Dynamic tailoring and tuning for space-based precision optical structures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaves 227-236).Next-generation space telescopes in NASA's Origins missions require use of advanced imaging techniques to achieve high optical performance with limited launch mass. Structurally-connected Michelson interferometers meet these demands, but pose specific challenges in the areas of system dynamics and controls, uncertainty management and testing. The telescope optics must meet stringent positional tolerances in the presence of environmental and on-board disturbances, resulting in heavy demands on structural dynamics and control. In addition, fully integrated system tests are cost-prohibitive due to the size and flexibility of the system coupled with the severe differences between the on-orbit and ground testing environments. As a result, the success of these missions relies heavily on the accuracy of the structural and control models used to predict system performance. In this thesis, dynamic tailoring and tuning are applied to the design of precision optical space structures to meet aggressive performance requirements in the presence of parametric model uncertainty. Tailoring refers to changes made to the system during the design, and tuning refers to adjustments on the physical hardware. Design optimizations aimed at improving both performance and robustness are considered for application to this problem. It is shown that when uncertainty is high and performance requirements are aggressive, existing robust design techniques do not always guarantee mission success. Therefore, dynamic tuning is considered to take advantage of the accuracy of hardware performance data to guide system adjustments to meet requirements.(cont.) A range of hardware tuning techniques for practical implementation are presented, and a hybrid model updating and tuning methodology using isoperformance analysis is developed. It is shown that dynamic tuning can enhance the performance of a system designed under high levels of uncertainty. Therefore, robust design is extended to include tuning elements that allow for uncertainty compensation after the structure is built. The new methodology, Robust Performance Tailoring for Tuning creates a design that is both robust to uncertainty and has significant tuning authority to allow for hardware adjustments. The design methodology is particularly well-suited for high-performance, high-risk missions and improves existing levels of mission confidence in the absence of a fully integrated system test prior to launch. In the early stages of the mission the design is tailored for performance, robustness and tuning authority. The incorporation of carefully chosen tuning elements guarantees that, given an accurate uncertainty model, the physical structure is tunable so that system performance can be brought within requirements. It is shown that tailoring for tuning further extends the level of parametric uncertainty that can be tolerated at a given performance requirement beyond that of sequential tailoring and tuning, and is the only design methodology considered that is consistently successful for all simulated hardware realizations.by Rebecca Ann Masterson.Ph.D

Development and validation of empirical and analytical reaction wheel disturbance models

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 195-197).by Rebecca A. Masterson.S.M

Design and Test of a Deployable Radiation Cover for the REgolith X-Ray Imaging Spectrometer

The REgolith X-ray Imaging Spectrometer (REXIS) instrument contains a one-time deployable radiation cover that is opened using a shape memory alloy actuator (a "Frangibolt") from TiNi Aerospace and two torsion springs. The door will be held closed by the bolt for several years in cold storage during travel to the target asteroid, Bennu, and it is imperative to gain confidence that the door will open at predicted operational temperatures. This paper briefly covers the main design features of the radiation cover and measures taken to mitigate risks to cover deployment. As the chosen FD04 model Frangibolt actuator has minimal flight heritage, the main focus of this paper is the testing, results and conclusions with the FD04 while discussing key lessons learned with respect to the use of the FD04 actuator in this application

Modeling the Expected Performance of the REgolith X-ray Imaging Spectrometer (REXIS)

OSIRIS-REx is the third spacecraft in the NASA New Frontiers Program and is planned for launch in 2016. OSIRIS-REx will orbit the near-Earth asteroid (101955) Bennu, characterize it, and return a sample of the asteroid's regolith back to Earth. The Regolith X-ray Imaging Spectrometer (REXIS) is an instrument on OSIRIS-REx designed and built by students at MIT and Harvard. The purpose of REXIS is to collect and image sun-induced fluorescent X-rays emitted by Bennu, thereby providing spectroscopic information related to the elemental makeup of the asteroid regolith and the distribution of features over its surface. Telescopic reflectance spectra suggest a CI or CM chondrite analog meteorite class for Bennu, where this primitive nature strongly motivates its study. A number of factors, however, will influence the generation, measurement, and interpretation of the X-ray spectra measured by REXIS. These include: the compositional nature and heterogeneity of Bennu, the time-variable Solar state, X-ray detector characteristics, and geometric parameters for the observations. In this paper, we will explore how these variables influence the precision to which REXIS can measure Bennu's surface composition. By modeling the aforementioned factors, we place bounds on the expected performance of REXIS and its ability to ultimately place Bennu in an analog meteorite class.Comment: Presented at the SPIE Optics + Photonics Conference, 18 August 2014, San Diego, C

Design and Performance of the AERO-VISTA Magnetometer

We describe the design and performance of the magnetometer instrument for the CubeSat mission AERO-VISTA. AERO-VISTA requires in-situ vector magnetic measurements with magnetic precision and repeatability better than 100 nT at a minimum rate of 10 Hz. Our magnetometer system uses the three-axis Honeywell HMC1053 anisotropic magnetoresistive (AMR) sensor. As built, our instrument exhibits intrinsic magnetic noise better than 10 nTrms from 0.1 to 10 Hz, though self-interference effects degrade performance to about 50 nT to 200 nT uncertainty. The analog and mixed signal portion of each magnetometer occupies about 8 square centimeters of circuit board space and draws about 100 mW. We describe the selection of major components, detail the schematic design of the analog electronics, and derive a noise budget from datasheet component specifications. The theoretical noise budget matches experimental results to better than 20%. We also describe the digital electronics and software which operates an analog to digital converter interface and implements a sampling method that allows for improved separation of offset and magnetic field signal contributions. We show the spectral characteristics of the magnetic field noise floor including self-interference effects. Our magnetometer design can be used in whole or in part on other small satellites which plan to use similar AMR magnetic sensors

Improved reference genome of the arboviral vector Aedes albopictus

Background: The Asian tiger mosquito Aedes albopictus is globally expanding and has become the main vector for human arboviruses in Europe. With limited antiviral drugs and vaccines available, vector control is the primary approach to prevent mosquito-borne diseases. A reliable and accurate DNA sequence of the Ae. albopictus genome is essential to develop new approaches that involve genetic manipulation of mosquitoes. Results: We use long-read sequencing methods and modern scaffolding techniques (PacBio, 10X, and Hi-C) to produce AalbF2, a dramatically improved assembly of the Ae. albopictus genome. AalbF2 reveals widespread viral insertions, novel microRNAs and piRNA clusters, the sex-determining locus, and new immunity genes, and enables genome-wide studies of geographically diverse Ae. albopictus populations and analyses of the developmental and stage-dependent network of expression data. Additionally, we build the first physical map for this species with 75% of the assembled genome anchored to the chromosomes. Conclusion: The AalbF2 genome assembly represents the most up-to-date collective knowledge of the Ae. albopictus genome. These resources represent a foundation to improve understanding of the adaptation potential and the epidemiological relevance of this species and foster the development of innovative control measures

Aurora: A Software Radio for Electromagnetic Vector Sensors in Space

The AERO (Auroral Emission Radio Observer) and VISTA (Vector Interferometry Space Technology using AERO) missions will advance auroral radio science and radio interferometry technology. AERO is intended to qualify and validate electromagnetic vector sensor technology in space while also answering key scientific questions about the nature and sources of auroral radio emissions. These questions cannot be addressed from the ground due to shielding by the ionosphere. VISTA, together with AERO, will provide the first demonstration of interferometric imaging, beamforming, and nulling using electromagnetic vector sensors at low frequencies (100 kHz – 15 MHz) using Space based sensors. A key component of the AERO-VISTA joint mission is the Aurora software radio system which forms the primary mission payload when combined with an electromagnetic vector sensor antenna (VSA). This radio combines the analog, digital, and signal processing necessary to detect and digitize the signals associated with the radio aurora. We provide a detailed discussion of the radio design, implementation, and performance results from early testing of our engineering model units