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Solid Rocket Motor Cutaway and Grain

by devansic, published

Solid Rocket Motor Cutaway and Grain by devansic Aug 1, 2016

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Summary

Rocket Propulsion is related to nozzle shape and the solid fuel inside its motor. This project consists of a cutaway view of a solid rocket motor and its main components - the motor case, insulation, ignitor, and the solid rocket fuel, called "grain," that fits inside. The pattern of the grain influences the behavior of the rocket as the fuel is burned. I have modeled seven types of grain in this project.

These cross sections of motors and fuel allow for exploration of the physics concepts related to thrust and momentum as well as geometric concepts like surface area, volume, and scale. These models offer a good starting point for any #ScienceProject or #EngineeringProject that relates to rocketry. Teachers can also use this project to add a real-life application of #Math and #MathProjects through an exploration of surface area and reading graphs.

Print Settings

Printer Brand:

MakerBot

Printer:

MakerBot Replicator Mini

Rafts:

Yes

Supports:

No

Resolution:

Standard

Infill:

10%


Notes:

I've included both the plain STLs and #MeshMixer STLs for the cutaway views. In printing, I found that standing the cutaways on end and printing without Mesh Mixer actually turned out better. The Mesh Mixer versions were a little hard to scrape off for no apparent benefit in stability or how the print turned out.

The Motor Case and Insulation take about 3 hours to print together. Each cutaway of grain takes about 1:45 to print, and then the cross sections will take half and hour each. The little igniter plug takes less than 15 minutes.

Post-Printing

To show off the cut away view of a solid rocket motor, you'll need to print the motor case, insulation, ignitor, and any or all of the grain that you wish to display. The ignitor goes into the end that has the flared opening. The other end is where the insulation goes. On a real rocket, a nozzle of some sort would be attached at the insulation end to offer the surface for the expanding gasses to push against.

How I Designed This

These models were all designed using #OnShape and are constrained to be printed on the #MakerbotMini. The cut away pieces will all fit together and would look smashing if you print them in different colors to make them stand out when assembled.

The cross sections were taken directly from the models of the cutaway grains, so they are the size of the cutaways. If you want to have them larger to make things easier for smaller hands and larger measuring tools, you can resize them in MakerBot Desktop. To scale them up and be able to keep the thickness of the cross section under control, do your size modifications before you rotate the disk to lay flat. Scale up by whatever percentage or size you wish, then "uncheck" the box that keeps all changes proportional. Then, change the thickness back to 3 mm to whatever size you wish.

I created a public file of this project in #OnShape. If you would like to model different patterns or sizes, feel free to access the project here.

Standards

Overview and Background

Cutaway and Cross Sectional Models of Solid Rocket Motors

The race to space has become a commercial venture, with entrepreneurs, billionaires, and college students developing space craft and satellites. Our students will see a manned mission to Mars in their lifetimes. To understand how we get spacecraft off the ground (or missiles), this project provides an introduction to the design of solid rocket motors and how the design of the fuel inside influences the behavior of those rockets.

Objectives

Upon completion of this lesson, students will demonstrate an understanding of the impact of geometry, specifically surface area, on the behavior of rockets. They will gain an understanding of thrust and be able to demonstrate skills in reading thrust vs. time graphs.

Standards Breakdown

K-2-ETS1-1.
Ask questions, make observations, and gather information about a situation people want to change to define a simple problem that can be solved through the development of a new or improved object or tool.
K-2-ETS1-2.
Develop a simple sketch, drawing, or physical model to illustrate how the shape of an object helps it function as needed to solve a given problem.

*MS-PS3-1 Energy
Construct and interpret graphical displays of data to describe the relationships of kinetic energy to the mass of an object and to the speed of an object.

*MS-PS3-5 Energy
Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object.

*HS-PS3-1 Energy
Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.

*HS-PS3-2 Energy
Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motions of particles (objects) and energy associated with the relative positions of particles (objects).

*HS-PS1-4 Matter and its Interactions
Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.

Lesson Plan and Activity

Introducing the topic, examining the models, and performing an activity related to graphing, surface area, or hypothesizing about the appropriate grain configuration for a specified use could take a total of five one-hour sessions, or just two, depending on the depth of your studies.

To prepare for the lesson, print the models ahead of time. The Motor Case, Insulation, Ignitor, and Grain fit together to show the interior of a typical solid rocket motor. These are for examination and example, but you don’t need to print one for every group. Then, print the cross sections of the various types of grain configurations for your students to work with - these will need to be printed in sufficient number for your students to work individually or in small groups.. The printing times and settings for each are as follows:

To introduce rockets and the difference between liquid rockets and solid rocket motors, NASA is a great resource with a pictorial history of rockets as well as the behavior of model rockets. For a succinct explanation of the functions of both, the Bedford Astronomy Club put together this page, from which I created the design for the cutaway model of a solid rocket motor. UK Space has a nice page to show some of the various designs and sizes for rocket motors that were designed in the 1950’s and 60’s.

Thrust behavior in a solid rocket motor is directly dependent on the configuration of the grain inside the motor. The surface of the grain combusts, exposing more grain, which combusts, and the process continues. NASA has this GIF that illustrates this nicely. This webpage has the thrust graphs for each grain configuration that is available in this project. Richard Nakka has documented numerous designs of motors and nozzles if you or your students wish to model and print more varieties. His website features data from countless tests and a thorough background on rockets, propulsion, and propellants. He has a lot of good links for further information as well.

After introducing rockets and discussing solid rocket motors, you are ready to move on to evaluating the variety of grain configurations: students (or groups) should be given one grain cross section to work with.

In Math and Science, you can ask your students to:
Use a true size determined by you to calculate scale, or work backwards, knowing the scale but not the true size.
Since surface area affects thrust behavior, calculate the surface area of this particular grain configuration, given a length specified by you.
Determine the cross sectional area of their piece of grain.
Determine the mass of the grain in a rocket if it was a length and scale that you give to the group. To determine the mass from the volume, students would need a density, which could be given as 1.70 g/mL.
Using the graphs of thrust v. time for various cross sections, students can create an initial thrust vs. surface area graph as a class. (If you choose this activity, make sure you are using the six cross-sections that align with the thrust v. time graphs). A follow on activity for this would be to hypothesize on what the graphs would look like for those cross sections that we don’t have graphs for.

To incorporate more research and writing, this project can be expanded to ask students to hypothesize on the utility of a specific grain pattern and thrust v. time graph. In other words, “In what situation would you prefer to have the grain configuration that you have been assigned?” This activity will encourage students to investigate the various applications of rocket motors and to evaluate what rocket behavior would be preferred in those applications. For example, a booster rocket to launch a satellite would behave very differently from a surface to air missile or a bunker buster.

Skills Learned

  • K-2-ETS1-1
  • K-2-ETS1-2
  • MS-PS3-1 Energy
  • MS-PS3-5 Energy
  • HS-PS3-1 Energy
  • HS-PS3-2 Energy
  • HS-PS1-4 Matter

Rubric and Assessment

Students can be assessed on using measuring tools with accuracy and precision. They can also be assessed on mathematical computations, graphing skills, and communicating their results. If you pursue a research assignment, assessment can be based on ELA standards as well.

References

http://link.springer.com/chapter/10.1007/978-3-540-69203-4_4
http://www.nakka-rocketry.net/th_grain.html
http://www.nakka-rocketry.net/th_pix/grains4.gif
http://www.astronomyclub.xyz/chamber-pressure/chemical-rocket-propulsion.html
http://www.spaceuk.org/solids/solids.htm
https://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/rktengine.html
https://www.grc.nasa.gov/www/k-12/rocket/rktengperf.html has a gif of the thrust graph
https://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Rockets.html
http://aerospacengineering.net/?p=1255

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