Simulations of absorbed dose on the phantom surface of MATROSHKA-R experiment at the ISS

The health risks associated with exposure to various components of space radiation are of great concern when planning manned long-term interplanetary missions, such as future missions to Mars. Since it is not possible to measure the radiation environment inside of human organs in deep space, simulations based on radiation transport/interaction codes coupled to phantoms of tissue equivalent materials are used. However, the calculated results depend on the models used in the codes, and it is therefore necessary to verify their validity by comparison with measured data. The goal of this paper is to compare absorbed doses obtained in the MATROSHKA-R experiment performed at the International Space Station (ISS) with simulations performed with the three-dimensional Monte Carlo Particle and Heavy-Ion Transport code System (PHITS). The absorbed dose was measured using passive detectors (packages of thermoluminescent and plastic nuclear track detectors) placed on the surface of the spherical tissue equivalent phantom MATROSHKA-R, which was exposed aboard the ISS in the Service Zvezda Module from December 2005 to September 2006. The data calculated by PHITS assuming an ISS shielding of 3 g/cm² and 5 g/cm² aluminum mass thickness were in good agreement with the measurements. Using a simplified geometrical model of the ISS, the influence of variations in altitude and wall mass thickness of the ISS on the calculated absorbed dose was estimated. The uncertainties of the calculated data are also discussed; the relative expanded uncertainty of absorbed dose in phantom was estimated to be 44% at a 95% confidence level.     

The Burst Alert Telescope (BAT) on the SWIFT Midex Mission

he burst alert telescope (BAT) is one of three instruments on the Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and localizes the burst direction to an accuracy of 1–4 arcmin within 20 s after the start of the event. The GRB trigger initiates an autonomous spacecraft slew to point the two narrow field-of-view (FOV) instruments at the burst location within 20–70 s so to make follow-up X-ray and optical observations. The BAT is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed of 32,768 pieces of CdZnTe (4×4×2 mm), and the coded-aperture mask is composed of ∼52,000 pieces of lead (5×5×1 mm) with a 1-m separation between mask and detector plane. The BAT operates over the 15–150 keV energy range with ∼7 keV resolution, a sensitivity of ∼10⁻⁸ erg s⁻¹ cm⁻², and a 1.4 sr (half-coded) FOV. We expect to detect > 100 GRBs/year for a 2-year mission. The BAT also performs an all-sky hard X-ray survey with a sensitivity of ∼2 m Crab (systematic limit) and it serves as a hard X-ray transient monitor.     

Development Study on ATREX Engine

This is the status report of the development study on ATREX engine (Air Turbo Ramjet) that is now under way in the Institute of Space and Astronautical Science (ISAS) cooperation with the Ishikawajima Harima Heavy Industries (IHI), the Kawasaki Heavy Industries (KHI), the Mitsubishi Heavy Industries (MHI). ATREX engine will be applied for the propulsion system of fly-back booster of TSTO space plane. ATREX is the combined cycle (a fan-boosted ramjet) engine providing the effective thrust from sea level static to flight Mach number 6. ATREX is worked on the expander cycle with precooling the incoming air as shown in Fig. 1. ATREX employs the tip turbine configuration which allows the compactness and the light weight of turbo machinery and the variable geometry airintake and plugnozzle which allow the wide range operation conditions.From 1990 to 1992, “ ATREX-500“ has been tested at the sea level static conditions. ATREX-500 is the 1/4-scale model of which fan inlet diameter is 300 mm and overall length 2,200 mm. From 1992 have been performed the wind tunnel tests on the primary components of ATREX, the axisymmetric variable geometry airintakes, the precoolers and the variable geometry plug nozzles. In parallel to the windtunnel tests, the ram combusters have been tested simulating the hypersonic flight conditions and the application studies on advanced carbon-carbon composite for the tip-turbine and fan assembly has been proceeded.In 1994 initiated the flight test plan in which ATREX will be verified in the practical flight conditions by using an unmanned flying test bench.In 1995 will be tested ATREX-500 installing the precooler under the sea level static conditions to examine the engine performance and the icing on the precooler.The present paper addresses the high loading ram combuster experiment using the mixer with skewed lobes to generate swirl flow and the analytical studies and the designs on the precooler and the precooled ATREX engine and the flight test plan.     

Overview of Differential VLBI Observations of Lunar Orbiters in SELENE (Kaguya) for Precise Orbit Determination and Lunar Gravity Field Study

The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the target of VLBI observations over the period November 2007 to June 2009. These observations were made in order to improve the lunar gravity field model, in particular the lower degree coefficients and the model near the limb. Differential VLBI Radio sources, called VRAD instruments, were on-board the subsatellites, Rstar (Okina) and Vstar (Ouna), and the radio signals were observed by the Japanese VERA (VLBI Exploration of Radio Astrometry) network, and an international VLBI network. Multi-frequency and same-beam VLBI techniques were utilized and were essential aspects of the successful observing program. Multi-frequency VLBI was employed in order to improve the accuracy of the orbit determination obtained from the phase delay from the narrow-band satellite signals, while the same-beam VLBI method was used to resolve the cycle ambiguity which is inherent in the multi-frequency VLBI method. The observations were made at three S-band frequencies (2212, 2218 and 2287 MHz), and one X-band frequency (8456 MHz). We have succeeded in correlating the recorded signals from Okina/Ouna, and we obtained phase delays with an accuracy of several pico-seconds at S-band.     

An AO-free coronagraph experiment in vacuum with a binary-shaped pupil mask

We present our first results from laboratory experiments on a binary-shaped checkerboard mask coronagraph that was fitted inside a vacuum chamber for the development of skills to the direct observation of extra-solar planets. The aim of this work was to utilize a vacuum chamber for our coronagraph experiments in order to achieve an environment with higher thermal stability and which is free from air turbulence. We also aimed to evaluate and improve the performance of such a system consisting of a vacuum chamber with a coronagraph set inside the chamber. Both the raw contrast and the contrast after point spread function (PSF) subtraction are evaluated. We sited the vacuum chamber in a clean room, and we installed an optical fiber coupled to a visible He–Ne laser, appropriate coronagraph optics, a temperature sensor and heaters in the chamber. This provided a vacuum environment and a temperature-controlled environment with a visible light source, and was shown to improve the stability of the coronagraph. A contrast of 1.7×10^-7$1.7\times {10}^{-7}$ was achieved for the raw coronagraphic images by analyzing the areal mean of all of the observed dark regions. A contrast of 7.3×10^-9$7.3\times {10}^{-9}$ was achieved for the PSF subtraction by areal variance (1σ) of all of the observed dark regions. Speckles were a major limiting factor throughout the dark regions of both the raw images and the PSF subtracted images. The application of PSF subtraction for the Space Infrared telescope for Cosmology and Astrophysics (SPICA) and for other platforms is discussed.     

A comparison of total reaction cross section models used in particle and heavy ion transport codes

Understanding the interactions and propagations of high energy protons and heavy ions are essential when trying to estimate the biological effects of Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE) on personnel in space. To be able to calculate the shielding properties of different materials and radiation risks, particle and heavy ion transport codes are needed. In all particle and heavy ion transport codes, the probability function that a projectile particle will collide within a certain distance x in the matter depends on the total reaction cross sections, and the calculated partial fragmentation cross sections scale with the total reaction cross sections. It is therefore crucial that accurate total reaction cross section models are used in the transport calculations. In this paper, different models for calculating nucleon–nucleus and nucleus–nucleus total reaction cross sections are compared with each other and with measurements. The uncertainties in the calculations with the different models are discussed, as well as their overall performances with respect to the available experimental data. Finally, a new compilation of experimental data is briefly presented.     

Probing the nature of short swift bursts via deep INTEGRAL monitoring of GRB 050925

We present results from Swift, XMM-Newton, and deep INTEGRAL monitoring in the region of GRB 050925. This short Swift burst is a candidate for a newly discovered soft gamma-ray repeater (SGR) with the following observational burst properties: (1) galactic plane (b = −0.1°) localization, (2) 150 ms duration, and (3) a blackbody rather than a simple power-law spectral shape (with a significance level of 97%). We found two possible X-ray counterparts of GRB 050925 by comparing the X-ray images from Swift XRT and XMM-Newton. Both X-ray sources show the transient behavior with a power-law decay index shallower than −1. We found no hard X-ray emission nor any additional burst from the location of GRB 050925 in ∼5 ms of INTEGRAL data. We discuss about the three BATSE short bursts which might be associated with GRB 050925, based on their location and the duration. Assuming GRB 050925 is associated with the H_II regions (W 58) at the galactic longitude of l = 70°, we also discuss the source frame properties of GRB 050925.     

午后极光强度与太阳风-磁层耦合函数的相关

利用1997年和1998年南极中山站多通道扫描光度计的地面观测数据和Wind卫星在弓激波上游对行星际磁场和太阳风参数的观测数据,对午后高纬极光强度与太阳风-磁层耦合函数之间的相关性进行定量研究.研究表明,午后630.0nm极光强度与太阳风-磁层耦合函数间有很好的相关,而557.7nm的相关性差一些;在考察的所有耦合函数中,午后极光受太阳风电场和能量的影响更直接;同时,行星际磁场的时钟角对午后极光也有很强的控制作用.      

Simulations of MATROSHKA experiment outside the ISS using PHITS

The radiation environment at the altitude of the International Space Station (ISS) is substantially different than anything typically encountered on Earth in both the character of the radiation field and the significantly higher dose rates. Concerns about the biological effects on humans of this highly complex natural radiation field are increasing due to higher amount of astronauts performing long-duration missions onboard the ISS and especially if looking into planned future manned missions to Mars. In order to begin the process of predicting the dose levels seen by the organs of an astronaut, being the prerequisite for radiation risk calculations, it is necessary to understand the character of the radiation environment both in- and outside of the ISS as well as the relevant contributions from the radiation field to the organ doses.