The space shuttle, part of the space transportation system, is a spacecraft for orbital human spaceflight missions. Operational flights began in 1982 following four test flights. The system is scheduled to be retired from service in 2010.
Major missions of the space shuttle have included launching numerous satellites and interplanetary probes, conducting space science experiments. The united states funded sts development and shuttle operations.
At launch, the space shuttle consists of a dark orange colored external tank two white, slender solid rocket boosters and the sts orbiter vehicle which contains the crew and payload.
Payloads can be launched into higher orbits with either of two different booster stages developed for sts.
The shuttle stack launches vertically like a conventional rocket from a mobile launch platform. It lifts off under the power of its two solid rocket boosters and its three main engines, the latter fueled by liquid hydrogen and liquid oxygen from the external tank.
The space shuttle has a two stage ascent. The boosters are used only for the first stage, while the main engines burn for both stages. About two minutes after liftoff, staging occurs the srbs are released, and shortly begin falling into the ocean to be retrieved for reuse. The shuttle orbiter and external tank continue to ascend under power from the three main engines and their inertia.
Upon reaching orbit, the main engines are shut down, and the external tank is jettisoned downward and falls to burn up in the atmosphere, it is possible for it to be re used in orbit for various applications. At this point, the orbital maneuvering system oms engines may be used to adjust or circularize the achieved orbit.
A track is any of the concentric circles on the magnetic coating on a platter or floppy disk over which one magnetic head passes while it is stationary but the platter or floppy is spinning. In the case of cdroms, and other optical disks, there is a single spiral track formed in a plastic coating.
Each track on a modern hdd has a width of only a few microns, and there can be tens of thousands of tracks on each platter. The thinner the tracks, the greater the storage capacity of the disk. An important trend with regard to hdds has been the steady reduction in track thicknesses, which has been made possible by improvements in magnetic materials, in magnetic heads and in head control mechanisms.
The density of tracks is measured in terms of tracks per inch. It varies widely according to the type of disk and when it was produced. A typical floppy disk has a track density of 135tpi, whereas modern hdds have densities of thousands of tracks per inch.
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