NASA's oldest working spaceship, the space shuttle Discovery, re-entered Earth's atmosphere for the last time in early March, completing its 39th mission since 1984, and tallying about one year's worth of days in space. A few months later on July 21, the 30-year-old U.S. space shuttle program officially ended with the landing of space shuttle Atlantis at Kennedy Space Center. The NASA program had 135 successful missions and sent more than 300 astronauts into space, a historic run marred by the 1986 Challenger and 2003 Columbia disasters that claimed the lives of 14 astronauts. The United States will now depend on Russia for transport to and from the International Space Station at a cost of $51 million per seat.