Science - The Space Shuttle Design Concept - Idealized Functionality!

Stripped to the essentials, NASA's Space Transportation System (STS), the Space Shuttle, needed an Orbiter vehicle to accommodate crew and mission requirements, plus the propulsive power to accelerate many millions of pounds of personnel, hardware and fuel to orbiting velocity; plus all back-up, contingency and emergency equipment that could conceivably be necessary for foreseeable and unforeseeable exigencies. Among the forcing-functional-considerations (after the primary concern for safety and reliability) was cost and the minimization of factors which would necessitate long preparation periods between flights (the "shuttle" concept).

The Orbiter vehicle would house the astronauts as they circled Earth, containing also all requisite systems, materials, supplies and equipment for: life support during the voyage; communication with Earth; mission objectives (space experiments to be carried out); and requirements for the return to Earth: mechanisms for de-celeration from orbital speed, critical insulation or heat protection for the reentry phase, and means for flight control and landing upon a standard length runway (glider modus operandi, no propulsive power), and conventional control surfaces: wing flaps, rudder flaps, wheels and brakes.

The propulsive system evolved into a three engine configuration (providing increased reliability and stability), integrated into the Orbiter vehicle structure; engine fuel contained in a large central tank attached to the Orbiter (droppable when empty, with altitude-opening parachutes) and two strap-on solid rocket boosters (reliable gigantic "fire-crackers), droppable and recoverable from the ocean (similar parachutes). The propulsion system requirement was extremely demanding, to achieve lift-off and acceleration to reach orbit velocity, lifting over seven million pounds of total weight.

The most reliable and efficient configuration for assembly of the elements and for optimum launch sequence was quickly determined to be the two giant solid rockets bolted to the launch pad (huge explosive bolts anchoring the rocket flanges to the concrete pad); the Orbiter vehicle attached (removably) to the rockets; finally the gigantic fuel tank (removably) attached to the Orbiter. The launch sequence was initiated by firing of the on-board engines, then the firings of the solid rockets and their flange bolts exploded - separating the STS assembly from Earth. The Space Shuttle system would then rise, slowly at first and vertically, increasing in speed and altitude until clear of the Cape Canaveral launch facility, then adjusting to an angled horizontal climb; taking advantage of the direction of Earth's rotation (reducing the STS requirement to reach orbit speed) by about 1000 miles per hour. As the solid rocket boosters complete their firing, they are dropped, to be salvaged from the ocean for reuse. The orbiter engines continue to power the system until orbit is reached and the fuel tank is depleted, when it also is blasted free of the orbiter.

What is generally not known is that once the Shuttle drops its fuel tank, the orbiting vehicle no longer has propulsive capability - coasting along at 18,000 miles per hour in the vacuum of space. The mechanisms aboard the vehicle for maneuvering are the Space Shuttle Orbital Maneuvering System (OMS), a system of rocket engines used for final orbit injection, modification or maneuvering at the Space Station. The OMS consists of two protrusions at the back of the Shuttle, on either side of the vertical stabilizer. Each contains a hypergolic engine with 6,000 lb thrust and a specific impulse of 313 seconds. The OMS pods also contain the rear set of small reaction control system engines.

For the initial ventures into space, the Mercury and Apollo programs, the reentry approach was for "over-kill" - to protect the astronauts from the extreme heat of reentry by covering the bottom of the circular capsule (the face to reentry) with many inches of ablatable material, fiber-glass and resin, which melts and vaporizes, the transformation from a solid to a gas dissipating the enormous heat of reentry, protecting the astronauts. As the slowing capsule falls to a low altitude, a trio of parachutes is deployed - the capsule drops into the ocean, with a quick pick-up by naval vessels on close standby.


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