High-Efficiency Thrust Vector Control Allocation

A generalized approach to the allocation of redundant thrust vector slew commands for multi-actuated launch vehicles is presented, where deflection constraints are expressed as omniaxial or elliptical deflection limits in gimbal axes. More importantly than in the aircraft control allocation problem, linear allocators (pseudoinverses) are preferred for large booster applications to facilitate accurate prediction of the control-structure interaction resulting from thrust vectoring effects. However, strictly linear transformations for the allocation of redundant controls cannot, in general, access all of the attainable moments for which there is a set of control effector positions thatsatisfles the constraints. In this paper, the control allocation efficiency ora certain class of linear allocators subject to multiple quadratic constraints is analyzed, and a novel single-pass control allocation scheme is proposed that augments the pseudolnverse near the boundary of the attainable set. The controls are determined over a substantial volume of lhe attainable set using only a linear transformation; as such, the algorithm maintains compatibility with frequencydomain approaches to the analysis of the vehicle closed-loop elastic stability. Numerical results using a model of a winged reusable booster system illustrate the proposed technique\u27s ability to access a larger Fraction of the attainable set than a pseudoinverse alone

Development of a Nitrous Oxide-Based Monopropellant Propulsion System for Small Satellites

As the demand for highly capable microsatellite missions continues to grow, so too does the need for small yet effective satellite technologies. One area which needs to be addressed is compact propulsion systems capable of performing on-orbit maneuvers, station keeping, and de-orbit impulses with good efficiency. Another important consideration for propulsion systems is the safety and ease in handling, integrating, and testing the propulsion system. This is particularly important for small satellites in order to maintain simplicity by avoiding toxic propellants such as hydrazine. In response to this demand, the Space Flight Laboratory has developed its next generation propulsion system which builds on the experience of the Canadian Nanospace Advanced Propulsion System (CNAPS), a cold gas system that enabled the successful CanX-4/CanX-5 formation flying mission in 2014. The new propulsion system uses nitrous oxide (N2O) as the propellant. The benefits of nitrous oxide are that it is safe to handle, non toxic, cheap, and much easier to access and transport than traditional propellants. Nitrous oxide also self pressurizes to 50.5 bar (733 psi) at 20 °C and thus does not require the addition of a pump or pressurant gas to move the propellant; this allows the tank and feed system design to be much simpler than for liquid propellants. Nitrous oxide can also be used as monopropellant, that is to say that it can be exothermically decomposed to provide an increase in efficiency from an input power point of view. This paper summarizes SFL\u27s effort in the development of this system. A 100 mN resistojet was initially developed. The performance using nitrous oxide was verified with a specific impulse of 100 s and input power ofdevelopment, a monopropellant version of the thruster was developed. The 100 mN monopropellant thruster has successfully demonstrated sustainable nitrous oxide decomposition with a specific impulse of 148 s and operational endurance of greater than 50 hours. Current research focuses on evaluating different catalysts and further extending the operational lifetime of the system

Thoracoabdominal Aortic Aneurysm Repair: Current Endovascular Perspectives

Thoracoabdominal aneurysms account for roughly 3% of identified aneurysms annually in the United States. Advancements in endovascular techniques and devices have broadened their application to these complex surgical problems. This paper will focus on the current state of endovascular thoracoabdominal aneurysm repair, including specific considerations in patient selection, operative planning, and perioperative complications. Both total endovascular and hybrid options will be considered

Non-additive response of the high-latitude Southern Hemisphere climate to aerosol forcing in a climate model with interactive chemistry

A suite of chemistry‐climate model simulations, forced by pairs of anthropogenic forcings [comprising greenhouse gases (GHGs), ozone depleting substances (ODSs), or aerosols], were employed to investigate whether the high‐latitude Southern Hemisphere (SH) circulation response to these forcings is linearly additive, a common assumption in attribution studies. We find that the geographical pattern of sea‐level pressure (SLP) response to a combination of GHGs and ODSs is linearly additive. However, we find significant differences in the SLP response when combining GHGs and aerosols compared to the sum of the individual forcings, a non‐additivity that is currently masked by the dominance of the ODSs forcing. This non‐linearity also results in changes to the SH split jet. These results were obtained using a coupled chemistry‐climate model, indicating that the non‐linear response is due to chemical interactions between the forcing agents. As such, future simulations investigating a post‐ozone hole Southern Hemisphere climate should consider this chemical interaction

A Practical-Time Attack on the A5/3 Cryptosystem Used in Third Generation GSM Telephony

The privacy of most GSM phone conversations is currently protected by the 20+ years old A5/1 and A5/2 stream ciphers, which were repeatedly shown to be cryptographically weak. They will soon be replaced in third generation networks by a new A5/3 block cipher called KASUMI, which is a modified version of the MISTY cryptosystem. In this paper we describe a new type of attack called a sandwich attack, and use it to construct a simple distinguisher for 7 of the 8 rounds of KASUMI with an amazingly high probability of $2^{ -14}$. By using this distinguisher and analyzing the single remaining round, we can derive the complete 128 bit key of the full KASUMI by using only 4 related keys, $2^{26}$ data, $2^{30}$ bytes of memory, and $2^{32}$ time. These complexities are so small that we have actually simulated the attack in less than two hours on a single PC, and experimentally verified its correctness and complexity. Interestingly, neither our technique nor any other published attack can break MISTY in less than the $2^{128}$ complexity of exhaustive search, which indicates that the changes made by the GSM Association in moving from MISTY to KASUMI resulted in a much weaker cryptosystem

Practical-Time Related-Key Attack on GOST with Secret S-boxes

The block cipher GOST 28147-89 was the Russian Federation encryption standard for over 20 years, and is still one of its two standard block ciphers. GOST is a 32-round Feistel construction, whose security benefits from the fact that the S-boxes used in the design are kept secret. In the last 10 years, several attacks on the full 32-round GOST were presented. However, they all assume that the S-boxes are known. When the S-boxes are secret, all published attacks either target a small number of rounds, or apply for small sets of weak keys. In this paper we present the first practical-time attack on GOST with secret S-boxes. The attack works in the related-key model and is faster than all previous attacks in this model which assume that the S-boxes are known. The complexity of the attack is less than $2^{27}$ encryptions. It was fully verified, and runs in a few seconds on a PC. The attack is based on a novel type of related-key differentials of GOST, inspired by local collisions. Our new technique may be applicable to certain GOST-based hash functions as well. To demonstrate this, we show how to find a collision on a Davies-Meyer construction based on GOST with an arbitrary initial value, in less than $2^{10}$ hash function evaluations

Improved Single-Key Attacks on 8-round AES

AES is the most widely used block cipher today, and its security is one of the most important issues in cryptanalysis. After 13 years of analysis, related-key attacks were recently found against two of its flavors (AES-192 and AES-256). However, such a strong type of attack is not universally accepted as a valid attack model, and in the more standard single-key attack model at most 8 rounds of these two versions can be currently attacked. In the case of 8-round AES-192, the only known attack (found 10 years ago) is extremely marginal, requiring the evaluation of essentially all the 2^{128} possible plaintext/ciphertext pairs in order to speed up exhaustive key search by a factor of 16. In this paper we introduce three new cryptanalytic techniques, and use them to get the first non-marginal attack on 8-round AES-192 (making its time complexity about a million times faster than exhaustive search, and reducing its data complexity to about 1/32,000 of the full codebook). In addition, our new techniques can reduce the best known time complexities for all the other combinations of 7-round and 8-round AES-192 and AES-256

Reuseable Orbital Transfer Vehicles: Why it is the Future for LEO, Cislunar Space and Beyond

The emerging Low-Earth-Orbit commercial economy brings exciting opportunities for technological innovation in space at unprecedented speed. This vibrant new commercial space age is disrupting the status quo, driving down costs, and revolutionizing general accessibility and sustained presence in LEO. Today, however, there is a reluctance in the space industry to embrace reusable spacecraft because of the perception of increased mission risk for no additional return on investment. This hesitation appears similar to the industry’s initial caution in adopting reusable launch vehicles in the early 2000s. In this work we share our vision of the future: reusable orbital service vehicles (OSVs) will transform the space economy and grow the emerging on-orbit servicing sector. A reusable OSV serves as a satellite’s ‘connecting flight’ that provides multiple on-orbit destinations, analogous to the airline industry. Development of a reliable, reusable OSV will expand the utility of a single satellite, allowing for plane changes, escape trajectories, multi-orbit missions and more. OSVs further enable payload upgrades, satellite constellation maintenance, deorbiting at the end of operational life, and orbital debris removal. These added capabilities differentiate reusable OSVs from single orbit mission alternatives and increase the on-orbit economic opportunity. Once a network of OSVs has been established in LEO, rendezvous and transfers can be scheduled efficiently to minimize on-orbit wait times between connections. This poster emphasizes current trends in the industry and presents an OSV architecture and logistics model that enables expanded access to space. Safety and reliability aspects are considered, and a satellite constellation design reference mission discussed. Future work will leverage 6 decades of hard-won lessons and insights from the commercial airline industry with its hub and spoke carrier models to improve OSV reliability and cost effectiveness. Just like reusable launch vehicles drastically reduced launch costs, and well-placed hub airports transformed the costs and safety of commercial air travel, reusable OSVs and orbital infrastructure have the potential to increase space asset safety and return on investment. These vehicles have utility in LEO and cislunar space, as well as far reaching deep space missions to Mars and beyond. Ultimately, more affordable, sustained access to space will enable the next deep space telescope, space station, or other similarly bold and impactful endeavors to be built and deployed in orbit at a fraction of the cost of a terrestrially built equivalent

Polar stratospheric clouds initiated by mountain waves in a global chemistry-climate model: A missing piece in fully modelling polar stratospheric ozone depletion

An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is the temperature fluctuations induced by mountain waves. These enable stratospheric temperatures to fall below the threshold value for PSC formation in regions of negative temperature perturbations or cooling phases induced by the waves even if the synoptic-scale temperatures are too high. However, this formation mechanism is usually missing in global chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate in detail the episodic and localised wintertime stratospheric cooling events produced over the Antarctic Peninsula by a parameterisation of mountain-wave-induced temperature fluctuations inserted into a 30-year run of the global chemistry–climate configuration of the UM-UKCA (Unified Model – United Kingdom Chemistry and Aerosol) model. Comparison of the probability distribution of the parameterised cooling phases with those derived from climatologies of satellite-derived AIRS brightness temperature measurements and high-resolution radiosonde temperature soundings from Rothera Research Station on the Antarctic Peninsula shows that they broadly agree with the AIRS observations and agree well with the radiosonde observations, particularly in both cases for the “cold tails” of the distributions. It is further shown that adding the parameterised cooling phase to the resolved and synoptic-scale temperatures in the UM-UKCA model results in a considerable increase in the number of instances when minimum temperatures fall below the formation temperature for PSCs made from ice water during late austral autumn and early austral winter and early austral spring, and without the additional cooling phase the temperature rarely falls below the ice frost point temperature above the Antarctic Peninsula in the model. Similarly, it was found that the formation potential for PSCs made from ice water was many times larger if the additional cooling is included. For PSCs made from nitric acid trihydrate (NAT) particles it was only during October that the additional cooling is required for temperatures to fall below the NAT formation temperature threshold (despite more NAT PSCs occurring during other months). The additional cooling phases also resulted in an increase in the surface area density of NAT particles throughout the winter and early spring, which is important for chlorine activation. The parameterisation scheme was finally shown to make substantial differences to the distribution of total column ozone during October, resulting from a shift in the position of the polar vortex

A world wide web informational reference source for viral ocular disease

This World Wide Web page is a quick reference source for anyone wishing to research ocular viral disease. Doctors and medical students will find the web site helpful to aid in the diagnosis and treatment of ocular viral disease. Topics within the site are cross-linked and presented in subjective, objective, assessment, plan format (SOAP). Photographs are included as are references for further study