Physical Science

Physical Science

I have learned from my twenty years of service in the U. S. Air Force, significant background knowledge of the history of the space shuttle. In September 1969, two months after the first manned lunar landing, a Space Task Group appointed by the President of the United States to study the future course of U. S.

space research and exploration made the recommendation that “…the United States accept the basic goal of a balanced manned and unmanned space program.To achieve this goal, the United States should …develop new systems of technology for space operation…through a program directed initially toward development of a new space transportation capability…” According to Cox (1962), many responsible observers felt that we were devoting too many of our resources to increasing an already affluent volume of private consumption and too little for public services, including space-flight programs. In early 1970, NASA initiated extensive engineering, design, and cost studies of a space shuttle.These studies covered a wide variety of concepts ranging from a fully reusable manned booster and orbiter to dual strap-on solid propellant rocket motors and an expendable liquid propellant tank. Each concept evaluated development risks and costs in relation to the suitability and the overall economics of the entire system. On January 5, 1972, President Richard M.

Nixon announced that NASA would proceed with the development of a reusable low cost space shuttle system.NASA and its aerospace industry contractors continued engineering studies through January and February of 1972; finally on March 15, 1972, NASA announced that the shuttle would use two solid propellant rocket motors. The decision was based on information developed by studies that showed that the solid rocket system offered lower development cost and lower technical risk. On September 17, 1976, the first orbiter spacecraft, Enterprise, was rolled out. A total of thirteen test flights were performed. The Enterprise was built as a test vehicle and not equipped for space flight.

Five captive flights, with the Enterprise perched atop a 747 jumbo jet with no crew and unpowered, were conducted to test the structural integrity of the craft. Three crewed captive flights followed with the crew operating the flight control systems in preparation for the first orbiter free flight. Finally, five free flights occurred with an astronaut crew separating the orbiter from the 747 shuttle carrier and maneuvering to a landing at Edwards Air Force Base. For all of the captive flights and the first three free flights, the orbiter was outfitted with a tail cone covering its aft section to reduce aerodynamic drag and turbulence.

The final two free flights were made without the tail cone, and the three simulated space shuttle main engines and two orbital maneuvering system engines were exposed aerodynamically. After numerous tests across the United States, the Enterprise was ferried across the Atlantic for several air shows across Europe. Finally, on November 18, 1985, the Enterprise was ferried from Kennedy Space Center to Washington, D. C. and became the property of the Smithsonian Institution.

The second orbiter, Columbia, was the first to fly into space.Perched atop the 747 shuttle carrier, Columbia arrived at Kennedy Space Center from Dryden Flight Research Facility on March 25, 1979 to be readied for the space shuttle’s first flight on April 12, 1981. The space shuttle is launched in a vertical position, with thrust provided by two solid rocket boosters, called the first stage, and three space shuttle main engines, called the second stage. At liftoff, both the boosters and main engines are operating. To achieve orbit, the shuttle must accelerate from zero to a speed of almost 28,968 kilometers per hour (18,000 miles per hour), a speed nine times as fast as the average rifle bullet.

To travel that fast, it must reach an altitude above most of Earth’s atmosphere so that friction with the air will not slow it down or overheat it. The journey starts relatively slowly: at liftoff, the shuttle weighs more than 2. 04 million kilograms (4. 5 million pounds) and it takes eight seconds for the engines and boosters to accelerate the ship to 161 kilometers per hours (100 mph. ) But, by the time the first minute has passed, the shuttle is traveling more than 1,609 kilometers per hour (1,000 mph) and it has already consumed more than one and a half million pounds of fuel.

Rutondo (1994) emphasized that the craft should possess sufficient thrust to allow it to pass through the speed of sound as rapidly as possible During the first stage ascent I have learned that after about two minutes, when the shuttle is about 45 kilometers (28 miles) high and traveling more than 4,828 kilometers per hour (3,000 mph), the propellant in the two boosters is exhausted and the booster casings are jettisoned. They parachute into the Atlantic Ocean, splashing down about 225 kilometers (140 miles) off the Florida coast.The empty boosters — the largest solid rockets ever built — are recovered by special NASA ships to be eventually refilled with fuel and launched again. The solid fuel used by the boosters is actually powdered aluminum — a form of the same metal you find in foil wraps in your kitchen — with oxygen provided by a chemical called ammonium perchlorate.

After the main engines shut down, the shuttle is in an egg-shaped orbit that, if nothing changed, would cause it to re-enter the atmosphere above the Pacific Ocean, the same as what happens to the external fuel tank.But, about 35 minutes after the main engines have shut down, usually when the shuttle has reached the highest point of the egg-shaped orbit, the two orbital maneuvering system engines, located on the left and right side of the shuttle’s tail, are fired for about three minutes. The orbital maneuvering system engines use two propellants that automatically burn whenever they contact one another, and the three-minute firing circularizes the shuttle’s orbit at a safe altitude, one that will keep it above the atmosphere.The shuttle is the only spacecraft ever built that can retrieve large satellites from orbit and bring them back to Earth.

Using the Canadian-built robotic arm, called the Remote Manipulator System, mounted on the left-hand edge of the cargo bay, shuttle crews can move large objects into or out of the payload bay. The arm also can maneuver spacewalking astronauts into positions for satellite repairs and maintenance, as have been performed on the Hubble Space Telescope, or space construction, as is being conducted for the International Space Station.The largest shuttle crew ever flown, I have learned numbered eight people, but the average crew ranges from five to seven people. Crew members include pilot astronauts, called the commander and pilot who fly the shuttle, and mission specialist astronauts who are scientists and engineers trained to conduct the experiments onboard or perform specific tasks in orbit.

Occasionally, the crew also may include payload specialist astronauts in charge of the operations of a specific cargo. The shuttle can launch as much as 28,803 kilograms (63,500 pounds) of cargo into orbit.It has remained in orbit for as long as 17 days before returning to Earth. Eating, sleeping and personal hygiene equipment is located on the lower deck of the shuttle, called the middeck. The top deck, called the flight deck, is the shuttle cockpit, with flight controls located on both the front and back walls. A small lower “deck,” called the equipment bay, is inaccessible unless the floor panels of the middeck are lifted up.

This under-floor area houses avionics equipment, electronics equipment and a trash compartment. The crew cabin’s total pressurized volume is about 74. 3 cubic meters (2,625 cubic feet).The cabin includes a circular side hatch, about a meter (3 feet) in diameter that is used for entry and exit from the shuttle before launch and after landing. The shuttle’s airlock, used to seal spacewalkers off from the rest of the cabin and depressurize to begin an extravehicular activity, is located in the payload bay just aft of the main cabin and attached to the middeck by a short tunnel. An inner airlock hatch can be closed to seal the lock from the rest of the cabin.

An outer hatch can be opened to exit into space. The airlock’s volume is about 4. 24 cubic meters (150 cubic feet).A docking mechanism to attach to the International Space Station is located atop the airlock The three main engines of the space shuttle, in conjunction with the solid rocket boosters, provide the thrust to lift the orbiter off the ground for the initial ascent.

I have learned the main engines continue to operate for 8. 5 minutes after launch, the duration of the shuttle’s powered flight. After the solid rockets are jettisoned, the main engines provide thrust, which accelerates the shuttle from 4,828 kilometers per hour (3,000 mph) to over 27,358 kilometers per hour (17,000 mph) in just six minutes to reach orbit.They create a combined maximum thrust of more than 1.

2 million foot-pounds. I have learned that as the shuttle accelerates (it transforms into the worlds biggest gas guzzler), the main engines burn a half-million gallons of liquid propellant provided by the large, orange external fuel tank. The main engines burn liquid hydrogen — the second coldest liquid on Earth at minus 423 degrees Fahrenheit (minus 252. 8 degrees Celsius) — and liquid oxygen. The engines’ exhaust is primarily water vapor as the hydrogen and oxygen combine.

As the engines push the Shuttle toward orbit, I have learned they consume liquid fuel at a rate that would drain an average family swimming pool in less than 25 seconds generating over 37 million horsepower. Their turbines spin almost 13 times as fast as an automobile engine spins when it is running at highway speed. The main engines develop thrust by using high-energy propellants in a staged combustion cycle. The propellants are partially combusted in dual preburners to produce high-pressure hot gas to drive the turbo pumps. Temperatures in the main engine combustion chamber can reach as high as ,000 degrees Fahrenheit (3,315. 6 degrees Celsius).

Each space shuttle main engine operates at a liquid oxygen/liquid hydrogen mixture ratio of 6 to 1 to produce a sea level thrust of 179,097 kilograms (375,000 pounds) and a vacuum thrust of 213,188 (470,000 pounds). The engines can be throttled over a thrust range of 65 percent to 109 percent, which provides for a high thrust level during liftoff and the initial ascent phase but allows thrust to be reduced to limit acceleration to 3 g’s during the final ascent phase. The engines are gimbaled to provide pitch, yaw and roll control during the ascent.The solid rocket boosters (SRB) operate in parallel with the main engines for the first two minutes of flight to provide the additional thrust needed for the orbiter to escape the gravitational pull of the Earth. At an altitude of approximately 45 km (24 nautical miles), the boosters separate from the orbiter/external tank, descend on parachutes, and land in the Atlantic Ocean.

They are recovered by ships, returned to land, and refurbished for reuse. The boosters also assist in guiding the entire vehicle during initial ascent. Thrust of both boosters is equal to 5,300,000 lb.In addition to the solid rocket motor, the booster contains the structural, thrust vector control, separation, recovery, and electrical and instrumentation subsystems.

The solid rocket motor is the largest solid propellant motor ever developed for space flight and the first built to be used on a manned craft. The huge motor is composed of a segmented motor case loaded with solid propellants, an ignition system, a movable nozzle and the necessary instrumentation and integration hardware. I have learned each solid rocket motor contains more than 450,000 kg (1,000,000 lb. of propellant, which requires an extensive mixing and casting operation at a plant in Utah. The propellant is mixed in 600 gallon bowls located in three different mixer buildings.

The propellant is then taken to special casting buildings and poured into the casting segments. Cured propellant looks and feels like a hard rubber typewriter eraser. The combined polymer and its curing agent is a synthetic rubber. Flexibility of the propellant is controlled by the ratio of binder to curing agent and the solid ingredients, namely oxidizer and aluminum.The solid fuel is actually powdered aluminum—a form similar to the foil wraps in your kitchen—mixed with oxygen provided by a chemical called ammonium perchlorate. External Tanks The external tank, or ET, is the “gas tank” for the orbiter; it contains the propellants used by the space shuttle main engines.

The tank is also the “backbone” of the shuttle during the launch, providing structural support for attachment with the solid rocket boosters and orbiter. The tank is the only component of the space shuttle that is not reused.Approximately 8. 5 minutes into the flight, with its propellant used, the tank is jettisoned. At liftoff, the external tank absorbs the total (7.

8 million pounds) thrust loads of the three main engines and the two solid rocket motors. I have learned that when the solid rocket boosters separate at an altitude of approximately 45 kilometers (28 miles), the orbiter, with the main engines still burning, carries the external tank piggyback to near orbital velocity, approximately 113 kilometers (70 miles) above the Earth.The now nearly empty tank separates and falls in a preplanned trajectory with the majority of it disintegrating in the atmosphere and the rest falling into the ocean. The three main components of the external tank are an oxygen tank, located in the forward position, an aft-positioned hydrogen tank, and a collar-like intertank, which connects the two propellant tanks, houses instrumentation and processing equipment, and provides the attachment structure for the forward end of the solid rocket boosters.

The hydrogen tank is 2. times larger than the oxygen tank but weighs only one-third as much when filled to capacity. The reason for the difference in weight is that liquid oxygen is 16 times heavier than liquid hydrogen. The skin of the external tank is covered with a thermal protection system that is a 2.

5-centimeter (1-inch) thick coating of spray-on polyisocyanurate foam. The purpose of the thermal protection system is to maintain the propellants at an acceptable temperature, to protect the skin surface from aerodynamic heat and to minimize ice formation.The external tank includes a propellant feed system to duct the propellants to the orbiter engines, a pressurization and vent system to regulate the tank pressure, an environmental conditioning system to regulate the temperature and render the atmosphere in the intertank area inert, and an electrical system to distribute power and instrumentation signals and provide lightning protection. The tank’s propellants are fed to the orbiter through a 43-centimeter (17-inch) diameter connection that branches inside the orbiter to feed each main engine.I have learned the cockpit, living quarters and experiment operator’s station are located in the forward fuselage of the orbiter vehicle. Payloads are carried in the mid-fuselage payload bay, and the orbiter’s main engines and maneuvering thrusters are located in the aft fuselage.

The cockpit, living quarters and experiment operator’s station are located in the forward fuselage. This area houses the pressurized crew module and provides support for the nose section, the nose gear and the nose gear wheel well and doors. The 65. -cubic-meter (2,325-cubic-foot) crew station module is a three-section pressurized working, living and stowage compartment in the forward portion of the orbiter.

It consists of the flight deck, the middeck/equipment bay and an airlock. Outside the aft bulkhead of the crew module in the payload bay, a docking module and a transfer tunnel with an adapter can be fitted to allow crew and equipment transfer for docking, Space lab and extravehicular operations. The two-level crew module has a forward flight deck with the commander’s seat positioned on the left and the pilot’s seat on the right.The flight deck I have learned is designed in the usual pilot/copilot arrangement, which permits the vehicle to be piloted from either seat and permits one-man emergency return. Each seat has manual flight controls, including rotation and translation hand controllers, rudder pedals and speed-brake controllers.

The flight deck seats four. The on-orbit displays and controls are at the aft end of the flight deck/crew compartment. The displays and controls on the left are for operating the orbiter, and those on the right are for operating and handling the payloads.More than 2,020 separate displays and controls are located on the flight deck.

According to The Encyclopedia Americana International Edition, Vol 25, (1998), the shuttle’s crew uses five independent computers to monitor and control the various systems of the shuttle. Virtually every moment of the shuttle’s flight—certainly those in which the craft or any of its systems under-goes a change or a maneuver—requires the skilled operation of the crew working in efficient coordination with the computerized controls.Six pressure windshields, two overhead windows and two rear-viewing payload bay windows are located in the upper flight deck of the crew module, and a window is located in the crew entrance/exit hatch located in the midsection, or deck, of the crew module. The middeck contains provisions and stowage facilities for four crew sleep stations. Stowage for the lithium hydroxide canisters and other gear, the waste management system, the personal hygiene station and the work/dining table is also provided in the middeck.

The nominal maximum crew size is seven.The middeck can be reconfigured by adding three rescue seats in place of the modular stowage and sleeping provisions. The seating capacity will then accommodate the rescue flight crew of three and a maximum rescued crew of seven. The airlock provides access for spacewalks, known as extravehicular activity, or EVA.

It can be located in one of several places: inside the orbiter crew module in the middeck area mounted to the aft bulkhead, outside the cabin also mounted to the bulkhead or on top of a tunnel adapter that can connect the pressurized Spacehab module with the orbiter cabin.A docking module can also serve as an EVA airlock. The airlock contains two spacesuits, expendables for two six-hour payload EVAs and one contingency or emergency EVA, and mobility aids such as handrails to enable the crew to perform a variety of tasks. The airlock allows two crewmen room for changing spacesuits. I have learned that in addition to forming the payload bay of the orbiter, the midfuselage supports the payload bay doors, hinges and tiedown fittings, the forward wing glove and various orbiter system components. Each payload bay door supports four radiator panels.

When the doors are opened, the tilting radiators are unlatched and moved to the proper position. This allows heat radiation from both sides of the panels, whereas the four aft radiator panels radiate from the upper side only. Some payloads may not be attached directly to the orbiter but to payload carriers that are attached to the orbiter. The inertial upper stage, pressurized modules or any specialized cradle for holding a payload are typical carriers. The Remote Manipulator System, or RMS, is a 15. 2-meter (50-foot) long articulating arm remotely controlled from the flight deck of the orbiter.

The elbow and wrist movements permit payloads to be grappled for deployment out of the payload bay or retrieved and secured for return to Earth. I have learned a television camera and lights near the outer end of the arm permit the operator to see on television monitors what his hands are doing. In addition, three floodlights are located along each side of the payload bay. The aft fuselage consists of the left and right orbital maneuvering systems, space shuttle main engines, body flap, vertical tail and orbiter/external tank rear attachments. The forward bulkhead closes off the aft fuselage from the idfuselage.

The upper portion of the bulkhead attaches to the vertical tail. The internal thrust structure supports the three space shuttle main engines, low-pressure turbopumps and propellant lines. I have learned the US Space Shuttle program is an important step toward the construction and operation of a space station and toward the development of a “space plane” system allowing such a vehicle to take off or be launched into space and return, completely intact and reusable, with minimal increase in g-force and with a high degree of safety and reliability.Works Cited Donald Cox (1962). The Space Race. Chilton Company Publishers, Philadelphia & New York Louis Rotundo (1994).

Into The Unknown. Smithsonian Institution Press, Washington & London The Encyclopedia Americana International Edition, Vol 25, (1998), Grolier Incorporated, Connecticut