Engineering topics
Robinson, J.
Publications and source records attributed to Robinson, J..
Clocking Auger electrons
Intense X-ray free-electron lasers (XFELs) can rapidly excite matter, leaving it in inherently unstable states that decay on femtosecond timescales. The relaxation occurs primarily via Auger emission, so excited-state observations are constrained by Auger decay. In situ measurement of this process is therefore crucial, yet it has thus far remained elusive in XFELs owing to inherent timing and phase jitter, which can be orders of magnitude larger than the timescale of Auger decay. Here we develop an approach termed ‘self-referenced attosecond streaking’ that provides subfemtosecond resolution in spite of jitter, enabling time-domain measurement of the delay between photoemission and Auger emission in atomic neon excited by intense, femtosecond pulses from an XFEL. FUrthermore, using a fully quantum-mechanical description that treats the ionization, core-hole formation and Auger emission as a single process, the observed delay yields an Auger decay lifetime of \(2.2_{ - 0.3}^{ + 0.2}\) fs for the KLL decay channel.
Megahertz-compatible angular streaking with few-femtosecond resolution at x-ray free-electron lasers
Highly brilliant, coherent, femtosecond x-ray pulses delivered by free-electron lasers (FELs) constitute one of the pillars of modern ultrafast science. Next generation FEL facilities provide up to megahertz repetition rates and pulse durations down to the attosecond regime utilizing self-amplification of spontaneous emission. However, the stochastic nature of this generation mechanism demands single-shot pulse characterization to perform meaningful experiments. Here we demonstrate a fast yet robust online analysis technique capable of megahertz-rate mapping of the temporal intensity structure and arrival time of x-ray FEL pulses with few-femtosecond resolution. We performed angular streaking measurements of both neon photo- and Auger electrons and show their applicability for a direct time-domain feedback system during ongoing experiments. Here, the fidelity of the real-time pulse characterization algorithm is corroborated by resolving isolated x-ray pulses and double pulse trains with few-femtosecond substructure, thus paving the way for x-ray-pump–x-ray-probe FEL science at repetition rates compatible with the demands of LCLS-II and European XFEL.
Advanced Multilayer Coatings for National Security
This project advanced the state-of-the-art in multilayer interference coatings with customtailored properties for national security applications, by understanding and overcoming limitations in the physical properties of these coatings. We focused on improving the properties of two major types of multilayers: the reflectance of hard x-ray aperiodic multilayer coatings (MLs) and the laser damage resistance of dielectric multilayer coatings (MLDs). We developed a new class of hard x-ray MLs for imaging in the 17 – 59 keV photon energy range for applications including target diagnostics and astrophysics. We elucidated the physical and chemical properties of nanoscale layers of ML materials and their interfaces and developed generalized protocols for aperiodic ML design and deposition. We revealed the origin of important laser damage-prone precursors and the underlying mechanism upon exposure to high energy and intensity nanosecond (ns) lasers in the ultraviolet (UV) region. In both ML and MLD coatings, we investigated the relationships between deposition conditions and performance. We then applied deposition process modifications specific to each type of ML and MLD coatings to dramatically improve the ML reflective performance and the MLD laser-damage resistance.
Introduction to Medical Extensible Dynamic Probabilistic Risk Assessment Tool (MEDPRAT)
A key component in the development of NASA Human Research Programs (HRP) next generation risk model, the Medical Extensible Dynamic Probabilistic Risk Assessment Tool (MEDPRAT) intends to deliver a means to quantify how HRP products impact astronaut medical and health risks. MEDPRAT is extensible to the majority of exploration missions. Similar to other risk models, the tool utilizes the available space and terrestrial medical data. MEDPRAT is designed to be extended with additional human health research information, medical equipment, space and terrestrial standards and practices to assess space flight medical risk in a manner consistent with other risk measures used in spacecraft and mission design. This tool provides risk-based medical system design information necessary to evaluate new technologies, procedures, research insights and mission plans.
High-Payoff Space Transportation Design Approach with a Technology Integration Strategy
A general architectural design sequence is described to create a highly efficient, operable, and supportable design that achieves an affordable, repeatable, and sustainable transportation function. The paper covers the following aspects of this approach in more detail: (1) vehicle architectural concept considerations (including important strategies for greater reusability); (2) vehicle element propulsion system packaging considerations; (3) vehicle element functional definition; (4) external ground servicing and access considerations; and, (5) simplified guidance, navigation, flight control and avionics communications considerations. Additionally, a technology integration strategy is forwarded that includes: (a) ground and flight test prior to production commitments; (b) parallel stage propellant storage, such as concentric-nested tanks; (c) high thrust, LOX-rich, LOX-cooled first stage earth-to-orbit main engine; (d) non-toxic, day-of-launch-loaded propellants for upper stages and in-space propulsion; (e) electric propulsion and aero stage control.
A NASA Spaceliner 100 Propulsion Oriented Technology Assessment
In response to a NASA request, the National Space Propulsion Synergy Team (SPST) team agreed to provide technical and programmatic support to NASA in formulating a Spaceliner 100 Technology Program. The SPST offered a broad cross-section of expertise and experience. Its membership consists of senior level, volunteer representatives from across government, industry, and academia. The purpose of this paper is to provide a summary of the SPST support of SL100, which culminated in a propulsion technologies assessment and prioritization workshop conducted at MSFC. The results of this workshop and the follow-up analysis are part of this report. Also included, is a review of some "lessons learned" that were solicited from the workshop participants.
External tank space debris considerations
Orbital debris issues associated with maintaining a Space Shuttle External Tank (ET) on orbit are presented. The first issue is to ensure that the ET does not become a danger to other spacecraft by generating space debris, and the second is to protect the pressurized ET from penetration by space debris or meteoroids. Tests on shield designs for penetration resistance showed that when utilized with an adequate bumper, thermal protection system foam on the ET is effective in preventing penetration.
The influence of nonlinear damping on the random response of panels by time domain simulation
The effects of nonlinear damping on the large-deflection response of symmetrically laminated composite panels is studied by time-domain simulation in an attempt to quantify experimentally observed phenomena. A single-mode deflection approach is used in the equations of motion and in the linear and nonlinear damping models. The probability, peak-probability, and spectral-density data are compiled for both strains and deflection. The rms responses as a function of input excitation level are also obtained and compared to linear, equivalent-linearization, and Fokker-Planck equation solutions.
Estimation of distributed acoustic lasers
The purpose of this paper is to present the results of a preliminary investigation of an indirect method which can be used to generate a set of equivalent point loads approximating an applied distributed acoustic load. The method combines the source information with the structure's modal characteristics and forces which give the same response as the applied acoustic load. The technique is demonstrated by predicting a set of point forces acting on a thin aluminum panel which simulate a normally-incident random pressure. The technique is verified by comparing measured strain autospectrums with estimated strain autospectrums generated using the predicting forces. Strain errors within 5 dB were achieved. A limited amount of information about the acoustic load could be deduced using the predicted force autospectrums and phase differences between these forces.
Force prediction using singular-value decomposition
Results of a preliminary investigation into a method which can be used to improve the results of an experimental force prediction analysis is presented. The method uses a singular value decomposition technique to reduce measurement noise present in the measured input data matrix. The fundamental theory for the method along with an experimental example is shown. The method is shown to provide encouraging force prediction improvements when the input data matrix contains high levels of measurement noise.
Manned Mars mission schedule report
The schedules for hardware for the initial manned Mars mission are provided. The mission is determined to be a 1999 opposition mission and the vehicle hardware configuration for the mission is depicted.
Statistical considerations in design of spacelab experiments
After making an analysis of experimental error sources, statistical models were developed for the design and analysis of potential Space Shuttle experiments. Guidelines for statistical significance and/or confidence limits of expected results were also included. The models were then tested out on the following proposed Space Shuttle biomedical experiments: (1) bone density by computer tomography; (2) basal metabolism; and (3) total body water. Analysis of those results and therefore of the models proved inconclusive due to the lack of previous research data and statistical values. However, the models were seen as possible guides to making some predictions and decisions.
Sterilizable liquid propulsion system Quarterly progress report
Module truss, propellant tanks, and functional tests for sterilizable bipropellant liquid propulsion system exposed to ethylene oxide
Evaluation of be-38 percent al alloy final report, 27 jun. 1964 - 28 feb. 1965
Mechanical properties, microstructural features, and general metallurgical quality of beryllium- aluminum alloy