The world’s longest flight took place on Friday, but you can’t buy tickets just yet.

Australian airline Qantas wants to test just how long humans can last in the air with its first-ever direct flight from New York to Sydney.

The flight, called Project Sunrise, is set to land in Sydney on Sunday morning. It is expected to finish the 10,200-mile venture in 19-and-a-half hours, having departed from John F. Kennedy International Airport on Friday.

50 passengers and crew signed up to be the airline’s test subjects for the long-haul flight. But their takeoff experience was a bit different from other flights, as they were kept awake for six hours with food sprinkled with spices and hot peppers. Pilots wore brain-monitoring equipment to keep track of how awake they are doing the long haul flight.

Qantas says they’re looking to “conduct scientific research on passengers and crew on an ultra-long haul flight, with the aim of increasing health and wellness, minimising jetlag and identifying optimum crew rest and work periods.” They’ll be assessed on how much they sleep, how they move about the cabin, among other things.

There are a few concerns with the flight. Passengers can experience blood clots in leg tissue, which is known as deep vein thrombosis. Jet lag can also be a problem for passengers.

“The scientific protocol is whatever they are most comfortable doing they will do,” Phil Capps, Qantas’ head of customer experience, told CNBC. “If someone is sound asleep when it’s time to do stretches we’ll leave them sleeping.”

Qantas wants to begin commercial flights in 2022.