Modern space missions are increasingly venturing across cislunar space, requiring expansion of space awareness functions. Legacy space domain awareness (SDA) systems were not originally built to detect and track cislunar objects, and this could require acquisition of new sensor systems. There are numerous parameters, including sensing type, altitude, and number of platforms that could be varied for each system. One of the proposed options is a pole-sitter satellite located at 2.5 million km above either the North or South Pole. One key advantage to any “pole-sitter” is that it has a position well outside the ecliptic plane and offers a unique, in some cases orthogonal viewing geometry that here to fore have not been developed for operational deployment. Such orbits offer continuous watching and tracking of candidate objects with the advantages of efficiency and characterization. The efficiency results from not having to repeatedly reacquire the object due to blockage by Earth eclipse; and once detected and continuously tracked, any behavior of the object begins to reveal its characteristics, pattern of life, and potential intents. In this paper, the physics of the pole-sitter trajectory, the trade of fuel usage against altitude, and updates in required technology are discussed. All these elements point towards the feasibility of demonstrating a pole-sitter SDA capability in the near term. In addition, this paper devises a proposed prototype using small spacecraft in conjunction with ground-based sensors along with descriptions of current technology ready for deployment.

To overcome the technical readiness levels (TRL) 4 – 7 "Valley of Death" and accelerate new technology development, the US Space Force (USSF) started an in-Space Developmental Test (iSDT) initiative with its instantiation of a persistent iSDT platform called the Advanced Space-Based Testbed (XST). For risk-reduction, a scaled-down Mini-XST is proposed for proof-of-concept. Its key space systems include the spacecraft bus, test payloads, tender servicer to deliver test payload to the Mini-XST spacecraft, and robotic servicer to attach test payloads to the Mini-XST platform. In this paper, the proposed Mini-XST taking advantage of recent proliferated small satellite technologies as well as standard interface to support its successful operation will be discussed and illustrated.

In order to accelerate new technology development, overcome the technical readiness levels (TRL) 4 – 7 “Valley of Death”, and reduce acquisition cost, the US Space Force (USSF) started an In-Space Developmental Test (iSDT) initiative, which is alternatively called Advanced Space-Based Testbed (XST) in its realization form. This persistent test platform is unmanned, highly autonomous, and capable of in-space assembly (iSA) morphing in shape and in-space servicing (iSS) to accommodate as many test payloads as possible. In this paper, the architecture, requirements, operational concepts, potential test candidates, XST modeling, cost analysis, a sample test plan, and tentative launch schedule will be discussed.

The Psyche mission was selected by NASA as the 14th mission in the Discovery Program in 2017. The Psyche spacecraft utilizes solar electric propulsion, and will journey to the asteroid (16) Psyche during a 3.5 year trajectory after its planned 2022 launch. The spacecraft instrument suite includes a magnetometer, a multispectral imager, a gamma ray neutron spectrometer, and an X-band radio telecommunications system. It also includes the Deep Space Optical Communication technical demonstration. These instruments along with other spacecraft components require pointing accuracy to meet their scientific and engineering performance requirements. Early on in the project development, the team established a methodology by which pointing accuracy (knowledge and control) is analyzed against the system requirements by means of pointing error budgets and requirement allocations. A margin policy was implemented to ensure the instrument and engineering component pointing accuracy requirements will be met during verification and in flight. Psyche's pointing management framework defines detailed rationales for the system and subsystem error allocations of the top level pointing accuracy requirements, with sufficient project level pointing margin, and supports end-to-end pointing requirement verification. This paper will present an overview of the Psyche project's pointing error budget development process, and discuss the rationale behind the methodology. Psyche's pointing budget methodology integrates best practices and lessons learned from heritage missions, while focusing on the specific needs of the Psyche spacecraft and its science instruments. Key challenges in the pointing error budget development will be reviewed, and a deep dive into two key Psyche pointing budgets are presented. The systems engineering of Psyche's pointing budget methodology outlined in this paper will serve as a resource for future deep space missions.

The goal of this paper is to determine whether there is a correlation between awareness of global warming, and where global warming occurs.This theory is carried out by analyzing maps containing various forms of data that have to do with global warming, such as precipitation and surface temperature, and comparing it with a map of engagement from tweets which mention global warming.This paper found that there is no solid correlation between mentioning global warming in tweets and global warming's effect, although there was a steady increase in both.This is most likely due to Twitter's user base increasing over the years.Therefore it appears that although the effects of global warming have increased, the percentage of people aware of it on major social media sites has not.This then concludes that before trying to find a solution or preventative measure to global warming, an approach must first be made to create awareness for it on social media platforms.

Jetted and grouted precast piles (JGPPs) are prefabricated piles installed utilizing jetting and pressure grouting. These piles are well-suited for urban environments as they overcome the inherent drawbacks of currently chosen deep foundations (e.g., noise and vibration disturbances due to pile driving, quality control issue with cast-in-place construction). Past studies in a large test chamber facility have shown that JGPPs can support very high axial and torsional loads owing to their improved skin and tip resistances subsequent to the side- and tip-grouting. However, this new pile has not yet been implemented in practice due to the lack of field verification of its constructability as well as load resistance. This paper presents the full-scale field construction of two JGPPs and the load test program performed to investigate the applicability of the new pile as a foundation for miscellaneous structures. As such structures are subjected to high torsion and lateral load during severe wind-loading (e.g., hurricanes), the test program included combined torsion and lateral loading as well as simple lateral loading. An actual pole – mast arm assembly was used in the coupled torsion and lateral load test to simulate the typical field-loading scenario. The load was applied using a crane and the pile’s rotations and translations were monitored using the novel instrumentation systems. The field tests showed that JGPPs possess high torsion and lateral resistances compared to identically sized drilled shafts, which is a common foundation type used for such structures. The two methods available for predicting axial resistance of the new pile are found to be suitable for the estimation of torsional resistance as well. It was also found that the concurrent application of torsion significantly reduces lateral resistance of the new pile foundation as observed for drilled shafts. In general, the study reveals that the JGPPs are well-suited foundations for miscellaneous structures.

Noise and vibration are critical issues associated with pile driving operations in an urban environment. Alternative foundations such as drilled shafts and augercast piles alleviate much of the operational noise and vibration. However, the cast-in place installation process may raise concerns in quality control if not adequately monitored. Post grouting the drilled shaft base has been widely used to mobilize a larger portion of the tip resistance prior to construction of the superstructure, thereby controlling the axial displacement during the service. In response to the operational challenges in urban environments, the Florida Department of Transportation and the University of Florida have recently developed a new generation of deep foundation, namely "Jetted and Grouted Precast Pile". The process consists of pressurized water jetting a concrete pile instead of a hammer-driven installation, and subsequent side and tip grouting the pile, which significantly improve skin and tip resistance, respectively, as well as lateral and torsional stiffness. Several studies have been focused on such increase in axial and torsional resistance by grouting techniques. However, there has been little field data available to support quantifiable noise and vibration reduction by jetting and grouting processes. This paper presents field measurements of noise and ground surface vibration during full-scale installation of jetted and grouted piles. Comparison of measured data to recommended noise and vibration limits suggests that jetting and grouting techniques are a viable solution for urban geo-infrastructure development.

Following several reaction wheel on-orbit anomalies and ensuing lifetime extension of the Globalstar 2nd generation fleet, a hybrid control algorithm using two wheels and magnetic torque bars was developed and implemented in the satellites in low Earth orbit. Since the control torque by magnetics is much smaller than that by reaction wheel and its strength varies with satellite position and attitude on the orbit, satellite operations engineers must take special care during station keeping, yaw slew, etc. This paper will present some on-orbit data and lessons learned associated with this new hybrid control algorithm.

Drilled shaft foundations supporting mast arm assemblies are subjected to significant torsion and lateral load during severe wind loading (e.g., hurricane). Past centrifuge studies in granular soils suggest that the design of such foundations should be performed for a coupled load case, since the lateral resistance is considerably reduced by the concurrent application of torsion. However, current design practice still considers lateral load and torsion independently due to the lack of field verification of centrifuge results. This paper reports on a full-scale test program to investigate the coupled load behavior of drilled shafts. A novel load test setup (with a heavy-duty mast arm assembly) and instrumentation were used for the combined torsion and lateral loading (e.g., wind loading). The study revealed a significant reduction in lateral resistance due to the influence of torque as observed from previous centrifuge studies. Torsional resistance was reduced (approximately 20%) by the impact of lateral load when compared with the anticipated torsional resistance based on unit skin friction values, derived from the axial load test results (i.e., no influence of lateral load). A comparison of measured torsional resistance during the combined loading with the predicted values using different approaches was also made. O’Neill and Hassan’s beta (β) method (sand) and alpha method (clay) are found to predict the torsional resistance reasonably well (±10%), while all other methods based on the standard penetration test and cone penetration test considered in the study overpredicted or underpredicted the resistance.

A Globalstar 2nd generation satellite experienced a reaction wheel mechanical failure, and in response Globalstar has been closely monitoring reaction wheel bearing friction. To prevent another reaction wheel hardware failure and subsequent shortened satellite mission life, a friction data processing methodology was developed as an on-orbit monitoring tool for the ground to issue early warning and take appropriate action on any hardware degradation or potential failure. The methodology, reaction wheel friction behavior, and its application to an on-orbit anomaly experience will be presented.

In this paper, results from a recent survey of star tracker anomalies are presented. The star tracker survey task was sponsored by NASA Marshall Space Flight Center's Office of the Chief Engineer. The objective of the survey was to better understand the nature of star tracker anomalies and assist in preventing anomalies to minimize future risks. Star tracker anomaly data was collected from three main sources: The Aerospace Corporation's (Aerospace) Space Systems Engineering Database, Aerospace subject matter experts who have experience with particular star tracker anomalies, and public websites. The collected anomaly data includes 72 cases including many recent and some as far back as 30 years. The data analysis was done using three classification methods: by development phase, by subsystem, and by severity of the anomaly. Among the identified anomalies, the majority were design issues related with software and electronic subsystems. The majority of anomalies were considered minor (e.g., they did not impact mission performance). However, 43% of the anomalies were moderate to major and required corrective actions or had a major impact to the mission (for example, early termination).

The pressure grouting of drilled shaft tips has become popular worldwide due to its effectiveness in mobilizing a larger portion of the available tip resistance under service displacements. This paper presents experimental and numerical studies on the load transfer mechanism and factors controlling the axial response of base grouted drilled shafts in cohesionless soils. The study found that the increased axial capacity of grout-tipped drilled shafts under service loads and displacements depended mainly on preloading effects and the increased tip area provided by the grouting process. A simple prediction approach for estimating the tip capacity of grouted shafts utilizing cone penetration resistance was suggested based on the results of the study. The validity of the proposed approach was verified by the analysis of full-scale case studies of grouted shafts reported in the literature.

Post-grouting of deep foundations following installation is a proven technique for enhancing axial resistance. The grouting is performed either below the tip of the foundation only (e.g., post-tip-grouted drilled shafts) or at both the side and the tip (e.g., jetted, side, and tip-grouted precast piles). The interaction of such foundations in group placement is currently unknown. This research focused on the group behavior of post-tip-grouted drilled shafts and jetted, side, and tip-grouted piles at a center-to-center spacing of three times the pile/shaft diameter. The study revealed that the post-tip-grouted drilled shafts acted independently within the group (i.e., negligible group interaction), whereas jetted, side, and tip-grouted piles behaved as a block under axial loading. It was determined that side grouting of a foundation prior to tip grouting significantly increases the grout pressure developed during tip grouting and helps in the formation of a tip grout bulb via a spherical cavity expansion process. Thus, the side and tip grouting of adjacent foundations within a group increases the confining stress and relative density of the soil mass within the group, resulting in block behavior under top-down loading. In contrast, tip-only grouted foundations showed little if any increase in radial stress and radial soil displacement, resulting in minimal improvement of the soil stiffness between shafts; as a result there was no block behavior and a negligible group effect at the tip.

Reliability-based design, such as LRFD, aims at meeting desired probability of failure levels for engineered structures. The present work attempts to contribute to this field by analyzing the influence of spatially variable soil/rock strength on the axial resistance uncertainty of single and multiple shafts in group layouts. This includes spatial variability over the individual shaft surfaces, effects of limited data, random measurement errors, and workmanship. A possible correlation between boring data inside or near the footprint of a foundation and the foundation itself is considered. In a geostatistical approach, spatial averaging (upscaling) and a degenerate case of ordinary kriging are applied to develop variance reduction charts and design equations for a series of foundation group layouts (single, double, triple, and quadruple). For the potential situation of an unknown horizontal correlation range at a site, the worst case scenarios are identified and demonstrated in an example problem. Resulting probabilities of failure are applied to the whole foundation (i.e., group) rather than single objects. It is found that a boring at the center of a group footprint can significantly reduce resistance prediction uncertainty, especially under the worst case scenario for unknown horizontal correlation range. In contrast, independent of the presence of a center boring or not, the uncertainty reduction through additional borings becomes small, once four or five borings are available. DOI: 10.1061/(ASCE)GT.1943-5606.0000728. (C) 2013 American Society of Civil Engineers.

With increased urbanization, deep foundation (bridges, signage, walls, etc.) selection is moving toward the minimization of disturbance and installation time, as well as addressing quality control and assurance issues. Unfortunately, many types of deep foundations involve noise and vibration during installation (e.g., driven piles) or integrity and reduced resistance issues (e.g., drilled shafts, both conventional and post grouted tip, continuous flight auger piles). This paper presents a new foundation type, a jetted and grouted precast pile, which uses the advantages of several proven deep foundation installation techniques. The installation of the new pile is comprised of three distinct phases: (1) pressurized water-jetting of a precast pile into the ground; (2) side grouting of the pile; and (3) tip grouting. The pile has two separate side grouting zones, each with its own grout delivery system. Each grout zone is covered with a semirigid membrane, which results in radial expansion of the soil during side grouting and horizontal orientation of the major principal stress. Small-scale testing revealed excellent bonding between the pile and the grout, as well as improved mobilized pile-soil skin and tip resistance. Both experimental and FEM modeling of the grouting and axial loading were performed on various sized jetted and grouted precast piles in cohesionless soil. On the basis of this study, a methodology that predicts expected grout pressures during grouting, unit side and tip resistance, and the load-displacement response of a pile in cohesionless soil is proposed. Further testing and research is required to validate the proposed methodology before it can be implemented in practical situations.