Radiation measurements and doses at SST altitudes

Radiation components and dose equivalents due to galactic and solar cosmic rays in the high atmosphere, especially at SST altitudes, are presented. The dose equivalent rate for the flight personnel flying 500 hours per year in cruise altitudes of 60,000-65,000 feet (18-19.5 km) in high magnetic latitudes is about 0.75-1.0 rem per year averaged over the solar cycle, or about 15-20 percent of the maximum permissible dose rate

Estimates of radiation exposure from solar cosmic rays in SST altitudes

Factors influencing crew and passenger exposure to solar and galactic cosmic rays that is expected to occur during flights of supersonic transport aircraft are discussed, and some possibilities are considered for decreasing such exposure

Nozzle Clogging Prevention and Analysis in Cold Spray

Cold spray is an additive manufacturing method in which powder particles are accelerated through a supersonic nozzle and impinged upon a nearby substrate, provided they reach their so-called critical velocity. True to its name, the cold spray process employs lower particle temperatures than other thermal spray processes while the particle velocities are comparably high. Because bonding occurs mostly in the solid state and at high speeds, cold spray deposits are distinguished for having low porosity and low residual stresses which nearly match those of the bulk material. One complication with the cold spray process is the tendency for nozzles to clog when spraying (in general) low-melting-point or dense metal powders. Clogging occurs when particles collide with the inner nozzle wall and bond to it rather than bouncing off and continuing downstream towards the substrate. The particles accumulate and eventually plug the nozzle passage. Clogging is inconvenient because it interrupts the spraying process, making it impossible to complete a task. Furthermore, when particle buildup occurs inside the nozzle, the working cross-sectional area decreases, which decreases the flow velocity and therefore the particle velocity, ultimately jeopardizing the particles’ ability to reach critical velocity at the substrate. In this work, computational fluid dynamics (CFD) is used to study various aspects of nozzle clogging. Nozzle cooling with supercritical CO2 as the refrigerant is investigated as a means to prevent clogging. The effects of nozzle cooling on both the driving gas and the particles are addressed. Simplified pressure oscillations at the nozzle inlet are imposed to determine whether such oscillations, if present, can cause clogging. Subsequently, more realistic and complicated flow oscillations are introduced to isolate a potential root cause of clogging. Finally, several novel nozzle internal geometries are evaluated for their effectiveness at preventing clogging. A recommendation is provided for a nozzle to be tested experimentally because it might completely prevent clogging

Device Design for Inducing Aneurysm-Susceptible Flow Conditions Onto Endothelial Cells

Aneurysms are a deadly asymptomatic cardiovascular disease that may occur especially where there are bends and bifurcations in the cerebral vasculature. A region where these features are especially prominent is the Circle of Willis (COW) in the brain, where aneurysms are known to occur. In the carotid artery, which feeds into the COW, the Reynolds number of blood flow is typically around 200-500. Even with such a low Reynolds number, turbulent-like flow, or tortuous flow, can occur due to bends, bifurcations and highly pulsatile flow which lower the effective Reynolds number where tortuous flow can occur. Highly pulsatile flow is unsteady flow that is high in magnitude and changes over time. Endothelial cells (ECs) line the inner wall of the blood vessel and experience the friction force of blood flow. This work is focused on designing a device that can expose ECs to forces they would undergo in an aneurysm-susceptible site. This is accomplished by exposing ECs to physiologically relevant Wall Shear Stress (WSS) and vibrations simultaneously. Vibrations in the body occur due to flow separation at the vessel wall, which leads to pressure changes. These pressure changes induce vibrations onto ECs. The fluid flow in the designed Parallel Plate Flow Chamber (PPFC) is laminar to induce a predictable WSS onto the cells, while the vibrations will induce a rapid cyclical force to simulate pressure fluctuations that may occur in vivo. The aneurysm-susceptible flow will simulate a more turbulent-like flow in the carotid artery; higher maximum WSS (around 2.2 Pa) with vibrations. The aneurysm-protective flow will have a lower WSS maximum (around 0.5 Pa). The PPFC, made of polycarbonate, is small and light enough to be conveniently vibrated using an electromagnetic vibration stage. The PPFC can be driven by a syringe or peristaltic pump, allowing for either steady or transient waveforms. The PPFC’s fluid domain will not change upon vibration, isolating the effect of vibration on the cells. Also, two side-by-side glass slide slots were included to allow for both protein and mRNA quantification from the same experiment, increasing experimental efficiency and flow-related consistency between the two cell areas. Simulations using ANSYS Fluent verified the flow field and WSS waveform on the cells for the designed geometry for 3D and 2D cases, as well as verified equal WSS values throughout all areas of ECs. Then, Particle Image Velocimetry (PIV) was done to verify the predicted flow rate in the machined PPFC given a steady flow rate driven by a syringe pump. Preliminary cell experiments were performed in an incubator under flow and vibration conditions to demonstrate cell survivability

Evaluation of the hazard from exposure to electron irradiation simulating that in the synchronous orbit

The electron spectrum predicted for the synchronous orbit was simulated to determine the effects that might occur to astroscientists exposed to such irradiation while on a prolonged space station mission in that region. Miniature pigs were exposed to monoenergetic and spectral-fractionated irradiations with 0.5 to 2.1 MeV electrons. Clinical and pathological alterations observed in biopsies were correlated with depth-dose pattern and length of post irradiation period up to one year. With monoenergetic electrons, the lowest dose causing a recognizable lesion was 1450 rad and with increasing dose lesions appeared earlier and were more severe. At the highest dose given, 2650 rad, ulceration extending into the dermis was present by twenty one days and required about four months for complete healing. Spectral-fractionated irradiations, in which the total dose range was essentially comparable to that of the monoenergetic series, resulted in very minimal outer dermis edema at 1790 rad and at no dose employed did necrosis of epidermis or ulceration into dermis occur

Evaluation of GPM-DPR precipitation estimates with WegenerNet gauge data

The core satellite of the Global Precipitation Measurement (GPM) mission provides precipitation observations measured with the Dual frequency Precipitation Radar (DPR). The precipitation can only be estimated from the radar data, and therefore, independent validations using direct precipitation observation on the ground as a true reference need to be performed. Moreover, the quality and the accuracy of the measurements depend on various influencing factors. In this way, a validation may help to minimise those uncertainties. The DPR provides three different radar rain rate estimates for the GPM core satellite: Ku-band-only rain rates, Ka-band-only rain rates and a product combining the two frequencies. This study presents an evaluation of the three GPM-DPR surface precipitation estimates based on the gridded precipitation data of the WegenerNet, a local scale terrestrial network of 153 meteorological stations in southeast Austria. The validation is based on a graphical and a statistical approach using only data where both Ku- and Ka-band measurements are available. The data delivered from the WegenerNet are gauge-based gridded rainfall observations; the meteorological winter is excluded due to technical reasons. The focus lies on the resemblance of the variability within the whole network and the over- and underestimation of the precipitation through the GPM-DPR. During the last four years 22 rainfall events were observed by the GPM-DPR over the WegenerNet and the analysis rests upon these rainfall events. The WegenerNet provides a large number of gauges within each GPM-DPR footprint. Its biases are well studied and corrected, thus, it can be taken as a robust ground reference. This work also includes considerations on the limits of such comparisons between small terrestrial networks with a high density of stations and precipitation observations from a satellite. Our results show that the GPM-DPR estimates basically match with the WegenerNet measurements, but absolute quantities are biased. The three types of radar estimates deliver similar results, where Ku-band and dual frequency estimates are very close to each other. On a general level, Ka-band precipitation estimates deliver the best results due to the high number of light rainfall events

Measured and Calculated Neutron Spectra and Dose Equivalent Rates at High Altitudes; Relevance to SST Operations and Space Research

Results of the NASA Langley-New York University high-altitude radiation study are presented. Measurements of the absorbed dose rate and of secondary fast neutrons (1 to 10 MeV energy) during the years 1965 to 1971 are used to determine the maximum radiation exposure from galactic and solar cosmic rays of supersonic transport (SST) and subsonic jet occupants. The maximum dose equivalent rates that the SST crews might receive turn out to be 13 to 20 percent of the maximum permissible dose rate (MPD) for radiation workers (5 rem/yr). The exposure of passengers encountering an intense giant-energy solar particle event could exceed the MPD for the general population (0.5 rem/yr), but would be within these permissible limits if in such rare cases the transport descends to subsonic altitude; it is in general less than 12 percent of the MPD. By Monte Carlo calculations of the transport and buildup of nucleons in air for incident proton energies E of 0.02 to 10 GeV, the measured neutron spectra were extrapolated to lower and higher energies and for galactic cosmic rays were found to continue with a relatively high intensity to energies greater than 400 MeV, in a wide altitude range. This condition, together with the measured intensity profiles of fast neutrons, revealed that the biologically important fast and energetic neutrons penetrate deep into the atmosphere and contribute approximately 50 percent of the dose equivalant rates at SST and present subsonic jet altitudes

Errors in GNSS radio occultation data: relevance of the measurement geometry and obliquity of profiles

Atmospheric profiles retrieved from GNSS (Global Navigation Satellite System) radio occultation (RO) measurements are increasingly used to validate other measurement data. For this purpose it is important to be aware of the characteristics of RO measurements. RO data are frequently compared with vertical reference profiles, but the RO method does not provide vertical scans through the atmosphere. The average elevation angle of the tangent point trajectory (which would be 90° for a vertical scan) is about 40° at altitudes above 70 km, decreasing to about 25° at 20 km and to less than 5° below 3 km. In an atmosphere with high horizontal variability we can thus expect noticeable representativeness errors if the retrieved profiles are compared with vertical reference profiles. We have performed an end-to-end simulation study using high-resolution analysis fields (T799L91) from the European Centre for Medium-Range Weather Forecasts (ECMWF) to simulate a representative ensemble of RO profiles via high-precision 3-D ray tracing. Thereby we focused on the dependence of systematic and random errors on the measurement geometry, specifically on the incidence angle of the RO measurement rays with respect to the orbit plane of the receiving satellite, also termed azimuth angle, which determines the obliquity of RO profiles. We analyzed by how much errors are reduced if the reference profile is not taken vertical at the mean tangent point but along the retrieved tangent point trajectory (TPT) of the RO profile. The exact TPT can only be determined by performing ray tracing, but our results confirm that the retrieved TPT – calculated from observed impact parameters – is a very good approximation to the "true" one. Systematic and random errors in RO data increase with increasing azimuth angle, less if the TPT is properly taken in to account, since the increasing obliquity of the RO profiles leads to an increasing sensitivity to departures from horizontal symmetry. Up to an azimuth angle of 30°, however, this effect is small, even if the RO profiles are assumed to be vertical. For applications requiring highest accuracy and precision it is advisable to exclude RO profiles with ray incidence angles beyond an azimuth of 50°. Errors in retrieved atmospheric profiles decrease significantly, by up to a factor of 2, if the RO data are exploited along the retrieved TPT. The tangent point trajectory of RO profiles should therefore be exploited whenever this is possible

Subdaily meteorological measurements of temperature, direction of the movement of the clouds, and cloud cover in the Late Maunder Minimum by Louis Morin in Paris

We have digitized three meteorological variables (temperature, direction of the movement of the clouds, and cloud cover) from copies of Louis Morin’s original measurements (source: Institute of History/Oeschger Centre for Climate Change Research, University of Bern; Institut de France) and subjected them to quality analysis to make these data available to the scientific community. Our available data cover the period 1665–1713 (temperature beginning in 1676). We compare the early instrumental temperature dataset with statistical methods and proxy data to validate the measurements in terms of inhomogeneities and claim that they are, apart from small inhomogeneities, reliable. The Late Maunder Minimum (LMM) is characterized by cold winters and falls and moderate springs and summers with respect to the reference period of 1961–1990. Winter months show a significantly lower frequency of the westerly direction in the movement of the clouds. This reduction of advection from the ocean leads to a cooling in Paris in winter. The influence of the advection becomes apparent when comparing the last decade of the 17th century (cold) and the first decade of the 18th century (warm). Consequently, the unusually cold winters in the LMM are largely caused by a lower frequency of the westerly direction in the movement of the clouds. An impact analysis reveals that the winter of 1708/09 was a devastating one with respect to consecutive ice days, although other winters are more pronounced (e.g., the winters of 1676/77, 1678/79, 1683/84, 1692/93, 1694/95, and 1696/97) in terms of mean temperature, ice days, cold days, or consecutive cold days. An investigation of the cloud cover data revealed a high discrepancy, with the winter season (DJF, -14.0 %), the spring season (MAM, -20.8 %), the summer season (JJA, -17.9 %), and the fall season (SON, -18.0 %) showing negative anomalies of total cloud cover (TCC) with respect to the 30-year mean of the ERA5 data (1981–2010). Thus, Morin’s measurements of temperature and direction of the movement of the clouds seem to be trustworthy, whereas cloud cover in quantitative terms should be taken with caution