How high do astronauts go?

Most human spaceflight today happens in a narrow band of low Earth orbit. The International Space Station keeps an orbit of roughly 400 km, high enough that atmospheric drag is manageable and low enough that cargo and crew vehicles can reach it cheaply; it still needs periodic reboosts. Crew Dragon and Soyuz missions that visit the station therefore live at that altitude, and free-flying missions have gone somewhat higher: SpaceX's Inspiration4 in 2021 flew an orbit reaching about 585 km, and Polaris Dawn in 2024 raised its apogee to roughly 1,400 km, the highest Earth orbit flown by humans since Apollo.

At the bottom of the scale sit suborbital flights. New Shepard and, in its operating years, SpaceShipTwo carried passengers to the edge of space; the Kármán line at 100 km is the internationally common boundary, while the United States has traditionally used 50 miles, about 80 km.

The Space Shuttle reached its highest crewed altitudes on Hubble Space Telescope servicing flights, near 570 km, because the telescope itself orbits there. Everything above that belongs to Apollo. Nine crews travelled to the Moon between 1968 and 1972, and the single greatest distance from Earth was set by Apollo 13 in April 1970: because the spacecraft swung around the far side of the Moon on a free-return trajectory while the Moon was near apogee, the crew ended up about 400,000 km away, further than anyone before or since.

Between low orbit and the Moon lie the Van Allen radiation belts, which make lingering at intermediate altitudes unattractive. Apollo crossed them quickly. The practical result is a gap: crews either stay a few hundred kilometres up, or they leave for the Moon.