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
generated by a propulsion system to overcome the
of the rocket. For full scale satellite
the weight of the
is only a small portion of the lift-off weight.
Most of the weight of the rocket is the weight of the
As the propellants are burned off during
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
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
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.
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
Due to IT
security concerns, many users are currently experiencing problems running NASA Glenn
educational applets. The applets are slowly being updated, but it is a lengthy process.
If you are familiar with Java Runtime Environments (JRE), you may want to try downloading
the applet and running it on an Integrated Development Environment (IDE) such as Netbeans or Eclipse.
The following are tutorials for running Java applets on either IDE:
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
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.
While they can not fly all the way to orbit, there are
You can study the flight characteristics of a two stage model rocket by
And you can use the
simulation program to investigate the velocity and altitude requirements for