History Of Space Shuttle Engineering Essay

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Before man can walk on the moon, the space age started decades ago with aviation history that dated in the year 1903. Orville Wright, one of the Wright brothers took off for a mere distance of 120 feet in 12 seconds using the world's first ever powered, sustained, and controlled flight [1]. This was the start of aviation and rocket era. The modern rocketry era as we know it was started by three distinguish figures, Dr Robert Goddard, Hermann Oberth and Kanstantin Tsiolkovsky of Russia. Tsiolkovsky didn't invent any rockets in that matter but he did many of the priciples of astraunotics, designed suitable rockets and was known as the father of "Cosmonautics" in Russia [1]. He produces a lot of journals regarding the liquid propellant rockets, attainable velocities, fuel compositions and the oxygen suplly required for space travellers.

In 1926, Dr Robert Goddard launch the first liquid-powered rocket. The rocket was fuelled by liquid oxygen and gasoline and was able to reach 41 feet above the ground on its first flight. Before liquid oxygen is used as fuel, rockets back then were fuelled by solid fuels such as gunpowder. These solid fuels did not have the required power to launch a rocket high up into space. Besides changing the fuel type, Goddard later on came up with movable deflector vanes that was installed in a rocket exhaust nozzle for stability and steering. He also patented a design for multistage rocket, develop fuel pumps for liquid-rokcet motors, experimented with self-cooling and variable thrust motors, and also develop parachutes that automatically deployed for recovering his instrumental rockets [1].

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On october 3, 1942, the space age as we know it began with the succesful launch of the V-2 by the Germans that was led by Von Braun. The V-2 was invented as a weapon of war and not for science nor discovery. It was 46 foot long with a velocity of 3500 mph and could carry 1,650 pounds of explosive warheads to a range of 200 to 250 miles [1]. The Americans came up with Bell X-1, a military plane that was almost able to reach the speed of Mach 1 ( the speed of sound). Later on, a new version of that plane was created. By the year 1959, the X series had produces its crown jewel, the X-15 which can travel at four times the speed of sound and can fly up to the lower edge of space.

The Russian was able to beat the Americans in the race to space by launching one of their earth orbitting satellite, Sputnik I in october 1957. It shocked the world when beeping radio signal was send from the satellite that was circling the earth for a time of 90 minutes. Sputnik II was launch a few month after the succesfull launch of Sputnik I. Sputnik II has a different approach where inside it carried a dog name Laika. Laika was the first ever live organism that was launch to space. Despite dying when her oxygen supply depleted, the Russian scientist were able to understand the effects of weightlessness and space travel on living animals. The Americans soon followed by the launching of Explorer I, in 1958. Explorer was the first American satellite launch into space on board the Jupiter C rocket which was the version of Von Braun's Redstone.

The Space Shuttle

In 1957, the US Airforce conducted a series of classified studies on the next generation space transportation systems and concluded that semi-reusable designs were the cheapest source [2]. In 1968, NASA (National Aeronautics and Space Administration) came up with the ILRV (Integrated Launch and Re-entry Vehicle) and also studied the design of a spacecraft that could deliver a payload to orbit but also could return back to earth. During the administration of President Nixon, the Space Shuttle Development program was launched.

The space shuttle is an orbital sapcecraft designed for reuse with functions such as carrying payloads to Low Earth Orbit, provides a crew rotation system for the International Space station and also servicing the satellites. Other than that, the shuttle can retrieve satellites and other form of things from the orbit and bring them bcak to earth. The space shuttle has a life span of 10 years or equivalent to a 100 launches. For it to be able to accommadate large sized satellites and to meet the requirement of calssified USAF missions, the size and shape of the shuttle were the major factors in building the shuttle orbitter. Ech space shuttle composed of three main assemblies: the reuseable Orbitter Vehicle, the external tank and the two reusable solid rocket boosters [3].

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The orbiter vehicle is designed such that it looks like a conventional aircraft. Four evelons, which has a function like an elevator and also roll-on system was mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabalizer, with the body flap, control the orbiter during descent and landing [4]. A huge payload bay was installed in the orbiter comprimising most of the fuselage. The symetrical pahload doors hinged on each side of the bay comprimise its entire top. All of the payloads are inserted horizontally into the orbiter when its still on earth and will be offload vertically by robotics arms situated inside the bay when in a near-weightless environment. The orbiter structure is made out of primarily aluminium alloy, while its engine structure is made from titanium alloy. There are a lot of add-ons that can be put onto the orbiter depending on the mission. Those add-ons include Space laboratories, boosters for launching payloads further into space, Extended Duration Orbiter, Multi-pupose Logistics Modules and Canadam [4] a mechanical arm used to maneuver a payload from the payload bay [5].

The external tank of the Space Shuttle is to supply the liquid oxygen and also hydrogen fuel to the main engines [4]. Besides that, the external tank provides the attachment points for the solid rocket boosters and also the orbiter itself. This is the only part of the shuttle system that cannot be reuse. There are two solid rocket boosters attached to the shuttle lauch system. It will provide the shuttle with 12.5 million newtons of thrust at lift off [6]. The solid rocket boosters may be reused many times before it would be eventually been replace.

All of the spcae flights taken place was launch from the Kennedy Space centre. Before any launch, weather citeria has to be taken into consideration. The launch pad or along the flight path cannot have a tempreature above 37 degrees, any cloud cover must allow direct visual observation of the shuttle through 8,000 feet elevation and there must not be a 20% or greater chance of lightning within a 9km radius [7]. Eventhough the shuttle is made out of aluminium and can protect the electrical system, there is a possibilty of it to be struck by mlightning because during take off, the shuttle send out a long exhaucst plume taht can provide a current path to the ground. On the day of the launch, when the countdown is at T minus 9 minutes, the shuttle goes through its final preparations for launch, and the countdown is automatically controlled by the Ground Launch Sequencer, software at the launch Control Centre, which stops the count if it senses a critical problem with any of the shuttle on-board system [4]. At T minus 10 seconds, hydrogen igniters are activated under each engine bell to quell the stagnant gas inside the cones before ignition [4].If the gassses failed to burn, it can trip the onboard sensors and possibly create an overpressure and explosion of the shuttle during the firing phase. The main engine turbopumps also begin charging the combustion chambers with liquid hydrogen and liquid oxygen at this time [4]. The computers reciprocate this action by allowing the redundant computer systems to begin the firing phase [4]. At T minus 0 seconds, the shuttle's engine fired up and we have lift off.

After clearing the tower the shuttle begins a roll and pitch program to set its orbital ionclination so that the vehicle noe is belo the external tank and also the shuttle's rocket booster. When the shuttle reaches a point call Max Q, the level of aerodynamics forces is at its maximum, the main engine will temoprarily send it to reverse to avoid overspeeding and also oversteering the shuttle. At this moment, the shuttle is travelling at supersonic speed. 126 seconds after lift off, the explosive bolts that connects the boosters to the external tank will explode causing the SRB's to be pushed away from the shuttle.The parachutes will autimatically be deployed and lands in the ocean so that it can be reuse again. After the shuttle contnues its journey towards outerspace, it uses its main engine to gain and maintain the altitude while it accelerates horizontally towards the orbit. Finally, the last few seconds of the main engine burn, the mass of the shuttle i low enough that the engine mus be throttled back to limit the shuttle's acceleration for the comfort of the astraunut at 3g.

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While in orbit, the shuttle will perform numerous tasks. During the year 1980 and 1990, most of the task were space science missions on the onboard spacelab or lauching of various satellites and also science probes. Between 1990 and 2000, the focus shifted to repairing or servicing the space stations with fewer satellite launches. Usually a space mission will take up a couple of days to two weeks. This space exploration can be leghten by using the Extended Duration Orbiter add-on or jusy simply by attaching itself to the space station.

For re-entering the atmostphere and landing, it is normally perform by the onboard computer system or autopilot. But in the case of emergency, the shuttle can be flown manually. The re-entering procedures take place while the shuttle is being flown upside down, backside first, in the opposite direction to orbital motion for approximately three minutes. This reduces the shuttle's speed which will lower its orbital perigree down into the upper atmosphere. After that, the shuttle will be flipped over so that it is pushing its nose down. The shuttle will face different kind of air density throughout the re-entering process that requires it to perform a series of four steep S-shaped banking turns so that it will dissipates speed sideways rather than upwards. By the end of the last turn, the transition to an aircraft is almost completed. The shuttle then will level its wings, lower down its nose into a shallow dive and begins its approach to the landing site. Upon landing, parachute will be deployed to slower down the approaching shuttle. After landing, the vehicle stands on the runway for several minutes to permit the fumes from poisonous hydrazine to dissipate, and for the shuttle's fuselage to cool down before the astraunuts disembark. There are six shuttle that has been made throughout the years. They are, Enterprise, Columbia, Challenger, Discovery, Atlantis and Edeavour.

The Space Shuttle Challenger

On 28 January 1986, a few seconds after the launch of its shuttle, Challenger, the shuttle exploded and instantly killing all the seven crew members that was inside it. It was one of NASA's greatest tragedies after 25 flights since the Shuttle program. Before explaining what really happened on that tragic day, we take a look at the making of this shuttle.

Space Shuttle Challenger (OV-099) was NASA's second orbiter space shuttle after the Columbia. The Challenger's maiden flight was on April 4th 1983 and continued to be in service for another 9 missions before the fatefull crash. Challenger was named after its two previous vessels, first, HMS Challenger, a british corvette from the year 1872 to 1876 was the command ship for the "Challenger expedition", conducting pioneering global marine search [8], and second would be the Apollo 17 lunar module Challenger which landed on the moon in 1972 [8].

The Space Shuttle program decided to make a vehicle that later on could be converted to a flight vehicle because of the low production of orbiters. In order to prevent damage during structural testing, STA-099 a test vehicle was put through a qualification tests, where a factor of safety of 1.2 times the design limit loads were performed and also use the same test to validate computer models and compliances with the required 1.4 factor of safety shown by analys [8]. NASA's plan was to refit the prototype Enterprise as its secon vessel but however, design changes made for constructing the Columbia would have required extensive rework. So, NASA then decided that it would less expensive to convert the test vehicle STA-099 into the OV-099 (Challenger) rather than refitting the Enterprise. Other than that, fewer tiles of thermal protection system were put into the Challenger compared to its predecessor the Columbia. Most of the tile on the pay load bay doors, upper wing surface, and rear fuselage surface were replaced with DuPont white nomex felt insulation and this allows the Challenger to carry more payload [8]. An new head-up display system were installed for landing purposes.

After its maiden flight in 1983, the Challenger became NASA's number one spacecraft as it has flown far more missions per year than the Columbia. With the addtion of the Discovery and Atlantis to is fleet, NASA still uses the challenger as its main vessel, flying three missions from 1983 to 1985. For the 1986 mission, the Challenger were suppose to deploy the Ulysses probe with the Centaur (a rocket stage designed for use as the upper stage of space launch vehicle [9]) to study the polar regions of the Sun. Onboard the shuttle, the crew included the first ever American women, African-American, Canadian in space.

What Happened?

For a better understanding on what really happen on that tragic day, we take alook at hte various components of a space shuttle and how they work. The main components of the whole system is the orbiter, the reuseable, winged craft containing the crew and the payload. The two large Solid Rocket Boosters attached at the side of the External Tank generates a large enough thrust to send the orbiter and its payload to orbit. They are made from several segment containing solid fuel and is surrounded by metal casing [10]. These segments of the boosters are joined at a factory before being shipped to the Vehicle Assembly Building at NASA's Kenedy Space Station. During the shuttle assembly, two rubber O-rings are inserted at their field joints. Under the heat generated by the burning propellant within the boosters, these rubber seal expand to fill the field joints and prevent the hot exhaust from escaping [10].

Solid rockets are cheaper an less complex if compared to the one on the orbiter but they have a disadvantage. Once they are ignited, they cannot be throttled or turned off. They will continue to burn at full force until it ran out of fuel. At 150,000 feet, the SRBs will be disconnected from the shuttle. Then parachutes will be deployed so that the SRB will safely on the ocean bed and recovered by tugboats that will tow it bcak to shore for refurbishmnet and use for future launch. The purpose of the external tank, is to carry the liquid fuel needed by the three main engines located in the aft section of the Orbiter [10]. These engines are the one responsible for the Orbiter to reach the orbit. It is filled with two third liquid hydrogen and one third liquid oxygen. These cryogenically-cooled propellants are loaded onto the External Tank several hours before flight and during launch it is feed into the Orbitter to supply the three main engines [10].

According the theory published and heard, investigators said that neither the primary nor the secondary O-rings were properly sealed at the field joint of the right SRB. This is located near the lower strut connecting the SRB to the external tank. With the failure of the O-rings, it allowed massive tempreature at 3,315 degress celcius of exhaust gases from the rocket motor chamber to escape and led to other chain of events. Most of the sources cited that the air tempreature had drop to -8 degrees celcius the night before and 2 degrees celcius on the morning of the launch [10]. There were no flight attempt below 11 degrees celcius before this. The manufacturer of these boosters, Morton Thiokol, had insufficient data on how the boosters would react in low tempreature condition. There were a concern from the manufacturer's engineers on the day of the launch asking for it to be delayed, but many believes that the boosters can operate safely despite the low tempreature condition.

There are a few factors contributing to failure of the O-rings. The fist factor is that a stiff breeze blew past the shutlle's launch pad during the night an early morning preceeding the Challenger's launch [10]. The breeze causes the air to become super-cooled and descent towards the ground behind the External Tank because it passes the boosters that were already filled with cryogenic cooled liquid hydrogen and oxygen. This phenomenon was recorded from a photography service tower the night before. The passing of the wind in this matter is unlikely unusual because a wind passing through the External Tank is known to create a layer of ice even in warm tempreatures. But what was unusual about this case was the direction of the wind blowing. It resulted in super-cooled air descended directly into the lower portion of the right SRB. It was the Ice Team resposibilty to check the thickness of the ice formed using infra red cameras. They did recorded a -13 degrees celcius readings of the right SRB but the information didn't get to the engineers.. If the wind had blown in any other direction, the O-rings would be warmer and this dreadful event can be avoided.

Besides the factors that has been discuss, investigators found something else. Despite being super-cooled, the O-rings did their job well into the mission. It did partially failed at ignition emanating smoke from the aft field joint. These "blow-by" indicated that the joint wasn't sealed completely. There were no more "blow-by's" during the launch since the joint apparently sealed itself. The temporary seal was well remained intacted for almost a minute before the Challenger passed through the worst wind shear in history. The wind causes the booster to flex out and dislodged the aluminium oxide plug that had sealed the O-rings temporarily [10]. Soon after that, small flickering flame emerged. It continued to grow and became cought up in the aerodynamic flowfield of the accelerating shuttle. If the flame had been blown into any other direction, the Challenger's boosters might had made it until the booster separation sequence.

The liquid hydrogen tank began to leak as a direct result from the loss of preasure in the chamber. It then instantaneously vaporized into gas and could be seen by a cloud of vapour coming out of the External Tankk. This vapourized gas fed the flame from the right SRB. After a few seconds, the External Tank was disintegrating. The final break up of the shuttle started of with the lower struck that connects the right SRB gave way and allowed the booster to rotate around the upper attachment strut [10]. Then, vapor blooming pattern was formed at the bottom dome of the External Tank resulting in the entire aft dome dropping away from the rest of the tank and releases massive amounts of liquid hydrogen. Immidiately, the escaping liquid hydrogen and oxygen began to burn intensely and engulf the enitre space shuttle.

The momentum of the crew cabin, containing the seven astraunuts, carried it upward to an altitude of about 64,000 feet before it begab a balistic free-fall into the ocean [10]. Even though there were no solid evidence on what happened to the crew at the time, it is believed that the crew did survive the initial break up of the Challenger as it was experiencing only a 4g gravitational force for a short period. However, the electrical cicuits of the shuttle might had been damaged and indirectly cut off the oxygen supply in the cabin. Therefore the crew at that time was knocked unconcious. Whether it is tru or not, the huge impact that the cabin went through when crashing down the ocean surface would have killed all the crew instantly.

What can we learn from the disaster

There are a lot of things that can be learn from the Challenger disaster. New steps were taken to avoid this kind of incident from being happening. In any large or complex programs should have an overall risk management and assessment which includes a comprehensive method for identifying potential failure modes and hazards associated with the system, a specific quantitative methodology for identifying and assessing the safety risks of the system, and also amanagement process by which the safety risks can be brought to levels or values that are acceptable to the final approval authority [11]. With this program management, the organization such as NASA can achieve their goals by any means without comprimising the safety issues.

The system that is being made should have a System Safety Engineers at the organization headquarters and also the manufacturing side so that they will be involve in the designing, development, validation and also the qualification activities. With this, the engineers can produce an output on whether the system is qualified to get the safety certification to the program director. There are certain basic steps that NASA has put together for its risk management system [12] :

1. Identification of failure modes and effects

2. Establishment of design criteria for redundancy

3. Identification of hazards

4. identification of critical items

5. Evaluation on the probability of occurance

6. Establishment of safety level criteria

7. Design and certification test programs

8. Objective assessment of safety risk

9. Quantitative evaluation of flight data

10. Overall system safety risk assessment.

Besides the basic steps from NASA, the disaster could be avoided if the higher management would delay the launch. NASA had a big preasure put on them because the Challenger mission was delayed for a couple of time due to its inconsistency. The preasure was even greater when the first ever teacher would be flown into outer space was in their crew. She was also the first women to go into space. Public's demands was the cause that NASA couldn't afford to delay its launch as its integrity was on the line as it gets more coverage from television networks all around the world. For NASA, if this goes well, it means that they are looking at a brighter future as more funds are directed their way. Besides funding, NASA wanted to show the world that space travel is a thing that a normal (not trained) person can do by sending a teacher into space.

The O-ring was a known problem long before the disaster. But for some reason, all the flights precednig the Challenger's launch was a success. Despite knowing the problem, NASA's engineers insist on using it as a new method to overcome the problem would set them back a few months and would delay the launch. Other than that, new studies will require more funding, the one thing that NASA didn't have at that moment. From my point of view, if only the Ice Team reported what they had found by inspecting the SRBs, all of the seven crew members had the chance to live. Its their negligence towards their job cost the astraunouts their lives.