As geostationary (GSO) satellites remain in an essentially fixed position relative to the ground at all times, they can communicate with fixed ground stations continually. Medium Earth orbit (MEO) and low Earth orbit (LEO) satellites appear to “fly by” overhead and have a shorter communication window for a given station, from ten minutes for a LEO satellite to two hours or more for a MEO satellite. Satellites in highly elliptical orbits may be in communication with a fixed ground station for up to eight hours.
Satellites in use have four basic applications: communications, remote sensing, navigation, positioning and timing, and scientific experimentation (generally using a suite of sensors with variations of some or all of the other types). The sidebar describes the various satellite orbits.
China’s Shenzhou (“Divine Vessel”) launched two taikonauts into orbit in 2005 for a mission lasting more than 115 hours. It was China’s second human launch, following the launch of one taikonaut in October 2003. China’s next human mission is expected to launch in 2007. The Shenzhou capsule bears many design similarities to Russia’s Soyuz reentry crew capsule.
Russia’s Soyuz has been the workhorse of Roscosmos, having been in production for more than 40 years. The vehicle’s separated reentry capsule and laboratory module optimize space with a minimum of weight. In 2005, Soyuz took its third space tourist, Gregory Olsen, to the ISS. Currently, the vehicle is used to rotate the crew of the ISS, (a service for which NASA pays), launching to the station twice in 2005.
The space shuttle returned to flight in 2005, ending a two year hiatus that followed the Columbia tragedy. Discovery’s STS-114 crew tested new safety measures and delivered supplies to the International Space Station (ISS). Digital cameras installed for the first time on a shuttle flight captured a chunk of foam shed from the external fuel tank.