Yusaku Maezawa plans to sell a 30% stake in his online fashion-retail company, Zozo, to Yahoo Japan. As part of the $3.7 billion tender offer, Maezawa will resign and pocket $2.3 billion.

During a press conference, Maezawa reportedly said one of his main reasons for departing Zozo was to make time to train for a 2023 voyage around the moon with Starship: a new rocket system planned by SpaceX.

Maezawa also indicated he was planning to launch on a less ambitious spaceflight around Earth before his "#dearmoon" mission with SpaceX, which was founded by the tech mogul Elon Musk.

SpaceX is working feverishly in South Texas and Florida to develop and test-launch prototypes of the system. Once complete, Starship may stand about 400 feet tall and be fully reusable.

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Yusaku Maezawa, a key investor in SpaceX's next-generation rocket system, called Starship, plans to sell a 30% stake in his online fashion-retail company, Zozo, to Yahoo Japan.

As part of the $3.7 billion tender offer, Maezawa will resign as CEO of Zozo, receive about $2.3 billion in cash, and maintain a 6% stake in the company he founded, according to Forbes.

Yusaku Maezawa with a Starship model and SpaceX spacesuit helmet on October 9. Koji Sasahara/AP Photo Maezawa spoke about the deal during an emotional two-hour-long press conference on Thursday. Although he raised misgivings about how he managed the company in recent years, saying he regretted mistakes that hurt the company's bottom line, Forbes reported that he rationalized his departure in another and far more personal way: a need to prepare for his 2023 flight around the moon inside Starship.

Maezawa also indicated he'd fly on a less ambitious space mission before SpaceX's privately funded circumlunar voyage.

"Training to go into space will to take up much of my time," Maezawa said, according to Forbes.

Maezawa first announced his bid for a weeklong Starship flight around the moon during a September 2018 presentation about the launch system by Elon Musk, SpaceX's founder and CEO. (It was then called Big Falcon Rocket, but it has since been redesigned and renamed Starship; however, the craft's core goals and capabilities are similar.)

The fashion mogul, who is also an avid collector of art, named his experimental mission #dearMoon. He plans to handpick a crew that includes a "painter, musician, film director," and other artists, and maybe a couple of astronauts, to "inspire the dreamer within each of us" with the trip.

When a reporter asked Musk about his possible participation in the #dearMoon mission, he said (seemingly half-seriously), "maybe we'll both be on it."

Musk says progress on Starship is accelerating 'exponentially'

Starhopper — SpaceX's first Mars Starship prototype — hovers over its launchpad during a test flight in Boca Chica, Texas, on August 27. Trevor Mahlmann/Reuters

If Starship is realized as envisioned by Musk, it will be a roughly 400-foot-tall two-stage steel-bodied vehicle. It'd also be the world's largest, most powerful, and paradoxically most affordable launch system because — unlike any orbital-class rockets today — it'd be fully reusable.

Musk said he may beat NASA back to the lunar surface with Starship and launch the first humans to Mars with the system, perhaps 100 at a time. Musk is also dreaming up an even larger version of Starship, the scale of which stretches the imagination.

Read more: SpaceX is eyeing these 9 places on Mars for landing its first Starship rocket missions

Musk said in September 2018 that it'd cost between $2 billion and $10 billion to develop Starship into an operational system, and that Maezawa's contributions are all going directly toward that goal.

"He's paying a lot of money that would help with the ship and its booster," Musk said. "He's ultimately paying for the average citizen to travel to other planets."

Maezawa would not disclose at the time how much he's paying SpaceX, or on what schedule. However — after tweeting in May that he has "no money" because he uses it all "immediately" — the fashion tycoon's new influx of cash may help SpaceX realize Starship in the absence of government funding.

An illustration of SpaceX's upcoming Starship spaceship (left), Super Heavy rocket booster (right), and an integrated Starship-Super Heavy launch system (center). © Kimi Talvitie "Progress is accelerating," Musk tweeted in August, later adding that it's moving along "exponentially."

SpaceX has two development sites for Starship: one in Boca Chica, Texas, and a second in Cocoa, Florida. So far, most of the work has occurred at the Texas launch site, where SpaceX started to build its first prototype, called Starhopper, in 2018.

The vehicle was a test bed to prove SpaceX's new Raptor rocket engines worked on a flying vehicle. It performed a few short test launches, or "hops," in April and July, then made its last experimental launch from Texas in August. That final flight took Starhopper about 490 feet (150 meters) into the air before it landed on a nearby concrete pad.

SpaceX is now pushing to complete two bigger, roughly 180-foot-tall (55 meter), prototypes, called Starship Mk 1 and Mk 2 in Texas and Florida, respectively. Each should be capable of orbiting Earth to prove out and refine launch, reentry, and landing-system technologies.

Newly released FAA documents refer to this part of Starship's development program as "Phase 3." As part of that phase, Musk tweeted on August 28 that SpaceX would try launching Starship Mk 1 about 12.4 miles (20 kilometers) above Texas in October before the company attempts an orbital launch "shortly thereafter."

Musk added that he would provide an update on the overall Starship development program on September 28. Previously, he said he would deliver that presentation from Boca Chica — possibly to do so with a fitting backdrop.

"Starship Mk 1 will be fully assembled by that time," he said.

SpaceX representatives did not immediately respond to Business Insider's request for comment about Maezawa's latest remarks, the #dearMoon mission, or overall on the Starship development program.

This story has been updated.