and Crew Dragon capsule will lift off from launchpad 39A, the same one from which Neil Armstrong, Buzz Aldrin and Michael Collins departed to the moon on Apollo 11.
It will be the first time astronauts have been launched into orbit from US soil since the end of the space shuttle programme in 2011, and the first time by the private sector.
The flag they will bring back flew on the first orbital space shuttle mission in 1981.
In 2011 it was left behind on the space station in a ceremony. Hurley piloted that final space shuttle mission.
At the time President Barack Obama said the flag would "reside on the ISS until an American commercial space company launches astronauts to the station".
Mr Obama added: "I understand it will be kind of like a capture-the-flag moment for commercial spaceflight. So good luck to whoever grabs that flag."
No-one thought it would take a decade.
"I think we will probably grab it [the flag] from Chris [Cassidy, current commander of the ISS] and put it in a safe place while we do our work on the space station," said Hurley, a retired Marine colonel.
"Then we'll bring it back when we come back later this summer."
The historic flight will be a milestone in the effort to commercialise space, and a key step in ending US dependence on Russian rockets.
Hurley and Behnken have been quarantining with their families in the lead up to the mission.
Behnken, who has done six spacewalks, said: “It’s probably a dream of every test pilot school student to have the opportunity to fly on a brand new spaceship, and I’m lucky enough to get that opportunity with my good friend."
Hurley said he considers the SpaceX capsule a safe, "pretty tried and true" design. The veteran astronaut said he particularly liked the Crew Dragon capsule's "launch pad-to-orbit abort capability" to save a crew in an emergency.