Patrick Harkness

Drag Sail for End-of-Life Disposal from Low Earth Orbit

International standards are moving toward the requirement that spacecraft should be removed from orbit at the end of their operational lives. The feasibility of a deployable aerodynamically stable drag-enhancement structure is considered for the end-of-life disposal of low-Earth-orbit spacecraft, and how this structure could fulfil NASA deorbit guidelines is demonstrated. The concept is a thin membrane supported by deployed struts. A shuttlecock like geometry is chosen to take advantage of the small stabilising effect caused by oscillatory motion in, and descent through, the free molecular flow during deorbit. The shuttlecock is approximated to a cone, and the aerodynamic loads due to orbital and rotational motion are calculated and used to model the stabilisation and descent of a deployed system toward final reentry. Finally it is is shown that this system can provide an effective and mass-efficient deorbit solution for future missions.

A Strategy for Delivering High Torsionality in Longitudinal-Torsional Ultrasonic Devices

A composite longitudinal-torsional vibration mode has applications in ultrasonic motors, ultrasonic welding and ultrasonic drilling. There are two ways to obtain this vibration behaviour using a single transducer, namely (i) coupling of a longitudinal and a torsional mode, which is known to be difficult; and (ii) degenerating a longitudinal mode to deliver longitudinal-torsional behaviour at the horn tip. A mode-degenerating horn is achieved by incorporating helical or diagonal slits in an otherwise traditional exponential horn driven by a Langevin transducer. However, it is often difficult with this configuration to avoid coupling of unwanted bending modes, low responsiveness, and loss of ultrasonic energy due to boundaries between tuned components. Therefore, in this study the mode-degenerating characteristics are achieved by incorporating the helical slits and exponential geometry features in the front mass of the transducer itself. Finite element analysis and vibration experimental analysis show that this strategy prevents coupling of bending modes, increases responsiveness, and reduces energy losses. Most importantly the transducer delivers a very high torsionality.

Planetary science and exploration in the deep subsurface : results from the MINAR Program, Boulby Mine, UK

The authors would also like to acknowledge the funding provided by the STFC Impact Acceleration Fund. Claire R. Cousins is supported by a Royal Society of Edinburgh Research Fellowship. The development of the ExoMars PanCam, the AUPE2 system and the PanCam data processing pipeline has been supported by funding from the UK Space Agency (lead funding agency) and the European Community’s Seventh Framework Program.

Variable-geometry solar sailing: the possibilities of the quasi-rhombic pyramid

Variable geometry solar sailing potentially offers enhanced delta-V capabilities and new orbital solutions. We propose a device with such capabilities, based upon an adjustable quasi-rhombic pyramid sail geometry, and examine the benefits that can be derived from this additional flexibility. The enabling technology for this concept is the bevel crux drive, which can maintain tension in the solar sail across a wide range of apex angles. This paper explores the concept of such a device, discussing both the capabilities of the architecture and the possibilities opened up in terms of orbital and attitude dynamics.

Coupling and degenerating modes in longitudinal–torsional step horns

Longitudinal-torsional vibration is used and proposed for a variety of ultrasonic applications including motors, welding, and rock-cutting. To obtain this behavior in an ultrasonic step horn one can either, (i) couple the longitudinal and torsional modes of the horn by incorporating a ring of diagonal slits in the thick base section or, (ii) place helical flutes in the thin stem section to degenerate the longitudinal mode into a modified behavior with a longitudinal-torsional motion. This paper compares the efficacy of these two design approaches using both numerical and experimental techniques.

Ultrasonic rock sampling using longitudinal–torsional vibrations

In the last years several European and US space projects have been focused on the development of surface rovers for planetary missions, such as ExoMars and Mars Exploration Rovers. The main function of these vehicles consists of moving across planet surfaces, and drilling and retrieving samples for in situ analysis. Recent research has shown that drilling of rock materials can be achieved using axially oscillating tuned devices which, compared with conventional rotary drills, operate at lower power and highly reduced preload requirements. As a result, at present, ultrasonics is considered a very promising technology for exobiological prospecting. In this work, two novel ultrasonic rock samplers, both operating in a longitudinal-torsional composite mode, are proposed along with the conceptual design of a full coring apparatus, for preload delivery and core removal. To assess the penetration capability of the excited composite vibrations, preliminary drilling trials were conducted. Since sand constitutes a significant portion of the Martian surface, sandstone was used in the trials.

Maximization of the effective impulse delivered by a high-frequency/low-frequency planetary drill tool

Ultrasonic tools are used for a variety of cutting applications in surgery and the food industry, but when they are applied to harder materials, such as rock, their cutting performance declines because of the low effective impulse delivered by each vibration cycle. To overcome this problem, a technique known as high-frequency/low-frequency (or alternatively, ultrasonic/sonic) drilling is employed. In this approach, an ultrasonic step-horn is used to deliver an impulse to a free mass which subsequently moves toward a drilling bit, delivering the impulse on contact. The free mass then rebounds to complete the cycle. The horn has time between impacts to build significant vibration amplitude and thus delivers a much larger impulse to the free mass than could be delivered if it were applied directly to the target. To maximize the impulse delivered to the target by the cutting bit, both the momentum transfer from the ultrasonic horn to the free mass and the dynamics of the horn/free mass/cutting bit stack must be optimized. This paper uses finite element techniques to optimize the ultrasonic horns and numerical propagation of the stack dynamics to maximize the delivered effective impulse, validated in both cases by extensive experimental analysis.

A brief overview of space applications for ultrasonics

Sonics and space are two topics which are not commonly considered together. However, sonic and ultrasonic models, devices and systems have space applications in both science and engineering, as well as showing promise in fields such as cleaning, healthcare and construction. This short paper describes some of these activities and appears as results start to come in from the Curiosity rover, which landed on Mars on the 6th of August, 2012, with over 20 piezoelectric and mechanically-resonant components on board.

Ultrasonic rock drilling devices using longitudinal-torsional compound vibration

Nasa funded studies have proven that ultrasonics is a viable technology for extraterrestrial drilling. Previous research by the authors has indicated that ultrasonic longitudinal-torsional coupled vibrations may improve rock excavation. In this study, two approaches to the development of torsional output from a Langevin transducer are pursued: coupling the longitudinal mode with a torsional mode and degenerating the longitudinal mode to output torsional motion at the tip using helical flutes cut into the sides of the horn. The amplitude of the output motion and the electrical properties of the horn whilst these modes are being driven are investigated and the findings are validated experimentally.

Architectures for ultrasonic planetary sample retrieval tools

Traditional rotary corers and sample retrieval mechanisms for planetary drilling suffer from a variety of technical difficulties. A heavy and rigid drillstring must be assembled on-site and deployed with considerable applied preload and torque, and these mechanical loadings are difficult to react in a low gravity environment. Furthermore the entire drillstring must often be removed to retrieve samples, unless an augering approach is taken, in which case stratigraphic sequencing is lost. Ultrasonic tools which operate by converting an ultrasonic frequency to a low impacting frequency at the tool end can resolve the mechanical problems because they require very low applied preload and no torque to operate. In developing such a tool, however, several fundamental design decisions must be taken regarding the architecture of the transducer, horn and stack. These include the choice of solid or hollow transducers and the employment of single or multiple free-masses at the ultrasonic to low frequency conversion location. This paper addresses the layout of such a system by contrasting the pros and cons of these architectural choices and concludes that a solid system with a single free-mass provides the best performance in the parameter range here discussed.