The National Aeronautics and Space Administration suspended all space shuttle flights indefinitely (Saturday), hours after the Columbia disaster.
NASA had planned five more shuttle flights this year -- all to the International Space Station. With Columbia's loss, the United States now has just three space shuttles.
The next launch date was to have been March 1st; shuttle Atlantis was supposed to take a new crew to the space station and return to Earth with the current crew -- two American astronauts and one Russian cosmonaut who have been in orbit for the past 10 weeks.
The space-station crewmen are not stranded, even if the shuttles do not fly. They can return to Earth, if necessary, using a Russian Soyuz spacecraft attached to the station.
Russia also regularly launches unmanned cargo ships that bring supplies to the space station.
However, space-shuttle flights are a crucial element of the International Space Station program, because only the American spacecraft have enough cargo capacity to ensure construction of the orbital laboratory can continue.
If all three shuttles are grounded for a lengthy period, NASA may be forced to shut down the space station once the current crew is safely back home.