Thermal and elastic properties of Cu–Zr–Be bulk metallic glass forming alloys

The compositional dependence of thermal and elastic properties of Cu–Zr–Be ternary bulk metallic glass forming alloys was systematically studied. There exists a linear relationship between the glass transition temperature Tg and the total Zr concentration. G decreases linearly with increasing Zr concentration as well. The results also show that Tg, shear modulus G, and Poisson's ratio nu are very sensitive to changes in compositions. Low Tg, low G, and relatively high nu can be achieved with high Zr and Ti concentration

An integrated traverse planner and analysis tool for future lunar surface exploration

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 161-168).This thesis discusses the Surface Exploration Traverse Analysis and Navigation Tool (SEXTANT), a system designed to help maximize productivity, scientific return, and safety on future lunar and planetary explorations,. The goal of SEXTANT is twofold: to provide engineers with a realistic simulation of traverses to assist with hardware design, and to serve as an aid for astronauts that will allow for more autonomy in traverse planning and re-planning. SEXTANT is a MATLAB-based tool that computes the most efficient path between user-specified Activity Points across a lunar or planetary surface for a suited astronaut or transportation rover. Currently, SEXTANT uses an elevation model of the lunar south pole generated from topography data from the Lunar Orbiter Laser Altimeter instrument aboard the Lunar Reconnaissance Orbiter. The efficiency of a traverse is derived from any number of metrics: the path distance, time, or the explorer's energy consumption. Energy consumption is either the metabolic expenditure of an astronaut or the power usage of a transportation rover over the terrain. The user can select Activity Points and visualize the generated path on a 3D mapping interface. The capabilities of SEXTANT are further augmented by the Individual Mobile Agents System (iMAS) astronaut assistant, developed by NASA Ames. SEXTANT leverages iMAS's speech dialog interface to provide the explorer with real-time guidance and navigation along the most efficient path. SEXTANT can also calculate the sun position and shadowing with respect to points along the traverse and the time the explorer arrives at each of them. This data is then used to compute the thermal load on suited astronauts, or the solar power generation of rovers. Example traverses are presented for both types of explorers, showing the capabilities of SEXTANT and the dynamics of the thermal and power systems given different environmental conditions. All of its capabilities make SEXTANT the traverse planning tool with the most accurate and comprehensive representation of lunar and planetary traverses.by Aaron William Johnson.S.M

An Integrated Traverse Planner and Analysis Tool for Planetary Exploration

Future planetary explorations will require surface traverses of unprecedented frequency, length, and duration. As a result, there is need for exploration support tools to maximize productivity, scientific return, and safety. The Massachusetts Institute of Technology is currently developing such a system, called the Surface Exploration Traverse Analysis and Navigation Tool (SEXTANT). The goal of this system is twofold: to allow for realistic simulations of traverses in order to assist with hardware design, and to give astronauts an aid that will allow for more autonomy in traverse planning and re-planning. SEXTANT is a MATLAB-based tool that incorporates a lunar elevation model created from data from the Lunar Orbiter Laser Altimeter instrument aboard the Lunar Reconnaissance Orbiter spacecraft. To assist in traverse planning, SEXTANT determines the most efficient path across a planetary surface for astronauts or transportation rovers between user-specified Activity Points. The path efficiency is derived from any number of metrics: the traverse distance, traverse time, or the explorer’s energy consumption. The generated path, display of traverse obstacles, and selection of Activity Points are visualized in a 3D mapping interface. After a traverse has been planned, SEXTANT is capable of computing the most efficient path back home, or “walkback”, from any point along the traverse – an important capability for emergency operations. SEXTANT also has the ability to determine shadowed and sunlit areas along a lunar traverse. This data is used to compute the thermal load on suited astronauts and the solar power generation capacity of rovers over the entire traverse. These both relate directly to the explorer’s consumables, which place strict constraints on the traverse. This paper concludes by presenting three example traverses, detailing how SEXTANT can be used to plan and modify paths for both explorer types.Massachusetts Institute of Technology (Donald W. Douglas Fellowship)National Space Biomedical Research Institute (Grant HFP00003

Assembly of Molybdenum/Titanium μ-Oxo Complexes via Radical Alkoxide C−O Cleavage

Three-coordinate Ti(NRAr)_3 [R = C(CD_3)_2(CH_3), Ar = C_6H_3Me_2] was prepared in 73% yield by sodium amalgam reduction of ClTi(NRAr)_3 and in 83% yield upon treatment of TiCl_3(THF)_3 with 3 equiv of Li(NRAr)(OEt_2) in the presence of TMEDA. Ti(^tBuNPh)_3 was prepared similarly in 75% yield by treatment of TiCl_3(THF)_3 with 3 equiv of Li(^tBuNPh)(OEt_2) in the presence of TMEDA. Reaction of Ti(NRAr)_3 with NMo(O^tBu)_3 in hydrocarbon solvents at −35 °C generates a thermally unstable intermediate formulated as (^tBuO)_3Mo[μ-N]Ti(NRAr)_3, which readily loses a tert-butyl radical and isomerizes at 25 °C. Kinetics of the latter process were obtained over the temperature range 20−60 °C; the process exhibits clean first-order behavior. The following activation parameters were obtained:  ΔH⧧ = 21.4 ± 0.2 kcal mol^(-1) and ΔS⧧ = −3.7 ± 0.6 cal mol^(-1) K^(-1). The oxo-bridged product (^tBuO)_2(N)Mo[μ-O]Ti(NRAr)_3 was isolated in 83% yield from this reaction. Full characterization of the latter diamagnetic complex included an X-ray crystal structure and an ^(15)N NMR study. Ti(NRAr)_3 (1 equiv) reacts further with (^tBuO)_2(N)Mo[μ-O]Ti(NRAr)_3 to generate a species formulated as a second paramagnetic nitrido-bridged intermediate, (^tBuO)_2Mo{[μ-O]Ti(NRAr)_3}{[μ-N]Ti(NRAr)_3}, which at 25 °C loses a tert-butyl radical and isomerizes to give the final product, (^tBuO)(N)Mo{[μ-O]Ti(NRAr)_3}_2, isolated as an orange powder in 91% yield. Characterization of the latter diamagnetic complex included an ^(15)N NMR study. Attempts to displace a third tert-butyl radical by treatment of (^tBuO)(N)Mo{[μ-O]Ti(NRAr)_3}_2 with Ti(NRAr)_3 led to no reaction. Treatment of (^tBuO)(N)Mo{[μ-O]Ti(NRAr)_3}_2 with neat methyl iodide led to the isolation of (MeO)(N)Mo{[μ-O]Ti(NRAr)_3}_2 in 51% yield; ^(13)C and nitrido-^(15)N derivatives of this species were prepared for spectroscopic characterization. O_2Mo{[μ-O]Ti(^tBuNPh)_3}_2 was prepared in 59% yield upon treatment of MoO_2(O^tBu)_2 with 2 equiv of Ti(^tBuNPh)_3 in benzene at 65 °C. Full characterization of O_2Mo{[μ-O]Ti(^tBuNPh)_3}_2 included a single-crystal X-ray diffraction study. Previously reported (^iPrO)_3V[μ-O]Ti(NRAr)_3 was oxidized with ferrocenium triflate to give TfOTi(NRAr)_3 and OV(O^iPr)_3. TfOTi(NRAr)_3 was prepared independently in 80% yield by treatment of Ti(NRAr)_3 with ferrocenium triflate. (^iPrO)_3V[μ-O]Ti(NRAr)_3 is stable in the presence of methyl iodide. ITi(NRAr)_3 was prepared independently by treatment of Ti(NRAr)_3 with the stoichiometric amount of iodine. Paramagnetic (^tBuO)_3V[μ-O]Ti(NRAr)_3 was prepared as orange-brown needles in 94% yield and was found to be thermally stable. The relatively robust μ-nitrido compound (Me_2N)_3Mo[μ-N]Ti(^tBuNPh)_3, which was prepared in 77% isolated yield, showed no decomposition when heated in benzene at 70 °C for 13 h

Evaluation of a Surface Exploration Traverse Analysis and Navigation Tool

SEXTANT is an extravehicular activity (EVA) mission planner tool developed in MATLAB, which computes the most efficient path between waypoints across a planetary surface. The traverse efficiency can be optimized around path distance, time, or explorer energy consumption. The user can select waypoints and the time spent at each, and can visualize a 3D map of the optimal path. Once the optimal path is generated, the thermal load on suited astronauts or solar power generation of rovers is displayed, along with the total traverse time and distance traveled. A field study was conducted at the Mars Desert Research Station (MDRS) in Utah to see if there was a statistical difference between the SEXTANT-determined energy consumption, time, or distance of EVA traverses and the actual output values. Actual traverse time was significantly longer than SEXTANT-predicted EVA traverse time (n=6, p<0.01), traverse distance was not significantly different than SEXTANT-predicted distance, and explorer energy consumption was significantly greater than SEXTANT-predicted energy consumption (n=5, p<0.01). A second study was done to see if mission re-planning, or contingency planning, was faster and less work when using SEXTANT in the habitat or in the field using an iPad. Time and workload measurements were collected for each subject under both conditions. Contingency planning in the habitat was not significantly different than contingency planning in the field. There was no significant workload difference when contingency planning in either location, however there was a trend that suggested contingency planning was faster in the habitat (n=3, p=0.07). Every subject commented that it was a hassle to carry the mission planner in the field and it was difficult to see the screen in the sunlight. To determine if gloves were a factor in the difference between mission re-planning time, subjects were asked to plan a contingency indoors with and without gloves. Performance and workload were not significantly different when re-planning with and without the gloves. The SEXTANT mission planner will continue to be improved according to the results and the recommendations of subjects in this study.United States. National Aeronautics and Space Administration (NASA Astrobiology Institute)Massachusetts Space Grant Consortiu

Glassy steel optimized for glass-forming ability and toughness

An alloy development strategy coupled with toughness assessments and ultrasonic measurements is implemented to design a series of iron-based glass-forming alloys that demonstrate improved glass-forming ability and toughness. The combination of good glass-forming ability and high toughness demonstrated by the present alloys is uncommon in Fe-based systems, and is attributed to the ability of these compositions to form stable glass configurations associated with low activation barriers for shear flow, which tend to promote plastic flow and give rise to a toughness higher than other known Fe-based bulk-glass-forming systems

Motivations and Preliminary Design for Mid-Air Deployment of a Science Rotorcraft on Mars

Mid-Air Deployment (MAD) of a rotorcraft during Entry, Descent and Landing (EDL) on Mars eliminates the need to carry a propulsion or airbag landing system. This reduces the total mass inside the aeroshell by more than 100 kg and simplifies the aeroshell architecture. MAD’s lighter and simpler design is likely to bring the risk and cost associated with the mission down. Moreover, the lighter entry mass enables landing in the Martian highlands, at elevations inaccessible to current EDL technologies. This paper proposes a novel MAD concept for a Mars helicopter. We suggest a minimum science payload package to perform relevant science in the highlands. A variant of the Ingenuity helicopter is proposed to provide increased deceleration during MAD, and enough lift to fly the science payload in the highlands. We show in simulation that the lighter aeroshell results in a lower terminal velocity (30 m/s) at the end of the parachute phase of the EDL, and at higher altitudes than other approaches. After discussing the aerodynamics, controls, guidance, and mechanical challenges associated with deploying at such speed, we propose a backshell architecture that addresses them to release the helicopter in the safest conditions. Finally, we implemented the helicopter model and aerodynamic descent perturbations in the JPL Dynamics and Real-Time Simulation (DARTS)framework. Preliminary performance evaluation indicates landing and helicopter operations can be achieved up to +5 km MOLA (Mars Orbiter Laser Altimeter reference)

Castable Bulk Metallic Glass Strain Wave Gears: Towards Decreasing the Cost of High-Performance Robotics

The use of bulk metallic glasses (BMGs) as the flexspline in strain wave gears (SWGs), also known as harmonic drives, is presented. SWGs are unique, ultra-precision gearboxes that function through the elastic flexing of a thin-walled cup, called a flexspline. The current research demonstrates that BMGs can be cast at extremely low cost relative to machining and can be implemented into SWGs as an alternative to steel. This approach may significantly reduce the cost of SWGs, enabling lower-cost robotics. The attractive properties of BMGs, such as hardness, elastic limit and yield strength, may also be suitable for extreme environment applications in spacecraft