In an email on Saturday night after splashdown, a spokesman for the mission said donations had reached $160 million. That was a significant increase from the approximately $130 million that had been raised when the mission launched. A website for the mission showed the number continuing to climb.

In a statement, Richard C. Shadyac Jr., president and chief executive of ALSAC, the fund-raising organization for St. Jude, expressed the organization’s gratitude for the support.

“This week, the world witnessed not only the dawn of a new era in citizen space travel but the power of aligning passion with purpose to make a difference in the lives of others,” Mr. Shadyac Jr. said.

Mr. Shadyac Jr. said St. Jude’s was also inspired by the other three astronauts: Sian Proctor, Chris Sembroski and Hayley Arceneaux, a physician assistant at St. Jude who had been a patient.

When she was 10, Ms. Arceneaux was treated for bone cancer at the hospital. During the week’s flight, she and her crewmates took questions from some of the hospital’s patients while in orbit.

The mission may raise more money as it auctions off items that it brought to space, such as a ukulele played by Mr. Sembroski, the mission’s specialist, and art made by Dr. Proctor, the flight’s pilot.

Kenneth Chang contributed reporting.

What if you just want to go for the ride and the views?

For now, orbital spaceflight is probably not for you.

“The long term vision is that spaceflight becomes airline-like,” said Benji Reed, the senior director for human spaceflight at SpaceX. “You buy a ticket and you go. But right now, the appropriate thing is that we still train people.”

Mr. Reed said the Inspiration4 crew’s training was essentially the same as what NASA astronauts get. The next private mission that SpaceX will fly, to the International Space Station, is being operated by a Houston-based company, Axiom Space. The Axiom mission will be commanded by an Axiom employee, Michael López-Alegría, a former NASA astronaut, but the three paying customers still have to learn about the operations of the SpaceX capsule and also the space station. That has already begun at Johnson Space Center, the Houston site where NASA’s astronauts work.

Space tourists who have flown to space on Russian Soyuz rockets have similarly also trained for months.

“As we look for ways to evolve toward that airline-like model,” Mr. Reed said, “we’ll look for how we can, you know, cut back on the amount of training that’s necessary to ensure safety.”

“We’re going to learn some things that are very fundamental,” said Dorit Donoviel, executive director of the Translational Research Institute for Space Health, or TRISH, at the Baylor College of Medicine in Houston, which is coordinating research during the Inspiration4 flight.

One of the passengers, Hayley Arceneaux, exemplifies those possibilities. At 29, she is younger than most space travelers, a cancer survivor and will be the first person in space with a prosthesis — metal rods that were implanted after a tumor was removed from her left leg.

During the flight, the Inspiration4 crew members took tests to gauge their mental performance, used an ultrasound instrument to track possible changes in their eyes and blood flow. That data could give clues to solve vision changes and space sickness experienced by some astronauts.

“We’ve also been taking several swabs of different parts of our body to evaluate the microbiome and how that changes in these three days in space,” Ms. Arceneaux, the medical officer for the mission, said during a broadcast from the capsule on Friday.

It’s unclear exactly what that health screening might consist of. Health researchers working with Inspiration4 said the astronauts were to undertake some experiments that gauge their sense of balance — standing without swaying and moving between sitting and standing positions.

They will also perform a series of tests measuring their cognitive performance — the same ones they performed before liftoff and each during orbit.

A NASA medical requirements overview from the era when astronauts flew on the space shuttles provides an idea of what doctors look for in astronauts returning from shorter flights in space.

For flights that last less than 30 days, doctors screen the astronauts’ vital signs and look for neurological issues as well as problems with chest and lungs.

Headaches, dizziness, vertigo and feeling faint are among the neurological symptoms that doctors screen for in astronauts.

The functions of the eyes of returning astronauts are also checked, and they are asked to perform a series of tasks, including: touching their finger to their nose, rising from a chair, lifting a leg and hopping, walking in a straight line and then turning, and a heel-toe-walk.

If the doctors observe enough issues, they may decide that an astronaut needs to undergo additional testing.

Even before splashdown, the four astronauts have already gone through a series of health screenings while they were in space in hopes of furthering human exploration of space. They have been screened for heart activity, sleep, blood oxygen saturation, and blood.

“I’m very bullish on the tourism market and the tourism activity,” Phil McAlister, NASA’s director of commercial spaceflight development, said during a news conference in May. “I think more people that are going to fly, they’re going to want to do more things in space.”

The trip shows that a private citizen, at least someone with a couple hundred million dollars and a few months to spare, is now able to essentially rent a spacecraft to circle the planet.

In this case, it was Jared Isaacman, founder of Shift4 Payments, a company that processes payments for restaurants and other businesses. In deciding to spend a sizable slice of his fortune, Mr. Isaacman did not want to just bring along some friends. Instead, he opened opportunities to three people he did not know.

The result is a mission with a crew that is more representative of wider society — Hayley Arceneaux, a 29-year-old physician assistant at St. Jude Children’s Research Hospital; Sian Proctor, a 51-year-old Black community college professor; and, Christopher Sembroski, a 42-year-old data engineer.

With his crew of everypersons, Mr. Isaacman has achieved a goal of science fiction authors and space enthusiasts: to open space to everyone, not just professional astronauts and wealthy space tourists.

“The difference with this flight is that we have three very ordinary people who are basically on the flight, and they’re going to show us what it means to open this up,” said Timiebi Aganaba, a professor of space and society at Arizona State University.

A trip like Inspiration4 is still affordable to only to the richest of the rich. But it is no longer impossible.

“There was some challenges post splashdown,” he said. “Folks didn’t feel well, and you know, that is the way it is with a water landing, even if you’re not deconditioned like we’re going to be.”

Mr. Hurley acknowledged that vomiting would not be unexpected.

“There are bags if you need them, and we’ll have those handy,” he said. “We’ll probably have some towels handy as well. And you know, if that needs to happen, it certainly wouldn’t be the first time that that’s happened in a space vehicle.”

But not long after the splash down, he asked SpaceX’s mission controllers to tell flight surgeons monitoring their health that, “we’re doing pretty good so far.”

The crew will also be returning minutes before sunset on Saturday. SpaceX’s last astronaut splash down in May occurred in the dark, and it was the first night water landing by astronauts since 1968.

Steve Stich, manager for NASA’s Commercial Crew program, said that consistently calm nighttime weather at the splash down site, ample moonlight and additional factors made landing in the dark advantageous.

“When we weighed all those options, it just looked like this was the best time to come home,” he said on NASA TV earlier in the year.

Another advantage of a nighttime landing could be that fewer private boats are likely to be around. That was a problem in August 2020 when the first crewed SpaceX capsule splashed down. More than a dozen boats — one of them flying a Trump campaign flag — converged on the singed capsule, and a few went in for a closer look.

The episode raised concerns among NASA and SpaceX officials about security and safety procedures. If there had been an emergency, NASA officials said, the private boats might have impeded recovery efforts. They added that there could have been poisonous fumes from the capsule that posed a risk to the boaters.

With that concern in mind in May, the Coast Guard set up an 11.5-mile safety zone around the splashdown site to chase away any interlopers.

The Crew Dragon capsule containing the Inspiration4 crew is orbiting at more than 17,000 miles per hour. At 6:16 p.m. Eastern time, the capsule’s thrusters will begin firing for 10 minutes to drop it out of orbit.

As it falls, the capsule actually speeds up until it enters the thicker part of the atmosphere. Then the drag of air resistance acts as a brake. The compression of air against the heat shield at the bottom of the capsule generates temperatures as high as 3,500 degrees Fahrenheit.

If it comes in at too shallow an angle, it will bounce off the atmosphere back into space. If it re-enters too steeply, it could burn up. But capsules like Crew Dragon have for decades successfully navigated through re-entry. It is rocket science, but it is well-understood rocket science.

For the most part, the spacecraft’s computer handles everything. It tracks the spacecraft’s position, fires short thruster bursts to keep the capsule oriented with the heat shield to absorb the heat and deploys the parachutes, while the crew members sit back for the ride.

But what if something goes wrong?

Like NASA astronauts, the Inspiration4 crew trained how to handle contingencies, especially during a 30-hour session they spent in a Crew Dragon simulator. Outside the simulator, the SpaceX mission controllers communicated with the astronauts as if they were in space. A separate team at SpaceX imagined emergencies that could come up and then unleashed them during the simulation. Neither the crew members in the simulator nor the controllers outside were given advance knowledge of what was happening. They had to diagnose the problem and figure out a fix on the fly.

“It was totally like an Apollo 13 moment by the time we were done with 30 hours,” said Jared Isaacman, the billionaire who financed the trip and serves as the mission’s commander.

The simulation included crashes of the spacecraft computer and failures in the communication system, so that there were periods where the astronauts could not talk to mission control.

When the re-entry burn started, Mr. Isaacman said it became apparent that the capsule was off target. “It was way overshooting the target landing zone,” he said.

As it was programmed to do, the capsule gave the command to fire its thrusters to try to get back on the right track. But that meant the thrusters could have run out of propellant or failed from firing so long. The simulated mishaps were potentially cascading into a simulated fatal accident. Without the thrusters during the hottest part of re-entry, “you’ll tumble and it might be unsurvivable,” Mr. Issacman said.

Mission control was able to override the computer that was trying to push the capsule to its planned landing site, Mr. Isaacman said. That preserved propellant for passage through the atmosphere.

At the end of the simulation, splashdown was far from where it was supposed to be. “But we survived,” Mr. Isaacman said.

That scenario is not far-fetched. Something similar occurred in December 2019 during a test flight with no astronauts of Boeing’s Starliner capsule, the other spacecraft that is expected to take NASA crews to the International Space Station.

By the time that Boeing’s controllers on the ground figured out what was going on and sent corrective commands, the spacecraft had expended too much propellant and a planned docking at the space station was called off. (That and a series of other problems have prevented the Starliner from carrying astronauts to orbit, but it may get another chance in 2022.)

Boeing and NASA officials said that if astronauts had been aboard, they would have quickly realized what was wrong and shut down the thrusters, which could have allowed the mission to proceed to the space station.

The first major step of the landing will begin at 6:11 p.m. Eastern time. That’s when the Crew Dragon will jettison its trunk, the bottom portion of the spacecraft that contains systems that are not needed for landing. The trunk will burn up in the atmosphere.

Five minutes later, at 6:16 p.m., the deorbit burn will begin, a firing of the thrusters that drops the capsule out of orbit and back into the atmosphere. This will last for 15 minutes.

Four minutes later, at 6:35, the spacecraft will close its nose cone, the location of the spacecraft’s cupola that gave the crew its views of Earth during their orbits.

At that point, it’s all automatic — the capsule should be hurtling through the atmosphere toward its destination until 7:02 p.m. when the drogues — a smaller set of parachutes — deploy to slow and stabilize the spacecraft’s descent. One minute later, the main, larger parachutes will deploy.

Three minutes later, the spacecraft will settle into the water, and the crew will begin procedures to be raised out of the ocean and taken back to land.

This flight path makes Inspiration4 more like some of NASA’s Mercury and Gemini missions during the 1960s that preceded the Apollo missions to the moon. It is also reminiscent of space shuttle flights before the construction of the space station. Some of those flights were the last times humans went this far from Earth.

Because Inspiration4 is not going to the space station, that allowed for a major modification to Resilience. SpaceX removed the docking port from the top of the capsule and installed a glass dome that will allow the crew to get a 360-degree view of space. It is the largest contiguous window ever to be flown in space. There was also a camera that for taking pictures of the crew members peering into space.

“It’s like an extended camping trip,” Mr. Sembroski said during a news conference on Tuesday. “You’re in a camper van with some of your closest friends for three days.”

The crew members were able to pull out sleeping bags and secure themselves in their flight seats, “so you don’t float into each other during the middle of the night,” Mr. Sembroski said.

“There will be a couple unique challenges maintaining privacy here and there,” he added. He said they had received good tips from NASA astronauts who previously traveled to space in the capsule.

“We’ll let you know more about how successful they were when we come back,” Mr. Sembroski said.

While food for spaceflight has made great advancements in quality since the 1960s, dining may not be a highlight of this orbital trip. In the Netflix documentary about Inspiration4, Ms. Arceneaux said during a taste test that she didn’t think she’d eat much in space. SpaceX has also not said who prepared the meals for this mission.

One of the planned meals was cold pizza. According to a SpaceX commentator, a member of the crew said during the meal, “Can’t believe we’re eating cold pizza in space. It’s extraordinary!”

But the crew didn’t just sleep and eat.

The Inspiration4 crew members will spend a fair amount of their time in orbit helping to advance medical research on how the human body reacts to being in space.

Other activities were more fun. Dr. Proctor, for instance, made some artwork, while Mr. Sembroski brought a ukulele to provide some live musical entertainment.

The crew also spoke to pediatric patients from St. Jude Children’s Research Hospital about being in space on Thursday, and rang the closing bell of the New York Stock Exchange from orbit on Friday. And they had conversations with other V.I.P.s from orbit, including the movie star Tom Cruise and Elon Musk, the founder of SpaceX, as well as members of their families.

Later on Saturday, shortly before preparing to land, the vehicle will jettison what SpaceX calls the “trunk” section of the spacecraft — the cylindrical compartment below the gumdrop-shaped capsule. The trunk will burn up in the atmosphere.

Then the capsule will begin firing its thrusters to drop out of orbit. Once it is low enough in Earth’s atmosphere, parachutes will deploy to gently lower the capsule into the sea.

The evening sky was nearly devoid of clouds when the nine engines of the Falcon 9 rocket ignited, lifting the rocket and its passengers to space.

Once the flight launched, the crew’s enthusiasm was unbowed by the forces pressing down on them, as a video inside the capsule showed Sian Proctor, the flight’s pilot, and Christopher Sembroski, the mission specialist, fist-bumping.

The capsule then headed to an orbit some 360 miles up, higher than the International Space Station and the Hubble Space Telescope. Indeed, the Inspiration4 crew will be farther from Earth than anyone else since the space shuttles worked on the Hubble in the 1990s.

In the event that weather prevented the astronauts from returning, the crew could circle the planet for an extended period of time. In response to a CNBC reporter’s question about the potential for a delayed return to Earth because of weather or other factors, Jared Isaacman, the billionaire who commands the mission and financed it, said on Tuesday they would be able to stay in space for “about a week.”

She applied twice more and was not even among the finalists.

She still pursued her space dreams in other ways. In 2013, Dr. Proctor was one of six people who lived for four months in a small building on the side of a Hawaiian volcano, part of an effort financed by NASA to study the isolation and stresses of a long trip to Mars.

She is the pilot on the Inspiration4 mission, the first Black woman to serve as the pilot of a spacecraft.