The shuttle orbiter takes off like a rocket, but lands on a runway like an ordinary aircraft. It returns as a glider, not a plane, for its descent is unpowered. The primary landing site for the shuttle is the runway at the Kennedy Space Center, a few kilometres from the launch pads. But the majority of orbiters have touched down at the Edwards Air Force Base in the Mojave Desert in California, where the runway is exceptionally long and the weather is more reliable than at Cape Canaveral. Other landing sites are available for emergency use at home and overseas, including White Sands in New Mexico (where STS-3 landed), Zaragoza in Spain and Banjul in the Gambia, West Africa. When orbiters land away from the Kennedy landing site, they have to be transported back there piggy-back by specially modified Boeing 747 carrier jet. Preparations for return to Earth from orbit begin with the orbiter being manoeuvred by firing the RCS (reaction control system) thrusters into a tail-first attitude. A de-orbit burn from the OMS (orbital manoeuvring system) engines reduces the orbiter's speed so that it drops from orbit. Afterwards it manoeuvres back to a nose-first attitude and, about 45 minutes later, it re-enters the atmosphere. Air friction rapidly brakes its descent and causes the outer surfaces of the orbiter to heat up. The 30,000 or so ceramic tiles and other insulation of the thermal protection system prevent the heat from penetrating the airframe. During re-entry there is a communications blackout of about 20 minutes between the orbiter and ground control because of the ionization of the surrounding air. By the time the orbiter emerges from the blackout it is flying aerodynamically, manoeuvring by its wing elevons and tail rudder. After a series of turns to cut speed, it swoops down 20 times faster and seven tines steeper than an airliner towards the runway. Just before touchdown the pilot brings up the nose and lowers the tricycle undercarriage. Touchdown speed is about 350 km/h. Time elapsed since the de-orbit burn is about one-and-a-quarter hours.
