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Space Shuttle
(National Space Transportation System --NSTS)

Brief History

Concept of reusable space transportation system originated in the 1960's
Development of shuttle system begun in 1970's
Major components contracted to various companies
- IBM -- computers
- Morton Thiokol -- solid rocket boosters (SRB's)
- Rockwell -- orbiter vehicle (OV)
- Martin-Marietta -- external tank (ET)
- General Electric -- kitchen and toilet
Delays in development of thermal protection system (heat tiles) and the turbo-pumps on main engines
First orbiter -- Enterprise (named by popular demand of Star Trek fans)
- Not flight-qualified
- Test vehicle for landing checkout only
- Now at Dulles Airport near Washington, DC
First complete system launched April 12, 1981 -- Columbia orbiter
List of orbiters:
- Enterprise, Columbia, Challenger (replaced by Endeavor), Discovery, and Atlantis

Major Subsystems

(textbook covers most of these -- notes here describe some unusual aspects). An excellent source of detailed information is the NASA News Media Reference Manual (it's originally dated 1988, but the pages are all constantly updated as modifications are made by NASA).

The Launch Assembly (Stack)
- Orbiter (crew, payloads, main engines)
- ET (liquid hydrogen and liquid oxygen for main engines in orbiter)
- SRBs (reusable solid chemical engines)
Thermal protection system (heat tiles)
- Previous s/c (Mercury, Gemini, Apollo) employed ablative heat shields. During atmospheric re-entry,, a layer of glass-phenolic material chars as it reaches high temperatures, and the hot particles are sheared away by the high-velocity air flow -- this is the ablation process. The hot particles carry the heat away from the s/c. Major disadvantages are weight of the shield and non-reusability (since a new shield cannot be easily bonded to the s/c).
- Shuttle orbiters use a system of 30,000 tiles made of a silica compound that does not ablate, but does rapidly radiate heat away from the orbiter. These tiles can be repaired in space. Major disadvantages are fragility (tiles easily damaged before launch and by orbital debris -- lots of tile damage due to debris since anti-satellite tests in mid-80's) and complexity (many people needed to manually attach tiles to orbiter in a tedious and time-consuming process, and to inspect them all before launch).
Computers -- five processors to monitor status of the orbiter and automatically control engines, life support, etc.

Meteors burn up when they hit the Earth's atmosphere. Why doesn't the space shuttle?

When a small meteor enters the Earth's atmosphere, it goes from traveling through a vacuum to traveling through air. Traveling through a vacuum is effortless -- it takes no energy. Traveling through air is another story. A meteor moving through the vacuum of space typically travels at speeds reaching tens of thousands of miles per hour. When the meteor hits the atmosphere, the air in front of it compresses incredibly quickly. When a gas is compressed, its temperature rises. This causes the meteor to heat up so much that it glows. The air burns the meteor until there is nothing left. Re-entry temperatures can reach as high as 3,000 degrees F (1,650 degrees C)! Obviously, it would not be good for a spacecraft to burn up when it re-enters the atmosphere! Two technologies are used to allow spacecraft to re-enter: Ablative technology Insulating tile technology In ablative technology, the surface of the heat shield melts and vaporizes, and in the process, it carries away heat. This is the technology that protected the Apollo spacecraft. The space shuttles are protected by special silica tiles. Silica (SiO2) is an incredible insulator. It is possible to hold a space shuttle tile by the edge and then heat up the center of the tile with a blow torch. The tile insulates so well that no heat makes it out to the edges. This page discusses the tiles: Aerobraking tiles are produced from amorphous silica fibers which are pressed and sintered, with the resulting tile having as much as 93% porosity (i.e., very lightweight) and low thermal expansion, low thermal conductivity (e.g., the well known pictures of someone holding a Space Shuttle tile by the corners when the center is red hot), and good thermal shock properties. This process can be readily performed in space when we can produce silica of the required purity. These tiles keep the heat of re-entry from ever reaching the body of the shuttle. These links will help you learn more: Ablative heat shield Protective Shuttle Tiles Insulate on Earth High-Temperature Insulations A Brief History of Composites in the U.S. Refractories How Space Shuttles Work How the Leonid Meteor Shower Works How big does a meteor have to be to make it to the ground?