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Ground-based spectroscopic observations of the cold Io torus made before, during and after the Voyager 1 encounter are compared to the published spacecraft data. During the encounter itself neither sodium nor sulfur emissions were detected. The implications of this finding for the injection and transport of plasma are assessed.
An experimental investigation was performed in the NASA Langley Low Speed Aeroacoustics Wind Tunnel to determine the extent of jet exhaust noise reduction that can be obtained using water injection in a hot jet environment. The effects of water parameters such as mass flow rate, injection location, and spray patterns on suppression of dominant noise sources in both subsonic and supersonic jets were determined, and extrapolations to full-scale engine noise reduction were made. Water jets and sprays were injected in to the shear layers of cold and hot circular jets operating at both subsonic and supersonic exhaust conditions. Use of convergent-divergent and convergent nozzles (2.7in. D) allowed for simulations of all major jet noise sources. The experimental results show that water injection clearly disrupts shock noise sources within the jet plume, with large reductions in radiated shock noise. There are smaller reductions in jet mixing noise, resulting in only a small decrease in effective perceived noise level when projections are made to full scale. The fact that the measured noise reduction in the direction upstream of the nozzle was consistently larger than in the noisier downstream direction contributed to keeping effective perceived noise reductions small. Variations in the operation of the water injection system clearly show that injection at the nozzle exit rather than further downstream is required for the largest noise reduction. Noise reduction increased with water pressure as well as with its mass flow, although the type of injector had little effect.
Aerothermodynamic measurements were obtained on two Apollo spacecraft during atmospheric entry at near-lunar-return velocities. Histories of measured pressure and of convective and radiative heating rates are compared with theoretical predictions and with wind-tunnel results. The comparisons show that pressures measured in the wind tunnel correspond to those measured in the flight environment of the entry face. Unexplained low pressures were obtained on the conical section. Measured radiative heating rates agree with predictions calculated for both visible and infrared radiation. Good agreement was found between convective heating rates measured in flight and predictions obtained by using cold wall theory adjusted for mass injection from the ablator.
A fast cold large diameter electron beam is injected into a uniform background plasma. The injected beam current is balanced by a field-aligned return current which gives rise to an ion acoustic instability. The plasma is essentially unbounded and collisionless on the time scale of the pulsed experiment. The fluctuations are analyzed by probe techniques in real time and space as well as in the frequency and wavenumber domains. Strong density fluctuations are observed in the entire ion acoustic spectrum reaching peak amplitudes at the low frequency end. The propagation of phase coherent test waves in the current carrying plasma is investigated. For the highly turbulent regime strong damping is observed while at lower drift velocities direction is observed. Oblique propagation of two strong test waves at different frequencies indicate the role of nonlinear ion Landau damping in absorption of wave energy.
The cooling of gas turbine components was the subject of considerable research. The problem is difficult because the available coolant, compressor bleed air, is itself quite hot and has relatively poor thermophysical properties for a coolant. Injecting liquid water to evaporatively cool the air prior to its contact with the hot components was proposed and studied, particularly as a method of cooling for contingency power applications. Injection of a small quantity of cold liquid water into a relatively hot coolant air stream such that evaporation of the liquid is still in process when the coolant contacts the hot component was studied. No approach was found whereby heat transfer characteristics could be confidently predicted for such a case based solely on prior studies. It was not clear whether disequilibrium between phases at the inlet to the hot component section would improve cooling relative to that obtained where equilibrium was established prior to contact with the hot surface.
Recent high-resolution imaging and spectroscopic observations have generated renewed interest in spicules' role in explaining the hot corona. Some studies suggest that some spicules, often classified as type II, may provide significant mass and energy to the corona. Here we use numerical simulations to investigate whether such spicules can produce the observed coronal emission without any additional coronal heating agent. Model spicules consisting of a cold body and hot tip are injected into the base of a warm (0.5 MK) equilibrium loop with different tip temperatures and injection velocities. Both piston- and pressure-driven shocks are produced. We find that the hot tip cools rapidly and disappears from coronal emission lines such as Fe xii 195 and Fe xiv 274. Prolonged hot emission is produced by preexisting loop material heated by the shock and by thermal conduction from the shock. However, the shapes and Doppler shifts of synthetic line profiles show significant discrepancies with observations. Furthermore, spatially and temporally averaged intensities are extremely low, suggesting that if the observed intensities from the quiet Sun and active regions were solely due to type II spicules, one to several orders of magnitude more spicules would be required than have been reported in the literature. This conclusion applies strictly to the ejected spicular material. We make no claims about emissions connected with waves or coronal currents that may be generated during the ejection process and heat the surrounding area.
The accurate characterization of the dynamic response of liquid jets to transient detonation wave passage is crucial for optimizing and modeling liquid-fueled rotating detonation combustors. To address this need, we have developed an optically accessible rocket RDE (RP-RDE), which utilizes liquid RP-1 and gaseous oxygen as propellants and operates at elevated pressures. The experimental setup features optical access from the oxidizer injection plenum to the combustor exit, allowing for detailed characterization of injection, mixing, and combustion processes and their impact on the detonation wave structure. To design and develop the liquid injection scheme for the RP-RDE test article, we employed a combined experimental and numerical approach that included cold-flow simulations. Our aim was to optimize the liquid injection process and ensure that the resulting fuel-oxidizer mixture is homogeneous and stable. To this end, high-speed optical imaging will be employed to provide qualitative visualization of the liquid and gaseous phases of the propellant as well as the local heat release during detonation wave propagation through the non-premixed medium. This work will provide critical insights into the behavior of the transient detonation waves in more relevant rocket conditions, which is essential for the optimization and modeling of rotating detonation combustors.
Analytical evaluation of secondary flow injection effects on rocket engine performance including cold flow and simulated hot flow data
Analytical evaluation of secondary flow injection effects on rocket engine performance including cold flow and simulated hot flow data
A theoretical explanation for the dependence of the Jovian decametric radiation on the position of its satellite Io is advanced in terms of electrostatic instabilities created by injection into the hot natural plasma of cold photoelectrons from Io. This may be tested with appropriately positioned and presently planned deep-space probes that search for variations of the Jovian decametric radiation at times following local sunset and sunrise at Io.
The feasibility of operating small rocket engines in the Molsink facility was demonstrated. A 0.44-N (0.1-lbf) hydrazine engine and a 0.18-N (0.04-lbf) thruster using cold gas from a hydrazine plenum system were operated for both flight duty cycles and off-nominal conditions. The exhaust gases from these thrusters contain NH3, N2, and H2. The chamber was also calibrated for larger bipropellant engines using nitrogen tetroxide/monomethyl hydrazine (NTO/MMH). The exhaust products of these engines contain CO2, CO, H2, H2O, and H2. A mixture of cold gases simulating the engine exhaust was injected through a nozzle under conditions simulating thrust levels up to 26.7-N (6 lbf). Pulsing and continuous operations were investigated. The chamber background pressure traces were compared with the traces obtained for the same thrusters operated with pure nitrogen at approximately equivalent thrust. Satisfactory recuperation times were encountered in all the pulsing modes. Test times greater than 20s were obtained in steady state operation before the vacuum chamber back pressure climbed to prohibitive values.
The formation and deposition of carbon (soot) was studied in the Carbon Deposition Model for Oxygen-Hydrocarbon Combustion Program. An empirical, 1-D model for predicting soot formation and deposition in LO2/hydrocarbon gas generators/preburners was derived. The experimental data required to anchor the model were identified and a test program to obtain the data was defined. In support of the model development, cold flow mixing experiments using a high injection density injector were performed. The purpose of this investigation was to advance the state-of-the-art in LO2/hydrocarbon gas generator design by developing a reliable engineering model of gas generator operation. The model was formulated to account for the influences of fluid dynamics, chemical kinetics, and gas generator hardware design on soot formation and deposition.
When the propellants in a liquid rocket engine burn, the rocket not only launches and moves in space, it causes forces that interact with the vehicle itself. When these interactions occur under specific conditions, the vehicle's structures and components can become unstable. One instability of primary concern is termed pogo (named after the movement of a pogo stick), in which the oscillations (cycling movements) cause large loads, or pressure, against the vehicle, tanks, feedlines, and engine. Marshall Space Flight Center (MSFC) has developed a unique test technology to understand and quantify the complex fluid movements and forces in a liquid rocket engine that contribute strongly to both engine and integrated vehicle performance and stability. This new test technology was established in the MSFC Cold Flow Propulsion Test Complex to allow injection and measurement of scaled propellant flows and measurement of the resulting forces at multiple locations throughout the engine.
As the Polar spacecraft apogee precessed through the magnetic equator in 2001, Polar encountered numerous substorm events in the region between geosynchronous orbit and 10 RE geocentric distance; most of them in the plasma sheet boundary layers. Of these, a small number was recorded near the neutral sheet in the evening sector. Polar/Thermal Ion Dynamics Experiment provides a unique perspective on the lowest-energy ion plasma, showing that these events exhibited a damped wavelike character, initiated by a burst of radially outward flow transverse to the local magnetic field at approximately 80 km/s. They then exhibit strongly damped cycles of inward/outward flow with a period of several minutes. After one or two cycles, they culminated in a hot plasma electron and ion injection, quite similar to those observed at geosynchronous orbit. Cold plasmaspheric plasmas comprise the outward flow cycles, while the inward flow cycles contain counterstreaming field-parallel polar wind-like flows. The observed wavelike structure, preceding the arrival of an earthward moving substorm injection front, suggests an outward displacement driven by the inward motion at local times closer to midnight, that is, a "snowplow" effect. The damped in/out flows are consistent with interchange oscillations driven by the arrival at the observed local time by an injection originating at greater radius and local time.
The injection-flow issuing from a porous medium in the cold-flow simulation of internal port flows in solid rocket motors is characterized by a spatial instability termed pseudoturbulence that produces a rather non-uniform (lumpy) injection-velocity profile. The objective of this study is to investigate the interaction between the injection- and the developing axial-flows. The findings show that this interaction generally weakens the lumpy injection profile and affects the subsequent development of the axial flow. The injection profile is found to depend on the material characteristics, and the ensuing pseudoturbulence is a function of the injection velocity, the axial position and the distance from the porous wall. The flow transition (from laminar to turbulent) of the axial-flow is accelerated in flows emerging from smaller pores primarily due to the higher pseudoturbulence produced by the smaller pores in comparison to that associated with larger pores. In flows with rather uniform injection-flow profiles (weak or no pseudoturbulence), the axial and transverse velocity components in the porous duct are found to satisfy the sine/cosine analytical solutions derived from inviscid assumptions. The transition results from the present study are compared with previous results from surveyed literature, and detailed flow development measurements are presented in terms of the blowing fraction, and characterizing Reynolds numbers.
To test the hypothesis that galactic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT Position Sensitive Proportional Counter (PSPC) observations of three such galaxies. The sensitivity of the PSPC to the presence of an extended, approximately 0.15 KEV halo of 10(exp 9) solar mass of gas, is quite high for the exposure times we used. We failed to detect this halo in all three cases and the observed x-ray luminosity of the galaxy is two orders of magnitude less than the hypothetical case in which the mass of gas that has been expelled by previous generations of star formation is equal to the stellar mass of the galaxy itself. This limit is much less than the actual mass of cold gas in these galaxies. Thus, we were unable to verify directly the presence of significant galactic winds in these three galaxies either because they are not operative, because their halos are not sufficiently massive to aid in the retention of this gas, or because the amount of injected gas is just a small percentage of the cold disk gas. If the latter reason is emblematic of low mass galaxies then we would not expect the detection of halos. We also report here the serendipitous detection of Abell 1560, a distance class 7 cluster of unknown redshift.
The Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) operates its instruments passively cooled at around 40 Kelvin (K), with a warm Instrument Electronic Compartment (IEC) at 300K attached to it. From the warm electronics all secondary signal and power harnesses have to bridge this 300-40K temperature difference and minimize the power dissipation and parasitic heat leak into the cold region. After an introduction of the ISIM with its instruments, the IEC with the electronics, and the harness architecture with a special radiator, this paper elaborates on the cryogenic wire selection and tests performed to establish current de-rating rules for different wire types. Finally failure modes are analyzed for critical instrument interfaces that could inject excessive currents and heat into the harness and cold side, and several solutions for the removal of such failures are presented.
The Labeled Release (LR) life detection experiment seeks detection of heterotrophic metabolism by monitoring radio-active gas evolution following the addition of a radioactive nutrient containing seven C-14 labeled organic substrates to surface material. LR results obtained on Mars prior to conjunction showed rapid evolution of radioactive counts upon addition of the nutrient to a fresh surface sample. The responses at both landing sites were quite similar. The additional results summarized in the present paper provide further information on the gas kinetics following a second injection of nutrient and on the effect of 'cold sterilization' of the Martian surface material. Specifically, it is shown that the production of gas from the LR nutrient is remarkably uniform; after reaction approaches completion, addition of more nutrient results in a net loss of the radioactive gas; the reactant in the Mars soil is completely inhibited by heating the soil to 160 C, and is largely inhibited by heating to 46 C. In contrast, exposure to 18 C for 2 sol (1 sol = 24.6 hr) does not appear to inhibit the reaction.