Hubble Space Telescope

The Hubble Space Telescope will employ magnetic torque controllers, which make use of the Earth's magnetic field augmented by four reaction wheels. DC torques are easily allowed for, but variations, orbit by orbit, can result in excessive wheel speeds which can excite vibratory modes in the telescope structure. If the angular momentum from aerodynamic sources exceeds its allocation of 100 Nms, the excess has to come out of the maneuvering budget since the total capacity of the momentum storage system is fixed at 500 Nms. This would mean that maneuvers could not be made as quickly, and this would reduce the amount of science return. In summary, there is a definite need for a model that accurately portrays short term (within orbit) variations in density for use in angular momentum management analyses. It would be desirable to have a simplified model that could be used for planning purposes; perhaps applicable only over a limited altitude range (400 to 700 km) and limited latitude band

Sensor failure detection and recovery by neural networks

A new method of sensor failure detection, isolation, and accommodation is described using a neural network approach. In a propulsion system such as the Space Shuttle Main Engine, the dynamics are usually much higher than the order of the system. This built-in redundancy of the sensors can be utilized to detect and correct sensor failure problems. The goal of the proposed scheme is to train a neural network to identify the sensor whose measurement is not consistent with other sensor outputs. Another neural network is trained to recover the value of critical variables when their measurements fail. Techniques for training the network with a limited amount of data are developed. The proposed scheme is tested using the simulated data of the Space Shuttle Main Engine (SSME) inflight sensor group

An analysis of the Dahl friction model and its effect on a CMG gimbal rate controller

The effects of friction, represented by the Dahl model, on a CMG rate control system was investigated by digital simulation. The conclusion from these simulation results is that gimbal pivot friction can be a significant effect on the gimbal rate control system. The magnitude of the problem this presents depends on the characteristics of the actual pivot. It would appear from this preliminary look that one solution is to insure that the control system natural frequency is higher by some prescribed amount than the natural frequency of the friction loop

Forum 10: COVID Vaccines: How did you get here?

We consider the supply chains for the distribution of the COVID-19 vaccine and other routine vaccines. We first outline new product development, manufacturing flow management, order fulfillment and vaccine distribution. Next, we focus on the vaccine supply chains in low and middle-income countries. We discuss the cold supply chain and challenges in these countries. Lastly, we discuss current drone delivery capabilities and how drones are being used to delivery the COVID-19 vaccine

Investigating Interactions between Neurotactin, Amalgam and Lachesin in Insects, Three Proteins that Function in Neuronal Cell Adhesion

Neurotactin (Nrt) is a transmembrane protein that interacts with Amalgam (Ama), a secreted protein, to promote cell:cell adhesion during nervous system development in Drosophila. The Ama/Nrt cell adhesion process has been shown to be involved in axon-pathfinding. Lachesin (Lac), another cell surface protein, may also play a role in Drosophila neurite outgrowth. Lac and Ama proteins are very similar in structure. Both consist of a signal sequence followed by one variable and two constant immunoglobulin domains and are 58% similar in amino acid sequence. A critical difference is that the Lac protein is linked to cell membranes by a phosphatidylinositol anchor as opposed to the secreted Ama protein. Functions of Ama and Lac in neuronal development are still rather unclear. However, it is clear that Ama binds to Nrt and that this binding allows Nrt-expressing cells to aggregate. To characterize potential Lac interactions with Ama and Nrt, a series of experiments was performed. The Lac gene was cloned from the Drosophila genome. Using in vitro mutagenesis, a new version of the Lac gene was created without the sequence coding for the membrane anchor to produce a secreted version of the Lac protein. To test the functional properties of Lac and secreted Lac (Lac sec) I utilized the S2 cell aggregation assay. Drosophila Schneider 2 (S2) cells normally exist as individual cells in suspension. However, if manipulated to express cell adhesion molecules, the S2 cells can form significant multicellular aggregates. Therefore, Drosophila S2 cells provide a perfect model with which to assay the ability of Lac to promote cell adhesion. Results confirmed previous findings that the secreted version of Ama binds to Nrt to form cellular aggregates. Also in agreement with past findings, Ama and Lac were able to act individually as homophilic cell adhesion molecules. Both were able to induce homophilic aggregates, which served as a control for Ama and Lac protein production. S2 cells expressing the membrane-bound version of Lac and cells expressing Nrt were combined and assayed for cell aggregation activity. No mixed aggregates were observed which could indicate an inability of the Lac protein to bind to Nrt. The secreted version of Lac was also assayed for the ability to promote aggregation of Nrt-expressing cells. When Lac sec protein was added to media with Nrt-expressing S2 cells no significant multicellular aggregates were observed suggesting that the difference in amino acid sequence of the Ama protein compared to the Lac accounts for different Nrt-binding properties. To identify Ama sequences that confer the specificity of the Ama:Nrt interaction as well as Ama:Ama and Lac:Lac interactions, chimeric Ama-Lac genes were generated. In the future these chimeric proteins will be tested in the S2 cell assay for their different binding properties. A new system for positive selection of transfected cells was tested and proven effective in the course of these experiments. This process utilizes resistance to the antibiotic Hygromycin B and is more advantageous than previous approaches used in the Seeger Lab due to the minimal cost of Hygromycin B. Advisor: Mark Seege

An Analysis of COVID-19 Vaccine Hesitancy in the U.S. at the County Level

Reluctance or refusal to get vaccinated, referred to as vaccine hesitancy (VH), has hindered the efforts of COVID-19 vaccination campaigns. It is important to understand what factors impact VH behavior. This information can help design public health interventions that could potentially increase vaccine uptake. We develop a random forest (RF) classification model that uses a wide variety of data to determine what factors affected VH at the county level during 2021. We consider static factors (such as gender, race, political affiliation, etc.) and dynamic factors (such as Google searches, social media postings, Stringency Index, etc.). Our model found political affiliation and the number of Google searches to be the most relevant factors in determining VH behavior. The RF classification model grouped counties of the U.S. into 5 clusters. VH is lowest in cluster 1 and highest in cluster 5. Most of the people who live in cluster 1 are democrat, are more internet-inquisitive (are more prone to seek information from multiple sources on the internet), have the longest life expectancy, have a college degree, have the highest income per capita, live in metropolitan areas. Most people who live in cluster 5 are republicans, are the least internet-inquisitive, have the shortest life expectancy, do not have a college degree, have the lowest income per capita, and live in non-metropolitan areas. Our model found that counties in cluster 1 were most responsive to vaccination-related policies and COVID-19 restrictions. These strategies did not have an impact on the VH of counties in cluster 5.Comment: 28 pages, 12 figures, 4 table

Data Processing on Large Interdependent Networks: An Application for Infrastructure Preparedness, and Restoration

This paper presents a method for validating and transforming data for use in interdependent infrastructure network analysis. Critical infrastructure are interdependent on each other for delivery of services and execution of restoration activities.  These interdependencies make infrastructure systems vulnerable to extreme events and highlights the needs for preparedness and response plans.  Optimization models have been used to create effective plans using interdependent infrastructure networks.  These models require accurate input data.  However, many data sources have inconsistencies or errors which inhibit the ability to use such optimization models.   This work identifies common errors in input network data and provides a method for processing and correcting these errors.  We demonstrate the effectiveness of this method on data representing the transportation network in Juan Diaz town, in Panama. Keywords: Data processing, network, infrastructure, interdependence

The solar array-induced disturbance of the Hubble Space Telescope pointing system

The investigation of the vibrational disturbances of the Hubble Space Telescope that were discovered soon after deployment in orbit is described in detail. It was found that the disturbances were particularly evident during orbital day-night crossings, and that the magnitudes of the disturbances were considerably larger than the design jitter requirements. This paper describes the process by which the vibrations were characterized and isolated to a particular mechanism. The analysis of the flight data and comparisons with computer simulation results showed that the source of the disturbances was the thermally driven deformation of the solar arrays in conjunction with frictional effects in the array mechanisms. The control system was successfully modified to attenuate the disturbances to tolerable levels pending mechanical and thermal redesign of the solar arrays. The new arrays were installed during the first space telescope servicing mission and, in combination with the enhanced control system algorithm, reduced the disturbances to satisfactory levels

Results of the Stable Microgravity Vibration Isolation Flight Experiment

This paper presents an overview of the STABLE microgravity isolation system developed and successfully flight tested in October 1995. A description of the hardware design and operational principles is given. A sample of the measured flight data is presented, including an evaluation of attenuation performance provided by the actively controlled electromagnetic isolation system. Preliminary analyses of flight data show that the acceleration environment aboard STABLE's isolated platform was attenuated by a factor of more than 25 between 0.1 and 100 Hz. STABLE was developed under a cooperative agreement between National Aeronautics and Space Administration, Marshall Space Flight Center, and McDonnell Douglas Aerospace. The flight hardware was designed, fabricated, integrated, tested, and delivered to the Cape during a five month period