Not only will this be the first time that the privately owned company is sending astronauts into space, but it will be the first time that astronauts have launched from the United States in almost a decade.
Many of these missions have been to deliver supplies to the International Space Station (ISS) or to loft satellites into orbit around the Earth.
When the Space Shuttle Atlantis took off from Kennedy Space Centre on July 8, 2011, few of us would've imagined that the next crewed launch from USA soil wouldn't happen for another nine years (unless you count the launch of Virgin Galactic's VSS Unity space plane in 2018).
The Demo-2 mission will launch atop a Falcon 9 rocket and carry the astronauts toward the International Space Station at around 17,000 miles per hour (27,360 km/h).
A SpaceX Falcon 9 rocket with the company's Crew Dragon spacecraft onboard is raised into a vertical position on the launch pad at Launch Complex 39A at NASA's Kennedy Space Center as preparations continue for the Demo-2 mission to the International Space Station, in Cape Canaveral, Florida, US. Among those that will be in attendance include President Donald Trump and Vice President Mike Pence.
But the X-37B is semi-secret, can't carry people and is nowhere near as potent a symbol of American power as a shiny new rocket built by private enterprise.
However, there is one guest that NASA is hoping won't attend Wednesday's launch: Mother Nature.
Forecasters put the odds of acceptable launch weather at 40%. Even if there are no thunderstorms around, a rocket can trigger its own lightning, like what happened during the launch of Apollo 12.
The weather around the Kennedy Space Center in Florida may have other ideas, however.
According to Mike McAleenan, launch weather officer for the U.S. Space Force's 45th Weather Squadron, there is now a 60% chance of good launch weather on Wednesday and a 40% chance of a weather violation due to precipitation and clouds, he said in the post-LRR briefing.
Not only does the weather need to be tranquil around the launchpad, but also downrange over the Atlantic Ocean in the event that the crew needs to abort and safely splash down in the ocean.
The next launch window would be Saturday, May 30.
Post-launch, Behnken and Hurley will spend 19 hours on orbit, with orbit-raising burns and also a manual flight test (the rest of the time Crew Dragon should be under fully automated control) for around 30 minutes just prior to docking. Funded along with Boeing to ensure that NASA has two redundant spacecraft available, the latter company's Starliner spacecraft has run into extensive delays after its orbital flight test (OFT) uncovered dangerously shoddy software and quality control.