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Computer drawing of a serial rocket as it stages.

The study of rockets is an excellent way for students to learn the basics of forces and the response of an object to external forces. All rockets use the thrust generated by a propulsion system to overcome the weight of the rocket. For full scale satellite launchers, the weight of the payload is only a small portion of the lift-off weight. Most of the weight of the rocket is the weight of the propellants. As the propellants are burned off during powered ascent, a larger proportion of the weight of the vehicle becomes the near-empty tankage and structure that was required when the vehicle was fully loaded. In order to lighten the weight of the vehicle to achieve orbital velocity, most launchers discard a portion of the vehicle in a process called staging. There are two types of rocket staging, serial and parallel.

In serial staging, shown above, there is a small, second stage rocket that is placed on top of a larger first stage rocket. The first stage is ignited at launch and burns through the powered ascent until its propellants are exhausted. The first stage engine is then extinguished, the second stage separates from the first stage, and the second stage engine is ignited. The payload is carried atop the second stage into orbit. Serial staging was used on the Saturn V moon rockets. The Saturn V was a three stage rocket, which performed two staging maneuvers on its way to earth orbit. The discarded stages of the Saturn V were never retrieved.

The other type of staging is called parallel staging.

Computer drawing of a parallel rocket as it stages.

In parallel staging, as shown in this figure, several small first stages are strapped onto to a central sustainer rocket. At launch, all of the engines are ignited. When the propellants in the strap-on's are extinguished, the strap-on rockets are discarded. The sustainer engine continues burning and the payload is carried atop the sustainer rocket into orbit. Parallel staging is used on the Space Shuttle. The discarded solid rocket boosters are retrieved from the ocean, re-filled with propellant, and used again on the Shuttle.

Some launchers, like the Titan III's and Delta II's, use both serial and parallel staging. The Titan III has a liquid-powered, two stage Titan II for a sustainer and two solid rocket strap-ons at launch. After the solids are discarded, the sustainer engine of the Titan II burns until its fuel is exhausted. Then the second stage of the Titan II is burned, carrying the payload to orbit. The Titan III is another example of a three stage rocket.

Let's investigate how rocket staging occurs by using a Java simulator.

You can initiate staging by clicking on the "Stage" button at the bottom of the simulator. "Serial" brings the rocket back to its original serial configuration and "Parallel" brings back a parallel configuration.

You can download your own copy of this simulator for use off line. The program is provided as Stage.zip. You must save this file on your hard drive and "Extract" the necessary files from Stage.zip. Click on "Stage.html" to launch your browser and load the program.

Button to Download a Copy of the Program

While they can not fly all the way to orbit, there are two stage model rocket kits available. You can study the flight characteristics of a two stage model rocket by using the RocketModeler II simulation program.


Guided Tours
  • Button to Display Previous Page Rocket Weight: Button to Display Next Page
  • Button to Display Previous Page Structural System: Button to Display Next Page

Activities:
Balloon Staging: Grade 6-10


Related Sites:
Rocket Index
Rocket Home
Exploration Systems Mission Directorate Home

 

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Editor: Tom Benson
NASA Official: Tom Benson
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