Speaker
Description
In the context of Design for Demise (D4D), there have been multiple attempts at incorporating energetic thermite powders inside hard-to-demise spacecraft components, to provide additional energy during re-entry. This philosophy is called Thermite for Demise (T4D).
Those attempts highlighted a multitude of problems and inefficiencies arising from the use of thermite in the form of loose powder.
In the EIC project THREAD, thermite consolidation strategies are being explored to solve this problem.
For this purpose, stoichiometric magnesium - silicon dioxide thermite was consolidated via Digital Light Processing (DLP) 3D printing with a solid loading of 60%. The composition was chosen for its overall favourable compatibility with the selected technology, based on powder granulometry, energy band gap, and lack of toxicity.
The complete production procedure has been fully detailed and reported.
The properties of the material were characterised in terms of ignition behaviour, burn rate, chemical kinetics, mechanical properties, friability, and Electrostatic Discharge (ESD) safety.
Mechanical properties were assessed by performing compression tests, obtaining results in terms of Young modulus and yield stress. Tumbling tests were employed to evaluate the behaviour of this material during handling and transport, a scenario where previous experiments conducted on pellets of simply pressed thermite showed remarkable fragility and a tendency to easily crumble.
Energetic properties were assessed by Differential Thermal Analysis (DTA) for the kinetic parameters, as well as for reaction onset temperatures at very low heating rates.
Igniting the samples on a resistive strip, heated by a controlled current source, allowed to recreate heating rates typical of re-entry. Temperature readings were performed using a pyrometer focused on the heating element, at the very base of the thermite sample.
The combustion reaction was captured via a high speed camera to determine the burn rate of the thermite under those conditions.
To guarantee the safety of people operating with this new material, ESD sensitivity testing was performed up to an energy of 0.05 J.
The material's mechanical properties were surprisingly almost unaffected by the high mass loading, when compared with samples of pure resin binder. Cylinders of the material also demonstrated great resilience to tumbling, losing little to no powder during the tests.
Precise controlled ignitions in the inert atmosphere of the DTA machine revealed an inhibited reactivity, when compared to the original loose powder, which is consistent with the presence of the binder. Ignitions on heated strips revealed a pulsed ignition behaviour, where the material alternated shedding its binder via pyrolysis and thermite ignitions in multiple steps. The burning rate was measured for each subsequent ignition event. The ignition temperatures recorded during said tests were consistently higher with respect to the ones seen during DTA analysis, underlying the difficulty of matching ignition data across those two diagnostics.
ESD testing revealed that both the loose powder and the consolidated one have no sensitivity to electrostatic discharges, an important feature for operational safety.
In conclusion, thermite consolidated via DLP 3D printing shows promising results in the creation of custom energetic components for possible future satellite demise applications.