Development of a switchable system for longitudinal and longitudinal-torsional vibration extraction

High-frequency/low-frequency drilling is an attractive technology for planetary exploration tools, and one which has seen considerable innovation in the techniques used to ensure rotation of the front-end cutting bit. This rotation is essential to prevent tooth imprintation in hard materials, and extracting the rotation from the high-frequency or ultrasonic system has obvious benefits in terms of simplicity and robustness. However, extracting the rotation from an ultrasonic horn raises the possibility of bit-walk if it is used to operate a coring device and the authors therefore propose an ultrasonic horn which uses an excitation applied to a single input surface to yield torsional and longitudinal vibration on two physically separated output surfaces. By engaging with the two output surfaces, longitudinal vibration can be extracted to achieve initial percussive drilling, even where a coring bit is applied, and the torsional output can subsequently be added to prevent tooth imprintation once the coring bit has settled into the site in question. In this manner, the horn provides a mechanism whereby high-frequency/low-frequency drilling technique can be applied to coring operations without the need for an exceptionally robust drill structure capable of resisting bit-walk forces

Optimisation of an ultrasonic drill horn for planetary subsurface sample retrieval

Ultrasonic tools can cut through foodstuffs, biological material and other soft matter with relative ease. However, when attempts are made to cut through harder material, the rate of progress markedly declines. Under such circumstances it is sometimes necessary to reduce the frequency of the blows delivered to the target, in order to ensure that each blow exceeds the compressive strength of the material, but for space applications the small size of high-frequency ultrasonic horns is extremely attractive. This paper therefore considers the optimization of horns for exploitation of the high-frequency/low-frequency drilling technique, whereby a free-mass oscillating between the horn and the target is employed to reduce the frequency at which impulse events are delivered to the target

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

Synchronized orbits and oscillations for free altitude control

No abstract available

Pocketqube Deorbit Times: Susceptibility to the Solar Cycle

Nowadays, as a new kind of femto-satellite with a low cost, Pocketqube has been developed to finish the space research task within the LEO region. During its lifetime the pocketqube is exposed to a high risk of collision with space debris. Taking the solar cycle as a main factor, predicting its deorbit time and evaluating its collision probability before the launch is of great importance for the mission designers to choose a right orbit and determine the proper launch time. This article presents a combined atmospheric density model based on the data from CIRA-2012 to describe the effects of the solar cycle on air density in LEO, and shows how the model is applied to calculate orbital lifetimes of pocketqubes in essentially circular equatorial orbits below 800 km altitude. Then the classical fourth order Runge-Kutta method is utilized in integrating the first order differential equations, which express the rates of change of semi major axis and eccentricity, in order to calculate the orbital lifetimes of pocketqube in LEO. The launch date within the 11-year solar cycle has been chosen as an independent variable to present the influence on lifetime prediction and probability evaluation. The result of lifetime calculation shows that the pocketqube launched at the minimum solar activity year does not necessarily get its longest lifetime. Meanwhile if the pocketqube at some specific starting altitudes is launched at the maximum solar activity year, it may remain in orbit for the longest time period. It also demonstrates how the sensitivity of pocketqube deorbit time to the launch date varies with the initial altitudes. From the figures, it can be obtained that 450 km is the altitude at which the deorbit time is most sensitive to the launch date with the percentage amplitude of 180% over its average value. Furthermore, the collision risk from space debris whose diameter is larger than 1 mm and 10 cm are evaluated by using the same method to integrate through its whole lifetime. It illustrates that for those orbits whose initial altitude is over 700 km, no matter which date is chosen to launch a pocketqube, the debris collision risk grows sharply with the starting altitude rising. Finally, by comparison with the trend of lifetime and collision risk, the interesting thing is that at some orbits with higher altitudes, like 800km, when the lifetime of the pocketqube reaches its maximum, the collision risk inversely reaches its local minimum, which can be useful for its designers to balance these two considerations

Design of a Solar Panel Deployment and Tracking System for Pocketqube Pico-Satellite

Modularized small satellites will have even greater potential with better energy supply. In this paper, a PocketQube solar panel deployment and tracking system will be presented. The system is designed for a 3P PocketQubes. During the designing phase, trade-off analysis is done to meet the balance of weight, dimension and efficiency. Reliability, manufacturability, and cost are also considered from the beginning, as commercial production and launch are expected. The CAD design, dynamics analysis, motion simulation, and rendering for the project are undertaken by Solidworks, whereas Abaqus CAE is utilized for the finite element analysis of the vibration test of the panels. In the gimbal subsystem, we use two micro stepper motor to drive the panels via a two-axis gearbox, enabling the panels to track the sun omnidirectionally. In the panel subsystem, two types of customized spring hinges are designed. Robust and verified parts, such as burner resistors, are chose for the control and deployment system. After the continuous optimization process throughout the design phase, by comparing different manufacturing processes technologies, materials, and design details, the full scale prototypes of the gimbal subsystem were built and tested. In the end, the most feasible solution, as well as the suggestions for the development, were put forward

Full and half-wavelength ultrasonic percussive drills

Ultrasonic-percussive drills are a leading technology for small rock drilling applications where power and weight-on-bit are at a premium. The concept uses ultrasonic vibrations to excite an oscillatory motion in a free-mass, which then delivers impulsive blows to a drilling-bit. This is a relatively complex dynamic problem involving the transducer, the free-mass, the drilling-bit and, to a certain extent, the rock surface itself. This paper examines the performance of a full-wavelength transducer compared to a half-wavelength system, which may be more attractive due to mass and dimensional drivers. To compare the two approaches, three-dimensional finite element models of the ultrasonic-percussive stacks using full and half wavelength ultrasonic transducers are created to assess delivered impulse at similar power settings. In addition, impact-induced stress levels are evaluated to optimize the design of drill tools at a range of internal spring rates before, finally, experimental drilling is conducted. The results suggest that full-wavelength systems will yield much more effective impulse but, interestingly, their actual drilling performance was only marginally better than half-wavelength equivalents

Attitude stability and altitude control of a variable-geometry Earth-orbiting solar sail

A variable-geometry solar sail for on-orbit altitude control is investigated. It is shown that, by adjusting the effective area of the sail at favorable times, it is possible to influence the length of the semi-major axis over an extended period of time. This solution can be implemented by adopting a spinning quasi-rhombic pyramidal solar sail which provides the heliostability needed to maintain a passive “sun-pointing” attitude and the freedom to modify the shape of the sail at any time. In particular, this paper investigates the variable-geometry concept through both theoretical and numerical analyses. Stability bounds on the sail design are calculated by means of a first-order analysis, producing conditions on the opening angles of the sail, while gravity gradient torques and solar eclipses are introduced to test the robustness of the concept. The concept targets equatorial orbits above approximately 5,000 km. Numerical results characterize the expected performance, leading to (for example) an increase of 2,200 km per year for a small device at GEO

Attitude and Orbital Dynamics of a Variable-Geometry, Spinning Solar Sail in Earth Orbit

At the ISSS 2013, a novel concept of variable-geometry solar sail was introduced: deployed in the shape of a three-dimensional quasi-rhombic pyramid (QRP), the sail exploited its shape and shift between center of mass and center of pressure to naturally achieve heliostability (stable sun-pointing) throughout the mission. In addition, mechanisms allowed to vary the flare angle of the four booms in opposite pairs, thus allowing to control the area exposed to the sun without the need of slew maneuvers. Using these adjustments in favorable orbital positions, it is possible to build a regular pattern of acceleration to achieve orbit raising or lowering without the need of propulsion system or attitude control. Subsequent more detailed investigations revealed that eclipses, even if lasting only a fraction of the orbit, have a substantial (and negative) impact on the heliostability effect: and even a small residual angular velocity, or disturbance torque, are enough to cause the spacecraft to tumble. In this work, we present a novel and improved concept which allows the sail to preserve its attitude not only with eclipses, but also in presence of disturbance torques such as the gravity gradient. The solution we propose is to add a moderate spin to the solar sail, combined with ring dampers. The gyroscopic stiffness due to the spin guarantees stability during the transient periods of the eclipses, while the heliostability effect, combined with the dampers, cancels any residual unwanted oscillation during the parts of the orbit exposed to the sun, and at the same time guarantees continuous sun-pointing as the apparent direction of the sun rotates throughout the year. Both theoretical and numerical analyses are performed. First, stability bounds on the sail design are calculated, obtaining conditions on the flare angles of the sail, in the different orbital regimes, to test the robustness of the concept. Then, a numerical analysis is performed to validate the study in a simulated scenario where all perturbations are considered, over extended amount of time. The concept targets equatorial orbits above approximately 5,000 km. Results show that an increase of 2,200 km per year for a small device at GEO can be achieved with a CubeSat-sized sail

Optimisation of the longitudinal-torsional output of a half-wavelength Langevin transducer

Numerous ultrasonic applications, such as high-frequency/low frequency drilling, require or can benefit from the inclusion of some torsional vibration behaviour within a primarily longitudinal pattern. Producing longitudinal-torsional (LT) vibration in a Langevin transducer using the mode degeneration method tends to give more robust results than the competing mode-coupling approach, and this work is concerned with optimizing the relative strengths of the longitudinal and torsional responses within the context of a half-wavelength Langevin transducer. Using numerical and experimental techniques, the output of such a system is predicted across a range of geometries and compared to experimental results obtained through laser vibrometry