lecture_25 - Notes from Lectures #25-27: The Space Shuttle...

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Notes from Lectures #25-27: The Space Shuttle For 24 years now (as of 2005), the Space Shuttle has been NASA’s only manned spacecraft. When the shuttle Columbia first flew in 1981, it ushered in a new era of reusable spacecraft. Prior to 1981, every single space vehicle ever launched had been expendable - a new one had to be built from scratch for each mission. To date, the Shuttle is the only reusable orbital vehicle in existence. Mind you, the Shuttle (whose official name is the Space Transportation System, or STS) is only partially reusable - that is, not all parts of the Shuttle system are reused. In the diagram at the end of these notes, you can see the four main parts of the Shuttle: the two Solid Rocket Boosters (SRBs), the External Tank (ET), and the Orbiter itself. It is the Orbiter (which comprises just 5% of the mass of the vehicle on the launch pad) which carries the astronauts and their cargo into space. The SRB’s and ET’s sole job is to get the orbiter into orbit. Most of the mass (about 90%) of the Shuttle on the launch pad is accounted for by the propellant alone. The orbiter and the SRB’s are all reused from one mission to the next; the ET is not, and a new external tank must be supplied for each mission. This is why the Shuttle is only a partially reusable launch vehicle. There are usually four vehicles in the Shuttle fleet. Before the destruction of the Columbia , the fleet consisted of the Atlantis, the Endeavor , the Discovery, and the Columbia . They would fly in rotation. And prior to 1986, there was also the shuttle Challenger. The four components of the Shuttle are assembled in the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC). The Shuttle sits upright on the crawler-transporter, with the nose pointing up. The crawler-transporter (which is the same one from the Apollo days that used to carry the Saturn V rocket) slowly conveys the Shuttle to the launch pad a couple of miles away. Just prior to launch, millions of gallons of water are released from a water tower near the launch pad, flooding the entire site. The purpose of all that water is to act as a sound buffer - if it weren’t there, the intense sound waves of the Shuttle’s exhaust would reflect off the launch platform and back onto the orbiter, possibly shaking off or loosening thermal tiles that cover the orbiter and which are needed for a safe reentry. The water absorbs much of this acoustic energy and alleviates the problem. The huge clouds of billowing white steam that you see during a Shuttle launch are due to the water being boiled away by the heat of the exhaust.
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The Shuttle’s Four Engine Systems and their Uses during a Mission The Shuttle carries four engine systems, each serving a specific purpose (or sometimes dual purposes): Engine System Type of Propellant Function Solid Rocket Boosters Solid Provide 80% of the thrust needed to (SRB) get the orbiter to orbital speed Space Shuttle Main Cryogenic Provide remaining 20% of thrust to
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lecture_25 - Notes from Lectures #25-27: The Space Shuttle...

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