Jeff Bezos is set to blast off into space on Tuesday but said he had been outperformed in training by his 82-year-old co-astronaut.
The richest man on Earth will lift off from Texas on the maiden crewed voyage of his Blue Origin space tourism company.
Accompanying him will be his brother Mark, along with Oliver Daemen, 18, a Dutch physics student who will become the youngest ever person in space, and octogenarian Wally Funk, who will become the oldest.
Sixty years ago Ms Funk was one of a group of 13 women who underwent the same rigorous Nasa testing as America’s original seven male astronauts in the Mercury programme.
None of the women went into space, and all of the men did.
Jeff Bezos and his rocket
Mr Bezos, sitting with Ms Funk ahead of the launch, said: "[60 years ago] they tested her, all the same tests they gave to the men, she outperformed all the men.
"We’ve been training here with Wally and I can assure you she is still outperforming all the men. At 82-years-old she can outrun all of us."
He said Ms Funk was a "whirlwind of energy, a role model for determination, resilience and positivity, she’s amazing."
As they surveyed their capsule, wearing cowboy hats, Ms Funk jumped up and down and yelled: "I’m gonna be in that window."
She said: "Some day I thought it [going into space] would happen. I’ve waited a long time but we’re going to do it now. I’m very excited, I want to do everything in that capsule that I can do."
Me Bezos with "82-year-old whirlwind" Wally Funk
Mr Bezos said he was "not nervous" and was satisfied with the New Shepard rocket which will blast him into space.
He said: "We really believe this flight is safe. I had friends say to me, ‘How about the second flight or the third flight, why do you have to go on the first flight?’
"If the vehicle’s not safe for me it’s not safe for anyone. We have never raced, our mascot is the tortoise, we have taken this one step at a time. We’re ready.
The rocket will reach speeds of 2,200mph and is fully autonomous. It cannot be piloted from on board.
Mr Bezos will travel beyond the Karman line, the internationally recognised boundary of space, 62 miles up.
When he flew on Virgin Galactic’s rocket plane on July 11 Sir Richard Branson did not cross the Karman line.
But he went above 50 miles, which the US Federal Aviation Administration regards as space and awards astronaut wings for.
There is said to have been some frustration that the mission will not include any of Blue Origin’s employees or staff astronauts.
The 60ft-tall New Shepard rocket and its capsule, which will reach speeds of 2,200mph, are fully autonomous and cannot be piloted from on board.
By contrast the Virgin Galactic ship, dropped from a carrier plane in mid-air, had two pilots, the company’s chief astronaut instructor, and an operations engineer on the trip.
Inside the Blue Origin capsule
Blue Origin’s decision to have a pilotless craft was taken years ago and was said to have been based on the "simple math" of running a space tourism business.
"If you design a system so that you don’t need a pilot or a co-pilot you can have more paying customers," a person familiar with the company’s strategy said.
Although four people will be on the first flight there is room to fit six customers on later ones.
Blue Origin’s paying customers will receive two days of training.
Just before the launch they will be helped to strap into their seats, and will then be given instructions over headsets.
Marco Caceres, a space analyst at the Teal Group in Virginia, said: "It’s kind of like getting on a ride at an amusement park. You just trust that everything has been checked out, is in good working order, and you just sit back and enjoy the ride."
He added: "One of the main goals of the New Shepard mission is to demonstrate that going to suborbital space is perfectly safe for the average person. So there is a benefit to having as many average people on these flights as possible."
Wally Funk as a young pilot
Both Mr Bezos and Sir Richard are set to be outdone by Elon Musk’s SpaceX.
It is planning to launch an all-civilian crew on an orbital flight lasting several days in September.
SpaceX has already launched astronauts and cargo runs to the International Space Station.
The Karman line is recognised as the boundary of space by the Federation Aeronautique Internationale, based in Lausanne, Switzerland, which certifies global aeronautical and astronautical records.
Just before Sir Richard’s flight Blue Origin launched a shot across his bows.
It said: "From the beginning, New Shepard was designed to fly above the Karman line so none of our astronauts have an asterisk next to their name.
"For 96 per cent of the world’s population space begins 62 miles up at the internationally recognized Karman line. Only 4 per cent of the world recognises a lower limit of 50 miles as the beginning of space."