Transwiki:Model rocket

Model rocketry is a hobby similar to model airplanes. In the United States today, there are two quite distinct areas of hobby rocket activity, amateur rocketry on the one hand and model and high-power rocketry on the other.

Amateur Rocketry
Amateur rocketry hobbyists experiment with fuels and make their own rocket motors, launching a wide variety of types and sizes of rockets. Amateur rocketeers have been responsible for significant research into hybrid rocket motors, and have built and flown a variety of solid, liquid, and hybrid propellant motors. 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. However, an appalling accident rate led individuals such as G. Harry Stine and Vernon Estes to make model rocketry a safe and widespread hobby by developing and publishing the National Association of Rocketry Model Rocket Safety Code, and by commercially producing safe, professionally-designed and manufactured model rocket motors. Model rocketry by definition then became a separate and distinct activity from amateur rocketry. The Tripoli Rocketry Association sanctions some amateur activities, which they call "experimental rocketry," provided certain safety guidelines are followed, and provided the motors are of relatively standard design.

Model and High Power Rocketry
Model rocketry and High powered rocketry involve professionally-manufactured solid-fuel or hybrid liquid/solid fuel rocket motors. Since these motors are professionally designed and constructed, they are far safer than motors produced by individuals for use in amateur or experimental rocketry. The motors also are tested and certified by the National Association of Rocketry or the Tripoli Rocketry Association and come in standardized sizes and powers.

Model Rocketry
Since the early 1960s, a copy of the Model Rocket Safety Code has been provided with most model rocket kits and motors. Model rocketry is a very safe hobby, provided precautions are taken as given in the safety code.



Small model rocket motors are single use engines, with cardboard bodies and lightweight molded ceramic nozzles, ranging in power class from 1/8-A 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).

What the Numbers Mean
Model rocket motors produced by companies like Estes Industries and Quest Aerospace are stamped with a code (such as A10-3T or B6-4) that tells several things about of motor. The letter at the beginning of the code indicates the motor's total impulse (in newton-seconds). Each successive letter in alphabetical order has up to twice the power of the letter preceding it. This means that a "C" motor has twice the impulse of a "B" motor. The number that comes after the letter indicates the motor's average thrust, measured in newtons. A higher thrust will result in higher liftoff acceleration, and can be used to launch a heavier model. Within the same letter class, a higher average thrust also implies a shorter burn time (e.g., a B4 motor will burn longer than a B6). The last number is the delay in seconds between the end of the thrust phase and ignition of the ejection charge. Motors that end in a zero have no delay or ejection charge, and motors that end in a "T" (for "tiny") indicate that they are for use in a smaller rocket than standard motors. "T" motors are 13 mm in diameter by 45 mm long, while standard A, B and C motors are 18 mm in diameter by 70 mm long. Larger C, D, and E class black powder motors are also available; they are 24 mm in diameter and either 70 (C and D motors) or 95 mm long (E motors).

Model rocketeers often 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 O 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 non-shattering aluminum motor casings with screw-on or snap-in ends (closures). 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. Reloadable motors are available from G through O class.

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.

Model rockets of special interest
Model rockets equipped with the Astrocam film camera or the Oracle digital camera, or with home built equivalents, can be used to take aerial photographs.

High Power Rocketry (HPR)
High power model rockets are propelled by larger motors ranging from H to O and can be up to 40 feet tall. Their motors are almost always reloadable rather than single-use in order to reduce cost. Recovery and/or multi-stage ignition may be initiated by small on-board computers, which use an altimeter or accelerometer for detecting when to ignite engines or deploy parachutes. Due to the extreme speeds (often over Mach 1) and high altitudes (often over 10,000 ft.) these rockets can attain, a small drogue parachute is often deployed at apogee, and a larger one deployed after the rocket reaches a lower altitude. This reduces the distance the rocket drifts considerably. High powered model rockets can carry large payloads, including cameras and instrumentation such as GPS units, and are not much different than their military counterparts. Since 9/11, the high powered model rocket hobby has been even more carefully monitored by the government. Strict measures are in place to control who can participate, and launch permits are required.

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&mdash;requiring an extensive educational and technical background &mdash; 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 &mdash; for example, via a model airplane, which are actually designed to be guided.

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 capable of detonation. 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.