RASSOR_Challenge_Mikel_Iturbe

Last crawled date: 1 year, 10 months ago

HOW THE DESIGN WORKS AND INTENDED FILL RATIO

a) How the design works
The present RASSOR design has four drums with two scoops each of them. Each drum differs 45 degrees from the other. Therefore, at any given time only one or two scoops are engaged in the regolith in order to keep the low reaction forces of the actual RASSOR design developed by NASA.
Each drum has two channels through which the regolith goes in and out during loading and unloading, respectively. These channels exceed the 180 degrees with constant distance among the walls (to avoid possible clogging) so by the time the lower scoop has captured a specific amount of lunar regolith and it is going up again, the mass inside the drum does not fall out through the upper scoop when it reaches an inclination that would unload the regolith inside the drum.
The process described to load lunar regolith within the present design is only possible if there are two channels per drum and if each drum has no inner connection with the other drums when holding material inside.
Due to the large channels that exceed 180 degrees and the clogging problems in the scoops addressed during testing phases of the 1st RASSOR design a structured roughness surface has been incorporated, see figure attached, to the walls of the channels as a passive solution to avoid possible clogging scenarios. As defined in [1] a structured roughness surface has a strong impact in avoiding possible clogging situations due to the shear stress produced by this type of surface. “Findings demonstrate the importance of the shear stress on the propensity of tapered channels to clog. The higher shear stresses inhibit the attachment of particles to the channel walls, thereby delaying channel clogging caused by particle build up at the channel walls” [2].

b) Intended fill ratio
The total area of each drum is 0,134m2 and the width of the scoops/channels is 85,5mm. This gives us a total volume of 11,547 litres per drum.
The intended area to be filled has a diameter of 351mm as shown in the image attached. Therefore, the intended volume to be captured would be approximately 8,273 liters/drum. (Considering that the width of the scoops/channels is 85,5mm)
Fill ratio = (8,273/11,547) x 100 = 71,6%
Total Volume intended to be captured = 4 Drums x 8,273 l/Drum = 33.092 liters

IS THE DESIGN REAL? CAN THE DESIGN WORK? CAN IT ACTUALLY BE CREATED?

The present RASSOR design uses Aluminium sheet metal for the scoops with a density of 2640 kg/m3. Bolts and nuts are intended to be made from carbon fiber with a density of 1500 kg/m3. The main structures and taps of the design are intended to be built with polymer matrix composites [3] which densities can vary from 1100kg/m3 to 1700kg/m3. For the present design, a density of 1200kg/m3 has been used.
The total mass of the current bucket drum is 4.838Kg

DIMENSION REQUIREMENTS

See blueprint attached

SIMULATION

A short simulation has been carried out with EDEM (A discrete element method software) in order to check the loading and unloading process of the present design. See figures attached in their respective folder “RASSOR Simulation_Images”. The simulation time was a critical parameter to consider in order to end up with some results for the simulation.11 seconds of simulation have been captured to show how the design works. From second 5 to second 10 the design works in a loading mode. From second 10 onwards the design works in an unloading mode.

REFERENCES

[1] MARTINEZ, A; DAVID FROST, J; THE INFLUENCE OF SURFACE ROUGHNESS FORM ON THE STRENGTH OF SAND–STRUCTURE INTERFACES, MARCH 2017, DOI: 10.1680/JGELE.16.00169
[2] SORELL , S MASSENBURG; · ESTHER AMSTAD; · DAVID A. WEITZ; CLOGGING IN PARALLELIZED TAPERED MICROFLUIDIC CHANNELS, JUNE 2016, DOI 10.1007/S10404-016-1758-6
[3] BURYACHENKO, V; MICROMECHANICS OF HETEROGENEOUS MATERIALS, 2007, SPRINGER PUBLISHING COMPANY, 1ST EDITION