Mini Rocket Engineers

In my current STEM lessons (science-technology-engineering-maths), we are figuring out how to make a mini rocket that can actually be launched (a few (centi)meters high). We're digging deeper into concepts like rocket engines, rocket fuel and 3D designing and printing prototypes.

for the rocket fuel: vinegar, baking powder, plastic test tube, cork that fits the tube

for the rocket: TinkerCAD, 3D printer, a small cork (test tube size)

The European Space Education Resource Office offers interesting lesson plans on their website:

https://eserobelgium.be/index.php/nl/bibliotheek-met-lesmateriaal-voor-het-secundair-onderwijs/

I used the one on making a rocket ('Een raket maken' in dutch). Start off by letting students find out about the difference between a rocket engine and an aircraft engine. In the end, you'll figure out together that you'll need an expanding gas and the third law of Newton (action-reaction). The combination of vinegar and baking powder creates CO2-gas. This will be the rocket fuel.

As mentioned in the lesson plan in the link above, make a vinegar-baking powder mixture in a plastic test tube by first adding vinegar. Next, hold the tube as horizontal as possible. Add baking powder without making contact with the vinegar. Add the cork. Turn the tube upside down in another recipient, take a step back and watch it launch into the air.

I had a very light test tube at first and it launched several meters into the air. Thicker tubes obviously don't launch as high.

Where the original lesson focusses on the chemistry of this rocket fuel (where you can add in an interesting lesson in chemistry and defining the ratios in which the materials react with each other), I decided to find out whether we can design our own plastic rocket. Tell the students they'll need to design their own rocket that will be fueled by the baking powder-vinegar mixture.

Let them think about the design specifications for this rocket.

We came up with the following specifications

• needs to be strong enough so it doesn't blow up
• there should be no leakage for the gas before enough pressure is built up to push the cork out
• the vinegar and baking powder should only make contact when you want them to
• mass as small as possible, but still printable
• it needs to be hollow to hold the volume of rocket fuel
• the cork needs to fit at the bottom
• shape: think about aerodynamics, it should launch upright and preferably stand upright without support
• it shouldn't have sharp edges for safety reasons

You see that each constraint needs some more investigation: what thickness can your printer print for an elongated shape, how much volume do you need for your rocket fuel, what tolerances do you need to fit a cork into a 3D printed shape....Depending on your time for this project, you can dig deeper into each one of them with your students.

In TinkerCAD, you can create a 'lesson' as educator. You can add students names, which will generate a class code and an alias for every student. If they use this account, you will have acces to all their designs. Show them the basic introduction into TinkerCAD and let them design their rocket, keeping in mind the design specifications.

In the picture, you see two of the many possibilities with only basic shapes. They will need to use the align tool (to center the smaller inner tube to subtract from the bigger one to make everything hollow), pay careful attention to the measurements (since it needs to fit the rocket fuel and the cork), think about how it will be printed (preferably without support structures)... I prefer not to give them an example, so they will start from their own imagination.

(The green one in the picture leaves some room for the cork to fit while the rocket is standing upright, but needs support structures to print).

As soon as you're happy with one of the designs (checking all design specifications), you can print out the rocket. The one I printed as a test, needed 2 hours to print. After it is printed, fuel it up (again, just a mixture of your choice of vinegar and baking powder), place the cork, turn it upright and watch it launch!

Please note you need a good fitting cork to make sure enough pressure will be built up before te cork flies out of the rocket by the expansion of the gas. The rocket will thus exert force on the gas and cork to push it downwards so the gas will in turn exert force on the rocket to launch it into the air (third law of Newton).

Now it's time to analyse the results and go back into the redesigning phase if needed. How can you make it fly higher (less mass, more fuel...). Were all specifications met? What improvements can you think of?

Depending on the time you have, you can add in more science. For example, you could analyse the movement of the launch with tracker software. Or you can carefully calculate the volume of rocket fuel needed.

Have fun tinkering this projects together with your students!