First came space tourism. Now comes an even bigger thrill for the crowds: space walking.

The stage is set for the first private spacewalk on Thursday. Tech billionaire Jared Isaacman will emerge from the hatch of an orbiting SpaceX capsule two days after blasting off from Florida on a chartered flight that took him and his crew higher than any of NASA’s moonwalkers . He partnered with SpaceX CEO Elon Musk to buy a series of rocket rides and help develop brand new spacesuits.

SpaceX is the first private company to attempt a spacewalk, so far in the field of just 12 countries. There’s a reason they’re such a specialized and elite group: Spacewalking is considered the most dangerous part of any flight after launch and reentry, and requires extensive training.

“Spacewalks are completely different than getting into a rocket and driving it and coming back,” said retired NASA astronaut Chris Cassidy.

Rich people will start walking in space – The dangers

Cassidy knows firsthand the dangers of spacewalking: He was working outside the International Space Station in 2013 when his partner, Italian astronaut Luca Parmitano, nearly drowned. Parmitano’s helmet filled with water from his clothing and he barely escaped. Another 30 minutes that day in that condition and “the outcome would have been different,” Cassidy said.

Astronaut

In this photo provided by NASA, astronaut Bruce McCandless uses a nitrogen jet backpack outside the space shuttle Challenger on February 12, 1984. (NASA via AP, File)

Cassidy worries that it will start a new fad of rich people walking in space.

Risk and disaster analyst Ilan Kelman of University College London said it was “expected and inevitable” that non-professionals would end up carrying out spacewalks. It foresees, however, deadly dangers.

“We can and should do a lot to reduce the risk,” Kelman said. “We have to be completely honest with anyone involved, especially about the low chance of rescue when something serious goes wrong.”