The Falcon Project based on Westcott Venture Park, the old Rocket Research Establishment near Aylesbury is one of only three companies who currently manufacture solid fuel rockets and rocket propellants in the UK.
Previously we used conventional high shear mixing to combine the propellant components such as aluminium powder, ammonium perchlorate, various binders and HTPB rubber; However, Falcon is adopting Resonant Acoustic Mixing (RAM) for new applications because RAM offers high yields >95, a 50, a 60, our problem is that the mixing action (which takes place in a closed vessel clamped to a table which vibrates at the resonant frequency of the vessel and table) is not fully understood.
For consistency, it’s critical that the propellant constituents are uniformly dispersed, and how that takes place is particularly where the components can have different sizes and densities let alone the effect of other additions to plasticise the HTPB rubber base is unclear.
Our objective is to develop a technique to enable us to follow the dynamic mixing process whilst it’s in progress both for quality control and optimisation of new formulations.
In presenting our challenge to A4I, NPL have agreed to work collaboratively and with the expertise and innovation focus of NPL to evaluate Laser Doppler Vibrometry (LDV), Laser Interferometry (LI), Acoustic Transmission Spectroscopy (ATS) and Raman Spectroscopy (RS) for RAM of solid propellants.
With LDV, the spectral content of the vibrating RAM vessel surface will be analysed to identify spectral narrowing in the drive frequency as the ingredients mix.
For LI a fringe counting laser interferometer will be built for the LabRAM which will measure the mixing vessel’s displacement amplitude and drive frequency, thereby establishing its motion and stability of the drive system over time.
ATS will be developed for the LabRAM to conduct parametric studies in acoustic through-transmission measurements through the propellants during the mixing process.
Finally, RS will be evaluated, using facsimile mixtures initially on a mix interrupted basis.
The project objectives are that each technique will be evaluated as it applies to RAM of propellants with outputs of a report and demonstrator.
The innovation is that none of these methods has been applied to monitor the progress of RAM let alone rocket propellant mixing.