The Debris Disk Explorer (DDX) is a proposed balloon-borne investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. DDX will measure the size, shape, brightness, and color of tens of disks. These measurements will enable us to place the Solar System in context. By imaging debris disks around nearby stars, DDX will reveal the presence of perturbing planets via their influence on disk structure, and explore the physics and history of debris disks by characterizing the size and composition of disk dust. The DDX instrument is a 0.75-m diameter off-axis telescope and a coronagraph carried by a stratospheric balloon. DDX will take high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Two flights are planned; an overnight test flight within the United States followed by a month-long science flight launched from New Zealand. The long flight will fully explore the set of known debris disks accessible only to DDX. It will achieve a raw contrast of 10−7, with a processed contrast of 10−8. A technology benefit of DDX is that operation in the near-space environment will raise the Technology Readiness Level of internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.
Increasingly, NASA exploration mission objectives include sample acquisition tasks for in-situ analysis or for potential sample return to Earth. To address the requirements for samplers that could be operated at the conditions of the various bodies in the solar system, a piezoelectric actuated percussive sampling device was developed that requires low preload (as low as 10N) which is important for operation at low gravity. This device can be made as light as 400g, can be operated using low average power, and can drill rocks as hard as basalt. Significant improvement of the penetration rate was achieved by augmenting the hammering action by rotation and use of a fluted bit to provide effective cuttings removal. Generally, hammering is effective in fracturing drilled media while rotation of fluted bits is effective in cuttings removal. To benefit from these two actions, a novel configuration of a percussive mechanism was developed to produce an augmenter of rotary drills. The device was called Percussive Augmenter of Rotary Drills (PARoD). A breadboard PARoD was developed with a 6.4 mm (0.25 in) diameter bit and was demonstrated to increase the drilling rate of rotation alone by 1.5 to over 10 times. The test results of this configuration were published in a previous publication. Further, a larger PARoD breadboard with a 50.8 mm (2.0 in) diameter bit was developed and tested. This paper presents the design, analysis and test results of the large diameter bit percussive augmenter.
Increasingly, NASA exploration mission objectives include sample acquisition tasks for in-situ analysis or for
potential sample return to Earth. To address the requirements for samplers that could be operated at the conditions of the
various bodies in the solar system, a piezoelectric actuated percussive sampling device was developed that requires low
preload (as low as 10N) which is important for operation at low gravity. This device can be made as light as 400g, can be
operated using low average power, and can drill rocks as hard as basalt. Significant improvement of the penetration rate
was achieved by augmenting the hammering action by rotation and use of a fluted bit to provide effective cuttings
removal. Generally, hammering is effective in fracturing drilled media while rotation of fluted bits is effective in
cuttings removal. To benefit from these two actions, a novel configuration of a percussive mechanism was developed to
produce an augmenter of rotary drills. The device was called Percussive Augmenter of Rotary Drills (PARoD). A
breadboard PARoD was developed with a 6.4 mm (0.25 in) diameter bit and was demonstrated to increase the drilling
rate of rotation alone by 1.5 to over 10 times. Further, a large PARoD breadboard with 50.8 mm diameter bit was
developed and its tests are currently underway. This paper presents the design, analysis and preliminary test results of
the percussive augmenter.
Piezoelectric stacks are being sought to be used as actuators for precision positioning and deployment of mechanisms in
future planetary missions. Beside the requirement for very high operation reliability, these actuators may be required to
operate in space environments that are considered harsh compared to normal terrestrial conditions. These
environmental conditions include low and high temperatures and vacuum or high pressure. Additionally, the stacks are
subjected to high stress and in some applications need to operate for extended time periods. Many of these
requirements are beyond the current industry design margins for nominal terrestrial applications. In order to investigate
some of the properties to assess the durability of such actuators and their limitations we have developed a new type of
test fixture that can be easily integrated in various test chambers for simulating environmental conditions, can provide
access for multiple measurements while being exposed to adjustable stress levels. We have designed and built two
versions of these test fixture and these fixtures were made to be adjustable for testing stacks with different dimensions
and can be easily used in small or large numbers. The properties that were measured using these fixtures include
impedance, capacitance, dielectric loss factor, leakage current, displacement, breakdown voltage, and lifetime
performance. The fixtures characteristics and the test capabilities are presented in this paper.
Future NASA missions are increasingly seeking to use actuators for precision positioning to accuracies of the order of
fractions of a nanometer. For this purpose, multilayer piezoelectric stacks are being considered as actuators for
driving these precision mechanisms. In this study, sets of commercial PZT stacks were tested in various AC and DC
conditions at both nominal and extreme temperatures and voltages. AC signal testing included impedance,
capacitance and dielectric loss factor of each actuator as a function of the small-signal driving sinusoidal frequency,
and the ambient temperature. DC signal testing includes leakage current and displacement as a function of the applied
DC voltage. The applied DC voltage was increased to over eight times the manufacturers' specifications to
investigate the correlation between leakage current and breakdown voltage. Resonance characterization as a function
of temperature was done over a temperature range of -180°C to +200°C which generally exceeded the manufacturers'
specifications. In order to study the lifetime performance of these stacks, five actuators from one manufacturer were
driven by a 60volt, 2 kHz sine-wave for ten billion cycles. The tests were performed using a Lab-View controlled
automated data acquisition system that monitored the waveform of the stack electrical current and voltage. The
measurements included the displacement, impedance, capacitance and leakage current and the analysis of the
experimental results will be presented.
Piezoelectric acoustic-electric power feed-through devices transfer electric power wirelessly through a solid wall
using elastic waves. This approach allows for the elimination of the need for holes through structures for cabling or
electrical feed-thrus . The technology supplies power to electric equipment inside sealed containers, vacuum or pressure
vessels, etc where holes in the wall are prohibitive or may result in significant performance degradation or requires
complex designs. In the our previous work, 100-W of electric power was transferred through a metal wall by a small,
piezoelectric device with a simple-structure. To meet requirements of higher power applications, the feasibility to
transfer kilowatts level power was investigated. Pre-stressed longitudinal piezoelectric feed-thru devices were analyzed
by finite element modeling. An equivalent circuit model was developed to predict the characteristics of power transfer
to different electric loads. Based on the analytical results, a prototype device was designed, fabricated and successfully
demonstrated to transfer electric power at a level of 1-kW. Methods of minimizing plate wave excitation on the wall
were also analyzed. Both model analysis and experimental results are presented in detail in this paper.
Piezoelectric acoustic-electric power feedthru devices that are able to transfer electric power through
metallic/ferromagnetic wall are investigated. Electric energy is converted to acoustic energy by piezoelectric transducer
at one side of the wall. The acoustic wave propagates through the wall and, then, it is converted back to electric energy
by another transducer on the other side. For high efficient transmission, it is critical that all the energy loss should be
minimized. In addition to the electrical, mechanical and electromechanical loss in the transducers and the thickness of
the wall, Lamb (plate) waves are excited by the transducers in the wall and they also result in energy losses. In this study,
the energy loss caused by the Lamb waves are analyzed analytically and by finite element simulations. The results and
the methods to reduce the loss are presented and discussed in this presentation.
There are numerous engineering applications where there is a need to transfer power and communication data thru
the walls of a structure. A piezoelectric acoustic-electric power feedthru system was developed in this reported study
allowing for wireless transfer of electric power through a metallic wall using elastic waves. The technology is applicable
to the transfer of power for actuation, sensing and other tasks inside sealed containers and vacuum/pressure vessels. A
network equivalent circuit including material damping loss was developed to analyze the performance of the devices.
Experimental test devices were constructed and tested. The power transfer capability and the transfer efficiency were
measured. A 100W feed though capability with 38 mm diameter device and 88% transmission efficiency were demonstrated. Both analytical and experimental results are presented and discussed in this paper.
Rock, soil, and ice penetration by coring, drilling or abrading is of great importance for a large number of space and
earth applications. Proven techniques to sample Mars subsurface will be critical for future NASA astrobiology missions
that will search for past and present life on the planet. The Ultrasonic/Sonic Drill/Corer (USDC) has been developed as
an adaptable tool for many of these applications [Bar-Cohen et al., 2001]. The USDC uses a novel drive mechanism to
transform the ultrasonic or sonic vibrations of the tip of a horn into a sonic hammering of a drill bit through an
intermediate free-flying mass. For shallow drilling the cuttings travel outside the hole due to acoustic vibrations of the
bit. Various methods to enhance the drilling/coring depth of this device have been considered including pneumatic
[Badescu et al., 2006] and bit rotation [Chang et al., 2006]. The combination of bit rotation at low speed for cuttings
removal and bit hammering at sonic frequencies are described in this paper. The theoretical background and testing
results are presented.
Resonance tracking control of harmonic oscillators whose natural frequency is unknown is investigated from a Lyapunov
stability perspective. In particular, a periodically-modulated cosine driver (PMCD) is investigated for this purpose. The
proposed resonance tuner is time-synchronized with periodic sampling of the harmonic oscillator's output to ensure that an
analytical relationship exists between the drive frequency and the tracking error. This relation defines a class of discrete time
nonlinear systems whose origin, is shown to be asymptotically stable.
The search for existing or past life in the Universe is one of the most important objectives of NASA's mission. For this
purpose, effective instruments that can sample and conduct in-situ astrobiology analysis are being developed. In
support of this objective, a series of novel mechanisms that are driven by an Ultrasonic/Sonic actuator have been
developed to probe and sample rocks, ice and soil. This mechanism is driven by an ultrasonic piezoelectric actuator that
impacts a bit at sonic frequencies through the use of an intermediate free-mass. Ultrasonic/Sonic Driller/Corer (USDC)
devices were made that can produce both core and powdered cuttings, operate as a sounder to emit elastic waves and
serve as a platform for sensors. For planetary exploration, this mechanism has the important advantage of requiring low
axial force, virtually no torque, and can be duty cycled for operation at low average power. The advantage of requiring
low axial load allows overcoming a major limitation of planetary sampling in low gravity environments or when
operating from lightweight robots and rovers. The ability to operate at duty cycling with low average power produces a
minimum sample temperature rise allowing for control of the sample integrity and preventing damage to potential
biological markers in the acquired sample. The development of the USDC is being pursued on various fronts ranging
from analytical modeling to mechanisms improvements while considering a wide range of potential applications. While
developing the analytical capability to predict and optimize its performance, efforts are made to enhance its capability to
drill at higher power and high speed. Taking advantage of the fact that the bit does not require rotation, sensors (e.g.,
thermocouple and fiberoptics) were integrated into the bit to examine the borehole during drilling. The sounding effect
of the drill was used to emit elastic waves in order to evaluate the surface characteristics of rocks. Since the USDC is
driven by piezoelectric actuation mechanism it can designed to operate at extreme temperature environments from very
cold as on Titan and Europa to very hot as on Venus. In this paper, a review of the latest development and applications
of the USDC will be given.
There are numerous engineering design problems where the use of wires to transfer power and communicate data thru the walls of a structure is prohibitive or significantly difficult that it may require a complex design. Using physical feedthroughs in such systems may make them susceptible to leakage of chemicals or gasses, loss of pressure or vacuum, as well as difficulties in providing adequate thermal or electrical insulation. Moreover, feeding wires thru a wall of a structure reduces the strength of the structure and makes the structure prone to cracking due to fatigue that can result from cyclic loading and stress concentrations. One area that has already been identified to require a wireless alternative to electrical feedthroughs would be the container of any Mars Sample Return Mission, which would need wireless sensors to sense a pressure leak and to avoid potential contamination. The idea of using elastic or acoustic waves to transfer power was suggested recently by [Y. Hu, et al., July 2003]. This system allows for the avoidance of cabling or wiring. The technology is applicable to the transfer of power for actuation, sensing and other tasks inside any sealed container or vacuum/pressure vessel. An alternative approach to the modeling presented previously [Sherrit et al., 2005] used network analysis to solve the same problem in a clear and expandable manner. Experimental tests on three different designs of these devices were performed. The three designs used different methods of coupling the piezoelectric element to the wall. In the first test the piezoelectric material was bolted using a backing structure. In the second test the piezoelectric was clamped after the application of grease. Finally the piezoelectric element was attached using a conductive epoxy. The mechanical clamp with grease produced the highest measured efficiency of 53% however this design was the least practical from a fabrication viewpoint. The power transfer efficiency of conductive epoxy joint was 40% and the stress bolts (12%). The experimental results on a variety of designs will be presented and the thermal and non-linear issues will be discussed.
Rock, soil, and ice penetration by coring, drilling or abrading is of great importance to a large number of space and earth applications. Proven techniques to sample Mars subsurface will be critical for future NASA astrobiology missions that will search for records of past and present life on the planet. An Ultrasonic/Sonic Drill/Corer (USDC) has been developed as an adaptable tool for many of these applications [Bar-Cohen et al., 2001]. The USDC uses a novel drive mechanism to transform the ultrasonic or sonic vibrations of the tip of a horn into a sonic hammering of a drill bit through an intermediate free-flying mass. The USDC design was modified to fabricate an Ultrasonic/Sonic Ice Gopher that is designed to core down to meters depth for in situ analysis and sample collection. This technology was demonstrated at Lake Vida in the Dry Valleys, Antarctica. Coring ice at -20°C as in Lake Vida has been a challenge and efforts were made to develop the required ice core cutting, ice chip handling and potential ice melting (and refreezing) during drilling. The analysis and fabrication challenges and testing results are presented in this paper.
Future NASA exploration missions will increasingly require sampling, in-situ analysis and possibly the return of material to Earth for further tests. One of the challenges to addressing this need is the ability to drill using minimal reaction force and torque while operating from light weight platforms (e.g., lander, rover, etc.) as well as operate at planets with low gravity. For this purpose, the authors developed the Ultrasonic/Sonic Driller/Corer (USDC) jointly with Cybersonics Inc. Studies of the operation of the USDC at high power have shown there is a critical need to self-tune to maintain the operation of the piezoelectric actuator at resonance. Performing such tuning is encountered with difficulties and to address them an extremum-seeking control algorithm is being investigated. This algorithm is designed to tune the driving frequency of a time-varying resonating actuator subjected to both random and high-power impulsive noise disturbances. Using this algorithm, the performance of the actuator is monitored on a time-scale that is compatible with its slowly time-varying physical characteristics. The algorithm includes a parameter estimator, which estimates the coefficients of a function that characterizes the quality factor of the USDC. Since the parameter estimator converges sufficiently faster than the time-varying drift of the USDC's actuator physical parameters, this extremum-seeking estimation and control algorithm potentially allows for use in closed-loop monitoring of the operation of the USDC. Specifically, this system may be programmed to automatically adjust the duty-cycle of the sinusoidal driver signal to monitor the quality factor of the USDC not to fall below a user-defined set-point. Such fault-tolerant functionality is especially important in automated drilling applications where it is essential not to inadvertently drive the piezoelectric ceramic elements of the USDC beyond their operation capability. The details of the algorithm and experimental results are described and discussed in this paper.
For a new class of tendon-driven robotic systems that is generalized to include tensegrity structures, this paper focuses on a method to jointly optimize the control law and the structural complexity for a given point-to-point maneuvering task. By fixing external geometry, the number of identical stages within the domain is varied until a minimal mass design is achieved. For the deployment phase, a new method is introduced which determines the tendon force inputs from a set of admissible, non-saturating inputs, that will reconfigure each kinematically invertible unit along its own path in minimum time. The approach utilizes the existence conditions and solution of a linear algebra problem that describe how the set of admissible tendon forces is mapped onto the set of path-dependent torques. Since this mapping is not one-to-one, free parameters in the control law always exist. An infinity-norm minimization with respect to these free parameters
is responsible for saturation avoidance. In addition to the required time to deploy, the expended control energy during the post-movement phase is also minimized with respect to the total number of stages. Conditions under which these independent minimizations yield the same robot illustrate the importance of considering control/structure interaction within this new robotics paradigm.
Passive damping of structural dynamics using piezoceramic electromechanical energy conversion and passive electrical networks is a relatively recent concept with little implementation experience base. This paper describes an implementation case study, starting from conceptual design and technique selection, through detailed component design and testing to simulation on the structure to be damped. About 0.5 kg. of piezoelectric material was employed to damp the ASTREX testbed, a 5000 kg structure. Emphasis was placed upon designing the damping to enable high bandwidth robust feedback control. Resistive piezoelectric shunting provided the necessary broadband damping. The piezoelectric element was incorporated into a steel flextensional device in order to concentrate damping into the 30 to 40 Hz frequency modes at the rolloff region of the proposed compensator. The effective stiffness and damping of the flextensional device was experimentally verified.