Rockets
Today's rockets are remarkable collections of human ingenuity that have their roots in the science and technology of the past. They are natural outgrowths of literally thousands of years of experimentation and research on rockets and rocket propulsion.
One of the first devices to successfully employ the principles essential to rocket flight was a wooden bird. The writings of Aulus Gellius, a Roman, tell a story of a Greek named Archytas who lived in the city of Tarentum, now a part of southern Italy. Somewhere around the year 400 B.C., Archytas mystified and amused the citizens of Tarentum by flying a pigeon made of wood. Escaping steam propelled the bird suspended on wires. The pigeon used the action-reaction principle, which was not stated as a scientific law until the 17th century.
About three hundred years after the pigeon, another Greek, Hero of Alexandria, invented a similar rocket-like device called an aeolipile. It, too, used steam as a propulsive gas. Hero mounted a sphere on top of a water kettle. A fire below the kettle turned the water into steam, and the gas traveled through pipes to the sphere. Two L-shaped tubes on opposite sides of the sphere allowed the gas to escape, and in doing so gave a thrust to the sphere that caused it to rotate.
Just when the first true rockets appeared is unclear. Stories of early rocket like devices appear sporadically through the historical records of various cultures. Perhaps the first true rockets were accidents. In the first century A.D., the Chinese reportedly had a simple form of gunpowder made from saltpeter, sulfur, and charcoal dust. To create explosions during religous festivals, they filled bamboo tubes with a mixture and tossed them into fires. Perhaps some of those tubes failed to explode and instead skittered out of the fires, propelled by the gases and sparks produced by the burning gunpowder.
The Chinese began
experimenting with the gunpowder-filled tubes. At some point, they attached
bamboo tubes to arrows and launched them with bows. Soon they discovered that
these gunpowder tubes could launch themselves just by the power produced from
the escaping gas. The true rocket was born. The date reporting the first
use of true rockets was in 1232. At this time, the Chinese and the Mongols were
at war with each other. During the battle of Kai-Keng, the Chinese repelled the
Mongol invaders by a barrage of "arrows of flying fire." These fire-arrows were
a simple form of a solid-propellant rocket. A tube, capped at one end, contained
gunpowder. The other end was left open and the tube was attached to a long
stick. When the powder was ignited, the rapid burning of the powder produced
fire, smoke, and gas that escaped out the open end and produced a thrust. The
stick acted as a simple guidance system that kept the rocket headed in one
general direction as it flew through the air. It is not clear how effective
these arrows of flying fire were as weapons of destruction, but their
psychological effects on the Mongols must have been formidable.
Following the battle of Kai-Keng, the Mongols produced rockets of their own and may have been responsible for the spread of rockets to Europe. All through the 13th to the 15th centuries there were reports of many rocket experiments. In England, a monk named Roger Bacon worked on improved forms of gunpowder that greatly increased the range of rockets. In France, Jean Froissart found that more accurate flights could be achieved by launching rockets through tubes. Froissart's idea was the forerunner of the modern bazooka. Joanes de Fontana of Italy designed a surface-running rocket-powered torpedo for setting enemy ships on fire.
By the 16th century rockets fell into a time of disuse as weapons of war, though they were still used for fireworks displays, and a German fireworks maker, Johann Schmidlap, invented the "step rocket," a multi-staged vehicle for lifting fireworks to higher altitudes. A large sky rocket (first stage) carried a smaller sky rocket (second stage). When the large rocket burned out, the smaller one continued to a higher altitude before showering the sky with glowing cinders. Schmidlap's idea is basic to all rockets today that go into outer space.
Nearly all uses of rockets up to this time were for warfare or fireworks, but there is an interesting old Chinese legend that reported the use of rockets as a means of transportation. With the help of many assistants, a lesser-known Chinese official named Wan-Hu assembled a rocket- powered flying chair. Attached to the chair were two large kites, and fixed to the kites were forty- seven fire-arrow rockets.
On the day of the flight, Wan-Hu sat himself on the chair and gave the command to light the rockets. Forty-seven rocket assistants, each armed with torches, rushed forward to light the fuses. In a moment, there was a tremendous roar accompanied by billowing clouds of smoke. When the smoke cleared, Wan-Hu and his flying chair were gone. No one knows for sure what happened to Wan-Hu, but it is probable that if the event really did take place, Wan-Hu and his chair were blown to pieces. Fire-arrows were as apt to explode as to fly.
During the end of the 18th century and early into the 19th, rockets experienced a brief revival as a weapon of war. The success of Indian rocket barrages against the British in 1792 and again in 1799 caught the interest of an artillery expert, Colonel William Congreve. Congreve set out to design rockets for use by the British military.
The Congreve rockets were highly successful in battle. Used by British ships to pound Fort McHenry in the War of 1812, they inspired Francis Scott Key to write "the rockets' red glare," words in his poem that later became The Star- Spangled Banner.
Even with Congreve's work, the accuracy of rockets still had not improved much from the early days. The devastating nature of war rockets was not their accuracy or power, but their numbers. During a typical siege, thousands of them might be fired at the enemy. All over the world, rocket researchers experimented with ways to improve accuracy. An Englishman, William Hale, developed a technique called spin stabilization. In this method, the escaping exhaust gases struck small vanes at the bottom of the rocket, causing it to spin much as a bullet does in flight. Variations of the principle are still used today.
Rockets continued to be used with success in battles all over the European continent. However, in a war with Prussia, the Austrian rocket brigades met their match against newly designed artillery pieces. Breech-loading cannon with rifled barrels and exploding warheads were far more effective weapons of war than the best rockets. Once again, rockets were relegated to peacetime uses.
Early in
the 20th century, an American, Robert H. Goddard (1882-1945), conducted
practical experiments in rocketry. He had become interested in a way of
achieving higher altitudes than were possible for lighter-than-air balloons.
He published a pamphlet in 1919 entitled A Method of Reaching Extreme
Altitudes. It was a mathematical analysis of what is today called the
meteorological sounding rocket.
In his pamphlet, Goddard reached several conclusions important to rocketry. From his tests, he stated that a rocket operates with greater efficiency in a vacuum than in air. At the time, most people mistakenly believed that the presence of air was necessary for a rocket to push against. A New York Times newspaper editorial of the day mocked Goddard's lack of the "basic physics ladled out daily in our high schools." Goddard also stated that multistage or step rockets were the answer to achieving high altitudes and that the velocity needed to escape Earth's gravity could be achieved in this way.
Goddard's earliest experiments were with solid-propellant rockets. In 1915, he began to try various types of solid fuels and to measure the exhaust velocities of the burning gases.
While working on solid-propellant rockets, Goddard became convinced that a rocket could be propelled better by liquid fuel. No one had ever built a successful liquid-propellant rocket before. It was a much more difficult task than building solid- propellant rockets. Fuel and oxygen tanks, turbines, and combustion chambers would be needed. In spite of the difficulties, Goddard achieved the first successful flight with a liquid- propellant rocket on March 16, 1926. Fueled by liquid oxygen and gasoline, the rocket flew for only two and a half seconds, climbed 12.5 meters, and landed 56 meters away in a cabbage patch. By today's standards, the flight was unimpressive, but like the first powered airplane flight by the Wright brothers in 1903, Goddard's gasoline rocket was the forerunner of a whole new era in rocket flight.
Goddard's experiments in liquid-propellant rockets continued for many years. His rockets became bigger and flew higher. He developed a gyroscope system for flight control and a payload compartment for scientific instruments. Parachute recovery systems were employed to return rockets and instruments safely. Goddard, for his achievements, has been called the father of modern rocketry.
A third great space pioneer, Hermann Oberth (1894-1989) born on June 25, 1894 in Hermannstadt (Transylvania), and died on December 28, 1989 in Nuremberg, Germany, published a book in 1923 about rocket travel into outer space. His writings were important. Because of them, many small rocket societies sprang up around the world. In Germany, the formation of one such society, the Verein fur Raumschiffahrt (Society for Space Travel), led to the development of the V-2 rocket, which was used against London during World War II. In 1937, German engineers and scientists, including Oberth, assembled in Peenemunde on the shores of the Baltic Sea. There the most advanced rocket of its time would be built and flown under the directorship of Wernher von Braun.
The V-2
rocket (in Germany called the A-4) was small by comparison to today's
rockets. It achieved its great thrust by burning a mixture of liquid oxygen
and alcohol at a rate of about one ton every seven seconds. Once launched,
the V-2 was a formidable weapon that could devastate whole city blocks.
Fortunately for London and the Allied forces, the V-2 came too late in the war to change its outcome. Nevertheless, by war's end, German rocket scientists and engineers had already laid plans for advanced missiles capable of spanning the Atlantic Ocean and landing in the United States. These missiles would have had winged upper stages but very small payload capacities.
With the fall of Germany, many unused V-2 rockets and components were captured by the Allies. Many German rocket scientists came to the United States. Others went to the Soviet Union. The German scientists, including Wernher von Braun, were amazed at the progress Goddard had made.
Both the United States and the Soviet Union realized the potential of rocketry as a military weapon and began a variety of experimental programs. At first, the United States began a program with high-altitude atmospheric sounding rockets, one of Goddard's early ideas. Later, a variety of medium- and long-range intercontinental ballistic missiles were developed. These became the starting point of the U.S. space program. Missiles such as the Redstone, Atlas, and Titan would eventually launch astronauts into space.
On October 4, 1957, the world was stunned by the
A few months after the first Sputnik, the United States followed the Soviet Union with a satellite of its own. Explorer I was launched by the U.S. Army on January 31, 1958. In October of that year, the United States formally organized its space program by creating the National Aeronautics and Space Administration (NASA). NASA became a civilian agency with the goal of peaceful exploration of space for the benefit of all humankind.
Soon, rockets launched many people and machines into space. Astronauts orbited Earth and landed on the Moon. Robot spacecraft traveled to the planets. Space suddenly opened up to exploration and commercial exploitation. Satellites enabled scientists to investigate our world, forecast the weather, and communicate instantaneously around the globe. The demand for more and larger payloads created the need to develop a wide array of powerful and versatile rockets.
Scientific exploration of space using robotic spacecraft proceeded at a fast pace. Both Russia and the United States began programs to investigate the Moon. Developing the technology to physically get a probe to the Moon became the initial challenge. Within nine months of Explorer 1 the United States launched the first unmanned lunar probe, but the launch vehicle, an Atlas with an Able upper stage, failed 45 seconds after liftoff when the payload fairing tore away from the vehicle. The Russians were more successful with Luna 1, which flew past the Moon in January of 1959. Later that year the Luna program impacted a probe on the Moon, taking the first pictures of its far side. Between 1958 and 1960 the United States sent a series of missions, the Pioneer Lunar Probes, to photograph and obtain scientific data about the Moon. These probes were generally unsuccessful, primarily due to launch vehicle failures. Only one of eight probes accomplished its intended mission to the Moon, though several, which were stranded in orbits between Earth and the Moon, did provide important scientific information on the number and extent of the radiation belts around Earth. The United States appeared to lag behind the Soviet Union in space.
With each launch, manned spaceflight came a step closer to becoming reality. In April of 1961, a Russian named Yuri Gagarin became the first man to orbit Earth. Less than a month later the United States launched the first American, Alan Shepard, into space. The flight was a sub-orbital lofting into space, which immediately returned to Earth. The Redstone rocket was not powerful enough to place the Mercury capsule into orbit. The flight lasted only a little over 15 minutes and reached an altitude of 187 kilometers. Alan Shepard experienced about five minutes of microgravity then returned to Earth, during which he encountered forces twelve times greater than the force of gravity. Twenty days later, though still technically behind the Soviet Union, President John Kennedy announced the objective to put a man on the Moon by the end of the decade.
In February of 1962, John Glen became the first American to orbit Earth in a small capsule so filled with equipment that he only had room to sit. Launched by the more powerful Atlas vehicle, John Glen remained in orbit for four hours and fifty-five minutes before splashing down in the Atlantic Ocean. The Mercury program had a total of six launches: two suborbital and four orbital. These launches demonstrated the United States' ability to send men into orbit, allowed the crew to function in space, operate the spacecraft, and make scientific observations.
The United States then began an extensive unmanned program aimed at supporting the manned lunar landing program. Three separate projects gathered information on landing sites and other data about the lunar surface and the surrounding environment. The first was the Ranger series, which was the United States first attempt to take close-up photographs of the Moon. The spacecraft took thousands of black and white photographs of the Moon as it descended and crashed into the lunar surface. Though the Ranger series supplied very detailed data, mission planners for the coming Apollo mission wanted more extensive data.
The final two lunar programs were designed to work in conjunction with one another. Lunar Orbiter provided an extensive map of the lunar surface. Surveyor provided detailed color photographs of the lunar surface as well as data on the elements of the lunar sediment and an assessment of the ability of the sediment to support the weight of the manned landing vehicles. By examining both sets of data, planners were able to identify sites for the manned landings. However, a significant problem existed, the Surveyor spacecraft was too large to be launched by existing Atlas/Agena rockets, so a new high energy upper stage called the Centaur was developed to replace the Agena specifically for this mission. The Centaur upper stage used efficient hydrogen and oxygen propelants to dramatically improve its performance, but the super cold temperatures and highly explosive nature presented significant technical challenges. In addition, they built the tanks of the Centaur with thin stainless steel to save precious weight. Moderate pressure had to be maintained in the tank to prevent it from collapsing upon itself. Rocket building was refining the United State's capability to explore the Moon.
The Gemini
was the second manned capsule developed by the United States. It was designed
to carry two crew members and was launched on the largest launch vehicle
available--the Titan II. President Kennedy's mandate significantly altered
the Gemini mission from the general goal of expanding experience
in space to prepare for a manned lunar landing on the Moon. It paved the
way for the Apollo program by demonstrating rendezvous and docking required
for the lunar lander to return to the lunar orbiting spacecraft, the extravehicular
activity (EVA) required for the lunar surface exploration and any emergency
repairs, and finally the ability of humans to function during the eight
day manned lunar mission duration. The Gemini program launched ten manned
missions in 1965 and 1966, eight flights rendezvous and docked with unmanned
stages in Earth orbit and seven performed EVA.
Launching men to the moon required launch vehicles much larger than those
available. To achieve this goal the United States developed the Saturn
launch vehicle. The Apollo
capsule, or command module, held a crew of three. The capsule took
the astronauts into orbit about the Moon, where two astronauts transferred
into a lunar module and descended to the lunar surface. After completing
the lunar mission, the upper section of the lunar module returned to orbit
to rendezvous with the Apollo capsule. The Moonwalkers transferred back
to the command module and a service module, with an engine, propelled them
back to Earth. After four manned test flights, Apollo 11 astronaut
Neil Armstrong became the first man on the moon. The United States returned
to the lunar surface five more times before the manned lunar program was
completed. After the lunar program the Apollo program and the Saturn
booster launched Skylab,
the United State's first space station. A smaller version of the Saturn
vehicle transported the United States' crew for the first rendezvous in
space between the United States and Russia on the Apollo-Soyuz mission.
During this manned lunar program, unmanned launch vehicles sent many satellites to investigate our planet, forecast the weather, and communicate instantaneously around the world. In addition, scientists began to explore other planets. Mariner 2 successfully flew by Venus in 1962, becoming the first probe to fly past another planet. The United State's interplanetary space program then took off with an amazing string of successful launches. The program has visited every planet except Pluto.
After the Apollo program the United States began concentrating on the development of a reusable launch system, the Space Shuttle. Solid rocket boosters and three main engines on the orbiter launch the Space Shuttle. The reusable boosters jettison little more than 2 minutes into the flight, their fuel expended. Parachutes deploy to decelerate the solid rocket boosters for a safe splashdown in the Atlantic ocean, where two ships recover them. The orbiter and external tank continue to ascend. When the main engines shut down, the external tank jettisons from the orbiter, eventually disintegrating in the atmosphere. A brief firing of the spacecraft's two orbital maneuvering system thrusters changes the trajectory to achieve orbit at a range of 185-402 kilometers above Earth's surface. The Space Shuttle orbiter can carry approximately 25,000 kilograms of payload into orbit so crew members can conduct experiments in a microgravity environment. The orbital maneuvering system thrusters fire to slow the spacecraft for reentry into Earth's atmosphere, heating up the orbiter's thermal protection shield up to 816° Celsius. On the Shuttle's final descent, it returns to Earth gliding like an airplane.
Since the earliest days of discovery and experimentation, rockets have evolved from simple gunpowder devices into giant vehicles capable of traveling into outer space, taking astronauts to the Moon, launching satellites to explore our universe, and enabling us to conduct scientific experiments aboard the Space Shuttle. Without a doubt rockets have opened the universe to direct exploration by humankind. What role will rockets play in our future?
The goal of the United States space program is to expand our horizons in space, and then to open the space frontier to international human expansion and the commercial development. For this to happen, rockets must become more cost effective and more reliable as a means of getting to space. Expensive hardware cannot be thrown away each time we go to space. It is necessary to continue the drive for more reusability started during the Space Shuttle program. Eventually NASA may develop aerospace planes that will take off from runways, fly into orbit, and land on those same runways, with operations similar to airplanes.
To achieve this goal two programs are currently under development. The X33 and X34 programs will develop reusable vehicles, which significantly decrease the cost to orbit. The X33 will be a manned vehicle lifting about the same payload capacity as the Space Shuttle. The X34 will be a small, reusable unmanned launch vehicle capable of launching 905 kilograms to space and reduce the launch cost relative to current vehicles by two thirds.
The first step towards building fully reusable vehicles has already occurred. A project called the Delta Clipper is currently being tested. The Delta Clipper is a vertical takeoff and soft landing vehicle. It has demonstrated the ability to hover and maneuver over Earth using the same hardware over and over again. The program uses much existing technology and minimizes the operating cost. Reliable, inexpensive rockets are the key to enabling humans to truly expand into space.
Soon, many people and machines were being launched into space. Astronauts orbited Earth and landed on the Moon. Robot spacecraft traveled to the planets. Space was suddenly opened up to exploration and commercial exploitation. Satellites enabled scientists to investigate our world, forecast the weather, and to communicate instantaneously around the globe. As the demand for more and larger payloads increased, a wide array of powerful and versatile rockets had to be built.
Since the
earliest days of discovery and experimentation, rockets have evolved from
simple gunpowder devices into giant vehicles capable of traveling into outer
space. Rockets have opened the universe to direct exploration by humankind.
from: http://exploration.grc.nasa.gov/education/rocket/TRCRocket/history_of_rockets.html
