20,167 research outputs found
Automatic crosswind flight of tethered wings for airborne wind energy: modeling, control design and experimental results
An approach to control tethered wings for airborne wind energy is proposed. A
fixed length of the lines is considered, and the aim of the control system is
to obtain figure-eight crosswind trajectories. The proposed technique is based
on the notion of the wing's "velocity angle" and, in contrast with most
existing approaches, it does not require a measurement of the wind speed or of
the effective wind at the wing's location. Moreover, the proposed approach
features few parameters, whose effects on the system's behavior are very
intuitive, hence simplifying tuning procedures. A simplified model of the
steering dynamics of the wing is derived from first-principle laws, compared
with experimental data and used for the control design. The control algorithm
is divided into a low-level loop for the velocity angle and a high-level
guidance strategy to achieve the desired flight patterns. The robustness of the
inner loop is verified analytically, and the overall control system is tested
experimentally on a small-scale prototype, with varying wind conditions and
using different wings.Comment: This manuscript is a preprint of a paper accepted for publication on
the IEEE Transactions on Control Systems Technology and is subject to IEEE
Copyright. The copy of record is available at IEEEXplore library:
http://ieeexplore.ieee.org
James Webb Space Telescope Optical Simulation Testbed I: Overview and First Results
The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a
tabletop workbench to study aspects of wavefront sensing and control for a
segmented space telescope, including both commissioning and maintenance
activities. JOST is complementary to existing optomechanical testbeds for JWST
(e.g. the Ball Aerospace Testbed Telescope, TBT) given its compact scale and
flexibility, ease of use, and colocation at the JWST Science & Operations
Center. We have developed an optical design that reproduces the physics of
JWST's three-mirror anastigmat using three aspheric lenses; it provides similar
image quality as JWST (80% Strehl ratio) over a field equivalent to a NIRCam
module, but at HeNe wavelength. A segmented deformable mirror stands in for the
segmented primary mirror and allows control of the 18 segments in piston, tip,
and tilt, while the secondary can be controlled in tip, tilt and x, y, z
position. This will be sufficient to model many commissioning activities, to
investigate field dependence and multiple field point sensing & control, to
evaluate alternate sensing algorithms, and develop contingency plans. Testbed
data will also be usable for cross-checking of the WFS&C Software Subsystem,
and for staff training and development during JWST's five- to ten-year mission.Comment: Proceedings of the SPIE, 9143-150. 13 pages, 8 figure
S-band antenna phased array communications system
The development of an S-band antenna phased array for spacecraft to spacecraft communication is discussed. The system requirements, antenna array subsystem design, and hardware implementation are examined. It is stated that the phased array approach offers the greatest simplicity and lowest cost. The objectives of the development contract are defined as: (1) design of a medium gain active phased array S-band communications antenna, (2) development and test of a model of a seven element planar array of radiating elements mounted in the appropriate cavity matrix, and (3) development and test of a breadboard transmit/receive microelectronics module
Passive Aeroelastic Tailoring
The Passive Aeroelastic Tailoring (PAT) project was tasked with investigating novel methods to achieve passive aeroelastic tailoring on high aspect ratio wings. The goal of the project was to identify structural designs or topologies that can improve performance and/or reduce structural weight for high-aspect ratio wings. This project considered two unique approaches, which were pursued in parallel: through-thickness topology optimization and composite tow-steering
On-sky single-mode fiber coupling measurements at the Large Binocular Telescope
The demonstration of efficient single-mode fiber (SMF) coupling is a key
requirement for the development of a compact, ultra-precise radial velocity
(RV) spectrograph. iLocater is a next generation instrument for the Large
Binocular Telescope (LBT) that uses adaptive optics (AO) to inject starlight
into a SMF. In preparation for commissioning iLocater, a prototype SMF
injection system was installed and tested at the LBT in the Y-band (0.970-1.065
m). This system was designed to verify the capability of the LBT AO system
as well as characterize on-sky SMF coupling efficiencies. SMF coupling was
measured on stars with variable airmasses, apparent magnitudes, and seeing
conditions for six half-nights using the Large Binocular Telescope
Interferometer. We present the overall optical and mechanical performance of
the SMF injection system, including details of the installation and alignment
procedure. A particular emphasis is placed on analyzing the instrument's
performance as a function of telescope elevation to inform the final design of
the fiber injection system for iLocater.Comment: 11 pages, 7 figure
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