Tasha – This vehicle was the beginning of the final phase of controlled manuevers. One uncontrolled flight was done with this vehicle configuration to characterize the pitch over after clearing the launch guide. This phenomenon is due to thrust offset which had also effected some earlier flights but was hard to predict. More than 20 degrees of pitch over occurred in the first second for this launch which led to a redesign of the rocket nozzles before any further launches were undertaken. The major reason for this redesign was to allow the safe implementation of control in an aerodynamically unstable configuration, which was a key project deliverable requirement for Rocket Lab.
Tasha II – This vehicle was used to complete the PhD research of Malcolm Snowdon and Avinash Rao. It provided data to retrospectively validate real-time 6DOF modelling and to further develop and test the analytical model-based control methodologies. These methods identify dynamics “on-the-fly” including accounting for complex disturbances like canard-fin vortex interaction. The disturbances are modelled by an equivalent piecewise constant fin angle which represents the effective torque applied to the rocket in a given time period as discussed in the publication “Hann, Snowdon, Rao et al, Minimal modelling approach to describe turbulent rocket roll dynamics in a vertical wind tunnel, Journal of Aerospace Engineering”. As a result of these analytical control methods, the rocket was controlled to within a fraction of a degree of vertical and was also pointed in various directions with errors around a mean of 0.1 degrees which is close to the sensor error. The final launch was an aerodynamically unstable configuration, which was achieved by using smaller tail fins to move the centre of pressure in front of the centre of mass. The rocket was initially tested in the wind tunnel in a gimbal frame. As soon as control was switched off wirelessly for a short time, the rocket collided with the side of the wind tunnel, proving that it was an unstable rocket. The launch at Birdlings flat was a complete success. The rocket was controlled to within a fraction of a degree of vertical, even though it was aerodynamically unstable with many disturbances and turbulence present. This launch proved the effectiveness of the minimal modelling, real-time identification and analytical control methodologies and provided the final validation and deliverable for the PhD research.