Payment-systems billionaire Jared Isaacman is funding the trip and donated the three other seats as part of an effort to raise money for charity. The launch window opens at 8:02 p.m. EDT on Wednesday.

Here is what you need to know about the coming mission.

What’s all the fuss about four civilians going into orbit on a SpaceX rocket?

This is the first time an all-civilian crew has been sent into orbit. Almost 600 people have flown higher than the 50-mile limit used by the U.S. to define where space begins—including 54 private citizens, though they were always part of professional or military crews.

Reaching space is still expensive—very expensive—but the pace of launches is increasing, bringing down the cost in increments and increasing understanding about the effects of orbital travel.

Hiring a SpaceX rocket and capsule for private travel is another marker of how the technology has matured to allow relatively safe and more frequent space trips beyond those dictated by government and military requirements.

When is the launch, and how can I monitor the mission?

The five-hour window for the planned launch from the Kennedy Space Center in Florida opens at 8:02 p.m. on Wednesday, with a backup opportunity some 24 hours later. The crew is due to orbit dozens of times and return to Earth around three days later, splashing down off the Florida coast. The schedule could change, depending on weather in the landing zone.

I’ve watched two billionaires blast off this year. Is this the future of space tourism?

Mr. Isaacman is paying an undisclosed sum for a full space experience for himself and three others, not a 10-minute suborbital jaunt. It comes with the attendant costs and risks of an orbital mission, especially re-entry.

Seats on another SpaceX launch with private citizens scheduled for next year have sold for around $55 million each, in line with that paid by previous privately funded journeys into space. The Inspiration4 crew has undergone months of training, including in centrifuges and fighter planes to mimic the physical stresses of launch and re-entry.

Orbital launch capacity for crewed flights remains limited beyond the requirements of government-driven missions. This will be the fourth crewed mission by SpaceX in 15 months, a pace unmatched by its Russian and Chinese peers, but a reminder that private citizens in orbit will remain a relative rarity for years.

Who is Jared Isaacman, and how did he select the crew?

The 38-year-old entrepreneur is the founder and chief executive of Shift4 Payments Inc., which has a market value of $6.5 billion. He is a trained pilot and aviation and space enthusiast. The Inspiration4 mission aims to raise $200 million for St. Jude Children’s Research Hospital through a fundraising drive linked to the mission. The charity said he has already committed $100 million to the goal.

The crew roster includes two selected via a sweepstakes run during this year’s Super Bowl and one picked as an ambassador by St. Jude. Mr. Isaacman will be joined by Hayley Arceneaux, 29, a physician assistant at St. Jude Children’s Research Hospital, Dr. Sian Proctor, 51, a geosciences professor and science communicator, and Chris Sembroski, 42, a Lockheed Martin Corp. engineer.

How is the Inspiration4 crew getting to space?

SpaceX will launch one of its Dragon capsules atop a reusable Falcon 9 rocket, the same combination that successfully flew crews to the International Space Station three times on missions backed by the National Aeronautics and Space Administration.

The capsule, which can hold up to seven people, is due to orbit at a height of 360 miles above Earth, well beyond the space station. It will travel at more than 17,000 miles an hour as it orbits the planet every 90 minutes.

How long are they in space, and what will they do up there?

The Crew Dragon capsule and Falcon 9 rocket are fully autonomous, so the Inspiration4 crew won’t have to direct it or position the space craft for re-entry after its planned three-day mission.

The four-person crew is expected to conduct a series of health-based experiments focused on the effects of space travel, as well as provide comparative data on their physical well-being before, during and after the mission.

There is also a big window. The docking door of the capsule has been converted to include a glass dome affording 360-degree views, in addition to the spacecraft’s side windows.

How does this compare to recent space flights with Jeff Bezos and Richard Branson?

Inspiration4 is going to space, no questions asked. Mr. Bezos and Mr. Branson squabbled over the definition of space after rising to the edge on specially developed rockets and aircraft, respectively, but neither tried to make it into orbit.

Mr. Bezos’s privately held Blue Origin LLC and Mr. Branson’s Virgin Galactic Holdings Inc. are, for now, targeting the suborbital market for well-heeled space travelers. That is some 50 miles to 65 miles above Earth with rides that provide only a few minutes of weightlessness.