Almost anyone. At least anyone who can afford it. Blue Origin, which is auctioning off a seat on a flight scheduled for July 20, said the winner must be able to endure three times the force of gravity for two minutes on ascent and five and a half times the force of gravity for a few seconds on the way down. Participants must be between five feet and 6 feet 4 inches tall and weigh between 110 and 223 pounds. During the sweepstakes for a seat on a SpaceX flight designed to raise money for St. Jude Children’s Research Hospital, organizers said participants must weigh less than 250 pounds, be shorter than 6 feet 6 inches tall and be “physically and psychologically fit for training.” Elon Musk, the founder of SpaceX, said that most people would be able to fly on the Dragon spacecraft. “If you can go on a roller-coaster ride, like an intense roller coaster ride, you should be fine for flying on Dragon,” he recently said. Virgin Galactic’s website doesn’t list any physical requirements for its future astronauts. “We will prepare every astronaut thoroughly, through a program of medical checkups and tailored training,” it promises.

How much does a ticket to space cost?

That depends. Flying to the International Space Station for a week on a trip commissioned by Axiom Space costs $55 million per person. Some of that goes to NASA, which under new private astronaut pricing guidelines charges $10 million a week per private astronaut for crew time, mission planning and communications. It also charges other, smaller fees, including $2,000 a day per person for food. Virgin Galactic, Richard Branson’s space venture, had been charging $250,000 for suborbital flights, where passengers would experience a few minutes of weightlessness before falling back to Earth. But when ticket sales reopen later this year, the company has said the cost would go up. It hasn’t said what the new price would be, but analysts have said they expect it to be $500,000. Jeff Bezos’s Blue Origin hasn’t announced prices for seats on its suborbital New Shepard spacecraft. But the online auction for a seat on its first human spaceflight mission has gone well over $3 million. It is expected to climb higher in the live auction scheduled for Saturday. (Bezos owns The Washington Post.)

What sort of training is involved to go to space?

Training for the suborbital space trips is nothing like what NASA astronauts go through. Blue Origin says on its website that the training for its flights lasts only a day. “The day before launch, you’ll learn everything you need to know to make the most of your experience as an astronaut.” The training “includes mission and vehicle overviews, in-depth safety briefings, mission simulation and instruction on your in-flight activities such as operational procedures, communications and maneuvering in a weightless environment.” Virgin Galactic said its goal is to offer its future astronauts “an unmatched safe and affordable journey to space without the need for any special prior experience or significant prior training and preparation.” The training is expected to last three days at Spaceport America in New Mexico, where passengers “will go through a customized medical screening and flight preparation process, including training for use of communication systems, flight protocols, emergency procedures and G-force training.” They’ll learn how “to exit their seats and experience weightlessness, floating about the cabin and positioning themselves at one of the many windows around the cabin sides and top. After enjoying several minutes of weightlessness, our astronauts will maneuver back to their own seats to prepare for reentry and the journey back into the Earth’s atmosphere.” Over the years, Virgin Galactic has built a community of want-to-be astronauts who have done training in coordination with Virgin Galactic by flying “Zero-G” parabolic flights and going to a centrifuge to help them adapt to increased gravity forces. Axiom Space, which offers a much more ambitious mission of a week on the International Space Station, has a training curriculum that lasts 17 weeks at facilities run by NASA and the Japanese and European space agencies. “Training prepares the participant as an astronaut, develops a deep camaraderie with fellow astronauts, and truly inaugurates one as a member of the exclusive space traveler family.” Passengers train alongside their mission commander. Axiom has said former NASA astronauts Michael Lopez-Alegria and Peggy Whitson will command the first two missions.

Is space tourism new?

Several civilians have already gone to space. In the 2000s, Russia flew eight missions to the International Space Station with wealthy private citizens, such as Dennis Tito, Charles Simonyi and Anousheh Ansari, on board. In 2004, Mike Melvill and Brian Binnie flew to the edge of space on SpaceShipOne, the first commercial vehicle to reach space and a predecessor to the spaceplane currently flown by Virgin Galactic. In the 1980s, two members of Congress flew, Sen. Jake Garn (R-Utah) and Rep. Bill Nelson (D-Fla.), who was later a senator and now serves as NASA administrator. Their costs were borne by NASA.