Kevin Worrall

A Parametric Study for the Design of an Optimized Ultrasonic Percussive Planetary Drill Tool

Traditional rotary drilling for planetary rock sampling, in situ analysis, and sample return are challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This paper seeks to optimize an ultrasonic percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view toward building an ultrasonic planetary core drill (UPCD) device. The UPCD is a descendant of the ultrasonic/sonic driller/corer technique. In these concepts, a transducer and horn (typically resonant at around 20 kHz) are used to excite a toroidal free mass that oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10 Hz and 1 kHz). This creates a series of stress pulses that is transferred through the drill bit to the rock surface, and while the stress at the drill-bit tip/rock interface exceeds the compressive strength of the rock, it causes fractures that result in fragmentation of the rock. This facilitates augering and downward progress. In order to ensure that the drill-bit tip delivers the greatest effective impulse (the time integral of the drill-bit tip/rock pressure curve exceeding the strength of the rock), parameters such as the spring rates and the mass of the free mass, the drill bit and transducer have been varied and compared in both computer simulation and practical experiment. The most interesting findings and those of particular relevance to deep drilling indicate that increasing the mass of the drill bit has a limited (or even positive) influence on the rate of effective impulse delivered.

Application of Inverse Simulation to a wheeled mobile robot

This paper presents the application of Inverse Simulation to the control of a mobile robot. The implementation of this technique for motion control has been found to provide highly accurate trajectory tracking. Since the input to the Inverse Simulation is a time history of the desired response, then greater control over the position and orientation of the mobile robot can be achieved. There are many situations where the desired path of a mobile robot is known e.g. planetary rover navigation, factory or warehouse floor, bomb disposal. Typically the robot is either controlled remotely or runs an online controller to navigate the desired path. For a given path, a navigation system generates the desired drive parameters (i.e. heading and velocity) and the associated controllers drive the corresponding actuators. Traditionally the controllers are required to be tuned using knowledge of the limitations of the mobile robot. Inverse Simulation provides a means of generating the required control signals with no need for controller tuning. The use of Inverse Simulation is suitable in cases where the cost of the mobile robot or actuators is high, desired drive requirements need to be met or for situations where tight tolerances on the trajectory are to be achieved. In this paper the benefits of applying Inverse Simulation to the control of a mobile robot are discussed and appropriate results presented.

An experimental study of ultrasonic vibration and the penetration of granular material

This work investigates the potential use of direct ultrasonic vibration as an aid to penetration of granular material. Compared with non-ultrasonic penetration, required forces have been observed to reduce by an order of magnitude. Similarly, total consumed power can be reduced by up to 27%, depending on the substrate and ultrasonic amplitude used. Tests were also carried out in high-gravity conditions, displaying a trend that suggests these benefits could be leveraged in lower gravity regimes.

Sun tracking controller for UKube-1 using magnetic torquer only

CubeSats relying solely on small microcontroller have very limited computational resources, which restricts any usage of sophisticated control algorithms. Most existing attitude control algorithms require full state information such as attitude information in terms of quaternion, angular rate and a desired target direction. UKube-1 is a CubeSat commissioned by the UK Space Agency and integrated by Clyde Space Ltd. in Glasgow, UK. It has various payloads and requires to produce a certain level of power using the solar panels. Hence, it needs to search for the sun direction and keep the desired attitude while the sun is visible to the satellite. A sun tracking algorithm is developed, which uses the information from the coarse sun detectors and/or the rate gyro, and the magnetic-torquer only. The rate gyro measurement can be replaced by the low-pass filtered magnetometer measurements. The performance of the algorithm is demonstrated in a high-fidelity simulator.

Ultrasonically-Assisted Penetration of Granular and Cemented Materials

Granular material can often be penetrated by the application of high-frequency vibrations. This effect may be seen in loosely packed granular material, in permafrost where the discrete grains exist in an icy matrix, and even where those grains have been compacted and cemented to form a sedimentary rock. For space applications, the vibrations may be reasonably generated by a Langevin transducer and their energy delivered to the target material by a number of different mechanisms, depending on the nature of the target and the depth or bore diameter of the desired drill campaign. The application of such vibrations is generally associated with reductions in weight-on-bit and power requirements when compared to more traditional techniques.

Autophage Engines: Toward a Throttleable Solid Motor

This paper describes the instrumented test firing of a rocket that seeks to combine the throttleability of a liquid-fueled engine with the simplicity of a solid motor. The concept is that a differe...

Granular Materials in Space Exploration

This paper describes the effects of ultrasonically-assisted penetration of granular materials, in high gravity situations. The experimental rig, instrumented to obtain penetration force, rate and power both with and without ultrasonic assistance, was used to drive a penetrator into a granular material inside the ESA Large Diameter Centrifuge at accelerations of up to 10 g during early September 2015. Ultrasonic penetration proved to be most beneficial at lower levels of accelerations, reducing the required overhead weight by 80%, and the total power consumption by 27%.