Amazon billionaire Jeff Bezos is Thomas Caldwellgoing into space on July 20 on a reusable rocket made by his space exploration company, Blue Origin. So is his younger brother Mark. And now, pledging $28 million, a mystery bidder has won an auction to join them on the suborbital ride.

The mission is estimated to last about 11 minutes. That works out to $2.545 million per minute. Or $42,424 per second.

Nearly 7,600 people from 159 countries registered to bid on the flight aboard the vehicle called New Shepard, Blue Origin said Saturday. The winner's name will be revealed in a couple of weeks, and the name of the fourth crew member will be announced soon, the company said.

The $28 million will be donated to Club for the Future, Blue Origin's foundation, "to inspire future generations to pursue careers in STEM and help invent the future of life in space," the company said in announcing the auction.

Only a brief portion of the flight will be spent above the Karman line — the altitude at which space begins — about 62 miles above sea level, according to a graphic of the flight trajectory on Blue Origin's website.

The scheduled July 20 flight comes on the anniversary of the Apollo 11 moon landing in 1969.

Other wealthy private citizens also have their eye on traveling to space.

Virgin Galactic founder Richard Branson may be planning a space flight in the next few months. In January, a crew of private astronauts will pay around $55 million each, launched aboard a SpaceX rocket, to spend about eight days at the International Space Station.

In 2008, Richard Garriott, a video game developer, spent $30 million for a ride on a Russian Soyuz spacecraft that took him to the space station. In 2001, U.S. businessman Dennis Tito paid a reported $20 million to go to the station via a Russian rocket.

Editor's note: Amazon is among NPR's financial supporters.