Large-angle slewing maneuvers for flexible spacecraft

A new class of closed-form solutions for finite-time linear-quadratic optimal control problems is presented. The solutions involve Potter's solution for the differential matrix Riccati equation, which assumes the form of a steady-state plus transient term. Illustrative examples are presented which show that the new solutions are more computationally efficient than alternative solutions based on the state transition matrix. As an application of the closed-form solutions, the neighboring extremal path problem is presented for a spacecraft retargeting maneuver where a perturbed plant with off-nominal boundary conditions now follows a neighboring optimal trajectory. The perturbation feedback approach is further applied to three-dimensional slewing maneuvers of large flexible spacecraft. For this problem, the nominal solution is the optimal three-dimensional rigid body slew. The perturbation feedback then limits the deviations from this nominal solution due to the flexible body effects. The use of frequency shaping in both the nominal and perturbation feedback formulations reduces the excitation of high-frequency unmodeled modes. A modified Kalman filter is presented for estimating the plant states

Research in slewing and tracking control

Technology areas are identified in which better analytical and/or experimental methods are needed to adequately and accurately control the dynamic responses of multibody space platforms such as the Space Station and the Radiometer Spacecraft. A generic space station model is used to experimentally evaluate current control technologies and a radiometer spacecraft model is used to numerically test a new theoretical development for nonlinear three-axis maneuvers. Active suppression of flexible body vibrations induced by large angle maneuvers is studied with multiple torque inputs and multiple measurement outputs. These active suppression tests identify the hardware requirements and adequacy of various controller designs

Transform methods for precision continuum and control models of flexible space structures

An open loop optimal control algorithm is developed for general flexible structures, based on Laplace transform methods. A distributed parameter model of the structure is first presented, followed by a derivation of the optimal control algorithm. The control inputs are expressed in terms of their Fourier series expansions, so that a numerical solution can be easily obtained. The algorithm deals directly with the transcendental transfer functions from control inputs to outputs of interest, and structural deformation penalties, as well as penalties on control effort, are included in the formulation. The algorithm is applied to several structures of increasing complexity to show its generality

Thermal kinetic inductance detectors for ground-based millimeter-wave cosmology

We show measurements of thermal kinetic inductance detectors (TKID) intended for millimeter wave cosmology in the 200-300 GHz atmospheric window. The TKID is a type of bolometer which uses the kinetic inductance of a superconducting resonator to measure the temperature of the thermally isolated bolometer island. We measure bolometer thermal conductance, time constant and noise equivalent power. We also measure the quality factor of our resonators as the bath temperature varies to show they are limited by effects consistent with coupling to two level systems.Comment: 8 pages, 4 figures. Submitted to Journal of Low Temperature Physic

Towards a Racial Justice Project Oral History Methodology Critical Race Theory and African American Education

Oral historians have declared the methodology a social justice project. This essay advances that discussion, positing that oral history methodology may represent a more specific racial justice project when coupled with critical race theory. An examination of the history of African American education scholarship, we argue, supports this contention. Two central questions guide this essay: (1) What does scholarship on the history of African American education demonstrate about the compatibility between oral history methodology and critical race theory? and (2) How does this methodological-theoretical pairing advance a racial justice project? We aim to show how critical race theory and oral history methodology complement one another as research tools that can strengthen the history of education’s capacity to inform current educational issues. Our essay draws on the work of historians of African American education to exemplify possibilities for any historian of education who examines systematically underserved communities of Colour. Ultimately, we argue that critical race theory and oral history methodology are compatible because they share several propositions apt for helping researchers subvert the silencing, marginalisation, and objectification of systemically underserved communities of Colour, thereby furthering a racial justice project. This essay, therefore, contributes primarily to interdisciplinary education and historical research methods literature

Black Baby Boomers, Gender, and Southern Education-Navigating Tensions in Oral History Methodology

Little to no extant scholarship examines procedural, epistemological aspects of conducting intergenerational oral history interviews with Black elders. Thus, in this multivocal piece, we, two Black women oral historians of education, discuss specific tensions we navigated in our respective projects that focused on Black baby boomers’ educational experiences in the US South. The baby boomer generation encompasses those born between 1946 and 1965, and our disparate studies, on which we draw here, sought to investigate how they remembered their raced, classed, and gendered educational experiences during the 1960s and 1970s. In our research processes, issues around identity arose, and this paper pursues two areas of inquiry related to those issues—trust and relationship building with narrators and race as an all-encompassing metalanguage; we contend this metalanguage superseded narrators’ perceptions of gender’s influence in their lives. It is our wish that our transparent reflexivity aids other scholars in wrestling with considerations similar to those we found ourselves navigating

Mobilizing Betrayal: Black Feminist Pedagogy and Black Women Graduate Student Educators

This article addresses Black women graduate students\u27 educational labor in higher education teacher training programs. We ground this reflective account of our respective teaching praxis in the educational betrayal we endured as younger students, connecting it to our engagement of Black feminist pedagogy. We illustrate how this praxis empowered us as undergraduate educators to implement pedagogies of equity and justice. Employing a structured vignette analysis framework, we draw on a Black feminist paradigm and Black feminist autoethnography to examine field notes of our teaching praxis. These two field notes, one from Francena and one from ArCasia, demonstrate challenges that emerged in our instruction of mostly white undergraduates. Despite the precarious nature of our political and professional positions, we discuss why working toward an anti‐oppression praxis remains our ultimate pedagogical aim

Multisegment Scheme Applications to Modified Chebyshev Picard Iteration Method for Highly Elliptical Orbits

A modified Chebyshev Picard iteration method is proposed for solving orbit propagation initial/boundary value problems. Cosine sampling techniques, known as Chebyshev-Gauss-Lobatto (CGL) nodes, are used to reduce Runge’s phenomenon that plagues many series approximations. The key benefit of using the CGL data sampling is that the nodal points are distributed nonuniformly, with dense sampling at the beginning and ending times. This problem can be addressed by a nonlinear time transformation and/or by utilizing multiple time segments over an orbit. This paper suggests a method, called a multisegment method, to obtain accurate solutions overall regardless of initial states and albeit eccentricity by dividing the given orbit into two or more segments based on the true anomaly