NASA began design, cost and engineering studies on a space
shuttle. Many aerospace companies also explored the concepts.
The concepts varied from a reusable, manned booster concept
to a shuttle lifted by solid rockets. In 1972,
President Nixon announced that NASA would develop a reusable
space shuttle or space transportation system.
NASA decided that the shuttle would consist of an orbiter attached to solid rocket boosters and an external fuel tank because this design was considered safer and more cost effective. NASA awarded the prime contract to Rockwell International.
At that time, spacecraft used ablative heat shields that would burn away as the spacecraft re-entered the Earth's atmosphere. However, to be reusable, a different strategy would have to be used. The designers of the space shuttle came up with an idea to cover the space shuttle with many insulating ceramic tiles that could absorb the heat of re-entry without harming the astronauts.
Remember that the shuttle was to fly like a plane, more
like a glider, when it landed. A working orbiter was built to
test the aerodynamic design, but not to go into outer space.
The orbiter was called the Enterprise after the "Star
Trek" starship. The Enterprise flew numerous flight and
landing tests, where it was launched from a Boeing 747 and
glided to a landing at Edwards Air Force Base in California.
Finally, after many years of construction and testing, the shuttle was ready to fly. Four shuttles were made, Columbia, Discovery, Atlantis and Challenger. The first flight was in 1981 with the space shuttle Columbia, piloted by astronauts John Young and Robert Crippen. Columbia performed well and the other shuttles soon made several successful flights.
In 1986, the shuttle Challenger broke up in flight when a flame from a leaky joint on one of the solid rocket boosters ignited the fuel in the external fuel tank. The Challenger exploded and the entire crew was lost. NASA suspended the shuttle program for several years, while the reasons for the disaster were investigated and corrected. After several years, the space shuttle flew again and a new shuttle, Endeavour, was built to replace Challenger in the shuttle fleet.
To date, the space shuttles have flown about one-fourth of their expected lifetime and have undergone many refits and design changes to make them safer and to carry heavier payloads into orbit.
The space shuttle consists of the following major components, two solid rocket boosters, external fuel tank and orbiter.
A typical shuttle mission
lasts seven to eight days, but can extend to as much as 14
days depending upon the objectives of the mission.
To lift the 4.5 million
pound shuttle from the pad to orbit (115 to
400 miles) above the Earth, the shuttle uses
two solid rocket boosters, three main engines of the orbiter, the external fuel tank
and the orbital maneuvering system on the orbiter.
The solid
rockets provide most of the main force or thrust
needed to lift the space shuttle off the launch
pad.
Once in space, the shuttle orbiter is your home for seven to 14 days. The orbiter can be oriented so that the cargo bay doors face toward the Earth or away from the Earth depending upon the mission objectives; in fact, the orientation can be changed throughout the mission. One of the first things that the commander will do is to open the cargo bay doors to cool the orbiter.
The orbiter consists of
a crew compartment, where the crew live and work,
and a forward fuselage. It has a forward reaction control system module, which
contains forward rocket jets for turning the orbiter in
various directions,
a movable airlock, used for spacewalks and a mid-fuselage, which
contains essential parts (gas tanks, wiring, etc.).
The orbiter also has cargo bay doors, which form the roof of the cargo bay and are
essential for cooling the orbiter,
the remote manipulator arm, located in the cargo bay and
used to move large pieces of equipment in and out of
the cargo bay. The arm also acts as a
platform for spacewalking astronauts. The aft fuselage
contains the main engines.
The orbiter must provide you with an environment similar to Earth. You must have air to breathe, food to eat, water to drink, and a comfortable temperature. The orbiter must also take away the wastes that your body produces (carbon dioxide, urine, feces) and protect you from fire. Earth's atmosphere is a mixture of gases (78 percent nitrogen, 21 percent oxygen, 1 percent other gases) at a pressure of 14 lbs/in. The space shuttle must provide a similar atmosphere. To do this, liquid oxygen and liquid nitrogen are carried on board in two systems of pressurized tanks. The cabin pressurization system combines the gases in the correct mixture at normal atmospheric pressure. While in orbit, only one oxygen system and one nitrogen system are used to pressurize the orbiter. During launch and landing, both systems of each gas are used.
Besides air, water is the most important quantity aboard the orbiter. Water is made from liquid oxygen and hydrogen in the space shuttle's fuel cells. The fuel cells can make 25 pounds of water per hour. The water from the fuel cells passes through a hydrogen separator to eliminate any trapped hydrogen gas. Excess hydrogen gas is dumped overboard. The water is then stored in four water storage tanks located in the lower deck. Drinkable water is then filtered to remove microbes and can be warmed or chilled through various heat exchangers depending upon the use (food preparation, consumption, personal hygiene). Excess water produced by the fuel cells gets routed to a wastewater tank and subsequently dumped overboard.
Space is an extremely cold environment
and temperatures will vary drastically in different parts of
the orbiter. You might think that heating the orbiter would be
a problem. However, the electronic equipment generates more
than enough heat for the ship. The problem is getting rid of
the excess heat. Radiators located on the inside surfaces of
the cargo bay doors radiate the collected heat to
outer space.
The orbiter has a galley-style kitchen along the wall next to the entry hatch, which is equipped with food storage compartments, food warmers, a food preparation area with warm and cold water outlets, and metal trays so the food packages and utensils do not float away.
All of the on-board systems of the orbiter require electrical power. Electricity is made from three fuel cells, which are located in the mid fuselage under the payload bay. These fuel cells combine oxygen and hydrogen from pressurized tanks in the mid fuselage to make electricity and water. The orbiter has a distribution system to supply electrical power to various instrument bays and areas of the ship.
The orbiter has five on-board computers that handle data processing and control critical flight systems. Computers control critical adjustments especially during launch and landing.
Within the mid-deck, there are are racks of experiments to be conducted during each mission. When more space is needed for experiments, the mission may call for the Spacelab module. The Spacelab module was built by the European Space agency. It fits into the cargo bay and can be accessed by a tunnel from the mid-deck of the crew compartment. It provides an environment in which the crew can work. The experiments will be in the areas of microgravity science, life science, space science, Earth science, engineering research and development, and commercial product development.
Because it is moving at about 17,000 mph, the orbiter will hit air molecules and build up heat from friction (approximately 3000 degrees). The orbiter is covered with ceramic insulating materials designed to protect it from this heat. The hot ionized gases of the atmosphere that surround the orbiter prevents radio communication with the ground for about 12 minutes.
After landing, the crew goes through the shutdown procedures to power down the spacecraft. This process takes about 20 minutes. Once the orbiter is powered down, the crew exits the vehicle.
