The Elon Musk-led SpaceX is preparing to undertake a historic mission to orbit with an all-civilian crew headed by a wealthy entrepreneur. The astro-tourist group, called Inspiration4, will board the SpaceX Crew Dragon capsule on Wednesday for a three-day voyage into orbit.

Here are the most important details regarding the mission.

It's the first non-professional spaceflight

For the first time, four private citizens - and no professional astronauts - will board SpaceX's Crew Dragon spaceship and blast out into space. This will be SpaceX's fourth crewed trip, but instead of astronauts from NASA and its international partners, the passengers will be four regular civilians.

All prior orbital space tourism flights (as well as future missions with stated crews) have featured at least one experienced astronaut to lead passengers through the drama of launch, microgravity, and landing.

When is it launching?

Inspiration4 will have a 24-hour launch window that begins on Sept. 15 at 8 p.m. 10:00 a.m. EDT (midnight on Sept. 16 GMT). Only a few days before launch, mission personnel will reduce that timetable down to a five-hour window.

According to SpaceX and Inspiration4 officials, the mission can launch at any moment, but the actual liftoff time will be determined mostly by weather forecasts from the 45th Weather Squadron for both the launch and landing locations.

Meet the crew

Jared Isaacman, a billionaire who founded Shift4 Payments and purchased the flight, is the mission's commander.

Hayley Arceneaux, a medical assistant at St. Jude Children's Research Hospital and a former patient, joins him. Arceneaux is a childhood bone cancer survivor who will act as the flight's medical officer.

The mission's pilot, Sian Proctor, is a geosciences professor at Arizona's South Mountain Community College and a science communicator who has wanted to fly to space since she was a child. During the Apollo 11 mission, which landed the first humans on the moon, Proctor's father worked for NASA at a tracking station in Guam.

Chris Sembroski is a former Air Force officer who now works for the aerospace giant Lockheed Martin. He is a former Space Camp counselor who will serve as the flight's mission specialist. Sembroski earned the seat after making a donation to St. Jude as part of an Inspiration4 fundraising drive.

The crew will not head to the International Space Station, but will instead free-fly around the planet. This is a departure from the capsule's last voyage, in which it transported people to the orbiting laboratory.

Without the need for a docking port, SpaceX replaced it with a dome window that will offer the crew spectacular views of Earth.