Showing papers by "Dale Lawrence published in 2015"

The MATERHORN: Unraveling the Intricacies of Mountain Weather

Abstract: Emerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain meteorology To address scientific needs and help improve the prediction of mountain weather, the US Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multi-institutional, and multinational group of researchers The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements The access to the Granite Mountain Atmospheric Sciences Testbed of the US Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platfor

Overview of Small Fixed-Wing Unmanned Aircraft for Meteorological Sampling

Abstract: Sampling the atmospheric boundary layer with small unmanned aircraft is a difficult task requiring informed selection of sensors and algorithms that are suited to the particular platform and mission Many factors must be considered during the design process to ensure the desired measurement accuracy and resolution is achieved, as is demonstrated through an examination of previous and current efforts A taxonomy is developed from these approaches and is used to guide a review of the systems that have been employed to make in situ wind and thermodynamic measurements, along with the campaigns that have employed them Details about the airframe parameters, estimation algorithms, sensors, and calibration methods are given

Tactics for Heliogyro Solar Sail Attitude Control via Blade Pitching

Abstract: Heliogyros generate attitude control moments by pitching their sail membrane blades collectively or cyclically, similar to a helicopter. Past work has focused on simple blade pitch profiles with the heliogyro normal to the sun; however, most solar sail missions will require sun angles of at least 35 deg. Furthermore, combination pitch profiles (e.g., cyclic plus collective) are needed for attitude control during all mission segments. The control moments for such situations vary in an unintuitive, nonlinear fashion. This paper explores heliogyro control moment authority with varying sun angles and combinations of pitch profiles, providing critical insight for future development of heliogyro attitude control schemes. Three tactics for generating control moments using various profile combinations are introduced for three-axis attitude control during a variety of practical mission scenarios. These tactics indicate that the heliogyro can generate control moments from any orientation, including edge-on to the s...

Recent Advances in Heliogyro Solar Sail Structural Dynamics, Stability, and Control Research

Abstract: Results from recent NASA sponsored research on the structural dynamics, stability, and control characteristics of heliogyro solar sails are summarized. Specific areas under investigation include coupled nonlinear finite element analysis of heliogyro membrane blade with solar radiation pressure effects, system identification of spinning membrane structures, and solarelastic stability analysis of heliogyro solar sails, including stability during blade deployment. Recent results from terrestrial 1-g blade dynamics and control experiments on "rope ladder" membrane blade analogs, and small-scale in vacuo system identification experiments with hanging and spinning high-aspect ratio membranes will also be presented. A low-cost, rideshare payload heliogyro technology demonstration mission concept is used as a mission context for these heliogyro structural dynamics and solarelasticity investigations, and is also described. Blade torsional dynamic response and control are also shown to be significantly improved through the use of edge stiffening structural features or inclusion of modest tip masses to increase centrifugal stiffening of the blade structure. An output-only system identification procedure suitable for on-orbit blade dynamics investigations is also developed and validated using ground tests of spinning sub-scale heliogyro blade models. Overall, analytical and experimental investigations to date indicate no intractable stability or control issues for the heliogyro solar sail concept.

Air-Deployed Microbuoy Measurement of Temperatures in the Marginal Ice Zone Upper Ocean during the MIZOPEX Campaign

Abstract: Air-deployed microbuoys (ADMBs) were developed as a means of measuring subsurface temperatures in the marginal ice zone (MIZ) over campaign-duration time scales to better understand how MIZ surface layer heat content accelerates melt rates at the edge of the ice pack. ADMBs are small, low-cost buoys deployable from unmanned aircraft and are capable of measuring temperatures to 0.1°C absolute accuracy at the surface, 1-m, and 2-m depth, along with GPS position. Each ADMB contains a microcontroller, GPS, 900-MHz radio, flash electrically erasable programmable read-only memory (EEPROM), battery, and a set of temperature sensors to monitor conditions for up to 10 days. A communications board on an overflying aircraft autonomously deploys each ADMB and collects data from previously deployed ADMBs for analysis. The 2013 Marginal Ice Zone Observations and Processes Experiment (MIZOPEX) campaign deployed ADMBs into the summer melt season MIZ north of Oliktok Point, Alaska, collecting over 400 h of data fr...

Heliogyro Orbital Control Authority

Abstract: Solar sailing is an elegant form of space propulsion that reflects solar photons to produce thrust. Different sail configurations exist, including a traditional flat sail (either square- or disc-shaped) and a heliogyro, which divides the sail membrane into a number of long, slender blades, analogous to a helicopter rotor. The magnitude and direction of the induced thrust force depends on the sail’s attitude with respect to the Sun, i.e. on the cone angle. At each cone angle, a flat sail can only generate force of particular magnitude and direction, while this paper demonstrates that a heliogyro can arbitrarily reduce the magnitude of the thrust vector through the additional control of pitching the blades. This gives the heliogyro more force control authority, which is exploited in this paper for orbital control. A linear-quadratic regulator feedback controller is used to quantify the maximum error in the injection state vector of a solar sail Sun-Earth sub-L1 halo orbit from which the nominal orbit can still be recovered. The conclusion is that approximately an order of magnitude larger error in position and velocity can be accommodated, demonstrating superior capabilities of the heliogyro over a flat sail for orbital control.

Optical Flow Techniques for Wind-Velocity Sensing on a Small Unmanned Aircraft System

Abstract: Nomenclature Comp = Number of computations Iij = Pixel intensity at index ij Im1 = First image Im2 = Second image lim = Physical length of image axis Ndisph = Number of pixels of possible displacement horizontally Ndisph = Number of pixels of possible displacement vertically Nh = Number of horizontal pixels in image Nv = Number of vertical pixels in image S = Correlation Similarity Factor Vres = Sensor velocity resolution Δt = Time between images

Evaluation of Routine Atmospheric Sounding Measurements using Unmanned Systems (ERASMUS) Science Plan

Abstract: The use of small unmanned aircraft systems (sUAS) with miniature sensor systems for atmospheric research is an important capability to develop. The Evaluation of Routine Atmospheric Sounding Measurements using Unmanned Systems (ERASMUS) project, lead by Dr. Gijs de Boer of the Cooperative Institute for Research in Environmental Sciences (CIRES- a partnership of NOAA and CU-Boulder), is a significant milestone in realizing this new potential. This project has clearly demonstrated that the concept of sUAS utilization is valid, and miniature instrumentation can be used to further our understanding of the atmospheric boundary layer in the arctic.