ROCKET   SCIENCE

Advanced Rocketry:  Multi Staging, Clustered engines, Altimeter based parachute deployment, Streamer and Glider recovery methods,  Mach 1+ flights

Glossary of Model and High Power Rocketry Terms

Air Start: Any motor that is started after first motion of the vehicle. Upper stage ignition of a multi stage rocket is a special case of air starting. Usually it is outboard boosters started after a central motor has lifted the vehicle, or visa versa. This can be done by a flashbulb/motion switch, timer, or simply a piece of fuse started by the exhaust of the pad start motor.

AP: Ammonium Perchlorate, the oxidizer used in composite rocket motors. Other components are Aluminum powder (fuel) and polybutediene rubber (the binder holding it all together). This is the propellant mixture that the Shuttle SRB's use.

Apogee: The highest point of a rocket's flight path. (More literally, the point farthest on the flight path from Earth.)

B/G: Boost Glider. A glider which is boosted to altitude by a rocket motor. The pod containing the expended motor may separate from the glider at ejection to be returned by streamer or parachute (this is typical but is not required). The more aerodynamically clean glider section is then free to glide more slowly.

Black Powder: Basically, gunpowder. The 'traditional' model rocket motor fuel. Used by Estes and most other model rocket companies through F range. Rocketflite has black powder motors through the H range. See also "AP" and "Composite Motor"

Booster: On a multi stage rocket this refers to the sections (stages) which drop off in mid-flight. On single stage payload rockets,the term is used for the lower powered portion to distinguish it from the payload section. See also "Air Start"

Burn Out Velocity: The velocity the rocket is traveling when the motor runs out of fuel. Usually the highest speed achieved by the rocket. See also "Hyperterminal Velocity"

CATO: A motor failure, generally explosive, where all the propellant is burned in a much shorter time than planned. This can be a nozzle blow-out (loud, but basically harmless), an end-cap blow-out (where all of the pyrotechnic force blows FORWARD which usually does a pretty good job of removing any internal structure including the recovery system) or a casing rupture which has unpredictable, but usually devastating, effects. Another form of CATO is an ejection failure caused by either the delay train failing to burn or the ejection charge not firing, but the result is the same: the model prangs. A CATO does not necessarily burn all of the fuel in a rocket motor (especially true for composite fuels, which do not burn well when not under pressure). For this reason you should be especially careful when approaching a CATO.

CG: Center of Gravity. The point about which a free body will rotate when disturbed by an outside force. For a model rocket, this is the point where the effects the masses of the individual components cancel out and the model will balance on a knife edge. As with a see-saw, a mass further from the CG will have a greater effect than the same mass closer in.

Cluster: A rocket that fires more than one motor simultaneously. Composite Material: Hi-Tech materials, other than paper, wood or metal, used in the construction of rockets (see also "Phenolic"). 

Composite Motor: The term used broadly to cover solid fuel rocket motors using propellants other than black powder. Composite motors require different igniters and igniter systems from black powder motors.

Composite Propellant: In Hobby Rocketry, any propellant other than black powder. In military parlance (where the term originated) the term is used to denote propellants that are mixtures of oxidizers and fuels and to distinguish them from Single, Double, and Triple base propellants (which are either monopropellants or mixtures of monopropellants). Note that by the military definition, black powder is itself a composite propellant because it consists of separate oxidizers (KNO3 and sulfur) and fuel (charcoal).

Continuity Check: A group of electrical techniques for checking the firing circuit through the igniter to ensure that the circuit is functional. .

CP: Center of (Aerodynamic) Pressure. The point on a rocket where stability-restoring forces due to airflow against the back part of the rocket (fins, etc.) exactly equal the disturbing forces against the part of the rocket ahead of that point.

A good rule of thumb for sport models (both high and low power)is to design the rocket with the CP one or two body diameters behind the CG.

Ejection Charge: A small quantity of black powder used to generate gas pressure within the rocket to deploy the recovery system. This is activated when the delay train (q.v.) burns through. On rockets with electronic ejection timers, this may be a separate small container of black powder which is triggered by a signal from a timer or other control unit.

Igniter: An expendable device used to ignite a rocket motor.

Impulse(Specific): A measure of the efficiency of a motor/propellant system. It is determined by taking the Total Impulse (q.v.) and dividing by the weight of propellants. This carries the potentially confusing units of "seconds" (as if it had something to do with the burn duration) but is due to weight and thrust both being force parameters hence canceling out (e.g. lb-sec/lb or N-sec/N). This is actually very handy since it makes the term independent of the units system (metric or English) since they both use "seconds" for time.

Impulse(Total): A measure of the total momentum imparted to the rocket by the motor. It is defined (for those who know calculus) as the integrated area under the thrust-time curve. For the rest of us, it can be thought of as the motor's average thrust times the duration of the burn. Measured in N-sec or Lb-sec.

Motor: Something that imparts or produces motion, such as a machine or engine. A device that converts any form of energy into mechanical energy (from *American Heritage Dictionary*). 

Newton & Newton-second: Metric units used to measure thrust and total impulse (q.v.)respectively. One pound = 4.448 newtons. 

Parabola: A shape produced by the formula y=x^2. Used to produce low drag nosecones. See also "Ogive"

Payload: Anything carried aloft by the rocket that is not part of the rocket itself. Common payloads include altimeters, computers, cameras, and radio transmitters. The Safety Code specifically prohibits the launching of live payloads. 

R/G: Rocket glider. A glider which is boosted to altitude by a rocket. The entire model glides down together. No part of the model separates, as in a boost glider. Technically, an R/G is a particular form of B/G.

RMSTM: Reloadable Motor System. The trademarked name of the AeroTech/ISP reloadable motors. Often used (incorrectly) as a generic name for all reloadable technology. 

RSO: The Range Safety Officer, the individual responsible for ensuring that rockets presented for launch are properly constructed, prepped and balanced for stability. 

Wadding: Any flame retardant material used to prevent the scorching of the recovery system do to the heat of the ejection charge. The material (usually a boron treated paper tissue) is placed in the body tube between the engine and the recovery system. See also "Ejection Baffle"

Waiver: The term used to describe the official permission given by the FAA allowing rockets with more than 113 grams of fuel or weighing more than 1 pound to be flown into FAA controlled airspace. See also "FAR 101"

Individuals: Jules Verne, K. E. Tsiolkovsky, Robert Goddard, Hermann Oberth, and Wernher von Braun.