Radiant ignition of a combustible solid with gas-phase exothermicity

An asymptotic analysis is presented for the ignition of a solid fuel that gasifies endothermically then reacts exothermically in the gas phase through a one-step Arrhenius process. The endothermic gasification was analyzed in an earlier paper; the present paper employs those results in treating the gas-phase reaction. It is shown that depending on values of the chemical parameters, the gas-phase ignition reaction may begin either at the time that gasification begins or during the later stage of transport-controlled gasification. In the former case, results for the gas-phase ignition time are similar to those for condensed-phase ignitions. In the latter case, a mixing layer develops in the gas-phase and moves away from the surface, the exothermic reaction being negligible until thermal runaway occurs somewhere within the mixing layer. Both early-time and late-time ignitions within the mixing layer are analyzed by solving partial differential equations derived from perturbations for large activation energies and a small ratio of gas to solid thermal responsivity. The theory serves to indicate how ignition by gas-phase reactions may be distinguished experimentally from ignition by condensed-phase or heterogenous reactions.     

OSIRIS-REx Flight Dynamics and Navigation Design

OSIRIS-REx is the first NASA mission to return a sample of an asteroid to Earth. Navigation and flight dynamics for the mission to acquire and return a sample of asteroid 101955 Bennu establish many firsts for space exploration. These include relatively small orbital maneuvers that are precise to ～1 mm/s, close-up operations in a captured orbit about an asteroid that is small in size and mass, and planning and orbit phasing to revisit the same spot on Bennu in similar lighting conditions. After preliminary surveys and close approach flyovers of Bennu, the sample site will be scientifically characterized and selected. A robotic shock-absorbing arm with an attached sample collection head mounted on the main spacecraft bus acquires the sample, requiring navigation to Bennu’s surface. A touch-and-go sample acquisition maneuver will result in the retrieval of at least 60 grams of regolith, and up to several kilograms. The flight activity concludes with a return cruise to Earth and delivery of the sample return capsule (SRC) for landing and sample recovery at the Utah Test and Training Range (UTTR).     

A numerical optimization of high altitude testing facility for wind tunnel experiments

High altitude test facilities are required to test the high area ratio nozzles operating at the upper stages of rocket in the nozzle full flow conditions.It is typically achieved by creating the ambient pressure equal or less than the nozzle exit pressure.On average,air/GN2is used as active gas for ejector system that is stored in the high pressure cylinders.The wind tunnel facilities are used for conducting aerodynamic simulation experiments at/under various flow velocities and operating conditions.However,constructing both of these facilities require more laboratory space and expensive instruments.Because of this demerit,a novel scheme is implemented for conducting wind tunnel experiments by using the existing infrastructure available in the high altitude testing(HAT)facility.This article presents the details about the methods implemented for suitably modifying the sub-scale HAT facility to conduct wind tunnel experiments.Hence,the design of nozzle for required area ratio A/A*,realization of test section and the optimized configuration are focused in the present analysis.Specific insights into various rocket models including high thrust cryogenic engines and their holding mechanisms to conduct wind tunnel experiments in the HAT facility are analyzed.A detailed CFD analysis is done to propose this conversion without affecting the existing functional requirements of the HAT facility.     

Comparative study of spermatogonial survival after x-ray exposure, high LET (HZE) irradiation or spaceflight.

Spermatogonial cell loss has been observed in rats flown on Space Lab 3, Cosmos 1887, Cosmos 2044 and in mice following irradiation with X-ray or with high energy (HZE) particle beams. Spermatogonial loss is determined by cell counting in maturation stage 6 seminiferous [correction of seminferous] tubules. With the exception of Iron, laboratory irradiation experiments (with mice) revealed a similar pattern of spermatogonial loss proportional to the radiation dose at levels less than 0.1 Gy. Helium and Argon irradiation resulted in a 5% loss of spermatogonia after only 0.01 Gy exposure. However, significant spermatogonial loss (45%) occured at this radiation level with Iron particle beams. The loss of spermatogonia during each space flight was less than 10% when compared to control (non-flight) animals. This loss, although small, was significant. Although radiation may be a contributing factor in the loss of spermatogonia during space flight, exposure levels, as determined by dosimetry, were not significant to account for the total cell loss observed.     

Adaptations of the vestibular system to short and long-term exposures to altered gravity.

Long-term space flight creates unique environmental conditions to which the vestibular system must adapt for optimal survival of a given organism. The development and maintenance of vestibular connections are controlled by environmental gravitational stimulation as well as genetically controlled molecular interactions. This paper describes the effects of hypergravity on axonal growth and dendritic morphology, respectively. Two aspects of this vestibular adaptation are examined: (1) How does long-term exposure to hypergravity affect the development of vestibular axons? (2) How does short-term exposure to extremely rapid changes in gravity, such as those that occur during shuttle launch and landing, affect dendrites of the vestibulocerebellar system? To study the effects of longterm exposures to altered gravity, embryonic rats that developed in hypergravity were compared to microgravity-exposed and control rats. Examination of the vestibular projections from epithelia devoted to linear and angular acceleration revealed that the terminal fields segregate differently in rat embryos that gestated in each of the gravitational environments.To study the effects of short-term exposures to altered gravity, mice were exposed briefly to strong vestibular stimuli and the vestibulocerebellum was examined for any resulting morphological changes. My data show that these stimuli cause intense vestibular excitation of cerebellar Purkinje cells, which induce up-regulation of clathrin-mediated endocytosis and other morphological changes that are comparable to those seen in long-term depression. This system provides a basis for studying how the vestibular environment can modify cerebellar function, allowing animals to adapt to new environments.     

Successful deployment of commercial ATE to an Air Force I-level (back-shop) repair facility

In today's world of constrained budgets, one of the problems the military faces is the challenge of trying to maintain organic maintenance capabilities. Historically, the US Air Force has desired to achieve an autonomous capability to maintain the equipment it uses. This has been achieved, traditionally, by setting-up three levels of maintenance: organizational; intermediate (back-shop); and depot. The I-level back-shops often utilize militarized automatic test equipment (ATE) and test program sets (TPSs) to test today's complex aircraft line replaceable units (LRUs). And even though this is still a cost-effective maintenance philosophy, it has become costly to develop militarized ATE. The Department of Defense (DoD) has been very active in trying to reduce the total ownership cost of ATE in the government inventory. One approach is to utilize commercial, instead of Mil-Spec, ATE. However, utilizing commercial ATE at an USAF back-shop is not without its tradeoffs and challenges as it represents a significant deviation from the way the USAF maintenance squadrons are accustomed to "doing business." This paper documents the current success story of replacing the legacy C-17 I-level ATE with a commercial ATE.