Showing papers by "Japan Aerospace Exploration Agency published in 2001"

Multisatellite observations of rapid subauroral ion drifts (SAID)

Abstract: We present the first conjugate observations of subauroral ion drifts (SAID) in the magnetosphere (∼9000 km altitude) and ionosphere and coincident measurements by four ionospheric satellites. The parameters measured include ion drifts, energetic precipitating electrons and ions, and the magnetic field perturbations associated with field-aligned currents. Observations indicate that SAID are very coherent features that occur simultaneously over a large magnetic local time (MLT) range, from at least 1600 to 2400 MLT. The equatorward extent of SAID, the ion precipitation, and the region 2 field-aligned currents (FAC) flowing into the ionosphere are all shown to be coincident at all MLT locations where SAID are observed. They also appear to be closely related to the conductivity distribution in the subauroral ionosphere and the midlatitude trough. This is interpreted as an indication that their latitudinal distribution is a consequence of the subauroral conductivity structure and the movement of the plasma sheet ion and electron boundaries. Conjugate measurements at diverse altitudes when mapped along field lines are nearly identical, indicating the absence of significant field-aligned potential drops. Temporally separated SAID measurements in similar MLT regions show a reduction with time in the field-aligned current densities with little reduction in the potential drop across the SAID. We interpret the results as an indication that the magnetosphere acts as a current generator in which large FAC are initially required to support the electric field gradient in a SAID event. Subsequent evolution in the E and F regions produces large conductivity gradients that are in the right sense to remove the intense FAC requirement but maintain the large subauroral electric fields. The reported potential drops in the subauroral region can be a significant fraction of the total, up to 60 kV or more, and must be taken into account when deriving any magnetospheric convection pattern.

High resolution Schottky CdTe diode detector

Abstract: We describe recent progress on the use of Schottky CdTe diode detectors for spectrometry. The low leakage current of the CdTe diode allows us to apply a much higher bias voltage than was possible with previous CdTe detectors. For a relatively thin detector of 0.5-1 mm thickness, the high bias voltage results in a high electric field in the device. Both the improved charge-collection efficiency and the low-leakage current lead to an energy resolution of better than 600 eV full-width at half-maximum at 60 keV for a 2/spl times/2 mm/sup 2/ device without any charge-loss correction electronics. Large-area detectors with dimensions of 21/spl times/21 mm/sup 2/ are now available with an energy resolution of /spl sim/2.8 keV. Long-term stability can be easily attained for relatively thin (<1 mm) detectors if they are cooled or operated under a high bias voltage.

Characterization of CdTe/CdZnTe detectors

Abstract: In order to characterize CdTe/CdZnTe detectors in a planar configuration, we have developed a new method to extract /spl mu//spl tau/ products. In this method, we prepare an analytic spectral model based on the charge transport properties in the device, which is intended to be used in fitting calculation. The low mobility-lifetime (/spl mu//spl tau/) products of carriers in CdTe/CdZnTe detectors produce a position dependency in the charge induction efficiency. The model takes the induction efficiency and interaction positions of photons into account. Since the model is parameterized by /spl mu//spl tau/ products, it can extract /spl mu//spl tau/ products. Here, we demonstrate how the model works based on the results from 2-mm-thick HPB CdZnTe and THM CdTe detectors.

Development Study of a Precooler for the Air-Turboramjet Expander-Cycle Engine

Abstract: A review of the development of a precooler for the air-turboramjet expander-cycle (ATREX) engine is given. Three types of precooler for the ATREX engine ground-testmodel were designed, manufactured, and tested under sea-level static conditions. The results suggested two problems affecting the precooler performance, heat transfer rate and air ow pressure drop. One is nonuniformity of the air ow through the tube banks. The other problem is frost formation on the heat transfer surfaces. Concerning nonuniformity of air ow, the shell conŽ guration was modiŽ ed based on analysis by computational  uid dynamics calculation. To improve the precooler performance under frosting condition, a new method to add a condensable gas into the air ow was proposed and examined by experiments on a subscale heat exchanger model. Addition of a small quantity of ethanol can effectively restrain the decline of the precooler performance due to frost formation.

Recent topics in fast-responding pressure-sensitive paint technology at National Aerospace Laboratory

Abstract: This paper reviews the recent advances in fast-responding Pressure-Sensitive Paint (PSP) technology at National Aerospace Laboratory in Japan. Since NAL started a research program on PSP in 1994, much effort has been focused on the development of PSP for unsteady pressure measurements. In recent study, we have made a substantial progress in the fast PSP formulations. This includes the development of a PSP using a high polymer called poly(TMSP) and chemisorptive PSPs based on anodized-aluminum. To investigate the response characteristics of these paints, we have made systematic tests using a pressure chamber with a fast-acting solenoid-type valve and a shock tube. A summary of these experimental investigations is given in this paper with an emphasis on the relationship between the response time and the physical properties of binder materials. In addition, the feasibility tests conducted in a short-duration hypersonic shock tunnel and a shock tube are present.

CdTe stacked detectors for gamma-ray detection

Abstract: We describe a stacked detector made of thin cadmium telluride (CdTe) diode detectors. By using a thin CdTe device, we can overcome the charge loss problem due to the small mobility and short lifetime of holes in CdTe or cadmium zinc telluride (CdZnTe) detectors. However, a CdTe detector with a thickness of more than 5 mm is needed for adequate detection efficiency for gamma-rays of several hundred keV. Good energy resolution and good peak detection efficiency are difficult to obtain using such a thick CdTe detector. The stacked detector enabled us to realize a detector with both high-energy resolution and good efficiencies for gamma rays up to several hundred keV. In order to verify this concept, we constructed a prototype made of ten layers of a 0.5-mm-thick CdTe diode detectors with a surface area of 21.5 mm/spl times/21.5 mm. With this, we have achieved 5.3-keV and 7.9-keV energy resolution [full width at half maximum (FWHM)] at 356 keV and 662 keV, respectively, at the temperature of -20/spl deg/C.

A counting CdTe pixel detector for hard X-ray and /spl gamma/-ray imaging

Abstract: A 0.5-mm-thick cadmium telluride (CdTe) semiconductor pixel sensor with 1024 pixels has been bump-bonded onto a two-dimensional (2-D) single photon counting pixel read out chip (MPEC 2.1) using a special gold-stud technique. The pixel size is 200 /spl times/ 200 /spl mu/m/sup 2/, the active area is 6.4 /spl times/ 6.4 mm/sup 2/. The successful operation of this high-Z imaging pixel device is demonstrated. Noise and threshold dispersion as well as the imaging performance are reported.

Applicability of CFRP materials to the cryogenic propellant tank for reusable launch vehicle (RLV)

Abstract: It is essential to utilize carbon fiber reinforced plastics (CFRP) for main structural materials of cryogenic propellant tanks in order to realize the drastic weight reduction needed for efficient reusable space transportation systems. Recently developed toughened CFRP materials, which are expected to show good cryogenic properties, are considered promising candidates for these kinds of applications. The present study investigates cryogenic properties of candidate materials and structural elements, including Y-joint structural models. 300 mm diameter filament wound tank and 600 mm diameter lay up tanks were fabricated and tested. Based on these experimental data, the feasibility of a CFRP cryogenic tank is discussed and future research tasks are proposed. This research is being conducted under the cooperation contract between NASDA and NAL.

Hope-X high speed flight demonstration program phase II

Abstract: A High-Speed Flight Demonstration (HSFD) program using scale vehicles is planned as part of NAL/NASDA joint research for the HOPE-X unmanned re-entry vehicle project. The program consists of two phases, and the objective of Phase II is to estimate the transonic aerodynamic characteristics of the HOPE-X configuration. The experimental method for Phase II is highly unique: the experiment vehicle is to be lifted to high altitude by a stratospheric balloon, from which it will be released and accelerate in free fall. During data acquisition, the vehicle will fly at a constant Mach number while changing its angle of attack quasi-statically. The vehicle's aerodynamic characteristics over a wide range of angles of attack will then be estimated from the flight data. After data acquisition, the vehicle will be recovered using parachute and airbag systems, and refurbished for the next flight. The flight of the vehicle is fully autonomous under the navigation, guidance and control of its on-board computer. The aerodynamic data obtained through the flight experiment will be used to reduce the uncertainties in the HOPE-X aerodynamic database, which are greater for the transonic region than for other speed regions, and to contribute reference data to improve wind tunnel testing and CFD (Computational Fluid Dynamics) technologies. The Phase II flight experiment will be conducted in collaboration with the Centre National d'Etudes Spatiales (CNES) of France, which will develop and operate the balloon system. Flight test data analysis will be conducted by

Optimization of polymer-based PSP for cryogenic wind tunnels

Abstract: In this paper, a new pressure-sensitive paint (PSP) formulation using a high polymer called poly(TMSP) is presented and its optimization for cryogenic wind tunnels is discussed. In our earlier work, we proved the feasibility of poly(TMSP)-PSP for pressure measurements at low temperature in low-oxygen environment of the cryogenic wind tunnel. However, we also found it difficult with this paint to achieve stable pressure measurements because its oxygen sensitivity was changed from a test to a test. In order to solve this problem, PSP samples with different polymer concentrations in solvent and/or dye concentrations were prepared and calibrated in air, low-oxygen, and cryogenic conditions. We found from these systematic tests that the characteristics of poly(TMSP)-PSP was sensitive to its preparation procedure, particularly to;polymer concentration in solvent. The PSP exhibited high sensitivity to oxygen when its polymer concentration was higher than a certain critical value. This dependency on polymer concentration was observed only at oxygen concentrations lower than 1000 ppm. The sample tests at cryogenic temperatures showed that Poly(TMSP)PSP had the maximum oxygen sensitivity when its polymer concentrations in solvent was from 8 to 10 mg/ml. It was also found that dye concentration in PSP had an influence on the shape of a Stern-Volmer curve. To validate the results obtained from the sample tests, poly(TMSP)-PSP with the optimized formulation was tested on a circular-arc bump model in the NAL 0.1-m Cryogenic Wind Tunnel. It was confirmed that the optimized poly(TMSP)-PSP could provide,a stable and high signal-to-noise pressure data at the temperature of 100 K and the oxygen concentration of 1000 ppm.

Open-system pressure sensitive paint for surface pressure measurements in a cryogenic wind tunnel

Abstract: Pyrene-, ruthenium-, and porphyrin-based, anodized aluminum pressure sensitive paint (AA-PSP) is developed for surface pressure measurements in a cryogenic wind tunnel. These AA-PSPs were calibrated to determine the pressure sensitivity by injecting a small amount of oxygen in the test gas. The mole fraction of oxygen was varied from 4 ppm up to 2000 ppm. The calibration tests were conducted in the 0.1 m Transonic Cryogenic Wind Tunnel (TCWT) at National Aerospace Laboratory, Japan. Luminophore choice affected the pressure sensitivity with a pyrene-based AA-PSP having the best sensitivity. These AA-PSPs were applied for surface pressure measurements on a 14% thick circular arc-bump model in the TCWT. The results of pyrene- and ruthenium-based AA-PSPs showed good agreement with pressure taps. Pressure sensitivity, signal level, and uniformity of luminescent coating affected the pressure measurements.

Analytical and experimental evaluation of impact dynamics on a high-speed zero G motion simulator

Abstract: In a new stage of space development, collision and contact tasks under micro-gravity, such as docking, orbital servicing, and touchdown to a minor body, are now increasingly being considered. A hybrid motion simulation consisting of both physical and numerical models is an effective method to test the motions of a spacecraft under zero G on the ground. The authors have developed a hybrid zero G motion simulator based on a highspeed parallel link mechanism. A wide response bandwidth and high stiffness of the simulator have made it possible to simulate the contact motions with high precision. In this paper, they evaluate analytically the simulator characteristics and verify experimentally the impact of dynamics on the hybrid motion simulation by comparing it with a collision experiment under zero G in a drop-shaft facility. The results imply that the simulator is highly reliable for the impact dynamics simulation under zero G.

Pressurizing test of CFRP model tank in cryogenic temperature

Abstract: The authors present in this study an approach demonstrating the performance of a toughened epoxy CFRP concept tank under internal pressure at a cryogenic temperature. Three tanks were prepared with eight-ply unidirectional (UD) quasi-isotropic lay-ups of two different patterns and cloth lay-up. Each tank was cylindrical with a diameter of 600mm and length of 1200mm, covered with an aluminum flange at one end and a 600mm hemispherical CFRP dome at the other. The gauge length used was the central 300mm of the cylindrical section with a wall thickness of I.imm and made from IM600/#133 toughened epoxy CFRP. Each of the tanks was installed into a metallic chamber with the outside being under vacuum in order to preserve the cryogenic condition. The inside of the tank was pressurized with liquid nitrogen (LN2) together with gaseous helium (GHe) with the aim of detecting the onset of damage from the GHe leakage. The experiments were performed as follows. Firstly, helium gas leakage was measured and indicated no damage resulting from a water pressure of 1 MPa at room temperature (R.T.). Secondly, LN2 storage was performed without pressurization in order to evaluate any damage onsets due to the cryogenic condition. Following LN2 storage, no damage was detected within the gauge section of the tank. Thirdly, the tank was pressurized with LN2 and GHe to 0.98 MPa at gauge pressure (MPaG) and indicated the gauge section to has kept intact. Therefore, it was concluded that the materials and concept CFRP tank structure were successfully demonstrated under pressurization in cryogenic conditions. Although technical steps remain regarding engineering structures, CFRP appears to be a promising candidate for the realization of lightweight pressure vessels such as launch vehicle cryogenic tanks.

Superplastic Deformation Behavior of Undoped and Doped High-Purity 3Y-TZP

Abstract: Superplastic deformation behavior was examined in undoped and doped high purity 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) with fine and coarse grains. In undoped 3Y-TZP, fine grain materials below 0.3 μm showed two deformation regions with a stress exponent of two, a grain size exponent of one and an apparent activation energy of 370 kJ/mol at high stress region and three, one and 630 kJ/mol at low stress region, while coarse grain materials above 1 um showed two deformation regions with a stress exponent of one, a grain size exponent of three and an apparent activation energy of 450 kJ/mol at high stress region and three, one and 550 kJ/mol at low stress region. On the other hand in alumina doped high purity 3Y-TZP, both the fine and coarse grain materials showed two deformation regions with a stress exponent of one, a grain size exponent and an apparent activation energy of 520 kJ/mol at high stress region and two, one and 590 kJ/mol at low stress region. The region of diffusional creep region with a stress exponent of one was first observed in 3Y-TZP. Deformation mechanism maps have been drawn for undoped and doped TZP, and the obtained deformation mechanism maps can predict these deformation regions.

Measurements of emission spectra from a shock layer of a blunt body in arc-heated gas

Abstract: Arcjet tests were conducted to investigate the catalytic effects of two types of thermal protection coating having different surface catalytic efficiencies. One is BHE (black high emittance) coating with lower catalytic efficiency, the other is RF (reference) coating with higher catalytic efficiency. Experiments consist of the measurements of emission spectra from the shock layer of the model and heat flux to the model. As a working gas, a mixture of 80 % N2 and 20 % 62 by volume was used in the tests. Spectroscopic measurements showed that the difference of catalytic efficiency between the two coatings slightly appeared on oxygen atomic spectra. The spectral intensities of atomic oxygen measured for the RF model were slightly smaller than those for the BHE model. In addition, time-averaged heat fluxes into the models were measured and the results showed that heat flux into the RF model was larger than that into the BHE model by 5.2 %.

Improvement of performance of the precooled cycle engine spoiled by icing

Abstract: The effectiveness of a method to improve the precooler performance under frosting condition was investigated by experiments on a sub-scale heat exchanger model. Addition of a methanol proved to be most effective compared with other possible substances in both cases of lower and higher cooling wall temperature than its melting point. Then the effectiveness of the methanol addition was ascertained for the practical condition that means the same tube configuration and flow velocity as the precooler designed for the ATREX engine firing test model. The result showed that the addition of the same quantity as the water vapor could restrain the frost layer from choking the flow in the duration of 300 seconds, which is sufficient time for precooler operation. The required methanol mass along the ATREX engine flight path was estimated to be less than 3 % of fuel hydrogen on board. Accordingly, the method came to be promising candidate for practical application.

Sea ice observation method

Abstract: PROBLEM TO BE SOLVED: To provide a sea ice observation method obtaining the draft value of requested sea ice from data obtained by a synthetic aperture radar SOLUTION: Sea ice thickness and drift speed observation using an under-sea mooring type ice thickness measuring sonar and a current meter, and sea ice observation by a high resolution aircraft SAR are synchronously performed to obtain the relation between the draft value profile of sea ice passing on the sonar, and an SAR back scattering coefficient profile The draft value of the requested sea ice is obtained from the relational expression and an SAR back scattering coefficient A back scattering coefficient of L-band HV polarization may be used as the SAR back scattering coefficient In detecting thin ice of about 10 cm or less, it is ideal to use a back scattering coefficient of X-band W polarization as the SAR back scattering coefficient COPYRIGHT: (C)2003,JPO

Simultaneous satellite and ground observations of transient events near the morningside magnetopause

Abstract: We present observations of transient events on April 13, 1996, using simultaneous measurements in the solar wind, near the magnetopause, at geosynchronous orbit, and on the ground at high latitudes. On this day, Geotail passed outbound through the morningside magnetopause. When Geotail was in the magnetosphere, a clear bipolar perturbation in the magnetic field component normal to the nominal magnetopause and transient outbound (from the magnetosphere to the magnetosheath)/inbound (from the magnetosheath to the magnetosphere) magnetopause crossings were observed. When Geotail was in the magnetosheath, inbound/outbound crossings were observed. During the bipolar magnetic field signature, Geotail observed asymmetric bipolar (less inward/more outward) flow normal to the nominal magnetopause accompanied by sunward flow. Inward flow was observed when the total magnetic field of the event was enhanced, whereas outward flow was observed when the total magnetic field was depressed. We observed that some of the transient outbound/inbound crossings show significantly different signatures in the plasma flow and magnetic field, that is, weak inward flow and enhanced magnetic field before the outbound crossing and strong outward flow and decreased magnetic field after the inbound crossing. The field and flow variations during the transient outbound/inbound crossings are qualitatively similar to those during the bipolar magnetic field signature. These observations suggest that the bipolar field signature and the transient magnetopause crossings would be similar phenomena on the magnetopause. We discuss whether the observed field and flow variations during the transient events are caused by inward/outward magnetopause motion due to compression/expansion of the magnetosphere by comparing the data sets obtained from different regions of the solar wind-magnetosphere system.

Unified constitutive equation of CTE-mismatch superplasticity based on continuum micromechanics

Abstract: Two types of micromechanics models for CTE-mismatch superplasticity have been proposed independently. They are developed about metal matrix composites and monolithic polycrystals. The present study compares and unifies these two models. Using a newly proposed geometrical factor, similar constitutive equations at low and high applied stresses are derived quantitatively. The unified model can be applicable to explain the CTE-mismatch superplastic behavior in any metal matrix composites and monolithic polycrystals.

Recovery guidance for the high speed flight demonstration vehicle

Abstract: A High-Speed Flight Demonstration (HSFD) program is planned as part of research for the HOPE-X unmanned re-entry vehicle project. The program consists of two phases, and the objective of Phase II is to estimate the transonic aerodynamic characteristics of the HOPE-X configuration. The experimental method for Phase n is highly unique: the experiment vehicle is to be lifted to high altitude by a stratospheric balloon, from which it will be released and accelerate in free fall. During data acquisition, the vehicle will fly at a constant Mach number. After data acquisition, the vehicle will be recovered using parachute and airbag systems, and refurbished for the next flight. The flight of the vehicle is fully autonomous under the navigation, guidance and control (GNC) of its on-board computer, and it is one of important missions for the GNC system to guide the vehicle to a designated recovery point with final flight conditions suitable for deploying a recovery parachute. A guidance system which satisfies this requirement was designed and a six degree-of-freedom flight simulation analysis including mathematical model errors was carried out to evaluate it. The results show that the vehicle can be guided to the target point within the required accuracy by the designed guidance system. NOMENCLATURE

Overview of basic research activities on cryogenic composite propellant tanks in japan

Abstract: Extensive application of composite materials is one of the major technical challenges for drastic reduction of structural weight of the planned space planes and reusable launch vehicles (RLV). Propellant tanks are the dominating structural components of the vehicle structure and thus the application of carbon fiber reinforced plastics (CFRP) to these components is one of the most promising but challenging technologies for achieving the goal of weight reduction. The overview of current activities on basic research related to the application of CFRP to cryogenic propellant tanks in Japan is given. These research projects indicate that the load-carrying performance of the state-of-the-art material systems is at the sufficient level to be used in the CFRP tanks, leaving the problems related to permeability, durability and fabrication yet to be extensively investigated. The preliminary evaluations of thermal insulation materials and adhesive materials are also under way at NASDA. The research project led by NAL-Kakuda also exhibits the promising results of the CFRP components.