Rocketry

History

Rockets have been an important part of our lives. Reports from as early as 400 B.C. described primitive flying objects, including wooden pigeons, that demonstrated basic principles of rocketry.

The Chinese were the first to use a gunpowder mixture for their fireworks. Bamboo tubes filled with gunpowder were tossed into fires. It is believed that some of the bamboo tube fireworks may have been launched accidentally. The Chinese realized this tube could be used for warfare. They attached arrows to the rockets and shot them with bows. Eventually, they realized the rockets could propel themselves. In 1232 A.D., the Chinese and Mongols were at war. During the battle of Kai-Keng, the Chinese used rocketry to send "arrows of flying fire" against their enemy. This attack surprised the Mongols who then produced their own rockets. Rocketry began to spread around Europe.

Until the 16th century, England, Germany, France, and Italy experimented with rocket design. Gunpowder formulas were improved. Flight accuracy was increased. Jean Froissart from France even shot rockets out of tubes similar to the current bazooka design.

During the 16th century, a German fireworks maker developed a "step rocket" which used multiple rockets to send fireworks higher into the sky. This multiple-stage rocket is a basis for rocketry today.

Sir Isaac Newton’s Three Laws of Motion explain how rockets work. People used Newton’s laws to design better rockets. In the 18th and 19th centuries, countries, such as the Netherlands, Germany, Russia, England, and India, began to use rockets for warfare. Warring countries found rocket accuracy to be problem. Rocket success was based more on volume rather than target accuracy. As a result, artillery, an accurate weapon, took rocketry’s place as a tool of war.

Rockets again became popular when in 1898 Konstantin Tsiolkovsky suggested space could be explored using a rocket. He recommended using liquid propellants to increase rocket range.

In the early 1900’s, other important scientists working on rockets included Robert H. Goddard who experimented with solid and liquid fueled rockets and Hermann Oberth, a German, who popularized rocketry in his country. Germany became very skilled at rocket design. One result of this was the V-2 rocket attack against London during the end of World War II. Wernher von Braun was a key developer of the V-2 rocket. He later came to the United States and helped improve our rocket technology.

After World War II, scientists from the Soviet Union and the United States identified the advantages of rocketry for use in ballistic missiles. These efforts were the beginning of the space programs.

Types of Rockets

There are many types of rockets that have special features designed for their mission. Even though their missions may be different, all rockets carry fuel and are very powerful so they can escape the Earth’s gravity.

Most rockets are built with several stages. The first stage is used to boost the rocket off the launch pad. When its fuel is gone, this stage drops off and the next stage fires to provide more thrust to the rocket. In many cases, rockets have three stages that continue to push the rocket into space. As the stages drop away, the rocket weight is reduced and the rocket can travel faster.

Some rockets have boosters. These are small rockets that are attached to the sides of the main rocket and help produce extra thrust at lift-off. When the boosters are finished, they drop off and fall to the ocean.

Most rockets use fuel and oxygen tanks. Rockets must have their own oxygen tanks because there is no oxygen in space. The fuel will not burn without oxygen. The fuel and oxygen mix in a chemical reaction. Hot gases are pushed out of the rocket nozzles. This provides the thrust for the rocket. The fuel can be solid, liquid, or a combination of the two.

The gunpowder used by the Chinese in their early rockets would be an example of a solid fuel. Solid propellants are reliable, simple, and easy to store. The disadvantage of solid fuel is that the fuel combustion cannot be stopped once it is started.

Liquid propellants, like liquid hydrogen, are dangerous to handle. The fuel flow can, however, be regulated. That means rockets with liquid propellants can be shut down if necessary. This is important when a mission has to be aborted before launch. Some rockets have both solid and liquid fuel. These combine the advantages of both types of fuels. The Space Shuttle is an example of a vehicle that uses solid and liquid propellants.

Two new propulsion systems are in use. One is called an ion engine. Ion technology has been studied since the 1950’s. Ion engines make thrust without a chemical reaction. Ions inside an engine chamber are attracted to an area in front of the nozzle by an opposite magnetic charge. This movement provides the engine thrust. The thrust from an ion engine is low. Ion propulsion is not powerful enough to either launch a spacecraft into orbit around the Earth or to escape the Earth‘s gravitational pull. Deep Space 1, launched on October 24, 1998, is an example of an ion propulsion system. The Deep Space 1 unit was launched using a Boeing Delta 7326 rocket. The ion propulsion technology is used to provide the small amount of thrust needed to keep the unit on its mission to view an asteroid and two comets. Ion propulsion was only activated after the spaceship was beyond the Earth’s main gravitational pull. Deep Space 1 began its flight with 178.2 lb. (81 kg) of xenon propellant. A mission update in November, 1999, said that Deep Space 1 is meeting all mission objectives. It has used up less than 48.5 lb. (22 kg) of xenon propellant. This technology appears promising.

The other new propulsion system is nuclear propulsion. This system is very controversial. Many people believe this system is hazardous due to the nuclear materials used. Scientists feel confident that the system is safe. The Cassini spacecraft, a cooperative effort between NASA, European Space Agency(ESA), and the Italian Space Agency(ASI), is presently testing nuclear technology. The Cassini spacecraft will explore Saturn and Titan. Cassini uses three radioisotope thermoelectric generators(RTGs) that use heat from decaying plutonium.

Scientists continue to look for new propulsion methods. One possibility is an electrodynamic tether. NASA tested a Tethered Satellite System in 1995 and 1996. This system was developed with the Italian Space Agency(ASI). In a tether test, a wire moves through a magnetic field and makes electric current. It may be used to propel spacecraft and to power electrical requirements.

Flight Aids

There are several steps scientists can take to make rockets work better. One is the launch site. If you launch close to the equator in an easterly direction, it is easier to lift-off. This is because you can use the Earth’s easterly rotation(centrifugal force) to help you escape gravity. The European Space Agency(ESA) currently launches from the Guiana Space Center in the northern part of South America, only 5 degrees latitude above the equator. ESA reports that this launch location allows them to increase payloads 15 to 20 % over what NASA can do from its Cape Canaveral site.

A slingshot orbit is an important help in planning long-term missions. This orbit saves fuel. The spacecraft flies close to a planet and is pulled closer by the planet’s gravity. This close swingby causes the craft to speed up and curve in a different direction. Some missions use many swingbys to help the craft. For example, Cassini, a current mission to study Saturn and its moons, plans four swingbys. Venus (twice), Earth, and Jupiter will serve as planets that will be used to help speed Cassini on its way.

Rockets have been an interesting part of our lives for hundreds of years and will continue to help our exploration of space.