INTRODUCTION A hundred years ago, on December 17, 1903, Wilbur and Orville Wright successfully achieved a piloted, powered flight. Though the Wright Flyer I flew only 10 ft off the ground for 12 seconds, traveling a mere 120 ft, the aeronautical technology it demonstrated paved the way for passenger air transportation. Man had finally made it to the air. The Wright brother’s plane of 1903 led to the development of aircrafts such as the WWII Spitfire, and others. In 1926 the first passenger plane flew holiday makers from American mainland to Havana and Bahamas. In 23 years the world had moved from a plane that flew 120 ft and similar planes that only a chosen few could fly, to one that can carry many passengers. Today air travel is worth billions. The military has produced planes for special purposes like SR-71 for high speed and high altitude flying, F-117 Nightbird the stealth fighter, and other world class dogfighters like Russian Sukhoi 37, French Mirage, British Harriers, and American F22 Raptor. In October 1957, man entered the space age. Russia sent the first satellite, the Sputnik, and in April 1961, Yuri Gagarin became the first man on space. In the years since Russia and United States has sent many air force pilots and a fewer scientists, engineers and others. But even after almost 50 years, the number of people who has been to space is close to 500. The people are losing interest in seeing a chosen few going to space and the budgets to space research is diminishing. The space industry now makes money by taking satellites to space. But a major factor here is the cost. At present to put a single kg into orbit will cost you between $10000 and $20000. This is clearly prohibitively high and a major objective for the coming years is to drop the cost to a fraction of today's value. Despite the fact that the space shuttle has regularly gone into orbit over the last two decades there is still no tourist business. This is due to the fact that to build an orbital hotel under present conditions will cost 100's of billions of dollars (at least). It is clear why there has been so little progress in orbital developments. The development of a plane which can fly to space at lower cost, which is reusable and can take more payloads, is very much required for further development of space industries. The Reusable Launch Vehicle, usually called Spaceplane or Hyperplane which can take crew and payload into orbit is being developed by various space agencies and private companies. The Spaceplane would make space travel cheap and will help in increasing space tourism and just like in the aviation industry, within a few decades, the space tourism industries would be worth billions. The Advantages The rockets which take satellites and other payloads have to carry the fuel and oxidizer with them as it uses conventional rocket engines. The combined weight of the fuel and oxidizer is very large due to the fact that a lot of energy is expended pushing the plane forwards. This is why today's rockets launch vertically as it maximizes the rocket's potential by allowing all the energy expended to be focused in the direction we want to go - upwards. With present technology it is the easiest and cheapest method of reaching space. Clearly then the way forward is to utilize jet engines in some manner. The main advantages of jet engines over rocket engines are that they do not need to carry their own oxidizer; instead they suck in air and use the oxygen present in the air as their oxidizer. This will greatly remove the need to carry oxidizer, as it will only be needed when at an altitude that the air contains insufficient oxygen for jets to operate. At this point the rocket engines will fire and burn the much smaller quantity of onboard oxidizer. This will dramatically reduce the take-off weight and also the cost of the craft. Reduction in take-off weight means the payload can be increased. Further to this the use of jet engines will make a substantial saving on the expensive rocket fuel. As a comparison to produce the same thrust, jet (air-breathing) engines require less than one seventh the propellants (fuel + oxidizer) that rockets do. For example, the space shuttle needs 143,000 gallons of liquid oxygen, which weighs 1,359,000 pounds (616,432 kg). Without the liquid oxygen, the shuttle weighs a mere 165,000 pounds (74,842 kg). Another advantage of jet-engine craft is that as they rely on aerodynamic forces rather than on rocket thrust, they have greater maneuverability, which in turn provides better flexibility and safety, for example missions can be aborted mid-flight if there is a problem. This is not the case for staged vehicles, which typically have complex "range safety" requirements as the stages detach and fall back to earth. Range safety is one of the main reasons that the US launches from Florida, where the rocket's flight path takes it out over open water almost immediately. The lack of such abort modes on the Shuttle requires incredible failure avoidance costs and massive overhauls. The space shuttle used by NASA is partially reusable. It still has to take off vertically with the help of multistage rocket and solid boosters. The use of rockets increases the cost of manufacturing parts for each launch as some rocket parts are not reusable. Further more, using rockets increases the amount of fuel and oxidizer required. Some of the components of the rocket get added to the space debris and continue orbiting the earth. This causes unwanted collisions with other debris or satellites. Thus using a jet-engine craft as a reusable launch vehicle is faster, efficient, and has increased affordability, flexibility and safety for ultra high-speed flights within the atmosphere and into Earth orbit. The Different Proposals Today three main concepts are being proposed. The difference is in way the RLV is launched. This difference results in differing levels of complexity in design. The major concepts are… Two Stage To Orbit (TSTO) This is the easiest method; firstly a large aeroplane takes off carrying a smaller rocket engine craft (called the orbiter) and reaches a fairly high altitude. Then the smaller craft launches from the carrier and as it is already at high altitude before firing its engines, the need for fuel is minimized. It also means that the wings on the orbiter can be made smaller. There is no doubt that this option certainly creates less engineering problems. This type of technology was around in the 1960's and was used during the testing of the X-15. One and a Half Stage To Orbit (OHSTO) There are various 'One and a Half Stages' ideas that are certainly innovative ideas and deserve mention. The most promising is that of mid-air fuelling, taking on the fuel and oxidizer for space once at a high altitude. These ideas do not overcome the problems of commercially viability that the 2-stage models suffer from; however it could be a good temporary measure. Single Stage To Orbit (SSTO) It is a reusable launch vehicle (RLV) that takes off and lands horizontally like a conventional plane. It is generally regarded that this method will be more efficient and safer than the 2-stage model, though that is not to belittle the 2-stage method which would be a considerable improvement on the vertical take off craft of today. It is also felt that while the 2-stage idea would be easier, the 1-stage would almost certainly be more commercially viable and would achieve a higher level of success in the objectives of a spaceplane. What is required here is further development of jet engines. The only possibility at the moment is ramjet working together with scramjet (Supersonic Combustion Ramjet). The major problem is that the scramjets are far from fully developed, offering many difficult aerodynamic problems. These, however, offer the only current hope of sustained hypersonic flight. Even with the advance of scramjet development there are still many problems to be addressed with horizontal take off of spaceplanes. This is because a Scramjet will only function at hypersonic speeds and a ramjet will only function at supersonic speeds. The design will therefore require: 1. A turbojet, once the air intake reaches to mach 1 (supersonic speed) the ramjet would fire. 2. The ramjet would accelerate the plane to about mach 4 (hypersonic speed) then the scramjet would fire. 3. The scramjet is expected to be able to reach speeds of mach 15, when finally the rocket engine would fire. 4. The rocket engine would accelerate the plane to mach 25 (escape velocity) and would be used in space operations. While this sounds very good in theory, in practice it is very doubtful whether such vehicles will have the efficiency to reach orbit, due to the excessive weight and complexity of such a system. Further to this such a design will not solve the other problem of heat build-up. These problems have not, however, removed the interest in this system and several proposals are currently being tested by NASA. What we are really looking for is the development of a combined jet engine that operates across the range, with maybe a switch to a rocket engine for the last stage and for space operations. The difficulties of designing a jet engine to perform at these levels are such that it can not even be seen how it could be done with present technology. The differences between the engines are how they physically take the air in. Nanotechnology could solve the problem by allowing the engine to reshape itself in flight, whether it could be shaped fast enough remains to be seen. Working The working of a RLV can be divided into 4 stages 1. First stage – subsonic and supersonic stage: The RLV with its payload takes off from the runway and climbs to about 100,000 feet or 30km using conventional jet-engines, or using a combination of conventional jet- engine and ramjet engine, or using another plane to carry or pull the plane to a lower height and using a booster rocket. A ramjet operates by subsonic combustion of fuel in a stream of air compressed by the forward speed of the aircraft. It doesn’t have or use very less moving parts compared to a conventional jet-engine with thousands of moving parts. The compression of air before burning of fuel is done in the ramjet by the addition of a diffuser at the inlet, while it is done by the turbine in conventional jet-engine. The flow of air is subsonic. The plane is accelerated to a speed of mach 4 or mach 5 and the flow inside the engine becomes supersonic. Then the scramjet is powered up. 2. Second stage - Hypersonic stage: When the spaceplane is at an altitude of about 100,000 ft and at a velocity of about mach 4, the scramjets are fired. Scramjets are basically ramjets. They introduce fuel and mix it with oxygen obtained from the air which compressed for combustion. The air is naturally compressed by the forward speed of the vehicle and the shape of the inlet, similar to what turbines or pistons do in slower-moving airplanes and cars. Rather than using a rotating compressor, like a turbojet engine does, the forward velocity and aerodynamics compress the air into the engine. Hydrogen fuel is then injected into the air stream, and the expanding hot gases from combustion accelerate the exhaust air to create tremendous thrust. While the concept is simple, proving the concept has not been simple. At operational speeds, flow through the scramjet engine is supersonic - or faster than the speed of sound. At that speed, ignition and combustion take place in a matter of milliseconds. This is one reason it has taken researchers decades to demonstrate scramjet technologies, first in wind tunnels and computer simulations, and only recently in experimental flight tests. The Scramjet engine takes the RLV to even greater heights and to speeds of up to Mach 15. This is the fastest speed an air breathing plane can go using current technologies. At Mach 15, the RLV is at a great height that there isn’t enough oxygen to sustain the scramjet engine. At this point the rocket engine fires up. 3. Third stage - Space stage: When the rocket engine fires by mixing oxygen from the onboard storage tanks into the scramjet engine, thereby replacing the supersonic airflow. The rocket engine is capable of accelerating the RLV to speeds of about Mach 25, which is the escape velocity. It takes the RLV into orbit. The rocket engine takes the RLV to the payload release site and the required operations are done. Once this is over it enters its last stage – the re-entry stage. 4. Fourth stage – Re-entry stage: Once the RLV finishes its mission in space, It performs de-orbit operations, including firing its thrusters to slow itself down, thereby dropping to a lower orbit and eventually entering the upper layers of the atmosphere. As the vehicle encounters denser air, the temperature of the ceramic skin builds to over 1,000 degrees C, and is also cooled by using any remaining liquid hydrogen fuel. It is here that the structure of the plane undergoes heavy thermal stress. If the heat shields do not protect the plane, it would simply burn off to the ground, just like the space shuttle Columbia. It enters a radio silence zone as due to the heat, radio contact is lost. Once it reaches dense air, it can use its aerodynamics to glide down to the landing strip. It can also use any remaining fuel to fire the ramjet or conventional jet (depends on the design) and change its course. Once on the landing strip it engages it slows down using a series of parachutes and engages the brake. CONSTRUCTION The construction of a true RLV that can take a payload to space is still in the design stage. It will sure have lot of designs taken from the space shuttle. Here are the main construction details. Body: The body of a RLV has to withstand very high stresses including thermal stresses during re-entry. The plane expands due to the high heat of nearly 1500˚C or more. It also has to cope with the rapid change in temperatures once in space. It changes from -250 degrees in the shade to 250 degrees in direct sunlight. This change in temperature between two sides of the same plane will put a lot of stress on its body. Titanium alloys are being used, being very strong and light. To cope with the high temperatures developed in parts of the wing and fuselage of the spacecraft today, reinforced carbon-carbon composite material is being added to the leading edges of the vehicle's nose and wings to handle the higher temperatures. Researches are being conducted to find the best materials for different parts of the plane. One of these materials, γ-TiAl (Titanium Aluminide), has superior high-temperature material properties. Its low density provides improved specific strength and creep resistance in comparison to currently used titanium alloys. However, it is inherently brittle, and long life durability is a potential problem along with the material’s sensitivity to defects. Wings: The wing of the spacecraft has to be designed so that it provides enough lift to fly to space and also reduce the friction during re-entry. Cockpit: The cockpit is the place where the astronauts will stay most of the time during the journey. It will have many windows, which are special double-paned glass, and each pane alone can withstand the pressure and force of flight and the vacuum. This doubling up ensures that if either window were to crack, the passengers would still be safe. The air inside the cockpit is made breathable by a three-part system. Breathable air is added at a constant rate by oxygen bottles. The exhaled carbon dioxide is removed from the cabin by an absorber system, and humidity is controlled by an additional absorber created to remove water vapor from the air. During the entire flight, the cockpit remains comfortable, cool and dry. The avionics system and display unit for navigating has to be computer controlled and free from bugs. It should give the pilot all the necessary data to make his choices. The avionics are very critical, and it also needs to be very precise for the pilot to do what he wants to do, and do it well. Electric Power: The electrical power required for the running of the spacecraft has to be taken from batteries. These batteries could be charged, if needed by using solar energy. Researches are being initiated to find better and reliable batteries, like the lithium-based (i.e., Li metal or Li-ion intercalation compound as negative electrode), polymer electrolyte regenerative battery system. Its advantages include reduced battery weight and volume, relative to conventional Ni-Cd and Ni-H2, which permits greater payloads and greater cell voltage, 3.5 volts vs. 1.2 volts, which permits use of fewer cells and results in reduced battery system complexity. Controls: When we're out in space, all you need to do is release a puff of air in a direction to give you a reaction force to push you the other way. That is called a reaction control system. High-pressure air is stored in bottles on the ship, and on the release of a little blast of air for about one second, for example, with the right wing tip pointing up. And that is enough when you're in space to push that wingtip down. It effectively rolls the aircraft, and that are the controls when it is out in space. Fuels: Many challenges have been overcome recently by the discovery and synthesis of propellants that can have higher performance than traditional O2/H2, and aircraft fuels. These propellants include high-density monopropellants for sounding rockets and upper stages, and onboard propulsion for small spacecraft. Higher energy fuels, such as N4, N6, BH4, and others, have a longer range development time and would be more applicable to future launch vehicles. Reusable Launch Vehicles The X-43 Hyper-X from NASA Hyper-X, NASA's multi-year hypersonic flight research program, seeks to overcome one of the greatest aeronautical research challenges - air-breathing hypersonic flight. Far outpacing contemporary aircraft of supersonic capability, three X-43A vehicles were built to fly at speeds of Mach 7 and 10. Ultimately, the revolutionary technologies exposed by the Hyper-X Program promise to increase payload capacities and reduce costs for future air and space vehicles. MicroCraft, Inc. of Tullahoma, Tenn., is the industry partner chosen by NASA to construct the X-43 vehicles. The contract award announcement occurred on March 24, 1997, with construction of the vehicles beginning soon thereafter. Orbital Sciences Corporation's Launch Vehicles Division in Chandler, Ariz. will construct the Hyper-X launch vehicles. The goal of the Hyper-X program is to flight validate key propulsion and related technologies for air-breathing hypersonic aircraft. The first X-43 was scheduled to fly at Mach 7. This is far faster than any air-breathing aircraft have ever flown. The world's fastest air-breathing aircraft, the SR-71, cruises slightly above Mach 3. The highest speed attained by NASA's rocket-powered X-15 was Mach 6.7, back in 1967. Hyper-X research began with conceptual design and wind tunnel work in 1996. Three unpiloted X- 43A research aircraft were built. Each of the 12-feet long, 5- feet-wide lifting body vehicles was designed to fly once. They are identical in appearance, but engineered with slight differences that simulate variable engine geometry, generally a function of Mach number. The first and second vehicles were designed to fly at Mach 7 and the third at Mach 10. At these speeds, the shape of the vehicle forebody serves the same purpose as pistons in a car, compressing the air as fuel is injected for combustion. Gaseous hydrogen fuels the X-43A. The first flight attempt in June 2001 failed when the booster rocket went out of control and the booster rocket and X-43A combination—was destroyed by ground controllers. The second attempt at Mach 7, in March 2004, was highly successful. At Mach 6.8—or almost seven times the speed of sound—the X-43A research vehicle was traveling nearly 5,000 mph during the March 2004 flight, easily setting a world speed record for a jet-powered (air- breathing) vehicle. Guinness World Records has recognized the accomplishment The tricky part in the development of this technology is that as the air is in the tube remains for mere milliseconds, getting such details as the fuel-air mixture right, is still very difficult. And the fact that what is right is different at different velocities makes the problem more complicated. The big challenge of designing a ―variable geometry engine‖ (as the professionals call it), which will be able to accommodate these differences, has not yet been still solved by engineers. So, for simplicity, the flights of the X-43A didn’t have to accelerate under its own power. Instead, it was carried by a booster rocket to the required speed and altitude. On 16 November, 2004, NASA's unmanned Hyper-X (X-43A) aircraft reached Mach 9.6. The X-43A was boosted to an altitude of 33,223 meters (109,000 feet) by a Pegasus rocket launched from beneath a B52-Bomber jet aircraft, which had taken off from Edwards Air Force Base in California in the U.S. Then the booster rocket lofted it to a height of 33,223 meters (109,000 feet). Thereafter the booster separated and the scramjet was ignited. Moments later the scramjet fired for about 10 seconds and the craft while flying on its own at about 7000 miles/hour (using its own gaseous hydrogen fuel) conducted a series of high speed maneuvers, before gliding away and crashing into the Pacific Ocean. The SpaceShipOne from SCALED COMPOSITES LLC The SpaceShipOne is a RLV built by the company Scaled Composites LLC for competing in the X – Price. The Ansari X Prize is a contest that promised a cash prize of $10 million to the first registered team to: Build a spaceship able to carry three adults (height up to 188 centimeters [6 feet, 2 inches] and weight up to 90 kilograms [198 pounds] each). Launch the spaceship with three soon-to-be astronauts to a height of 100 kilometers (62.5 miles), the internationally recognized altitude at which sub- orbital space begins. Return the spaceship to Earth safely -- no broken bones on the astronaut, no severe damage to the ship, etc. Repeat the flight within two weeks using the same ship, having replaced no more than 10 percent of the ship's parts (with the exception of fuel), thus classifying the spacecraft as a Reusable Launch Vehicle (RLV). Do it all without any government funding, using only private financing. The company designed and built another jet aircraft which would carry the SpaceShipOne to a height of about 50,000 feet. This turbofan powered aircraft, called the White knight takes off like a plane from a normal airstrip, with SpaceShipOne attached to its belly. The two ships fly together under White Knight's power to a predetermined altitude. Then White Knight releases SpaceShipOne and drifts away. Once clear of White Knight, SpaceShipOne begins its journey to sub-orbital space. The White Knight was designed with a high thrust-to-weight ratio and powerful speed brakes. These features help to simulate space flight maneuvers. On October 4th 2004, the SpaceShipOne flew to take the $10 million price. It was timed partially to coincide with the 47th anniversary of the Soviet launch of Sputnik. When the SpaceShipOne is released, it glides for about 10 seconds while the pilot sets up the aircraft for the rocket boost and he throws the switch, and the hybrid rocket motor in the SpaceShipOne accelerates the aircraft. The hybrid rocket motor has combined elements from both solid and liquid rocket motors. This makes for a unique motor capable of accelerating SpaceShipOne to twice the speed of sound. SpaceShipOne is propelled by a mixture of hydroxy-terminated polybutadiene (tire rubber) and nitrous oxide (laughing gas). The rubber acts as the fuel and the laughing gas as the oxidizer. The pilot immediately commences a pullout maneuver to go straight up. The ship continues to accelerate going straight out for a little over a minute. It flies for about one minute, straight up and then burn out about 150,000 feet, roughly. The motor stop burning at that point, but now the ship is moving over 2,000 miles per hour, straight out, and so it coasts. From there it coasts up another 150,000 feet roughly, up until it reaches apogee (the point at which SpaceShipOne is farthest from Earth). The pilot feels Zero g or weightlessness for some time at the topmost point. Then it falls back to earth. The pilot makes changes to the aerodynamics and the spacecraft slows down. It then glides down to the landing strip. In addition to meeting the altitude requirement to win the X-Prize, pilot Brian Binnie also broke the August 22, 1963 record by Joseph A. Walker, who flew the X-15 to an unofficial world altitude record of 354,200 feet. Brian Binnie's SpaceShipOne flight carried him all the way to 367,442 feet or 69.6 miles above the Earth's surface. Conclusion The recent development in the field of scramjets, hyperplanes, and truly Reusable Launch Vehicle will result in the development of space tourism. This advancement of technology helps us to understand more about science and also helps us to improve our life. In 1927, hotel magnate Raymond Orteig's announced an aviation contest, a price of $25,000 to be awarded to the first man to build and fly an airplane non-stop from New York to Paris. As a result of the successful flight of Charles Lindbergh's, in the United States: The number of airline passengers increased by 167,623 between 1926 and 1929. The number of pilot's license applications increased by 300 percent in 1927. The number of licensed aircraft increased by 400 percent. The number of airports doubled within three years. Once this technology will be common, people will start their pursuit towards even better technologies. Only time will tell if the Ansari X Prize will have a similar effect on the burgeoning sub-orbital flight industry as the 1927 $25,000 Orteig's price did. References 1. http://www.nasa.gov/missions/research/x43-main.html Official site of NASA X-43 spaceplane. 2.http://www.thespacesite.com/space/future/spaceplane.php Contains basic information about the Reusable Launch Vehicles and current projects. 3.http://trc.dfrc.nasa.gov/Newsroom/FactSheets/FS-040- DFRC.html Contains facts about the NASA X-43 Hyper-X plane. 4.http://trc.dfrc.nasa.gov/Gallery/Movie/Hyper- X/index.html Contains motion pictures of the X-43 . 5.http://trc.dfrc.nasa.gov/Gallery/Photo/X-43A/index.html Contains images of the X-43 spaceplane. 6.http://science.howstuffworks.com/x-prize.htm For details about X-Price. 7. http://www.lerc.nasa.gov/WWW/RT1999/intro/contents.html For advance papers on space research 8.http://www.scaled.com/index.htm For information on SpaceShipOne.
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