The Hitomi (ASTRO-H) mission is the sixth Japanese X-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. After a successful launch on 2016 February 17, the spacecraft lost its function on 2016 March 26, but the commissioning phase for about a month provided valuable information on the on-board instruments and the spacecraft

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the highenergy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-12 keV with high spectral resolution of ∆E ≦ 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.

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The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of ∆E 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.

A miniature loop heat pipe (LHP) with polytetrafluoroethylene (PTFE) wicks was fabricated and its evaporator thermal performance was investigated with parametric experiments. The variables considered were the clearance between the cylindrical evaporator casing and the wick, the working fluid inventory, the properties of the working fluids, and the sink temperature. Micro-gaps between the outer surface of the wick and inner surface of the evaporator casing were included in the experiments with variables of clearance to investigate their effect on the evaporator heat-transfer coefficient. Ethanol, acetone, and R134a were charged in the LHP to evaluate the effect of the properties of the working fluids. The LHP tests were conducted with several W/cm 2 of applied heat flux to the evaporator under controlled sink temperature. The clearance seriously affected the evaporator heat-transfer coefficient, with a gap of 20 μm between the wick and casing having the best effect on the evaporator heat transfer across a range of tested heat fluxes. The effects of the working fluid inventory and fluid properties on the evaporator heat transfer were also clarified.Finally, the developed LHP was tested using ethanol as a working fluid under a stepwise heat load and sink temperature.

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A transient mathematical model is developed to study the transient response and analyze the distribution of heat load in a loop heat pipe. The model is based on the one-dimensional and time-dependent conservation equations for heat and fluid flow. The momentum and energy conservation equations for each of the loop heat pipe components are solved. The model results are compared against the data obtained from two miniature loop heat pipes using polytetrafluoroethylene wicks, ethanol, and acetone as working fluids. The mathematical model satisfactorily predicts the dynamic behavior of the loop heat pipe unit. It is shown that the percentage of heat leak across the wick decreases and the ratio of latent heat increases with increasing heat load. Some temperature overshoots observed in the calculation results are not observed in the experimental data. When a new power is applied, no time lag is observed in the loop heat pipe response between the simulation and experimental results. Nomenclature A = cross section area, m 2 A s = surface area, m 2 C = heat capacity, J∕kg c = constant in Chisholm correlation c p = specific heat at constant pressure, J∕kg K D = diameter, m f = Darcy's friction coefficient G A B = thermal conductance between A and B, W∕K Gr = Grashof number g = gravity, m∕s 2 h = heat transfer coefficient, W∕m 2 K h lat = latent heat, J∕kg k = thermal conductivity, W∕m K L = length, m _ m = mass flow rate, kg∕s Nu = Nusselt number Pr = Prandtl number p = pressure, Pa _ Q A B = rate of heat transfer from A to B, W _ Q apply = heat load, W q = amount of heat transfer per volume, W∕m 3 Re = Reynolds number T = temperature,°C u = velocity, m∕s V = volume, m 3 X = ratio between vapor and liquid frictional pressure loss Greek β = coefficient of volume expansion, 1∕K ε = porosity ν = kinematic viscosity coefficient, m 2 ∕s ρ = density, kg∕m 3 τ w = wall shear stress, Pa Φ i = square root of ratio between the frictional pressure loss in single phase i and two-phase flow Subscript amb = ambient bay = bayonet tube cc = compensation chamber e = evaporator eff = effective fc = forced convection gr = groove hb = heater block int = interface l = liquid nc = natural convection sat = saturation sub = subcooled v = vapor 2f = two phase

The new Japanese x-ray astronomy satellite, ASTRO-H, will carry two identical hard x-ray telescopes (HXTs), which cover the energy range of 5 to 80 keV. The HXT mirrors employ tightly nested, conically approximated thin-foil Wolter-I optics, and the mirror surfaces are coated with Pt/C depth-graded multilayers to enhance the hard x-ray effective area by means of Bragg reflection. The HXT comprises foils 120-450 mm in diameter and 200 mm in length, with a focal length of 12 m. To obtain a large effective area, 213 aluminum foils 0.2 mm in thickness are tightly nested confocally. The requirements for HXT are a total effective area of >300  cm² at 30 keV and an angular resolution of <1.7^' in half-power diameter (HPD). Fabrication of two HXTs has been completed, and the x-ray performance of each HXT was measured at a synchrotron radiation facility, SPring-8 BL20B2 in Japan. Angular resolutions (HPD) of 1.9^' and 1.8^' at 30 keV were obtained for the full telescopes of HXT-1 and HXT-2, respectively. The total effective area of the two HXTs at 30 keV is 349  cm².