Glossary of Common Rocketry Terms

Ablative To wear away under stresses of heat, oxidation, and high velocity gas erosion.
Acceleration Increasing velocity with time.
Additive Propellant ingredient used to enhance physical or ballistic properties.
Aft Tail end of vehicle.
Barricade Sturdy structure meant to stop or deflect high velocity objects created in a test stand explosion.
Bates Grain Tubular grain uninhibited on the ends which can provide a nearly neutral burning characteristic (BAtch TESt motor).
Binder The rubbery fuel used in solid propellants - also in Hybrid fuels.
Blockhouse Strong construction used to house personnel and instruments in a static or flight test. Generally has extremely durable overhead construction.
Blowdown Pressurizing gas flowing through a fixed orifice with no other regulation to expel liquid propellants.
Boiler Plate Motor A very solid overdesigned thrust chamber used to test new propellants or new injector concepts.
Bolt Circle A ring of bolts used to hold a closure in place.
Bulkhead A wall between two areas - in rocketry usually between two tanks, instrumentation sections or between motor chamber and tank.
Bunker Less sophisticated observation area than a blockhouse. Generally has overhead protection to qualify as a bunker.
Burn Area The actively burning surface of a rocket grain, either solid or hybrid.
Burning Rate In solids, the rate at which the burning surface recedes as it combusts. Affected by pressure, temperature and the scrubbing of hot gases.
Burst Diaphragm A thin (metal) disc which fails at a known pressure, releasing pressurant, fuel or oxidizer into flow lines.
Cables In instrumentation, the shielded electrical lines which conduct signals from the transducers to the instrumentation recorders, amplifiers, DAS, etc. The shields are tied to one grounding point.
Case Bonded A propellant grain cast directly into a chamber and made to bond securely to the chamber wall.
Chamber Generally a tubular section of a rocket motor (solid, liquid, or hybrid) in which combustion takes place.
Chamber Pressure The pressure generated within a motor by the combustion of the rocket propellant(s).
Closure Any mechanical part which seals a port or chamber.
Chuff A low frequency instability in rocket motors in periods of up to several seconds - dangerous in that it can project a vehicle off a launcher and then it becomes an erratic projectile.
Chug Low frequency instability in a liquid motor.
Core The cavity within a solid or hybrid grain - often shaped to offer higher burning surface or a constant surface with regression.
Cryogenic Temperature at which gases liquefy at atmospheric pressure.
DAS Data Acquisition System
Density Specific weight per volume unit.
Discharge Coefficient Downrating of the area of an orifice or nozzle due to flow separation or friction.
Electric Match An electric igniter similar to a model rocket igniter.
End Burner A "cigarette burning" grain inhibited or case bonded on the external surface burning only on its face.
Erosive Burning Increased burning rate in solids and hybrids created by the action of high velocity gases.
Exit Area Largest section of a divergent cone on the exhaust section of a rocket nozzle.
Exit Cone Applies to the exit or expansion section of a rocket nozzle.
Expansion Ratio The ratio of the area of the exit diameter of the exhaust portion of a nozzle to the area of the throat - determines Cf (thrust coefficient).
Flex Member Spring steel leaf used in supporting test stand table at four corners.
Flex Hose Used in test stands to feed propellants to liquid or hybrid motors without imposing major loads on test structure; also used in some gimballed motors to permit swiveling motion.
Forward Towards the nose of the rocket.
Fuel Component(s) of the propellant which are Oxidized or burned.
Gimbal Used in attitude controlled vehicles to support motor so it can be deflected to produce control vectored thrust. Also the support of a gyroscope in a stable platform or in a rate gyro.
GOX Gaseous OXygen.
Grain Any size of monolithic propellant structure designed to be combusted as rocket propellant.
Half-Angle The divergence of the exhaust cone referring to the angle one side makes with the centerline. Conventionally 15 to 18 degrees but may be larger or smaller.
Hold Down A mechanical clamp for securing a motor to a test stand or to secure an entire vehicle to a launch pad and may be remotely released.
Hoop Stress The circumferential loading of a cylindrical mechanical body. Mustbe kept well below the yield strength of the material.
Hybrid Refers to the use of mixed states of matter in a bi-propellant system - solid-liquid, gas-solid, etc. Either oxidizer or fuel may be the liquid or gas component.
Hydrostatic Test Important operation used to determine the suitability of a vessel or motor chamber for pressure containment. Done with water-filled units taken to high pressures with small hand piston pumps (system is aerated prior to test) under appropriate safety conditions.
Hypergolic Propellants which ignite on contact.
Hysteresis Shift in calibration of transducer when on "return" from actuation load.
Inhibit Bonding non-propellant material to restrict the burning surface of a propellant grain.
Igniter Used to produce flame, hot particles, and gas pressure to ignite a rocket motor.  See electric match.
Injector A system of orifices used to direct propellant to create mixing and fog production for combustion.
Insulation Thermal protection used in motors to prevent heat transfer to temperature sensitive materials.
Liner An insulated sleeve made from phenolic, EPDM, fiberglass, impregnated cardboard, or any number of materials which protects the combustion chamber while the motor is burning.
Liquid Refers to liquid propellant in rocket terminology.
Load Cell Transducer which measures force as a function of resistance or voltage.
Neutral Pressure curve which is nearly constant with time.
Nichrome An alloy of nickel and chromium drawn into a wire of varying gauges typically used to heat a pyrogen to ignition with the application of sufficient voltage and amperage.
Nozzle The portion of the rocket motor which accelerates the gases to sonic velocity at the narrowest part of the nozzle (the throat) then expands them to greater velocity in the exit cone.  In experimental rocketry this is generally turned on a lathe from graphite and /or phenolic.
Oxidizer The component of a propellant which provides the combustion supporting element (generally Oxygen, but can be Fluorine, Chlorine, Sulfur, etc.)
Perforation Another term for core.
Plumbing Refers to tubing and hoses used as conduits for propellants and pressurants in a liquid or hybrid propulsion system.
Port Area The cross section of a core, perforation or port - used in Hybrid tocalculate G (Mass Flux Rate).
Pressure Measure of unit of force per unit area exerted by combustion products during rocket motor operation, or in a propellant or pressurant tank.
Pressure Port A threaded orifice which can be fitted with a pressure gauge or pressure transducer for determining the pressures within a motor while in operation.
Pressure Transducer Outputs electrical signal proportional to pressure.
Progressive Pressure time curve which shows increased pressure with duration.
Propellant Refers to a mixture of oxidizer and fuel or to either oxidizer or fuel used in rocket motors.
Recorder Any device which creates a semi-permanent display of data, generally on magnetic tape, chart paper, oscilloscope screen, digital display, etc.
Regressive Pressure vs Time curve in which the pressure decreases with duration.
Restrict Inhibiting a grain.
Rocket Device which provides propulsion through the expulsion of some mediumat high velocity.
Screech High frequency instability of liquid motors, generally destructive.
Sliver Remnant of propellant or fuel in solid or hybrid motors as a consequence of initial geometry.
Solid Fuel and/or oxidizer in a condensed, solid state of matter.
Specific Impulse The force per unit mass per unit time generated by a rocket propellant under fixed conditions of pressure, temperature, and mixture ratio.
Static Test Firing a rocket motor in a restrained, protected area for purposes of recording chamber pressure, thrust, wall temperature, plume characteristics, burning duration, etc.
Strand Burner A strand burner measures the burn rate of an energetic composition in an elevated pressure environment.  Also called a Crawford Bomb. 
Tailoff Refers to gradual reduction in pressure and thrust at end of burning of a rocket motor.
Tank Vessel which contains oxidizer, fuel or pressurant for a rocket motor.
Tap Referring to either threading of a hole or to the port in a chamber designed to take pressure measurements.
Test Stand Designed to restrain a motor during test and permit enough motion to actuate a load cell - see static test.
Thrust Force produced by a rocket motor by the efflux of matter at high velocity.
Total Impulse The product of specific impulse and weight of propellant, the product of thrust and duration.
Transducer Outputs electrical signal proportional to a force or pressure input.
Ullage Unfilled volume of a propellant tank and rarely the unfilled volume in a solid motor.
Unrestricted Refers to a free-standing grain which burns on all surfaces. This method leaves the chamber wall unprotected by propellant and is therefore seldom used.
Wall Thickness Is equal to 1/2 the difference between the inside diameter and outside diameter of a chamber or tank. The actual gauge of the material used to make the vessel.
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