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Most conventional spacecraft use one of two chemical rocket designs, liquid fuel or solid fuel. Both designs rely on the same core principle, a highly reactive fuel is supplied with an oxidising agent and then ignited. For a liquid rocket both the fuel and the oxidiser are kept in liquid or gaseous forms and then mixed together before ignition. A solid rocket has the two components premixed and compacted into a solid core. Both designs have advantages and disadvantages, but did you know that there exists a third type of chemical rocket?

This rocket is known as a hybrid rocket and it takes the advantages of the previous two types and mixes them together.

Diagram of a hybrid rocket engine. It shows fuel flowing from the oxidser tank to the pumping unit then through the flow channel that contains the solid fuel core.
Hybrid Rocket Engine

 

The hybrid rocket has a solid core of fuel which has a oxidiser pumped through it. Typical oxidisers include gaseous oxygen or liquid oxygen that is vaporized. As the oxidiser is in either a gaseous or vaporised form, it is easily able to cover the surface area of the fuel core. The fuel in the presence of this oxidiser is now able to be ignited, generating thrust. As you can see in the diagram below, such a rocket is an exceptionally simple device, requiring minimal pumping or mixing.

So why choose this hybrid engine over conventional designs? As I mentioned earlier a hybrid rocket takes many of the advantages offered by its two colleagues. A few of the most notable are listed below.

  • Simplicity of design – Whilst not as simple as a solid rocket, a hybrid rocket is far less complex in design than an equivalent liquid rocket. This is due to its single flowing fluid and lack of mixing chamber.
  • Controllability – Unlike a solid rocket, a hybrid rocket can easily be controlled by the flow of oxidiser within the system. This gives it similar characteristics to liquid rockets.
  • Safety – The clear mechanical separation, and different phase states of the oxidiser and fuel allow hybrid rockets to be far safer than either solid or liquid fuel designs.
  • Port design and custom regression rate – By changing the geometry of the oxidisers flow channel, different fuel regression rates may be achieved with minimal changes to the greater system.

However the most interesting advantage offered by these rockets is something quite new to the market, 3d printing. You see the fuel in a hybrid rocket can be almost any polymer. This means that materials such as abs plastic or petg can be used as fuel. Not only are these readily accessible, but they can also be 3d printed with almost any home setup.

Yes that’s right, you can 3d print a rocket at home. In fact 3d printed hybrid rockets are becoming very common amongst both universities as well as actual spacecraft companies. For instance Gilmour space, an Australian rocket company, has been developing such a rocket for several years now and plans to launch in 2018. 3d printing offers a world of new possibilities for hybrid rockets with the ability to custom design thrust profiles and times for any rocket using hybrid propulsion. An example of the complexity that 3d printing can offer is shown in the picture below.

3D Printed Rocket Fuel for a hybrid rocket.
3D Printed Rocket Fuel <https://en.wikipedia.org/wiki/File:3D_Printed_Hybrid_Rocket_Fuel_Grain.jpg>

Hybrid rockets are a fantastic propulsion method, and there are many new end exciting ways that they will be developed in the coming years. My mechanical engineering honours thesis will see me conduct more research into this area, likely looking into different 3d printed designs for these rockets. Stay tuned to these blogs in 2018 for more hybrid rockets!

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It’s one thing to design a satellite or rover, but without manufacturing you’re dead in the water. Over the years at BLUEsat the problem, or more specifically the cost, of manufacturing has been recurring issue for our mechanical engineering teams. It’s not unusual for the bill for manufacturing our designs to come in at several times our material costs, not to mention long lead times, lack of quality control and no second chances once the part comes in.

Late last year the society decided that enough was enough and purchased a CNC router. A CNC is a simple machine at its core. It consists of a rapidly spinning tool that cuts away at material, which is then mounted on driven guide rails, controlling its position in space. Using this system in combination with computer controls, a CNC router can cut out almost any geometry that we choose.

BLUEsat's CNC Router
BLUEsat’s CNC Router

The process for making a part on the CNC has three stages:

  1. Model the part in CAD, we use Autodesk Inventor.
  2. Create a tool path using CAM software, we use HSM
  3. Secure your material to the CNC router, load the tool path, and begin cutting.

One of the parts that we made recently was an aluminium work holding jig. The model is shown below. This part has some complex features such as bottom rails, notched sides, counterbored holes and raised supports. To make this part by hand would take days and a very competent machinist, and we don’t have access to either.

Jig Plate CAD model
Jig Plate CAD model

Using this model, a tool path was developed with CAM software. The program does most of the heavy lifting, but the user must define the positions of each feature, the speed the machine moves at and how fast it will spin. These speeds are very important to the quality of the final piece and must be tailored to each feature. Below is an example of what the tool path looks like on the computer, red lines indicate that the machine is moving, blue lines show it is cutting.

 

Jig Plate CAM operations
Jig Plate CAM operations

Finally, with our tool path created, we were ready to set up the CNC itself. The material needs to be secured to the surface of the bed to prevent any movement during the cutting operation. This can be done in a number of ways, such as using a machine vice or work holding clamps. For this piece, we started with work holding clamps and then secured it using holes drilled into the material itself.

Now onto the fun part, the cutting. The tool path is loaded onto the CNC and the machine is set to run. Generally, we do a single operation at a time. This gives us time to clean up after each cut and inspect if it was successful. Here are a few videos of cutting.

 

 

 

 

All up, this part took 6hrs to machine. That included the setup, cutting and cleaning up of the part. Below is the final part:

Completed Jig Plate
Completed Jig Plate
Bottom View
Bottom View

 

 

 

 

 

 

 

 

 

 

 

Using our CNC has allowed for rapid prototyping of parts, drastically reduced lead times and most importantly, cut manufacturing costs by an order of magnitude.