Back in October 2018 I joined one of my engineering school student non-profit organization : Air ESIEA.
It’s a small team of student (12-14 members) that tries to educate the school student to the aerospace fields of engineering. How ? By building small size rockets of course !
That is how I got involved in the design and manufacturing of a rocket…
Every project start with a specification sheet, here a summary of ours :
- The rocket height must respect the following contains :
- the global height must be bellow or equal to 25OO millimeters,
- the fuselage width must be bellow or equal to 150 millimeters,
- the rocket weight (without the rocket engine) must be bellow or equal to 8000 grams. (Otherwise it will not fit in the launch racks.)
- The rocket cannot have any guidance system.
- The rocket must have a recovery system (e.g : parachute).
- The rocket must carry an experiment.
With these requirements in mind we started working on it. After few hours of discussion with the team members, we’ve settled on the height, width, weight, materials, shape and others aspects of the rocket.
Sagittarius is one of the constellation that makes up the milky way and mean “archer” in Latin. It is commonly represented as a centaur pulling back and arrow, that’s why its symbol is a stylized arrow : ♐.
It is also the name of our rocket.
It will carryout in its fuselage a trajectography experiment that will enable us to recreate in 3D its fly.
Here are the specification of Sagittarius :
|Width (fuselage)||100 mm|
|Material||Glass Fibre reinforced Epoxy|
|Chute size||0,92 m²|
The rocket engine we work with is a Pro54-5G Classic™ form Cesaroni Technology. This engine is provided gratuitously by the CNES and Planète Sciences which are the organizations managing the launch campaign.
With these specifications our rocket should reach an apogee of 1621 meters at T+17,3s and deploy its chute to land gracefully around T+168s. All the simulation data is available in this excel document (in french ).
![Ballistic launch][ballistic] ![Ballistic launch with parachute][ballistic-with-chute]
With this rough idea of the shape we want Sagittarius to have in mind, I started to work on the CAD modeling of the rocket.
I used the student edition of Autodesk Fusion360 designed the entire rocket to get a 3D view of it. It helped us a lot to figure out how to integrate various elements of the rocket and to improve its mechanical structure. Sadly, because of issues on our CNC router, we did not have the chance to work with the CAM feature of Fusion360. But I hope we will for the next one!
Last part of the CAD : creating the blueprint of each part !
The manufacturing of Sagittarius is done is divided in couple parts, each one having its lot of fun, greasy / dirty hands and suspense.
The airframe of Sagittarius is made of several layers of glass fiber bounded together with a foam epoxy. With this method, we can create a self-supporting structure with good horizontal elasticity and proper vertical rigidity.
But there is a cost of using fiber glass : weight. That’s why we will try to use carbon fiber instead for the next version of this rocket.
Oh ! I almost forgot the fun part : wrapping the fiber glass around a PVC pipe !
The lower assembly of Sagittarius is composed of two main parts : the fins and centering rings. These parts are fastened together with bolt and locking nuts and then fixed to the fuselage.
The fins are made of 6 mm thick aluminum capable of resisting up top 5G of acceleration, which is the one given by the rocket engine we use.
Three of the four centering ring are made of polyoxymethylene (a.k.a Delrin™) and serve the centering of the engine. The last one is made of 10 mm thick 5G aluminum and transfer the trust of the engine to the whole rocket.
With the fuselage cleaned and the lower assembly mounted it is time to make the fairing and cut chute hatch open!
Well the fairing was a sort of failure because we did not manage to detach it from its mold… Bur why bother ?! It fit perfectly on the rocket. The hatch was openned with a Dremel and a release system is mounted on it so we can trigger it electrically.