The Space Shuttle

The final design of the STS or Space Shuttle has three main components: 1) the Orbiter, 2) the External fuel tank, and 3) the Solid Rocket Boosters (SRBs). The Orbiter and the SRBs are reusable, the External fuel tank is discarded shortly before reaching orbit, and is destroyed as it reenters.

Orbiter: The orbiter is 122 ft long, 57 ft high, and has a wingspan of 78 ft. Unfueled it weighs 160,000 lbs. There are three main sections, 1) the crew compartment, 2) the cargo bay, and 3) the propulsion/power supply compartment. The crew compartment has two main levels, the upper level contains the flight control systems, while the lower compartment contains the crew living quarters. On the lower deck is an airlock that allows the astronauts to enter the cargo bay. The crew compartment contains 2,600 cu ft of volume.

To allow the orbiter to sustain the high temperatures of reentry, it is covered with a complex system of thermal protection materials. The nose cone and leading wing edges (where reentry temperatures can reach 3,000 F) are coated with a "reinforced carbon-carbon" compound.

On the other high-heat-load areas (where temperatures remain below 2,300F), black tiles ("High-Temperature Reusable Surface Insulation Tiles", HRSI) are employed. These tiles are composed of amorphous, high-purity silicon fibers. 90% of the volume of these tiles is "void", with only 10% composed of silicon. Thus, they are surprisingly lightweight-9lbs per cubic foot (about 1/6 the density water). The thickness of the tiles varies from 1" to 5", depending on heat load. The average tile is 6" x 6" square.

On the rest of the orbiter (where reentry temperatures do not exceed 700F), "white blankets" of "Felt Reusable Surface Insulation" , an impregnated felt material, are used.

The majority of the volume of the Orbiter is consumed by the payload bay, the space where the cargo is stored. Its dimensions are 60 ft long by 15 ft. The shuttle can carry a payload of about 50,000 lbs to low-earth orbit.

The Orbiter is equipped with three main engines used to place the Shuttle in orbit. These engines are the most sophisticated ever developed for space flight, having different power settings (from 65% to 100%), and are gimbled to allow directional thrust to adjust the flight path. Once reaching orbit, any remaining LOX/LH2 is vented to space. Once in orbit, two smaller engines in the rear, the Orbital Maneuvering System ( "OMS" ) provide the Orbiter with power to adjust its orbit, and orient for reentry. The fuel is mono-methyl hydrazine with nitrogen tetroxide as the oxidizer. There are also reaction control rocketes located in the front to provide small-scale maneuvering capabilities in-orbit.

SRBS: The Shuttle uses two Solid-Fuel Rocket Boosters to allow it to achieve orbit. Each SRB is 149 ft long, and 12.2 ft in diameter. Each one weighs 1.3 million lbs, and generates 3.1 million lbs of thrust. The fuel is a combination of Aluminum powder, Ammonium Perchlorate powder, a small amount of iron oxide catalyst, and a polymer binder. This material has the consistency of pencil eraser. The SRBs are constructed of four segments that are shipped to, and assembled in Florida prior to launch.

The shape of the fuel within an SRBs is carefully designed to provide maximum thrust at liftoff. At 55 seconds into flight, the SRB thrust decreases to reduce stress on the spacecraft system. The exhaust nozzle can be directed to help in guidance. They burn for two minutes, and at an altitude of 19,000 feet explosively separate from the Orbiter assembly. Small rockets move them away from the orbiter. They parachute back to the ocean where they are recovered and reused.

External tank: Is simply the fuel reservoir that supplies the main engines with the LOX/LH2 combination to provide the thrust to put the Shuttle into orbit. The ET is 154 ft long, and 27.6 feet in diameter. It weights 66,000 lbs empty, 1,655,000 lbs fueled. The ET is the structural element that ties the STS system together. It absorbs all of the 6 million lbs of thrust required to orbit the Shuttle.

During ascent, fuel is supplied at a rate of 1,035 gallons per second. Eight minutes into the flight, at a height of 71 miles, the main engines shutdown and the tank is jettisoned . The ET burns up on reentry.

Program Milestones

The first space-ready orbiter, Columbia , was successfully launched on 4/12/81 ("STS-1"), the 20^th anniversary of Gagarin's flight (note that the Enterprise was built first for testing the landing systems, but was never flown in space). Among its milestones were the first use of the remote manipulator arm (STS-2), the first launch of a commercial satellite (STS-5), the first six person crew (STS-9), the first American spacecraft to carry a non-American (German Ulf Merbold). Columbia also hosted the European "Spacelab" in its cargo bay.

The second orbiter was the Challenger . Its first flight (STS-9) occurred in April of '83. Its main highlight was the capture, repair, and deployment of the Solar Maximum Mission (SMM) satellite. It also has the lowlight of the Shuttle program, exploding 73 seconds after launch on mission STS-51L (1/28/86), killing all seven astronauts (Jarvis, McAuliffe, McNair, Onizuka, Resnik, Scobee, Smith), Christa McAuliffe was to be the first "teacher in space". (More on the Challenger disaster can be found here. A moment-by-moment description of the accident, and its causes are described here. Drawings of the O-ring system that caused the failure, and its redesign, are shown here #1, #2.)

The third functional orbiter to be built was the Discovery . It first flew in August of '84. It deployed the Hubble Space Telescope, as well as capturing and returning to Earth a non-functioning satellite.

The fourth orbiter, Atlantis benefited from the experience gained in the construction of the preceding orbiters-it weighed 6,900 lbs less than Columbia, and was constructed with only 50% of the man hours. It also had about 160 modifications over previous designs, including not having tiles on the upper portions of the fuselage.

Atlantis was also modified to carry cryogens for DoD applications. A number of important astrophysics missions were launched (Compton Gamma-Ray Observatory, Magellan, and Galileo) from Alantis.

The final member of the Shuttle fleet is the Endeavour , first launched in May of '92. It had additional modifications, including plumbing that would allow extended, 28 day missions. Its most important contribution was the first Hubble Telescope servicing mission in December of '93. The new instruments and modifications to the HST brought its optics back to their original specifications. (The next mission, STS-103, will also service the HST.)

The Space Shuttle has opened-up space to persons other than trained military pilots, allowing normal scientists, doctors, and others to fly as mission specialists, it has also allowed people from countries other than Russia and the US to get to space, including astronauts from Italy, Germany, France, Japan, Canada, Switzerland, and the Netherlands. Before the Shuttle program, US astronauts had spent 22,503 man-hrs in space, by March of '95, US astronauts had already spent 94,800 man-hrs in space. As of September 389 different people have orbited the Earth (US & Russia combined).