CBS News Space Consultant Bill Harwood has been covering the U.S. space program full-time since 1984, first as Cape Canaveral bureau chief for United Press International and now as a consultant for CBS News. All four appeared healthy and in good spirits, smiling and waving as they exited. This was the fourth so-called "private astronaut mission" to the International Space Station sponsored by Houston-based Axiom Space, which works with NASA to provide privately funded research trips to the station. The company charges up to $70 million or so per seat to carry non-NASA astronauts, professional researchers and others to the space station who might otherwise have no other route to orbit. Axiom Space is using the missions to gain experience as the company presses ahead with plans to build a commercial space station that will provide a destination in low-Earth orbit for NASA and other nations after the International Space Station is retired in 2030. Peggy Whitson, America's most experienced astronaut, greets recovery crews with a broad smile as she begins re-adjusting to gravity after 20 days in weightlessness. Whitson, 65, has now logged more than 695 days in space across five missions -- three for NASA and two for the company she now works for, Houston-based Axiom Space. SpaceX Throughout their two-week mission, Whitson and her crewmates carried out a full slate of science research and technology demonstrations, along with interactive educational events with students and others in the crew's home countries. Researchers from 31 countries are helping evaluate data from the Ax-4 experiments and technology demonstrations. Whitson, a retired NASA astronaut, is the most experienced American space flier, with 695 days and six hours and 48 minutes in orbit during five spaceflights — three for NASA and two for Axiom Space. She now ranks eighth in the world for most time in space behind seven Russian cosmonauts. She also logged 10 spacewalks during her earlier flights, making her the most experienced female spacewalker and seventh in the world overall. Space & Astronomy More