The first crewed flight of Boeing’s Starliner spaceship was dramatically called off Saturday with just under four minutes left on the launch countdown clock, for reasons that aren’t yet clear. Starliner is poised to become just the sixth type of US-built spaceship to fly NASA astronauts, following the Mercury, Gemini and Apollo programs in the 1960s and 1970s, the Space Shuttle from 1981 to 2011, and SpaceX’s Crew Dragon from 2020.
