<p>  </p> <p>High altitude test facilities are needed for ground testing of upper stage rocket engines or small satellite thrusters with high expansion ratio nozzles to ensure full-flowing nozzle conditions. Rocket exhaust diffusers and ejector systems are essential components of these facilities and are frequently used to set desired simulated altitude/low pressure conditions and pump out rocket exhaust products. </p> <p>This dissertation combined experimental and numerical efforts on diffuser-ejector systems. The experimental efforts included the development of a Second Throat Exhaust Diffuser (STED) to aid with the qualification of space thrusters in the Purdue Altitude Chamber Facility. While performing these experiments, we characterized the single and two-stage ejector systems operating in conjunction with the diffuser to obtain and maintain specific simulated altitudes. </p> <p>The concurrent numerical effort focused on validating a Computational Fluid Dynamics (CFD) approach based on Reynolds-averaged Navier–Stokes equations flow simulations. After validating the ejector CFD, we used it to derive a corrective coefficient of a lumped parameter ejector model (LPM) developed previously for the ejectors used in the Purdue Altitude Facility. We created variable coefficient maps for the stages of the two-stage ejector system using the same LPM and the test data from one of our experiments. </p> <p>We designed, manufactured, and then validated a STED for altitude testing of a ~50 lbf hypergolic hybrid motor as a part of a NASA JPL project. The designed STED enabled the operation of the hybrid motor for the full duration of the test firing (about 2 seconds) at a simulated altitude of 102,000 feet, slightly above the targeted altitude of 100,000 feet. We also validated our diffuser CFD approach by creating a simulation using the measured diffuser back pressure and the average motor chamber pressure. </p> <p>We then devised an experiment to investigate several diffuser–ejector system configurations using cold gas thrusters with conical and bell nozzles. The main aim of that experiment was to explore the effects of different thruster nozzle geometries, diffuser geometries, and thruster/ejector operational parameters on the performance of a diffuser–ejector system. For all the configurations tested, we reported on the minimum starting and operating pressure ratios and corresponding correction factors on the normal shock method. The large hysteresis regions obtained mostly with bell nozzles having a high initial expansion angle provided an opportunity to economize the facility resources. In some cases which were later found to violate STED second throat contraction limits, we experienced a choking flow at the second throat. Then, we studied the second throat contraction limits in detail using CFD in addition to the experimental data and explored minimum diffuser second throats enabling diffuser starting and improving aerodynamic efficiency. </p> <p>Finally, we machined a larger scale cold gas thruster with different nozzle geometries (having throat diameters in the range of 0.367 – 0.52 inches) from acrylic rods to study possible flow separation and gas condensation events that could occur during tests in the altitude chamber. The main difference here with the previous experiment was that the diffuser (JPL STED) was fixed, and the two-stage ejector system was used to create the necessary back pressure. With the experiments performed at varying axial gaps between the nozzle exit and diffuser inlet, we were able to investigate the effect of that on the diffuser performance. The experimental data collected in this work and the complementary numerical efforts served to generate the operating envelope of the Purdue Altitude Chamber Facility.  </p>

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No description available.

<p> The abort mission refers to the mission where the landing vehicle needs to terminate the landing mission when an anomaly happens and be safely guided to the desired orbit. Missions involving crew on board demands for a robust and efficient abort strategy. This thesis focuses on solving the time-optimal abort guidance (TOAG) problem in real-time via the feature-based learning method. First, according to the optimal control theory, the features are identified to represent the optimal solutions of TOAG using a few parameters. After that, a sufficiently large dataset of time-optimal abort trajectories is generated offline by solving the TOAG problems with different initial conditions. Then the features are extracted for all generated cases. To find the implicit relationships between the initial conditions and identified features, neural networks are constructed to map the relationships based on the generated dataset. A successfully trained neural network can generate solution in real time for a reasonable initial condition. Finally, experimental flight tests are conducted to demonstrate the onboard computation capability and effectiveness of the proposed method. </p>

Våren 2007 offentliggjorde USA planerna på att upprätta ett missilförsvar i Polen och Tjeckien som ett skydd mot missilangrepp från Iran. Från Ryssland blev reaktionen mot planerna kraftfull. Retoriken från Moskva påminde om kalla krigets dagar. Vilka är de bakomliggande orsakerna till denna starka reaktion? Syftet med studien är att undersöka vilka orsaker, såväl externa som interna, det är som styr den ryska inställningen. Studien är teorianvändande med teorier inom den politiska realismen som verktyg. Analysen genomförs i två delar där först externa och därefter interna orsaker till motståndet kartläggs. Förklaringen till motståndet inom den externa dimensionen finns i att missilförsvaret med en framtida utbyggnad kan komma att utgöra ett hot mot rysk andraslagsförmåga och därmed hota Rysslands kapacitet till kärnvapenavskräckning. Interna orsaker till motståndet finns i att såväl den ryska makteliten som Rysslands befolkning anser att landet är utsatt för ett hot från USA. Då Ryssland är väl sammanhållet inom fyra avgörande interna områden ges möjligheten för den förda utrikespolitiken. / In the spring of 2007 the United States went public with its plans to build a missile defence system in Poland and the Czech Republic as a protection to missile attacks from Iran. The Russian reaction to the plans was harsh. The Moscow rhetoric reminded of the Cold War days. What are the underlying reasons to this strong reaction? The purpose of this essay is to analyse what reasons there are, both external and domestic, that direct the Russian attitude. The essay uses theories from the political realism as tool. The analysis is done in two parts where first external and then domestic reasons to the attitude are surveyed. The reason to the attitude is in the external dimension to be found in the fact that the missile defence, if in the future extended, may poses a threat to Russian second strike capacity and by that poses a threat to Russian nuclear deterrence capacity. Domestic reasons to the attitude are to be found in the fact that both the ruling political elite in Russia as well as the Russian population believes that the country is subject to threat from the United States. As Russia is well united in four crucial domestic areas, the possibility for the current foreign policy is given.

<p dir="ltr">The research presented in this thesis presents methods to solve multi-agent task allocation and path planning problems in the application of on-orbit servicing.</p>

<p dir="ltr">With increasing interest in cislunar operations and exploration of deep space destinations like Mars, a foundational understanding of cislunar dynamics and their potential for facilitating departure from the vicinity of Earth is essential. This investigation addresses this need by analyzing system departure characteristics from a variety of periodic orbit families with unstable members in the Earth-Moon Circular-Restricted 3-Body Problem (CR3BP).</p><p dir="ltr">Specifically, a cislunar-to-Mars transfer methodology is developed, leveraging multi-body dynamical systems theory, especially invariant manifolds of periodic orbits, to design lower energy deep space transfers in comparison to traditional methods. The proposed approach generates families of end-to-end transfers that vary in total maneuver delta-v cost and time-of flight, originating from different unstable cislunar orbits. The tradespaces of these transfer families are then analyzed and compared across various departure orbits to identify departure characteristics across orbit families and energy levels (Jacobi constants). The analysis reveals certain unstable Earth-Moon CR3BP orbit families with more favorable departure characteristics.</p><p dir="ltr">Additionally, this investigation compares the computed deep space transfer costs with those of traditional interplanetary transfers and others from existing literature. Although this transfer design strategy is specifically applied to Mars transfers in this investigation, the methodology is broadly applicable to other deep space destinations. Furthermore, the general findings on cislunar departure characteristics have implications for mission designs to destinations beyond the Earth-Moon region.</p>

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / The need for sophisticated tools in the expanding areas of Telemetry, Tracking and Control/Command (TT&C) and Communications (COMMS) system simulation, development, verification, analysis, maintenance, debug, and education is well understood. Emerging requirements for these toolsets include features, ease-of-use, performance, and price points that specifically address telemetry and signals work. And, while not yet as available, understood, or pervasively installed, these economical and focused tools are displacing high-cost, general-purpose Test and Measurement (T&M) equipment at an increasing rate.

Includes supplemental material. / Based on public law and Presidential mandate, ballistic missile defense development is a front-burner issue for homeland defense and the defense of U.S. and coalition forces abroad. Spearheaded by the Missile Defense Agency, an integrated ballistic missile defense system was initiated to create a layered defense composed of land-, air-, sea-, and space-based assets. The Ship Anti-Ballistic Response (SABR) Project is a systems engineering approach that suggests a conceptualized system solution to meet the needs of the sea portion of ballistic missile defense in the 2025-2030 timeframe. The system is a unique solution to the sea-based ballistic missile defense issue, combining the use of a railgun interceptor and a conformable aperture skin-of-the-ship radar system.

This thesis asks why Japan decided to procure BMD if it meant building an infrastructure which, because of its technological nature, had the potential to disrupt Japan’s preferred security strategy of hedging, that is, maintaining ambiguity of commitment, vis-à-vis China and the US. The investigation was divided into three parts dealing with the following questions – Why did Japan's BMD procurement matter? Who mattered? Why were the BMD and related decisions made? Such a structure of research was informed by “neoclassical realism,” according to which the relative material power of a country sets the parameters of its foreign policy, but the policy choices within these international constraints are made by political elites. A range of policymaking heuristics were used to investigate the domestic element of the approach. In addition to the conventionally specified policymaking actors such as MOD, MOFA, Prime Ministers, an original attempt was made to identify the possible influences of several elite networks. On the basis of the notes from the Japan-US Security Strategy Conference, two elite networks were analysed, namely the Japan’s Congressional National Security Research Group and Japan-US Centre for Peace and Cultural Exchange. It was concluded that they have probably had some influence on shaping Japan's BMD decisions. The conclusion of this research is that BMD was procured despite its disruptive potential because it was a tool of shifting Japanese policy from one hedging policy to another, that is, from one based on self-imposed restraints toward one exercised from the position of military strength. An analysis of international relations in East Asia in 1994-2007 and an analysis of the views of the security elites make Japan's transition toward a military strength-based hedging appear rational and confirm BMD's utility as a tool in this transition. Some negative consequences of a possible disruption to hedging, induced by BMD, can be contained exactly because of such a reformatting of hedging.