Jeffrey C. LaCombe

Pulsed electrodeposition into AAO templates for CVD growth of carbon nanotube arrays

Anodic aluminium oxide (AAO) templates for multi-walled carbon nanotube (MWCNT) growth were produced by anodization of aluminium followed by pulse-reverse electrodeposition of cobalt inside the AAO pores. Cobalt functioned as the catalyst for H2/C2H2 chemical vapour deposition (CVD) growth of fairly well graphitized MWCNTs initiating inside the majority of the AAO pores and quickly growing beyond the pore confines. A technique is introduced for the production of AAO templates that fill evenly during pulsed electrodeposition. The electrodeposition produced an active metallic catalyst in the pore bottoms, with minimal over-filling. This process also eliminates the reduction step necessary when alternating current (AC) electrodeposition is used for filling AAO pores.

Flight Testing of a 1-DOF Variable Drag Autonomous Descent Vehicle

This paper details the hardware development and testing of an autonomous descent vehicle. The developed vehicle utilizes a circular parachute and wind data to control the landing location. The benefit of this system over alternative precision aerial delivery techniques is the envisioned ability to use the large inventory of circular parachutes already in use for uncontrolled cargo and personnel deliveries with minimal training or system modifications. Parachute control is obtained via reversibly reefing of the canopy, thereby modifying the descent speed. For this study, the parachute size is assumed to be constant for the remainder of the descent; however, the desired parachute size computation is periodically updated to assist in reducing landing errors due to inaccurate wind data. A small mechanical reeling system has been developed, comprising a microcomputer, RF modem, electronic speed controller, and an electric motor. The hardware is coupled with a quarter-spherical canopy with four suspension lines, similar to those used in automotive drag racing. The combined weight of the parachute-payload system is 53.5N (12.0lb). Flight testing was conducted using a small single engine aircraft (Cessna 172), with preliminary flight testing conducted using an Arcturus T-20 UAV. Release ceilings were approximately 3050m (10,000ft) MSL. Typically, dropsondes were used to collect predicted wind for the descent vehicle. The time needed to collect the wind data, upload it into the descent vehicle software, takeoff, and reach the desired deployment location was approximately two hours. Preliminary testing of the parachute-payload system was performed to determine the appropriate control gains for the motor angle control routine to achieve the desired descent rate. Release altitudes were between 450m (1,500ft) and 610m (2,000ft) AGL. Using Zeigler-Nichols gain tuning rules and an experimental step response, gains were determined for both a Proportional-Integral (PI) controller and a Proportional-Integral-Derivative (PID) controller. Additional testing was conducted to verify the ability of these control gains to achieve a desired descent speed prior to flight testing the full path planning system and control algorithm. Flight testing results demonstrate the ability for the autonomous descent vehicle (ADV) to successfully navigate towards a target line segment when using accurate wind prediction data. As previously published results have noted, when the predicted wind data is inaccurate, the vehicle is not always capable of improving the landing location accuracy compared to an uncontrolled parachute. Additional considerations in developing a descent rate control system for use in circular parachutes are also presented.

Time-Varying Descent Rate Control Strategy for Circular Parachutes

This paper presents a time-varying control methodology for a variable-sized circular parachute to reach a target landing location. A trajectory is calculated for the immediate control horizon using wind forecast data. To create a parachute–payload trajectory, a three-degree-of-freedom kinematic model is developed. Using this, the performance envelope is determined, revealing the potential target range of the system during a descent. Next, this model is further developed into a control methodology to determine the necessary descent rate, to reach the desired landing target, to be controlled via parachute size manipulation. Finally, simulation results are presented to validate the control scheme. Various release locations were simulated with paired uncontrolled/controlled parachute descents from within the performance envelope. Results demonstrate the feasibility of the system, with controlled parachute descents actively navigating toward the target. With accurate wind data, the vehicle can overcome release...

Nanoporous Titanium Oxide Morphologies Produced by Anodizing of Titanium

A quick and dependable technique has been developed that allows us to selectively produce anodized TiO2 in the form of nanotubes. The process employs mild chemical conditions and ambient temperature. The method can consistently produce nearly 100% surface coverage of nanotubes within 10 min of anodizing. Anodizing in relatively high pH electrolytes for 1 hour permitted us to produce nanotubes of 2μm length. We attribute the repeatability of our results to a brief pre-anodizing etching step that consistently leads to excellent anodizing results. Without this etching step, we experienced very poor consistency in that only small patches of titania nanotubes were formed.

Velocity and radius transients during pressure mediated dendritic growth of succinonitrile

Abstract This study was part of a larger effort called the transient dendritic solidification experiment (TDSE), which uses the well known Clapeyron effect to study transient effects in dendritic solidification. The transient behaviour was studied between well defined steady states using pressure mediated changes since it is almost impossible to study the transient behaviour during growth of a dendrite from initial state to steady state. The time constants calculated for the velocity and radius transients are of the same order of magnitude. The velocity starts changing almost immediately after the pressure changes. The radius also changes rapidly but the change starts after an initial lag. This is attributed to its geometric memory and the fact that the change in velocity results from a change in the thermal field ahead of the tip, whereas a change in radius also entails a change in the lateral thermal field. These results affirm that pressure changes affect the growth behaviour and interfacial morphology of dendrites, which can be used for controlling solidification microstructure.

In-flight Landing Location Predictions using Ascent Wind Data for High Altitude Balloons

This paper presents a hardware and software system in which the landing location of a balloon–payload system is continually predicted and improved. Initial prediction parameters are corrected by estimating flight parameters using GPS data. The focus of this study is on small (less than 10 kg payload) balloon systems. For these systems, flight missions typically have a duration of a few hours (minimal loitering at altitude) and descend after the balloon bursts at an altitude in the range of 15-30 km. Prior to launch, weather predictions are typically used to predict the flight path and landing location of the balloon-payload system. The prediction accuracy greatly depends on the stability of wind data, as well as the accuracy in predicting the balloon ascent speed, balloon burst altitude, and parachute descent speed. Differences between the predicted and actual landing locations of 60 km are not atypical. Rather than relying on the pre-flight predictions, the system developed here measures ascent/descent speeds and wind speed during the balloon’s ascent. Unlike the pre-flight predictions, the system provides chase and recovery personnel with an accurate prediction of the landing location that is periodically updated as the mission progresses. During ascent, GPS data is logged to provide both actual ascent speed and up-to-date spatial and temporal wind data. The ascent speed along with the logged wind data and initial estimates of the parachute-payload flight characteristics (mass, parachute size, etc.) are used to correct the flight model up to the time of balloon burst. During descent, the actual descent speed is used to further enhance predictions as the mission progresses. Results calculated from post-processing actual balloon flight GPS data validate the methodology developed. Prediction accuracy is improved from an average predicted landing location error of 36% of the traveled range prior to launch. At the balloon burst location, prediction quality improves to 3.5% of the total range traveled on average. Additionally, real-time, in-flight prediction results verify the ability to perform the in-flight prediction updates on-board a balloon using a microprocessor and off-the-shelf radio communication equipment.

Path Planning of a Circular Parachute Using Descent Rate Control

This paper presents a time-varying control methodology for a variable-sized circular parachute to reach a target landing location. A trajectory is calculated for the immediate control horizon using wind forecast data. In order to create a parachute–payload trajectory, a 3–DOF kinematic model is developed. Using this, the performance envelope is determined, revealing the potential target range of the system throughout a descent. Next, this model is extended to develop a control methodology to determine the descent rate, via parachute size manipulation, needed to reach the desired landing target. Finally, simulation results are presented to validate the control scheme. Various release locations were simulated with paired uncontrolled/controlled parachute descents from within the performance envelope. Results demonstrate the feasibility of the system, with controlled parachute descents navigating towards the target. With accurate wind data the vehicle can overcome release location errors as well as vehicle uncertainties and perform significantly better than an uncontrolled parachute.

The make-it-yourself drop-tower microgravity demonstrator

Modern research-scale drop towers provide scientists with brief periods of apparent low-gravity from free-fall in which a wide variety of scientific experiments can be conducted. It is shown here that affordable, classroom-scale drop towers can assist in science education by demonstrating a wide range of physical principles in a high-impact, attention-getting manner. The equipment described here can be constructed for as little as a few hundred dollars, and when combined with readily available televisions and videotape recorders, make an excellent classroom teaching aid.

Lower Stratospheric Deployment Testing of a Ram-Air Parafoil System

This work continues the flight testing of ram-air parafoils from high altitude weather balloons. Previous work revealed the major challenge of a zero-speed deployment from a balloon combined with the low air density environment. If the parafoil fails to inflate upon initial release at high altitude, tumbling and tangling occur almost instantaneously, thus preventing the parachute from inflating even after it descends into the lower, denser atmosphere. This paper describes further balloon flight testing of two different canopy size systems conducted to collect performance data in the rarely tested high altitude flight regime. It describes problems encountered during testing and considerations for improving the reliability of a ram-air parafoil released in a low-density zero dynamic pressure environment.

Development of a Coupled Dropsonde-Autonomous Descent Vehicle System

This paper describes the benefits of using a dropsonde to automatically provide real time wind data to an autonomous descent vehicle (ADV). Two major sources of wind error are identified: wind errors resulting from large scale temporal and/or spatial differences between forecast and actual wind columns (Type A), and small scale wind fluctuations and/or measurement inaccuracies typically in the form of measurement noise (Type B). An autonomously coupled dropsonde-ADV system was developed in which a dropsonde is released preceding the descent vehicle, with enough lead time to descend to the ground prior to release of the ADV, and automatically telemeters wind data to the ADV, minimizing the more severe Type A wind errors. Simulations of the descent vehicle’s path (computed using actual wind data) are presented to compare the coupled dropsonde-ADV system to other ADV deployment scenarios. The simulations show that the use of a dropsonde to collect wind data can significantly reduce errors in the landing location of the ADV (89% in our simulations) as compared to an ADV that uses only forecasted wind data from prior to the descent. These results quantify the value of using spatiallyand temporallyrelevant wind data, and the potential benefits that can result from incorporating a coupled dropsonde-ADV system.