Billionaire Jeff Bezos will blast into space on Tuesday, in the first crewed flight of his rocket ship, New Shepard.
He will be accompanied by Mark Bezos, his brother, Wally Funk, an 82-year-old pioneer of the space race, and an 18-year-old student.
They will travel in a capsule with the biggest windows flown into space, offering stunning views of the Earth.
New Shepard, built by Bezos' company Blue Origin, is designed to serve the burgeoning market for space tourism.
"I'm excited. People keep asking me if I'm nervous. I'm not really nervous, I'm curious. I want to know what we're going to learn," Bezos said in an interview with CBS News.
"We've been training. This vehicle's ready, this crew is ready, this team is amazing. We just feel really good about it."
Ms Funk commented: "It's going to happen! I've waited a long time and I've dreamed a long time to get to go up." She said she would carry out somersaults and tumbles while weightless in space.
In the 1960s, Ms Funk was one member of a group of women called the Mercury 13, who underwent the same screening tests as male astronauts, but who never got to fly into space.
At 14:00 BST (09:00 EDT), the four passengers will lift off on a rocket from Bezos' private launch site near Van Horn, Texas.
The capsule, containing the Bezos brothers, Funk and student Oliver Daemen, separates from its booster around 76km (250,000ft) up. The rocket lands on its "legs" about 2 miles from the launch pad, while the capsule continues upwards to an altitude of around 106km (350,000ft).
"We're in zero-g for around four minutes, and we get to get out of our seats, unstrap, float around, look at the thin limb of the Earth's atmosphere," Bezos told CBS News.
"The views are going to be terrific, the zero-g will be an unusual experience that you really can't get in any good way on Earth."
After reaching its maximum altitude, the capsule begins its descent, parachuting down to a soft landing in the desert.
The launch is the latest salvo in what has been dubbed the "billionaire space race". It comes nine days after Bezos' space tourism rival, Sir Richard Branson, flew high above the Earth on his Virgin Galactic space plane.
Interviewed on the Late Show with Stephen Colbert last week, Sir Richard insisted it hadn't been important for him to beat Bezos, and even had some friendly advice: "Just absorb the view outside - really take it in. It is a once-in-a-lifetime opportunity."
Though the private spaceflight revolution is often billed as an effort to expand access to space for all, seats aboard one of Virgin Galactic flights will initially set customers back $250,000, while the regular ticket price for New Shepard has not been disclosed.
With a net worth of around $200bn, Bezos is the world's richest man. The 57-year-old recently resigned as chief executive of Amazon, the e-commerce giant he founded, to focus on special company initiatives and his other ventures such as Blue Origin.
Bezos' brother Mark, 53, founded an advertising agency and is now a senior vice president at Robin Hood, a New York-based charity.
The fourth passenger is the son of Joes Daemen, founder of Dutch private equity firm Somerset Capital Partners. Oliver had originally secured a seat on the second flight, but was drafted in to replaced the anonymous winner of a public auction.
This unnamed winner, who paid $28m (£20m) to join Bezos on New Shepard's first crewed flight, had to pull out "due to scheduling conflicts".
https://www.bbc.com/news/science-environment-57849364
