Thrust measurement of dimethyl ether arcjet thruster

The present paper describes thrust measurement results for an arcjet thruster using Dimethyl ether (DME) as the propellant. DME is an ether compound and can be stored as a liquid due to its relatively low freezing point and preferable vapor pressure. The thruster successfully produced high-voltage mode at DME mass flow rates above 30 mg/s, whereas it yielded low-voltage mode below 30 mg/s. Thrust measurements yielded a thrust of 0.15 N and a specific impulse of 270 s at a mass flow rate of 60 mg/s with a discharge power of 1300 W. The DME arcjet thruster was comparable to a conventional one for thrust and discharge power.     

Some useful coordinate systems to discuss the apogee motor firing optimization

This paper introduces five useful coordinate systems to optimize the apogee motor firing of a geostationary satellite. This optimization minimizes the propellant consumption for station acquisition manoeuvres. The coordinate systems used for this purpose must depict the optimization parameters together with the propellant consumption. In order to get the propellant consumption, some relations between parameters are derived and the equipropellant lines (planes) are drawn in the coordinate systems. These coordinate systems are used not only for the optimization of the apogee motor firing but also for the optimization of the station acquisition strategy, the transfer orbit setting and the apogee motor sizing.     

Hayabusa—Its technology and science accomplishment summary and Hayabusa-2

Hayabusa performed five descents last November, among which two touching-down flights were included. Actually Hayabusa made three touching-downs and one long landing on the surface of Itokawa during those two flights. This paper summarizes how series of descents were planned and operated. The contents focus their attention on the correction maneuvers planning as well as what kind of terminals with what kind of software tools were actually built and used. The project team had distilled and accumulated their experiences through the rehearsal flights and accomplished this difficult mission. This paper presents the entire story about it.     

Experimental study of impact-cratering damage on brittle cylindrical column model as a fundamental component of space architecture

The cylindrical column of brittle material processed from soil and rock is a fundamental component of architectures on the surface of solid bodies in the solar system. One of the most hazardous events for the structure is damaging by hypervelocity impacts by meteoroids and debris. In such a background, cylindrical columns made of plaster of Paris and glass-bead-sintered ceramic were impacted by spherical projectiles of nylon, glass, and steel at velocity of about 1–4.5 km/s. Measured crater radii, depth, and excavated mass expressed by a function of the cylinder radius are similar irrespective of the target material, if those parameters are normalized by appropriate parameters of the crater produced on the flat-surface target. The empirical scaling relations of the normalized crater radii and depth are provided. Using them, crater dimensions and excavated mass of crater on cylindrical surface of any radius can be predicted from the existing knowledge of those for flat surface. Recommendation for the minimum diameter of a cylinder so as to resist against a given impact is provided.     

滚珠丝杠在超精密定位中的应用

通过分析滚珠丝杠驱动机构的特点,对目前利用这种驱动方式实现大行程的具有纳米分辨率的定位系统的关键技术进行论述。     

Theory of magnetic pulsations

We present theory of long period (pc 3 to pc 5) magnetic pulsations. It consists of two parts; one (we call type A) deals with a resonant Alfvén wave excitation at a local field line by a monochromatic wave generated at the magnetopause, and the other (we call type B) deals with an excitation of a surface eigenmode by an externally applied impulse at a location with a rapid spatial change of plasma parameter(s).For the type A pulsations, the theory gives the frequency, the sense and the ellipticity of the polarization and the orientation angle of the major axis as a function of the magnetospheric parameters. In particular, it is shown that the orientation angle of the major axis of the polarization ellipse is a sensitive function of the direction of the wave propagation in longitude and the change of the number density and the magnetic flux density in the radial direction, hence it can be used as an important diagnostic parameter.In the type B pulsations, the theory gives the excitation frequency and the damping rate of the pulsations using the derived surface eigenmode. Example of an application to the observed magnetic field oscillations at the plasmapause is presented in which the observed frequency and the damping rate are used to estimate the plasmapause density and its radial density gradient.     

In-orbit deployment characteristics of large deployable antenna reflector onboard Engineering Test Satellite VIII

This paper describes design, ground testing, an in-orbit experiment, and a novel in-orbit operation for large deployable antenna reflectors (LDRs). Two LDRs (TX-LDR for transmitting and RX-LDR for receiving) are installed on Engineering Test Satellite VIII (ETS-VIII). The reflector design features that the antenna reflector whose aperture is 13 m in diameter (the mechanical dimension is ) consists of 14 basic modules, and each basic module consists of a gold-plated molybdenum mesh, a system of cables, and a deployable frame structures. Several ground tests had been performed using a modular nature to advantage. Prior to the launch of ETS-VIII, we performed an in-orbit deployment experiment using LDREX-2 which consists of seven half-scale modules of LDR, to confirm evaluation accuracy. The LDREX-2 was launched by ARIANE 5 launch vehicle as a piggy-back payload. Deployment characteristics were measured to evaluate the accuracy of analytical prediction obtained by ground deployment testing. ETS-VIII was launched by H-IIA launch vehicle on 18 December 2006. After the successful injection into Geo Synchronous Orbit, the RX-LDR and the TX-LDR were successfully deployed on December 25th and 26th, respectively. We confirmed adequacy of the proposed design and ground verification methodology.     

Characterization of Multiband Imager Aboard SELENE

The Multiband Imager (MI) is a high-resolution, multi-spectral imaging instrument for lunar exploration. It consists of two cameras, VIS and NIR, and is carried on the SELenological and ENgineering Explorer (SELENE), launched on Sep. 14, 2007. During the observation from January 2008 to June 2009, MI acquired about 450,000 scenes of multispectral image. The radiometric properties of the cameras were characterized using the pre-flight data derived in laboratory experiments with a calibrated integrating sphere. Twelve light source sets were used to examine the S/N ratio, linearity, and saturation level of the cameras. The dark field signal is quite stable in both cameras, having a noise level of less than 1 DN (VIS) and 2 DN (NIR). The fluctuation in the light field is also low (<2 DN), indicating that the spatial nonuniformity in the camera responses can be removed using a flat field. In order to remove the smear signals due to the frame transfer in the VIS data, we developed an iterate algorithm using all bands in the VIS camera. The S/N ratio, which is critical to the precision of the product, is estimated to exceed 160 for the VIS bands and 400 for the NIR bands under low illumination conditions (5% of lunar surface reflectance). Based on the S/N ratio, the radiometric error due to the noise is calculated to be less than 0.7% for VIS and 0.2% for NIR. The relationship between input and output of the VIS camera is linear with a residual of less than 0.6 DN, corresponding to a radiometric error of 0.3%. The NIR exhibits a non-linear response to the input radiance. A cubic function best fits the pre-flight data with an average residual of 8 DN (corresponds to an error of 0.8%). Validation using in-flight data indicated that the instability of the dark output has not changed, but the level of dark output has slightly changed in the NIR bands (less than 6 DN). The pixel-to-pixel sensitivity variation in the orbit has been changed from that in the pre-flight experiment. The difference between the in-flight data and the pre-flight data ranges within ±2%. There is also a small (less than ±1%) but nonnegligible difference between in-flight data of different cycles in both the VIS and NIR bands, suggesting that the coefficient for spatial ununiformity correction needs to be calculated for each cycle.     

八面体桁架结构在内冷通道中的流动传热特性研究

为探究八面体桁架结构在航空发动机热端部件内冷通道中的可应用性,掌握八面体桁架结构的流动传热特性,本文采用理论推导和三维数值模拟的方法,对八面体桁架单体的有效导热系数以及八面体桁架阵列结构的流动结构和传热性能开展了研究。首先,针对八面体桁架单体结构,推导出了考虑节点效应的有效导热系数关系式,并通过与数值计算结果对比,验证了其有效性。其次,针对八面体桁架阵列结构,开展了整体结构的三维数值计算,分析了其内部通道的流动结构和温度分布,获得了不同结构的流动阻力和对流传热系数随雷诺数的变化规律。最后,考虑到结构的综合传热性能,本文针对不同孔隙率的八面体桁架阵列结构,进行了基于相同泵功率下努塞尔数的对比。根据计算结果,本文给出了获得最佳传热性能的无量纲直径范围0.07~0.08,相应的孔隙率变化范围 0.872~0.841。分析其原因,由于随着结构孔隙率的减小,即固体率的增加,对流传热强度不断提高,然而,当孔隙率减小到84.1%以下时,由于内通道中流动阻力骤然增大,导致传热效率降低。将八面体桁架结构应用于航空发动机热端部件内冷通道中,是同时出于高效冷却和力学性能的考虑,本文掌握八面体桁架阵列结构的流动传热特性,为其在实际工程中的应用提供了理论支撑。