8/10/2019 A Rocket is a Machine That Develops Thrust by the Rapid Expulsion of Matter

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A rocket is amachine thatdevelops thrust bythe rapid expulsionof matter.The majorcomponents of achemical rocketassembly are arocket motor orengine,

propellant consisting of fuel and anoxidizer, a frame tohold thecomponents, controlsystems and a cargosuch as a satellite. Arocket differs fromother engines in thatit carries its fuel andoxidizer internally,therefore it will

burn in the vacuumof space as well aswithin the Earth'satmosphere. Thecargo is commonlyreferred to as the

payload. A rocket iscalled a launchvehicle when it isused to launcha satellite or other

payload into space.A rocket becomes amissile when the

payload is awarhead and it isused as aweapon. At present,rockets are the onlymeans capable ofachieving the

altitude and velocitynecessary to put a payload into orbit.

Terms

toDescribeRocket

Power

There are a number of terms used to describe the power generated by a rocket.

Thrust is the force generated, measured in pounds or kilograms. Thrustgenerated by the first stage must be greater than the weight of the completelaunch vehicle while standing on the launch pad in order to get it moving. Oncemoving upward, thrust must continue to be generated to accelerate the launchvehicle against the force of the Earth's gravity. To place a satellite into orbitaround the Earth, thrust must continue until the minimum altitude and orbitalvelocity have been attained or the launch vehicle will fall back to the Earth.

Minimum altitude is rarely desirable, therefore thrust must continue to begenerated to gain additional orbital altitude.

8/10/2019 A Rocket is a Machine That Develops Thrust by the Rapid Expulsion of Matter

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The impulse , sometimes called total impulse, is the product of thrust and theeffective firing duration. A shoulder fired rocket such as the LAW has anaverage thrust of 600 lbs and a firing duration of 0.2 seconds for an impulse of120 lbsec. The Saturn V rocket, used during the Apollo program, not onlygenerated much more thrust but also for a much longer time. It had an impulseof 1.15 billion lbsec.

The efficiency of a rocket engine is measured by its specif ic impul se (I sp).Specific impulse is defined as the thrust divided by the mass of propellantconsumed per second. The result is expressed in seconds. The specific impulsecan be thought of as the number of seconds that one pound of propellant will

produce one pound of thrust. If thrust is expressed in pounds, a specific impulseof 300 seconds is considered good. Higher values are better.

A rocket's mass rati o is defined as the total mass at liftoff divided by the massremaining after all the propellant has been consumed. A high mass ratio meansthat more propellant is pushing less launch vehicle and payload mass, resultingin higher velocity. A high mass ratio is necessary to achieve the high velocitiesneeded to put a payload into orbit.