Real World: Keeping the International Space Station in Orbit [Archived]

Each day, gravity pulls the International Space Station, or ISS, a little closer to Earth. See how drag causes the ISS to slow down. Learn about the challenges of keeping the ISS in orbit and how NASA counteracts orbital decay. (v2)
[Archived 2014 - Not all missions make it from design to launch. These archived videos describe missions that that would have taken humans back to the moon and unmanned aerial vehicles to Mars. While the actual missions were aborted, the technology and science behind the missions pushed innovation to new levels.]