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Model rocket

From Academic Kids

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Model_Rocket_Launch.jpg
A model rocket.

Model rocketry is a hobby similar to model airplanes. In the contemporary U.S., there are two distinct types of rocket hobbyist.

Contents

1 Model Rocketry

2 High Power Rocketry (HPR)
3 Controversy
4 See also
5 External links

Amateur Rocketry

Amateur rocketry hobbyists experiment with fuels and make their own rocket motors, often launching rockets hundreds of miles out to sea. Amateur rockets can be dangerous because noncommercial rocket motors fail more often than commercial rocket motors. Amateur rocketry was an especially popular hobby in the late 1950s, following the launch of Sputnik. An appalling accident rate led individuals such as G. Harry Stine and Vernon Estes to make model rocketry a safe and widespread hobby. The National Association of Rocketry Safety Code is provided with most rocket kits and engines.

Model and High Power Rocketry

Model rocketry and High powered rocketry involve professionally-manufactured solid-fuel or hybrid liquid/solid fuel rocket motors. Since they are professionally designed and constructed, they are far safer. The motors also are tested and approved by the National Association of Rocketry or the Tripoli Rocketry Association and come in standardized sizes and powers.

Model Rocketry

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Model_rocket_engine_diagram.png
thumb Anatomy of a model rocket engine. A typical engine is about three inches long

Small model rocket motors are single use engines, with cardboard bodies and lightweight molded ceramic nozzles, ranging in power from 1/4A to E. They contain a black powder propellant. Motors are electrically ignited with a short length of nichrome wire pushed into the nozzle and held in place with flameproof wadding or a plastic plug. On top of the propellant is a tracking delay charge which produces smoke but essentially no thrust as the rocket slows down and arcs over. When the delay charge has burned through, it ignites an ejection charge, which is used to push out a parachute or a streamer (there are other more complicated recovery devices, but parachutes and streamers are the most common).

Model rocketeers experiment with rocket sizes, shapes, payloads, multistage rockets, and recovery methods. Some rocketeers build scale models of larger rockets, space launchers, or missiles.

Larger rocket motors are also available, using composite propellants made of ammonium perchlorate and a rubbery binder substance contained in a hard plastic case. These motors range in impulse from the D to the I range. Composite motors produce more impulse per unit weight than do black powder motors. Reloadable motors are also available. These are commercially-produced motors requiring the user to put propellant grains, o-rings and washers (to contain the expanding gases), delay grains and ejection charges into special motor casings. The advantage of a reloadable motor is the cost: because the main casing is reusable, reloads cost significantly less than single-use motors of the same impulse.

Model rocketry is enjoyed by many different levels of hobbyist, from grade-school children launching 3 in (75 mm) tall models in the baseball field, to teams of adults launching 200 pound (100 kg) behemoths thousands of feet into the air. Model rocketry is often credited as the most significant source of inspiration for children who eventually become scientists and engineers. See National Association of Rocketry.

Model rockets of special interest

Model rockets equipped with the Astrocam film camera or the Oracle digital camera, or with homebuilt equivalents, can be used to take aerial photographs.

High Power Rocketry (HPR)

High power rockets are propelled by larger motors ranging from H to O. These motors are almost always reloadable ones rather than single-use motors. Recovery and/or second stage ignition may be initiated by small flight control computers, which use a barometer (or sometimes accelerometer) to detect apogee and open a small parachute, and also to open a main parachute at a preset altitude. These rockets can carry larger payloads, including cameras and instrumentation. See Tripoli Rocketry Association.

Controversy

Both amateur and model rocketry have come under controversy in the United States following the terrorist attacks on New York and Washington D.C., as federal and state authorities allege that model rockets can be modified to act as weapons used to shoot down aircraft within the United States. Authorities argue that all members of the hobby should have to be licensed and their purchases recorded and reported to federal agencies. Critics of such policies, particularly those involved in the hobby itself, including several ex-military members now involved in rocketry, argue that while building model rockets capable of going great distances is a relatively simple feat, guidance systems are exceedingly difficult to design—requiring an extensive educational and technical background — rendering the likelihood of anyone being capable of designing a guidance system for homing in on an aircraft extremely low. Advocates of regulation also neglect that there are many other easier, unregulated ways to accomplish any such illicit goal — for example, via a model airplane, which are actually designed to be guidable.

The ammonium perchlorate composite propellant (APCP) used in large rocket motors is classified by the government as a low explosive. This classification is being challenged in a lawsuit, based upon the fact that APCP is not actually detonable. Following President Bush's signing of the Safe Explosives Act in 2002, hobbyists who had routinely purchased engines and APCP for years had to be fingerprinted, submit to background checks, and allow local and federal investigators at any time into their homes for inspections to ensure proper storage of the propellant.

The amount of APCP regulated is 62.5 grams and above, estimated to be about enough for a motor five or six inches (125 to 150 mm) long, one inch (25 mm) in diameter, and with a thrust of ten pounds force (44 N) for two seconds (88 newton-seconds impulse). This is a "G engine", which cannot exceed 160 newton-seconds impulse and are the largest rocket engines allowed for model rocketry. An "O engine", which cannot exceed 40960 newton-seconds impulse is the largest rocket engine allowed for high powered rocketry, which already requires certification.

According to The Wall Street Journal, regulations on the transport of rocket fuel across state lines have been in place for many years but were not widely enforced until after the terrorist attacks on America, at which point authorities clamped down on regulations and added many new ones. Thereafter, amateur rocket enthusiasts have made use of a little-known law allowing the manufacturing of low explosives for personal purposes, initially intended for farmers who mixed fertilizer with fuel oil to create explosives to blast their own irrigation ditches. Amateur hobbyists use this law to justify "cooking parties," at which many gather and mix their own fuel legally and anonymously.

See also

External links

Template:Scale modelde:Modellrakete

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