Mechanics

Cuboid

The Cuboid Module has two functions. Firstly the cuboid conducts the heat flow created during the re-entry to the testing cells and secondly it protects the experiment from external influences.

These two functions require conflictive characteristics. On the one hand the heat conduction requires thin walls in order for the heat to be conducted to the testing cell quickly and without any loss. On the other hand the cuboid is exposed to high mechanical forces while landing and thus has to be very robust in order to protect the experiment.

The body of the cuboid is hollow and will be screwed on the coverplate. Only a thin wall separates the cuboid in two parts. This wall is necessary to protect the electronic components. On the top of the cuboid is a cap which will be fixed to the body with countersink screws. As an assembling aid the cap is provided with a chamfer. With this cap you have the opportunity to make modifications or change a test cell.

The cuboid has windows on both sides through which the test cells will be inserted. This has the advantage that the test cells can be assembled beforehand and subsequently only need to be inserted and mounted into the cuboid. These windows lie at height of 133 mm above the coverplate, so that an ideal heat development can be expected and disturbance will be avoided. The specimens will be secured from the outside by countersink screws above and beneath the windows.

The cuboid will be made out of aluminum which does not only conduct heat very well but also provides satisfactory stiffness and the required protection during landing. In addition aluminium is a very light material. This is important because the rocket can reach a higher altitude if you save weight.

Testcell

The test cell houses the specimens and the temperature sensors. Because multiple specimens have to be mounted on the cuboid, these specimens have to be the exact same in size so that the measurements of the different specimen can be compared to one another. For each specimen two thermo-elements will be used for measuring the surface temperature. From these two one element will measure the boundary temperature of the central measuring zone and the other element the temperature in the middle of the measuring zone. The thermo-elements on the surface of the specimen are mounted to the cuboid with the help of groovings and pockets. The thermo-elements which measure the surface temperature at the bottom side of the specimen will be fixed on copper plates that are embedded in a thin rubber layer inside pockets. Thus the thermo-elements do not have to be glued to the specimen and a non-destructive assembly and disassembly of the testing cell is enabled.

The rubber layer is made out of a very heat resistant material. Fluororubber has proved itself very suitable for aerospace because it can be utilized for temperatures over 200 °C and under vacuum conditions.

A second specimen is used as a boundary isolation, which will guarantee the same temperature at the bottom of the first specimen and the top of the second specimen, so that there will be “no” heat flow between these surfaces. In order not to influence the exactness of the measurement, the thickness of the specimen may not vary more than 2 % from another.

The experiment and thus the test cell are exposed to high acceleration forces and vibrations during the flight. This can lead to a detachment or displacement of the specimen. For this reason a pretension device has been constructed that is mounted to the mounting bracket. The pretension for the specimen consists of eight stacked disc springs according to DIN 2093 B and shall press the different layers of the testing cell against the wall of the cuboid and prevent displacement.

Camera Module

The mechanical fixation of the camera will be realized in two ways for reasons of redundancy. The fixation shall prevent the camera from becoming loose. The chosen camera has a mount on the top. With this mount the camera will be fixed to the coverplate. The front of the camera lies towards the bottom side of the coverplate. The lense looks through a hole in the coverplate facing towards the top of the rocket. In addition the camera will be secured with a cage. This cage will be set up over the camera and screwed on the coverplate. Four disc springs are placed between the cage and the coverplate and are responsible for a pretensioning force, which also prevents that the camera gets loose.

E-Box Module

The E-Box module is composed of two boardbrackets, two boards and all electrical components. The boardbrackets are screwed on the bottom side of the cuboid and are located in the upper part of the cuboid. Because of the heavy vibration, the arising forces and accelerations the boardbrackets are fixed additional to the cuboid. At the same time the E-Box module shall be designed in such a way that all necessary plugs are on the outside, so in order to connect the electronic components with the test cells the brackets do not have to be removed. This leads to a least 24 plugs for temperature sensors, three plugs for the REXUS communication system, one for the power supply, one for the communication link of the camera and one for the link to the computer, being on the outside of the brackets. All other necessary links are inside the E-Box module and will already be connected during the assembly of the E-Box module. In order to tell the plugs for the temperature sensor apart from another a color/matrix-combination system will be developed. It consists of different colors and combinations between numbers and letters similar to that on a chess board.

 

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