This study examined the utility of the conceot of interaction tendency in explaining personal spacing behavior. Interaction tendency v/as defined as an aggregate of feelings about an interaction situation and as a mediator between personal spacing behavior and the kind of associations connected with an interaction. It was hypothesized that as the positivity of the associations connected with an interaction increased, interaction tendency increased, and personal spacing decreased. Two levels of task (problem solving and conversation), two levels of associations connected with the task (positive and negative), and tv;o levels of associations connected with the other interactant (positive and negative) were manipulated, and the resultant seating behavior was observed. It was found that the independent variables were not predictive of seating behavior.

Dust problems raise significant concerns in planetary surface exploration. The unusual behavior of the dust particles that surround the vehicle after engine cutoff has the potential to have more of an influence on surface systems than the high velocity lunar rocket plume ejecta in the landing process. A prevailing hypothesis attributes the levitation and transport of dust particles on the surface of airless bodies to the electrostatic effects and electric field. However, there is no accurate model considering the inter-particle electrostatic interactions, especially when the particles are charged by plume. This dissertation aims to understand the behavior of charged lunar regolith with a discrete element method (DEM) approach focusing on the inter-particle interactions and contact charge transfer. To accomplish this, the grain dynamics is coupled with mechanical and electrical particle interactions, and both short-range and long-range interactions between particles are incorporated. A tribo-charging model based on instantaneous collisions is adopted and validated by simulation and experimental data. Sensitivity analysis is conducted to quantify the effects of initial charge, tribo-charging, and E-field on transport of lunar dust. DEM simulations are then performed for a near realistic lunar environment that show the differences of position and velocity distributions between charged particles and uncharged particles. The results indicate that the charged dust particles have higher dispersion and wider distribution of velocity due to the electrostatic effects. This provides a possible explanation for the phenomena of the approximately 30 s dust lofting following Apollo Lunar Module landing. It is shown that tribo-charging has a more considerable effect on the dynamics of charged particles with a large amount of charge, while the change of E-field does not significantly affect the results. Furthermore, superquadrics and multi-sphere approximations are introduced as two approaches to aspherical geometry to accomplish high-fidelity simulation of lunar dust in the future.

No description available.

No description available.

No description available.

No description available.

The safety of future spaceflight depends on space surveillance and space traffic management, as the density of objects in Earth orbit has reached a level that requires collision avoidance maneuvers to be performed on a regular basis to avoid a mission or, in the context of human space flight, life-endangering threat. Driven by enhanced sensor systems capable of detecting centimeter-sized debris, megaconstellations and satellite miniaturization, the space debris problem has revealed many parallels to the plastic waste in our oceans, however with much less visibility to the eye. Future catalog sizes are expected to increase drastically, making it even more important to detect potentially dangerous encounters as early as possible. Due to the limited number of monitoring sensors, continuous observation of all objects is impossible, resulting in the need to predict the orbital paths and their uncertainty via models to perform collision risk assessment and space object catalog maintenance. For many years the uncertainty models used for orbit determination neglected any uncertainty in the astrodynamic force models, thereby implicitly assuming them to be flawless descriptions of the true space environment. This assumption is known to result in overly optimistic uncertainty estimates, which in turn complicate collision risk analysis. The keynote of this doctoral thesis is to establish uncertainty realism for low Earth orbiting satellites via a physically connected quantification of the dominant force model uncertainties, particularly multiple sources of atmospheric density uncertainty and orbital gravity uncertainty. The resulting process noise models are subsequently integrated into classical and state of the art orbit determination algorithms. Their positive impact is demonstrated via numerical orbit determination simulations and a collision risk assessment study using all non-restricted objects in the official United States space catalogs. It is shown that the consideration of atmospheric density uncertainty and gravity uncertainty significantly improves the quality of the orbit determination and thus makes a contribution to future spaceflight safety by increasing the reliability of the uncertainty estimates used for collision risk assessment. / Die Sicherheit der künftigen Raumfahrt hängt von der Weltraumüberwachung und dem Weltraumobjektmanagement ab, da inzwischen die Dichte an Objekten im Erdorbit ein Niveau erreicht hat, welches regelmäßige Kollisionsvermeidungsmanöver erfordert um eine missions- oder, im Kontext der bemannten Raumfahrt, lebensgefährdende Situation zu vermeiden. Durch verbesserte Sensorsysteme, die in der Lage sind, zentimetergroße Objekte zu erkennen, Megakonstellationen und die Satellitenminiaturisierung hat das Weltraummüllproblem viele Parallelen zu den Plastikabfällen in unseren Weltmeeren offenbart, jedoch mit deutlich geringerer Sichtbarkeit für das Auge. Es ist zu erwarten, dass die Größe der Weltraumobjektkataloge in Zukunft drastisch ansteigen wird, was es umso wichtiger macht, potenziell gefährliche Begegnungen so früh wie möglich zu erkennen. Durch die begrenzte Anzahl an Überwachungssensoren ist eine kontinuierliche Beobachtung aller Objekte unmöglich, sodass die Umlaufbahnen und deren Unsicherheiten über Modelle vorausberechnet werden müssen, um die Bewertung von Kollisionsrisiken vorzunehmen und die Wartung der Objektkataloge sicherzustellen. Viele Jahre haben die zur Bahnbestimmung verwendeten Unsicherheitsmodelle jegliche Unsicherheit in den astrodynamischen Kräftemodellen vernachlässigt und somit implizit angenommen, dass diese fehlerfreie Beschreibungen der wahren Weltraumumgebung darstellen. Diese Annahme ist jedoch dafür bekannt, zu übermäßig optimistischen Unsicherheitsabschätzungen zu führen, was die Kollisionsrisikobewertung erschwert. Das Leitthema dieser Doktorarbeit ist die Berechnung realistischer Unsicherheiten von Objekten in einer niedrigen Erdumlaufbahn anhand einer Unsicherheitsquantifizierung mit physikalischem Bezug zu den Kräftemodellen, welche die größten Anteile an der Propagationsunsicherheit aufweisen. Dies sind insbesondere mehrere Quellen von atmosphärischer Dichteunsicherheit, sowie Gravitationsunsicherheit. Die resultierenden Prozessrauschmodelle werden anschließend in klassische und moderne Algorithmen zur Umlaufbahnbestimmung integriert. Die positiven Auswirkungen dieser Technik werden durch numerische Simulationen zur Orbitbestimmung, sowie durch eine Risikobewertungsstudie anhand aller nicht-sensitiven Objekte in den amerikanischen Weltraumkatalogen belegt. Es wird gezeigt, dass die Berücksichtigung von Unsicherheiten in der atmosphärischen Dichte und dem Gravitationsmodell die Qualität der Umlaufbahnbestimmung signifikant verbessert und somit durch zuverlässigere Unsicherheitsschätzungen bei der Kollisionsrisikobewertung einen Beitrag zur künftigen Sicherheit im Weltraum leistet.

Thin-ply composite laminates capable of enduring high strains are currently under investigation for compliant deployable spacecraft structures. Deployable structures such as booms fabricated from these materials can be flattened and coiled to high curvatures, achieving a compact configuration for stowage. Once in orbit, they are released with minimal actuation for deployment, allowing the operational geometry to be recovered. Previous studies have shown that the viscoelastic properties of the composite epoxy matrix can negatively impact final shape accuracy due to stress relaxation during stowage. In addition, since the strain energy stored is relied upon for deployment, considerable relaxation can potentially result in deployment stall. Stress relaxation in composites and the aforementioned effects it can have on deployment have not been analyzed sufficiently for space applications. The objective of this thesis is to investigate the moment relaxation and curvature recovery behavior of thin-ply composite laminates through a combination of analytical, numerical, and experimental approaches. The viscoelastic Kirchhoff plate model that serves as the theoretical basis of the analyses is first presented. An analytical solution for the recovery of a composite plate after stowage is derived. The numerical integration of the viscoelastic plate constitutive equations and its implementation as a user-defined subroutine in finite element programs is then described. The subroutine allows relaxation of 3D thin-shell structures to be modeled, and is applied to simulate stowage and recovery of a thin-ply composite currently of interest for solar sailing applications. The subroutine is then compared with results obtained from experiments for a thin-ply composite for bending relaxation and curvature creep recovery after being unloaded.

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No description available.