The two final crew members who will orbit Earth on a SpaceX ship, as part of the all-civilian Inspiration4 mission, have been revealed

• The final two crew members have been announced for Inspiration4's civilian mission to orbit Earth.
• Dr. Sian Proctor and Chris Sembroski have been named as additional crew members on SpaceX's ship.
• They are set to join Jared Isaacman and Hayley Arceneaux on the mission in September.

In an announcement earlier this week, SpaceX's Inspiration4, the world's first all-civilian rocket ride to orbit Earth, disclosed the final two members of the four-person crew that is expected to undergo a historic journey into space.

Chris Sembroski and Dr. Sian Proctor were the additional two people who won seats on SpaceX's Dragon spaceship.

They are set to accompany Jared Isaacman and Hayley Arceneaux on the mission, where all four are expected to ride aboard the Dragon spacecraft to be launched into orbit by SpaceX's Falcon 9 rocket.

SpaceX is planning for a liftoff of no earlier than September 15. The ship is scheduled to depart from Kennedy Space Center's Launch Complex 39A.

It is expected to orbit Earth for three days at an altitude of about 335 miles, where the crew intends to eventually touch down off the coast of Florida for retrieval.

Here's what we know about the four crew members

Jared Isaacman

Isaacman is a 38-year-old tech billionaire, entrepreneur, philanthropist, pilot, and the chief executive of Shift4 Payments, a Pennsylvania payment-processing company. He is expected to charter the flight.

Though he said he has spent more than 6,000 hours flying jets and ex-military aircraft, he has never been to space. Neither have his three fellow passengers, as Insider previously reported.

One of Isaacman's goals in planning this mission was to give a diverse community of people the opportunity to fly into space and raise money for St. Jude Children's Research Hospital in Memphis, Tennessee.

"The stars really aligned for us in terms of this group," he told The New York Times.

"We promised the crew representing some of the best of humanitarian qualities exemplifying our mission ideals of leadership, hope, prosperity and generosity. And I'm pleased to report that we've accomplished that goal," he said.

Isaacman intends to serve as the commander for the SpaceX mission.

Hayley Arceneaux

In February, Arceneaux, a 29-year-old childhood cancer survivor and physician assistant at St. Jude Children's Research, was announced as the second civilian to join the crew.

At the age of 10, Arceneaux had part of her femur removed from bone cancer. There are many sporting activities that she cannot do for fear of an uncontrolled fall. This is because of a metal rod in her left leg, which was implanted during her bone-cancer treatments as a child.

But now she has the chance to set herself free from all limitations. In an interview with Insider, she said her orthopedic surgeon told her, "There's going to be no limits on you in space."

Arceneaux would be the youngest American to fly into space and the first with a prosthetic body part.

Dr. Sian Proctor

Proctor, a geoscientist, science communication specialist, and analog astronaut, is one of the new crew members aboard SpaceX's Dragon spacecraft.

Proctor secured her seat after winning a contest sponsored by Isaacman's e-commerce company, Today reported.

The contest required all entrants to design an online store using Shift4 Payments' software and then tweet a video describing their space fantasies, The New York Times said.

Proctor told Business Wire, "This opportunity is proof that hard work and perseverance can pay off in unimaginable ways." She added, "I have always believed that I was preparing for something special, and that moment has arrived with Inspiration4."

Her excitement was palpable in an interview with Today's Tom Costello. "It's like opening up the chocolate bar and seeing the golden ticket to Willy Wonka and the chocolate factory!" she said.

Chris Sembroski

Joining the other three members is Sembroski, 41, a Lockheed Martin employee and Air Force veteran.

Sembroski was selected from nearly 72,000 entries in a contributing fundraising campaign for St. Jude. He is expected to act as a mission specialist, aiding payloads and science experiments during the flight.

"Joining the Inspiration4 crew and its mission of support for St. Jude is truly a dream come true. It is my hope that this flight will inspire others to pay that generosity forward by pledging their support for St. Jude and encouraging kids to dream the impossible, ushering in a new era of space exploration open to all," he said in a statement.

Sembroski first heard about the mission from an advertisement during this year's Super Bowl event.

"That was just kind of intriguing," he told The New York Times. "And so, it's like, 'All right, I'll donate to St. Jude and throw my name in the hat to see what happens.'"

The Inspiration4 crew is expected to undergo commercial astronaut training by SpaceX. They are set to receive emergency-preparedness training, as well as partial and full mission stimulations.

"This is about mental toughness," Isaacman told The New York Times. "Getting uncomfortable, staying uncomfortable - and how well you perform when you are uncomfortable."