For the first time, astronauts are about to head to the International Space Station aboard a craft made by a commercial company instead of a government agency.
But what if something goes wrong? Fourteen people died aboard NASA's space shuttles - seven on the Challenger in 1986, and another seven in 2003 aboard the Columbia.
While no one has died in SpaceX's previous launches, it too has had the occasional explosion. A Cargo Dragon capsule in 2015 was thrown off its Falcon rocket when part of the craft exploded two minutes after launching. And in 2016, an entire Falcon rocket blew up before it even got off the launchpad.
The crew for Thursday's historic launch, inside a Crew Dragon capsule aboard a Falcon 9 rocket, are experienced astronauts Doug Hurley and Bob Behnken. Hurley, the commander, was on the 135th and final shuttle flight aboard Atlantis in 2011, so would be all-too-aware of the risks involved.
New Zealand space commentator Matthew Pavletich, who attended the final shuttle launch, says SpaceX has learned a lot from its mishaps, and its Crew Dragon craft has much better safety systems in place than the shuttles ever did.
"I saw the test mission a few months back when there was nobody aboard and it did the abort test - it was really hairy to watch. You can find the footage online. It would be one heck of a ride."
In case of a problem with the massive Falcon rocket aboard the launch pad, the Crew Dragon capsule has mini rocket engines its crew can turn on, lifting the capsule away from the fuel-laden rocket below. It goes from sitting still to over 500km/h in a matter of seconds, rising a couple of kilometres before falling into the ocean via parachute.
A more leisurely alternative is to use a zipline from the capsule atop the rocket to the ground.
Once it's taken off, the software takes over - and can abort the mission at any time without any input from the crew or staff on the ground. Once in space, if something goes wrong with the rocket the crew can either abort and return to Earth, or abort into orbit and aim to still reach the International Space Station using just the Crew Dragon capsule's on-board systems.
The only deaths to have occurred in space happened in 1971, when three cosmonauts died after leaving the Salyut 1 space station when their craft depressurised. The Crew Dragon has a number of failsafes if that occurs, including being able to constantly pump more air into the cabin to maintain pressure, or directly into their spacesuits.
Pavletich says while SpaceX is in charge of the launch and NASA of the mission, it's a "joint venture in every way" and both will be responsible if something goes wrong.
If the astronauts are stranded in space, they'll have four days to get back to Earth before running out of supplies. Pavletich says they'll be more comfortable than past astronauts.
"It's the rocket equivalent of a Tesla basically. It's very luxurious inside the space capsule... I hope Tom Cruise enjoys his ride on it next year, because they're going to film a sequence for the Impossible Mission movie at the International Space Station."
The launch is at 8:33am NZ time.
