New reinforcement design for the Upper Hemisphere

Hej!

In the next days we will go through the design of the Ribs of the Upper Hemisphere. We want to redesign them since we have had couple of failures during the drop test.

The Ribs are the vertical supports attached to the Upper Hemisphere of the FFU.

The Ribs act as a lateral and rotational constrain and prevent any rotations or movements of the Upper Hemisphere with respect to the Internal Metal Ring. Thanks to the Ribs it is possible to screw together the Upper and the Lower Hemisphere. The Ribs are also crucial for what concern the Deployment System of the Parachute.

 

During the drop test we had two main problems concerning the Ribs.

First, all the failures have occurred because the Ribs were not well glued to the Hemisphere, this is due to the fact that they were made using PVC. Unfortunately it is not possible to glue properly PVC using Epoxy, and this led to the failures.

Second, since every Rib is glued by hand, the alignment between each Ribs and the Spikes of the Metal Ring were “adjusted” using sanding tools. This solution was good enough for the first prototypes tested in the drop test, but we have to find a better solution.

The new concept design will be based on the idea to add one ring, made by the same material of the sphere, at the border of the Upper Hemisphere. The Ring, that will have all the functions of the Ribs, must be designed in order to fit perfectly inside the hemisphere avoiding all eyebolts and screws.

Since the Ring will be made using the same material of the Hemisphere gluing it with Epoxy will not be as problematic as it was with the PVC. Moreover the ring will be cut using by laser cutting, so the positions of the holes will be precise and the holes will match perfectly with the Spikes.

 

Pictures of the new Ring will be published soon! Bye!!

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Parachute

The parachute will be housed, for the entire flight, under the upper hemisphere of the FFU.

Calculations of the terminal velocity has been made and the Top Flight ThinMill 30″ X-shape has preliminary been chosen. This parachute will be sufficient to achieve a landing speed of around 10 m/s for the preliminary mass estimate of the FFUs. Drop and deployment tests will be made, similar to previous KTH REXUS teams, which will determine the final parachute size.

An extra precaution has been made regarding the packed volume of the parachute. Volume estimates of a few parachutes has been made (including cords) and the ThinMill 30″ packs well inside the upper hemisphere and weighs only 28g/m2 (!). Folding tests were made with fabric of the same density and size as the ThinMill 30″ and the results were implemented the volume estimates. More folding experiments will be performed with the parachute and the ropes to find the most efficient and reliable packing method.

The connection between the parachute and the FFU will be through a long rope to ensure that the parachute ropes do not entangle during the descent. Tests will be done to determine that the parachute can withstand the shock force when deployed.