Re-entry
The most dangerous part of the return trip is re-entry into Earth's atmosphere. That's because the shuttle must lose nearly all of its orbital speed -- about 25 to 30 times the speed of sound. There are several ways to slow the craft down, but NASA currently uses a method called energy dissipation, which requires that the shuttle's kinetic energy be converted into heat as the craft passes through the atmosphere. To initiate the process, the shuttle pilot fires braking rockets while the shuttle is flown backwards and belly-up. This reduces the speed of the shuttle below the critical orbital velocity and causes the craft to descend into the atmosphere. Then the shuttle is positioned into its descent attitude, with the nose forward and slightly upward, and the belly facing downward. Ceramic tiles cover the belly and act as the main heat shield as the shuttle's computers guide the spacecraft through a fiery hour-long descent.
Image courtesy NASA
Space Shuttle Atlantis makes a rare night landing at Kennedy Space Center in 1996.
At about 25 miles (40 km) above Earth, the pilot once again assumes control, flying the shuttle like an airplane as it approaches KSC in Florida. The shuttle circles high over the spaceport to lose speed and finally descends onto a three-mile-long, canal-lined runway. When it touches down, the shuttle is still traveling about 215 miles per hour (346 kph). Using a parachute, rear brakes and several thousand feet of runway, the spacecraft comes to a complete stop, just down the road from its point of departure.
Next comes the post-mission debriefing session. During debriefing, astronauts and personnel from all aspects of the mission synthesize what happened throughout an expedition and present their findings. Astronauts provide invaluable first-hand accounts of systems and operations aboard the shuttle and space station, helping NASA understand how to redesign or retool various aspects of a mission to make future expeditions even more successful.
While the mission described above makes spaceflight seem routine, every trip into space is a razor's-edge walk between success and disaster. One of the earliest mishaps occurred in the Soviet Union in 1960. In what is now known as the Nedelin catastrophe, an R-16 rocket exploded during launch, killing 126 Soviet space and missile personnel.
The United States has not been immune to such tragedies. In 1967, while conducting a routine test of Apollo 1's Command and Service Module, astronauts Ed White, Gus Grissom and Roger Chafee died when a fire broke out in the cockpit. And two space shuttle tragedies have claimed the lives of 14 astronauts: the Challenger disaster in 1986 and the Columbia disaster in 2003. Christa McAuliffe, the first teacher in space, died in the Challenger explosion. |
For the scientifically curious, exploring space has its own benefits, but a person has to eat. Learn more about how astronauts are compensated for their hard work on the next page.
